This publication is number 86 in the Technical Report Series

of the Industrial Developrtlent Branch

::5.r ~;;J..3

C!? -:3 /~-..

:::;:t= J' ~ c -;r-FERROCEMENT FOR

CANADIAN FISHING VESSELS

-A Summary and Interpretation of Test Results-1969 - 1974

prepared by Arnold W. Greenius

B.C. Research Vancouver, Canada

for Vessels and Engineering Division

Industrial Development Branch Fisheries and Marine Service

Environment Canada

Project Officer G.M. Sylvester

Division Chief H.A. Shenker

March 1975

Opinions expressed and conclusions reached by the author are not necessarily endorsed

by the sponsors of this project

ABSTRACT

This report summarizes, integrates, and interprets the test results obtained at B.C. Research on the properties of ferrocement for fishing vessel construction during the five program years, 1969 to 1974. The programs were funded by the Industrial Development Branch, Fisheries and Marine Service, Environment Canada.

The work has examined many aspects of ferrocement, e.g. effect of sands, cements, admixtures, reinforcing rods, and reinforcing meshes on workability, strength, and durability. It has also examined patching, bolting, painting and other factors affecting performance.

The study is not an in-depth study of any specific engineering property or performance but is rather a preliminary broad survey to develop a IIfee1 11 for the engineering properties and behaviour of ferrocement as a material of construction for fishing vessels.

TABLE OF CONTENTS

A. I NTRODUCTI ON

1. Objectives 2. Historical Background 3. Scope of the Test Work 1969-1974 4. Applicability of the Test Results

B. DIGEST OF TEST RESULTS AND CONCLUSION~

1. Mortars 2. Reinforcements 3. The Reinforced Mortar Composite 4. Bibliography

C. TEST PROCEDURES AND RESULTS

1. The Component Materials - Mortars

Page

1

1 1 3 4

6

6 8

11 15

16

and Steel Reinforcements 16 2. Evaluation of Various Mortars 21 3. Evaluation of Various Reinforcements 41 4. Evaluation of a Typical Ferrocement Construction 73 5. Bolting Tests 98 6. Design Considerations 101 7. Patching Ferrocement 101 8. Protective Coatings 104 9. Quality Assurance 113

D. BIBLIOGRAPHY OF FERROCEMENT LITERATURE

E. ACKNOWLEDGEMENTS

F. REFERENCES

G. APPENDIX

1. Development of Mathematical Model - J. D. Smith 2. Regulations for Construction of Ferrocement Boats

- Canada Transport Ministry 3. Guidelines for the Construction of Ferro-cement

Vessels - American Bureau of Shipping 4. Bibliography of Ferrocement Literature

114

115

116

122

1

FERROCEMENT FOR CANADIAN FISHING VESSELS: A SUMMARY AND INTERPRETATION OF TEST RESULTS - 1969 to 1974

A. INTRODUCTION

1. Objectives

Since 1968 the Industrial Development Branch of Fisheries and Marine Services, Environmen~ Canada has funded a series of programs at B.C. Research, Vancouver, B.C., to evaluate some of the properties of ferrocement for fishing vessel construction. The objectives vf this report are to summarize and interpret the findings obtained and documented in five major reports during the last five years. This report pro¥ides some measure of the strengths and shortcomings of the test data obtained from programs designed to cover a wide range of properties and character­istics at the expense of in-depth completeness.

2. Historical Background

Ferrocement is defined most simply as a thin cement mortar shell highly reinforced with fine widely-di~tributed reinforcement. This definition is general enough to include the most common composites of steel mesh and rods in a matrix of Portland cement mortar, those which contain short steel fibres or no reinforcing rods, and those which have a matrix of polymer mortars. In its present state of practical develop­ment for fishing vessels, ferrocement is a Portland cement mortar containing a widely-distributed reinforcement of steel mesh of various kinds generally with steel rods.

Various advan~ages have been stated for ferrocement as a material of boat construction, e.g. good sound insulation, good thermal insulation, fire-resistance, resistance to marine borers, ease of fabri­cation, ease of repair, low cost, good abrasion resistance, good impact strength, good corrosion resistance, and others. Some of these are undoubtedly questionable.

Ferrocement as a boatbui1ding material has a long history dating back some 125 years. Although the construction of ferrocement boats in the years 1848 to 1896 by Lambot, Gabe1lini, and others is of historical interest, the re-invention and naming of ferrocement and the design and construction of several boats in the years 1941 to 1949 by P.l. Nervi mark the modern development of ferrocement. After a few

2

years of relative inactivity, a ferrocement renaissance in New Zealand and England in 1961 started a world-wide adoption of the ferrocement method of building boats. Although pleasure sailboats were of prime 1rtterest in 1961, China, Cuba, and many developing countries are now building ferrocement fishing boats, work and harbour boats, and shelter boats in great numbers.

In 1968, the activities of amateur and professional boat­builders, especially on Canada1s Pacific Coast, interested the Fisheries Service, Canada Department of Fisheries. These builders were constructing both pleasure and work boats. The Industrial Deve1pment Branch of the Fisheries Service commissioned B.C. Research to undertake a study of ferrocement as a construction material for fishing vessels. The stated aims of the first study were: l} to collect and collate the available data on ferrocement for boatbuilding, and 2} to undertake a limited test program to determine the properties of conventional ferrocement. This work was reported in 1968 by Kelly and English l to the Fisheries Service and by Kelly and Mouat2 to the Conference on Fishing Vessel Construction Materials, Montreal, Canada, October 1-3, 1968.

As a result of this first program of collecting and collating SOffie of the available data and of performing some tests, the Industrial Development Branch embarked on the funding of the first of five annual programs at B.C. Research to evaluate ferrocement for fishing vessel construction.

Since ferrocement is a non-homogeneous composite material of great variety, it was realized that the available fundtng would allow only a very general assessment of the properties and performance of ferrocement. It was hoped, however, that patently unsuitable materials and procedures would be identified and that a set of guidelines to aid persons wishing to make a f2rrocement boat and persons charged with the responsibility for certifying ferrocement boats would be developed. In fact, the five reports 3- 7 of the work submitted to the Industrial Develop­ment Branch over the past five years have recorded the results of tests covering a very broad range of properties. The engineering and perform­ance data obtained are not the results of in-depth investigations of a few properties but are rather the preliminary results of tests on a broad front. The reports were reproduced verbatim by the Branch for general distribution even though the complete documentation of the test results diminished the usefulness of the results to a prospective builder. Therefore, at the end of the fifth program, the Branch contracted with B.C. Research to summarize and interpret all the test results obtained so that prospective builders might more readily use them.

This summary has attempted to consolidate the findings on a single aspect, e.g. mortar strength, durability, and corrosion,

3

into an integrated section, to interpret the significance of the findings, and to draw some conclusions. The surrmary has "culled out" or ignored some results which now appear to be of little significance and has "gleaned" some useful information, not formerly appreciated, from some of the tests performed. And finally, it should be stated that this is not a "How-to-build-it" book, an aspect well covered in several practical guides. S- 14

3. Scope of the Test \~ork 1969-1974

The programs undertaken in the five annual contracts 1969-1970 to 1973-1974 are briefly summarized as follows:

1969-1970 - The mortar mix - various mixes of sands, cements, and water/cement ratios were tested in standard compression tests and tested as tiles reinforced with "standard ll

mesh reinforcements in bending, impact, and freeze­thaw and seawater exposure tests.

- The mesh reinforcement - various meshes were tested in tiles with "standard ll mortar mix in bending and impact.

- Repair - the use of mortar and polymers for patching was examined.

1970-1971 - The mortar mix - the use of admixtures was examined for improvements to workability, strength, and durability of mortar.

- The reinforcement - various kinds of mesh and rods were evaluated on the basis of mortar penetration, bond strength, bending and impact strengths.

- The effect of interrupted mortaring on strength was observed.

- The attachment of fittings by powder-activated tools was examined.

- The preliminary development of a mathematical model for the behaviour of ferrocement was considered.

4

1971-1972 - The behaviour of ferrocement under cyclic bending loads of constant deflection was briefly examined.

- The bolting strength of ferrocement was tested.

- Ceatings for ferrocement were evaluated in laboratory and marine exposure tests.

1972-1973 - More flexure data were obtained for the future develop­ment of a mathematical model for the behaviour and design of ferrocement.

- Additional seawater exposure tests on painted f~rro­cement specimens.

1973-1974 - The effect of crack size and thickness of mortar cover on the corrosion of the steel reinforcement was assessed.

- The behaviour of ferrocement under cyclic bending loads of constant magnitude was observed.

- Additional tests on interrupted or multi-stage mortaring were undertaken.

The programs over the five-year period also involved the up-dating of a bibliographic listing and maintaining a file of ferrocement literature at B.C. Research, advice to specific technical enquiries from persons interested in ferrocement construction, and various miscellaneous tests to assist experimenters, e.g. especially testing of a polymer­aggregate composites.

4. Applicability of t~e Test Results

None of the annual contracts for work presupposed or anticipated a subsequent contract. Each year's work was planned to be complete in itself and to provide information over as broad a range of variables as possible within the imposed limits of time and funding. No exhaustive in-depth study of any property was intended or undertaken and no attempt has been made to obtain an "optimum ferrocement construction".

Materials which have seemed unsuitable in the tests reported herein may prove acceptable when treated in a different manner. For example, expanded metal lath appeared unsuitable because of its anisotropic properties. It was also difficult to get good penetration

5

of the mortar into several layers of the mesh by trowelling.. However, one manufacturer uses expanded metal lath successfully by embedding it layer by layer into successive layers of mortar sprayed into a female mould. The potential innovative builder, therefore, will experiment with and evaluate the available materials in terms of his proposed construction techniques.

Although the more common relatively homogeneous materials are not always adequately characterized by the standard test specimens and procedures available, a reasonable correlation exists between the behaviour of a component and the results obtained from a standard test specimen of the material in the component. However, standard tests and procedures are not available for ferrocement in its present state of technical development. Each investigator of ferrocement properties has used such specimens for strength, flexure, and impact as suits his ferro­cement construction facilities and techniques and his testing equipment. It is unwise to try to quantitatively correlate the results presented herein with those of another investigator. The results are best used to compare ferrocement constructions in which one variable is changed, ego kind of mesh reinforcement. Satisfactory replication of tests has not been possible. The results presented apply only to the ferrocement constructions used in the tests. Much more work needs to be undertaken before a mathematical model can be developed which will enable test results obtained to be reliably applied to other ferrocement constructions.

In conclusion, the results presented herein are not "optimum" properties but are the results obtained over the past five years from various preliminary tests, often insufficiently replicated, performed on several constructions of ferrocement. It is believed that the test results provide a good "feel" for many of the properties of ferrocement, typical of the constructions which have been and will be used by the amateur and semi­professional builder of a ferrocement boat.

6

B. DIGEST OF TEST RESULTS AND CONCLUSIONS

Some of the test results and the conclusions drawn are briefly presented in this digest. The reader should refer to the pertinent sections of the main part of the report for the details of the tests performed. This will help him to judge what degree of confidence should be placed on the results and conclusions obtained from a test program which has not always allowed sufficient replication.

1. Mortars

Mortars of several sands, cements, and admixtures have been examined for the effect of the various components on workability (penetration of the mesh reinforcement), compressive and flexure strength, absorption, and durability in freeze-thaw and seawater environments.

The following sands, cements, and admixtures were used in the tests:

- dry bagged concrete sand (some plus 8-mesh) - dry bagged mortar sand (no plus 8-mesh) - sharp Del r·1onte silica sands (8-, 20-, and 3D-mesh grades}

- Type I cement (general construction) - Type II cement (moderate sulphate resistance) - Type III cement (better early strength) - Type V cement (superior sulphate resistance) - aluminous cement (improved strength)

- pozzolan (replaced 1/4 of cement) - water-reducing agent (6.5 f1.oz/bag cement) - air-entraining agent (3/4 f1.oz/bag cement) - Polyviny1acetate emulsion (pva/water, 1:1.44)

(a) Workability

Panels, 30 x 3D-in., were made with several layers of mesh. Mortars of various combinations of sands, cements, and admixtures were placed with vibrating trowels into the horizontal form moulds containing the mesh layers. The ease of placing the mortar and the penetration into the mesh layers were evaluated qualitatively. All mortars tested gave adequate penetration provided the cone slump value was greater than 3 in. The mortars containing sands with some plus 8-mesh material were more difficult to trowel smoothly. The various cements and admixtures appeared to giv~ no significant improvements.

7

The 36-in. panels made in the upright open frame moulds were somewhat more difficult to mortar. The vibrating trowel could not be used. Higher slumps (3 to 6 in.) were necessary for good penetration.

(b) Strength

Compressive strengths of the various mortars were obtained from 7-day and 28-day 2-in. cube specimens. The flexure strengths were obtained from unreinforced portions of the panels made. No important differences in strength were observed in the mortars made with the several sands, cements, and admixtures.

(c) Absorption

Specimens were soaked in water and subsequently dried to determine the voids. They absorbed about 7 percent water. The differences in water absorption for mortars of various sands and cements were not significant. The water-reducing agent appeared to reduce the absorption to about 4 percent.

(d) The Hydrogen Gas Problem

Gas bubbles in the form of blisters were encountered on panels which contained both rods and galvanized mesh. A galvanic reaction between the two kinds of reinforcement in the presence of the cement mortar causes hydrogen to evolve. Chromium trioxide was added to the mortar to prevent the reaction.

(e) Durability

Unreinforced mortar coupons were subjected to 350 freeze­thaw cycles, 10C to -4C. The kind of cements and sands used had no apparent effect on the freeze-thaw durability. No significant deterioration was observed after 350 cycles. Admixtures did not improve the durability. The upper unreinforced layer of coupons reinforced with wire mesh delaminated or disintegrated badly in a test of 76 cycles of freezing and thawing. It is concluded that differential expansion between the reinforced and unreinforced layers of the test coupons aggravated the stresses from freezing and thawing. It is also concluded that thick layers of unreinforced mortar padding in a boat hull should be avoided.

Mesh-reinforced coupons with various sands, cements and admixtures were tested in 350 ~/et-dry seawater cycles. No changes in visual appearance and hardness of the mortar were observed. It is con­cluded that all have good resistance to seawater.

8

(f) Conclusions

The tests of mortars with various sands, cements, and admixtures showed, in general, no real advantage for one type of sand or cement over another and no real improvement from the addition of admixtures. It appeared best to avoid coarse sands, to use a cement with at least some sulphate resistance, and to avoid the use of admixtures. It was therefore decided to use a "standard" mortar for all subsequent tests as follows:

- Dry bagged mortar sand (good tro\'/elling) 2 parts - Type II cement (moderate sulphate resistance) 1 part - Water/cement ratio, 0.4 to 0.5 (as close to 0.4 as

possible with acceptable slump values 3 to 6 in .. ) - Chromium trioxide (Cr03) 300 ppm of water was added

to prevent hydrogen gas problem when galvanized mesh used with ungalvanized rod reinforcement.

The following average compressive and flexural strengths were obtained for the many "standard" mortar batches (Type II cement, dry mortar sand) over the several years:

Comrressive Strength: ASTMC109, 2-in. cubes 7-day

28-day 5670 psi 7840 psi

ASTMC349, 1.575-in. prisms 28-day 10,070 psi

Flexural Strength: ASTM C348, 1.575-in. prisms

28-day 1360 psi

2. Reinforcements

(a) Strength

Several mesh and rod reinforcements have been tested alone and as components in a matrix of "standard" mortar, i.e. in a ferrocement composite.

The following tensile strengths of the six kinds of rods used were obtained:

hot-rolled black C1020 galvanized C1020 bright drawn C1010 nail wire double-drawn high-tensile A82 double-drawn extra high-strength A82 deformed double-drawn A82

70,000 psi 50,000 psi 73,000 psi 79,000 psi

101,000 psi 84,000 psi

9

It was observed that a "cross weld" with minimum heat imput did not seriously impair the strength of the double-drawn wire although it is possible that "kinking" at the joint may occur in hull areas with greater curvature.

The following breaking strengths of several of the meshes used were obtained:

1/2-in. 16-ga. galv. welded square mesh 1/2-in. 19-9a. galv. hardware cloth 3/8-in. 20-ga. black welded square mesh 1/2-in. 22-ga. galv. hexagonal mesh

- longitudinal direction - transverse direction

2.5 1b expanded metal 1/4-in. coil 20-ga. fire screening

400 lb/in. width 140 1b/in. width 154 lb/in. width

60 lb/in. width 20 lb/in. width

not done not done

Panels containing mesh only were tested in flexure. The results indicated tbat the flexure strength is essentially proportional to the weight of mesh per unit area of the panel, regardless of kind of mesh. This is not true for a mesh tested in its weaker direction, e.g. hexagonal mesh and expanded metal tested in transverse direction.

(b) Bond Strength

The bond strength of rods was determined from "hair pin" rod specimens encased in mortar. Black hot-rolled, pickled hot-rolled, and cleaned and lightly rusted double-drawn high-tensile rods gave similar bond strengths. Bright rods, especially with the drawing lubricant (or rust preventing), and galvanized rods gave lower bond strengths even after 4 1/2 months. The deformed douole-drawn rod had high bond strength but split the mortar coupons.

No formal bond tests were performed on mesh. The locking or keying of twisted and galvanized mesh and the \'/elded joints ir. welded square meshes overrides any tensile/bond differences.

10

(c) Specific Surface

The specific surface of the several meshes used have been determined. The values calculated for the lengthwise wires only are 3.26 1n.-1 for 1/2-in. 16-ga. ga1v. welded square mesh, 3.35 in.- 1 for 1/2-1n. 19-9a. ga1v. hardwar~ cloth, 4.17 in.- 1 for 1/2-in. 22-ga. galv. hexagonal mesh, and 4.67 in. 1 for 3/8-in. 20-ga. black welded square mesh, all with 1/16 in. mortar cover.

(d) Conformability and Costs

Other factors have been briefly considered. In general, meshes of woven and twisted wires are more conformable to compOlmd curvature than are welded square meshes. The difference in cost for equal weights of the various meshes will not be an overriding factor in the choice of mesh reinforcement.

(e) -Corros i on

Corrosion coupons cut from various test panels and specimens damaged in flexure tests were subjected to seawater exposure. These coupons and specimens contained galvanized reinforcements. The corrosion attack of the mesh was qualitatively assessed.

Shaped coupons containing a single ungalvanized bare wire embedded 0.5, 2.0, and 3.5 mm below the mortar surface were prepared. The mortar coupons were stressed to provide controlled cracks in the mortar 0,0.05,0.1,0.2, and 0.5 mm wide. Triplicate sets of each combination of mortar cover and crack size were immersed at mean tide at the Vancouver Kitsilano Base of the Canadian Coast Guard. A triplicate set of each combination was removed at 1, 2,4, and 8 months. (A set for 16 months exposure is still exposed ct the time of writing).

The coupons were examined visually, the loss of wire section was measured with a micrometer, and the loss of wire strength was obtained from tensile tests. The following observations were made:

- corrosion after 8 months exposure was not severe in wires with a crack <0.1 mm wide even with only 0.5 mm mortar cover

- corrosion after only 1 to 2 months exposure was severe if the crack width was >O.lmm regardless of the thickness of the mortar cover.

- a mortar cover of 2 mm protected the wire in uncracked coupons from corrosion for at least eight months. a mortar cover of 0.5 mm failed to protect the wire in uncracked coupons from corrosion for over two months.

11

It is concluded that cracks >0.1 mm cannot be tolerated and that a mortar cover of at least 2 mm should be used. It seems advisable to use galvanized mesh for marine applications of ferrocement.

3. The Reinforced Mortar Composite

(a) Effect of Rods and Meshes on Strength

Tests were performed to assess the contribution of the kind and spacing of rods to the flexure and impact strengths of panels of the ferrocement composite. The presence of rods is very important, as is their spacing. However, the kind of rods used, viz. hot-rolled, galvanized, or double-drawn high-tensile rods appears to have only a small ef&ect on the strength of the panels. Other considerations such as "kinkingll over stiffener nodes and attachment to stern and bow may be of some importance.

Tests \'Jere performed to compare the f1 exure and impact strengths of ferrocement panels containing approximately equal thicknesses of the several kinds of mesh reinforcement. The flexure strength of the specimens containing 1/2-in. 16-oa. welded square mesh was superior to that of specimens containing the~lighter gauge welded square meshes (1/2-in. 22-ga. and 3/8-in. 20-ga.) and markedly superior to that of specimens containing the 1/2-in. 22-ga. hexagonal mesh. It should be mentioned, however, that th~ differences were almost eliminated when rods were also present.

The drop-impact performance of panels reinforced with 1/2-1n. 22-ga. hexagonal mesh when rods were also present was still somewhat poorer than that of comparable panels of the welded square meshes.

The argument for using 1/2-in. welded square meshes in preference to 1/2-1n. hexagonal mesh (when rods are present) is not strong. Conformabi1ity over curved portions of the hull and fairness (waffle-effect of mesh pressed between rods) may be the overriding consideration. High­strength woven square meshes, extolled by some authorities, have not been tested.

It was also observed that the flexure strengths of specimens with the rods, mesh, or both oriented at 45 degrees to the specimen length were only 50 to 90 percent (depending on the particular configurations) of the flexure strengths of specimens with normal orientations.

(b) Strengths of Typical Ferrocement Constructions

Typical ferrocements have been examined in this study in somewhat greater detail. The "typical" ferrocements considered here had a mortar

12

matrix of Type II cement and dry mortar sand reinforced with 0.225-in. double-drawn high-tensile A-S2 rods spaced at 2-in. centres and two layers each side (Panel 207) or three layers each side (Panel 20S) of 1/2-in. 19-9a. galvanized hardware cloth.

A single tensile specimen prepared from each panel was tested but each specimen held a load only equal to the sum of combined strength of the mesh wires and the rod/mortar bond strength. (Tensile test specimens from panels containing rods do not adequately represent the strength of a "semi-infinite" ferrocement plate because of the lack of rod. anchoring).

The following tensile strengths and the values of elastic modulus obtained were obtained: 207 20S

No. of layers of mesh No. of wires in section Area of section, sq.in. Load at first visible crack, lb. Max. load held, lb. Modulus of elasticity, psi x 106

4 16 2

1300 1420

1.1

6 23 2

1450 1900

0.9

Specimens, 1 x 6 x 18, 24, and 36 in., were tested in third­point flexure on an lS-in. span. A modified extensometer measured the tensile strain in the centre portion of the span between the third-point loads. The beam deflections at the third-points and at mid-length 'were measured. The location of the mesh wires and the rods relative to the specimen beam surface were obtained at the third-points and mid-length for future work.

The flexure strengths at load of first visible crack, Pfvc at Pfvc f2, and at maximum load held (modulus of rupture) and the elastic mOdulus values from beam curvature and elastic formulas at the load of first visible crack, Pfvc' and at Pfvcf2 were calculated for six specimens from each plate.

The following average values for flexure strengths and elastic modulus were obtained: 207 20S

No. of layers of mesh 4 6 Flexure strength, psi, at Pfvc 2600 2900

at PpVCf2 l300 1450 Modulus of rupture, psi at max 3700 4400 Elastic modulus, psi x 106

E = ~M at Pfvc 1.5 1.6

at Pfvcf2 2.3 2.7

~ E = € at Pfvc

at Pfvct2

(c) Behaviour Under Repeated Flexure Loads

0.9

0.7

1.3

1.3

Tests under cyclic flexure loadings were performed on 4 x 12 x 1 in. specimens from several panels. The first tests used

13

an apparatus which loaded the specimens to constant deflection. The later tests used an apparatus which loaded the specimens in third-point loading to constant magnitude.

Specimens from a panel containing three layers of 1/2-in. 19-9a. galvanized hardware cloth on each side of 0.225 in rods (one of the "typical" constructions already described) were loaded with repeated unilateral third­point bending loads of 2500 psi to 1320 psi fibre stress. The specimen at 1320 psi fibre stress withstood 500,000 cycles without visible cracking.

The work needs greater replication and tests at lower fibre stress levels to obtain an endurance limit. A true endurance limit may not exist for fe~rocement (as for many other materials) but the values obtained give a "feel ll for the probable behaviour of "typical ll ferrocement construction under repeated bending loads.

The fracture surfaces of mesh wires in the specimens broken under a simple single bending load and under the repeated loadings were examined by means of the scanning electron microscope. The photomicro-graph of the single load fracture shows the "dimpled" appearance typical of a tensile failure \'/hereas that of the repeated load fracture shows the "striated ll

appearance typical of a bending fatigue failure.

(d) Bolted Strength

Preliminary tests were undertaken to determine the bolted strength of ferrocement. Specimens 4 and 8 in. wide were cut from one-inch thick panels with 0.225-in. dia. rods spaced at 2 in. and 2 layers of 1/2-in. 16-ga. welded square mesh, 5 layers of 1/2-in. 19-9a. hardware cloth, or 10 layers of 1/2-in. 22-ga. hexagonal mesh. The 4-in. wide specimens carried a co-planer load, transmitted by a single 1/2-in. bolt, of about 500 lb/in. width when the single bolt hole was 2 in. from the free edge and the "equivalent bolt hole pitch" was 4 in. A reinforced edge and a greater distance between bolt hole and free edge would allow the bolt joint to possibly fail in compressive bearing.

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(e) Design Considerations

The use of the mechanical properties developed in the program for design has not been pursued. Readers are referred to the excellent review - An Introduction to Design for Ferrocement Vessels by G.W. Bigg for the Industrial Development Branch, Fisheries Service, Canada Department of the Environment in 1972.

The preliminary mathematical model prepared by J.D. Smith early in the program is presented in the Appendix.

(f) Patching

Patching of ferrocement in which the mesh reinforcement has not been broken has been shown to give virtually the original flexure strength with either cement/sand mortars or with filled epoxy-resin patching compounds. Ferrocement with some broken mesh regained 50 to 80 percent of its original strength. A mu1ti~need1e pneumatic chipping and scaling tool was effective in breaking up most of the loose mortar debris and in opening up cracks without seriously damaging the mesh. The behaviour of the patch under weathering and conditions of thermal expansion has not been ascertained.

(g) Protective Coatings

The question of coatings has received considerable attention. Twelve coating systems of various materials for primers and topcoats were subjected to dry laboratory environment (control), Weather-Ometer, laboratory wet-dry cycling in s~awater, and marine tidal exposures.

The most satisfactory performance was obtained from the following systems:

- Primer - inorganic ethyl-silicate zinc-rich paint - Topcoat - same

- Primer - two-component clear epoxy finish - Topcoat - two coats of vinyl resin-base anti-fouling paint

- Primer - two-component pigmented epoxy resin - Topcoat - same

- Primer - po1yviny1ch1oride-based enamel - Topcoat - two coats of same.

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(h) Quality Assurance

Attention is drawn to testing of the components of the ferrocement composite and of the composite itself. The importance of the cement/sand and water/cement ratios, slump, compressive and flexure tests, strength of the reinforcement materials, reinforcements and layup, and mortar placement procedures is stressed. Testing of ferrocement specimens must realistically represent the properties of the hull. Non-destructive testing of the hull is not well developed. Tentative guidelines for construction of ferrocement hulls have been issued by the certifying inspection bodies, viz. Canada Transport Ministry, Lloyd's Register of Shipping, and American Bureau of Shipping.

4. Bibliography

The bibliographic listing of articles pertinent to ferrocement vessel construction has been maintained and is presented in the Appendix.

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c. TEST PROCEDURES AND RESULTS

1. The Component ~1ateri a 1 s - ~10rtars and Steel Rei nforcements

(a) General

The two main components of the ferrocement composite are the mortar and the steel reinforcement. The steel reinforcement, generally rods and wire mesh, provides the skeleton on which the mortar is applied. It resists the tensile loadings. The function of the mortar in a ferrocement vessel is to keep water out and to provide compressive strength to the mortar/mesh composite. In addition, mortar must resist chemical attack by seawater and disintegration from freezing and thawing and other forces. The mortars and reinforce­ments have been treated singly and jointly throughout the program.

(b) The Mortar

The mortar, as generally used in ferrocement construction, is a mixture of Portland cement, sand, and water, with or without one or more admixtures added to give special properties. It is generally agreed that the properties of mortar are related to the materials used, e.g. types of sand and cement; to the proportions of the components, e.g. cement/sand and water cement ratios; and to other variables, e.g. curing conditions. The number of possible combinations is great. It was necessary to limit the number of tests by maintaining some variables constant. For example. it was assumed that many amateur and semi­professional builders would not be able to adequately steam-cure a newly plastered boat. Effective steam-curing requires that the surrounding atmosphere be raised to 130F for at least 48 hours. Most builders will cover their hull with polyethylene sheeting and hose it down regularly for about a month. Our test panels were done in this manner. r·10rtar test specimens were wetted, wrapped in paper towels. placed in a plastic bag for testing after 7 ·days or 28 days. A cement/sand ratio of 1:2, a ratio commonly used by amateur and semi-professional builders, was used throughout the programs. The water/cement ratio was held as close to 0.4 as possible since a low water/cement ratio favours high strength. The water/cement ratio was adjusted to allow penetration of the mortar through the several layers of mesh reinforcement. The mortar variations assessed were restricted to several types of sands and cements and to a few admixtures. The mortars have been evaluated as an unreinforced material and as a reinforced mortar/steel composite.

17

The sand for Portland cement mortars should be clean, strong, hard, sharp, durable, and well-graded. However, tests reported by the widely distributed and accepted Concrete Manual of the Bureau of Reclamation U.S. Department of the Interior have shown that changes in sand grading over an extreme range have no material effect on compressive strength of mortar when the water-cement ratio and the slump are held constant. It suggests that a sand of the size shown in Table 1 should be suitable for corrosion-resistant mortar linings for steel pipes.

Tests were performed to determine any significant differ­ence in the workability,strength, and durability of mortars for ferro­cement constructi on when vari Ol.'S sands were used. The sands exami ned were a dry bagged concrete sand, a dry bagged mortar sand, and a blend of three sizes of sharp Del t10nte silica sand.

Portland cements are produced in five major types (Types I to V) for use under specific conditions. The types differ in their proportions of the four main chemical compounds, namely tricalcium silicate, dicalcium silicate, tricalcium aluminate, and tetracalcium alumino-ferrite.

Type I cement is used in general construction work when special properties are not required. Type I, with its high tricalcium aluminate content, is not resistant to sulphate attack. Type II cement is used where moderate sulphate conditions are present. Its relatively low tricalcium silicate content provides good resistance to sulphate solutions. Type III cement is used where the strength must be developed rapidly. Type IV generates less heat then the other types and at a lesser rate. It is used in massive structures. Type V ceme'nt is used for concret~ in contact with soils and waters of high sulphate content. The low tricalcium aluminate and tetracalcium alumino-ferrite contents give much greater resistance to sulphates.

All types are reported to have about equal strengths after two months but Types II, IV and V appear to surpass Types I and III after several years. Another cement, kno\'Jn as aluminous cement, has monocalcium aluminate as its chief component. It is strong, has good resistance to seawater, but it appears to suffer catastrophic disintegration in some humid climates. A description and the requirements of the several Portland Cements may be found in ASTM C150.

18

Tests were performed to determine significant differences in the performance of ferrocement mortars made with the several cements.

Admixtures fulfill an important function in modern concrete technology. They can be of benefit \.,rhen used as air-entraining agents, set-retarders, accelerators, water-reducing agents, and workability improvers. The Division of Building Research, National Research Council, Canada has pointed out that any benefits are contingent on proper use and a knowledge of any possible harmful side-effects. The admixtures are often proprietary and specific formulations may not be generally avail­able across the country.

It was decided ~hat unless admixtures showed a substantial improvement in the mortar it was best to avoid their use. A pozzolan, a water-reducing agent, an air-entraining agent, and a polyvinylacetate emulsion were evaluated in a limited test program.

Pozzolans are described as siliceous or siliceous and aluminous materials, possessing little or no cementitious value, which, in finely divided form and in the presence of moisture, will react chemically with calcium hydroxide at ordinary temp­eratures to form compounds with cementitious properties in concrete. No recommendations for the optimum proportions of pozzolans in mortar have been found.

Water-reducing agents are considered to lower the mix water requirement which results in an increased compressive strength. It should be possible to reduce the cement content for a given strength. The basic ingredient of the common water-reducing admixtures is either salts of lignosulphonic acid or hydroxycarboxylic acids. The water-reducing agent used in this study is described as nan aqueous solution of metallic salts of lignin sulfonic acids which contains a catalyst to counteract the hydration-retarding actionn.

Air-entraining agents have a reputation for producing concretes which can resist damage by frequent wetting and by cycles of freezing and thawing. ~4any specifications require concretes which contain about six percent entrained air. The agents are generally formulated from wood resins, sulphonated hydrocarbons, and synthetic detergents. The agent used in this study is described as lIan aqueous solution of purified and modified triethylamine salts of a sulfonated hydrocarbon and which contains a catalyst to promote more rapid and complete hydration of the Portland cement ll

•

Polyvinylacetate emulsions have been used to toughen concrete. The added polymer, in the right proportion, fills the voids in the cement gel structure and exerts a binding effect on this gel structure. The air spaces, formed by air entrainment, are not filled. A 1:5 emulsion/cement ratio is reported to improve the workability of concrete mixes and to allow a lower water/cement ratio to be used. The cost makes it a relatively expensive addition.

(c) The Reinforcement

19

Steel reinforcer.:ent materials in a \'/ide variety of rein­forcements have been used by builders of ferrocement boats. Each has undoubted advantages and disadvantages. One kind or combination of reinforcement may be acceptable for one method of construction and unacceptable for another. One part of the hull may require a reinforce­ment which can conform readily to a compound curve. Another part may accept a stiffer kind of reinforcement.

The general mode of constructing ferrocement boats is to build a "skeleton" of steel rods on which layers of mesh are laid. The longitudinals (stringers or horizontals) ~xtend from the stem to the stern. Transversals or diagonals mayor may not be used, depending on the size and design of the boat. Several layers of steel mesh are laid on each side of the rods. However, some boats, incorporating closely spaced ribs, have been built without rods. Some builders believe that the main purpose of rods is to act as spacers to maintain the mesh in the outer portions of the hull section thereby increasing the section modulus. Some believe that rods greatly add to the hull weight without contributing much to its strength. The size and shape of the vessel are of undoubted prime importance in deciding the need for and spacing of rods.

Steel rods of several kinds are available for ferrocement boat construction. Their strength, surface finish, protective coating, size and other factors affect their performance as reinforcing members of the composite. Rods of about 1/4 in. diameter are most commonly used. Hulls with longitudinal and transverse rods of this size are about one inch thick. Smaller sizes have been used, especially for transversals. One general requirement is that a steel rod should not kink where it passes over a frame since it will result in a hull shape which must b~ faired by mortar padding.

20

The following readily available kinds of reinforcing rod material were obtained for testing purposes:

hot-rolled black (C1020) 1/4-in. rounds galvanized (C1020) 1/4-in. rounds br1ght drawn (C1010) 1/4-in. nail wire double-drawn, high-tensile ASTt1 A82 0.225-in. rod double-drawn, high-tensile ASTI1 A82 0.225-in. rod,

extra high strength double-drawn, high tensile ASTM A82 0.225-in. rod,

defonned by passing through dimpling rolls.

The kinds of IIfinely divided steel reinforcement ll are ~lmost limitless. The reinforcement may be steel rods of many kinds, chopped wire or fibre, slitted and expanded mesh, woven or welded mesh. The material may be of various mesh sizes and geometrics, e.g. hexagonal mesh, and link mesh. The wires may be hard drawn, oil-tempered, annealed, bright,black, galvanized, plated or coppered.

Many kinds of IImeshes ll have been used by tne ferrocement boatbu11der'. Many, such as welded wire fabric and hardware cloth, hex­agonal mesh IIchicken ll wire, expanded metal lath, and woven screening are readily available in many gauges, opening sizes, and strengths. Others are specialty items, such as IIthree-dimensional ll It/ire IIplanksll. In pra'ctice, most boats have been built with a hexagonal mesh, welded square mesh, hardware cloth, or combinations of these. Expanded metal lath has been successfully used, at least in part of the structure, by Fibersteel Company and its licensees. High tensile woven mesh has been successfully used by the U.S. Department of the Navy.IS

It became evident in the early work of this program that only a few of the several varieties of mesh available locally could be examined. Various tests were undertaken with a view to ruling out patently unsuitable kinds. The following kinds, mainly 1/2-in. mesh, were chosen for examination:

25 gao 2.5 lb/sq. yd. expanded metal lath, galvanized before slitting and expanding.

1/2-in. 16-ga. welded square mesh, galvanized after welding.

1/2-1n. 16-ga. welded square mesh, as above with zinc coat removed.

1/2-1n. 22-ga. hexagonal mesh, galvanized before weaving - light coat.

1/2-in. 22-ga. hexagonal mesh, galvanized after weaving.

1/2-1n. 19-9a. welded galvanized hardware cloth. 1/4-1n. coil 19-9a. black and oiled fire screening

(curtain) . 3/8-1n. 20-ga. welded ungalvanized square mesh.

21

A few other meshes, only slightly different from those listed, were also examined in a preliminary way but are not worthy of record. It was not possible to purchase loose-woven 1/2-in. mesh screening locally at the time of the tests. Some high tensile drawn and oil-tempered woven screens were available but these seemed too stiff and too expensive to warrant testing at the time.

2. Evaluation of Various Mortars

(a) General Procedure

Tests were performed to evaluate the workability, compres­sive strength, flexure strength, impact strength, porosity (permeability), and durability (resistance to disintegration in freeze-thaw and seawater environments) of mortars made with several kinds of sand, cement, and admixtures. The mortar was tested alone and in combination with steel reinforcement as ferrocement test panels.

All batches of ferrocement mortars were prepared in a horizontal-arm mixer which was able to mix 120 lb. of dry cement and sand without difficulty.

All batches had the following proportions, viz. cement/ sand ratio 0.5, water/cement ratio 0.4 to 0.5. One or more slump tests (ASTM C143) were made from each batch. In general, the slumps ranged from 3 to 5 in. Compressive strength test specimens, 2-in. cubes (ASTt1 C109), were made from each batch. In later work, compressive strengths (AST~1 C349) were also determined from broken flexure prism specimens, 1.575 x 1.575 x 6.3 in., cast in steel moulds. Flexure strengths of the mortars were determined from unreinforced portions of the test panels and, in later work, from flexure prisms, 1.575 x 1.575 x 6.3 in. (ASTt1 C348). Curing times of 7 and 28 days were used. The compressive strengths obtained from the broken flexure prisms were generally higher than those from the 2-in cubes. This is considered to be partly due to better geometry of the moulds used.

The first test panels were made in a horizontal 30 x 3D-in. plywood mould lined with 5 mil plastic sheeting. Later panels were made in an open 36 x 36-in. frame mould in an upright position to mo ' ~e nearly simulate conditions encountered in. mortaring a hull. The mould and mould frame are shown in Figs. 1 and 2.

Test panels, 30 x 30 in., containing 12 layers of 1/2-in. 22-ga. galvanized hexagonal mesh, cut 27 x 30 in. to leave a three-in. unreinforced portion along one edge, were made with various sands, cements, and admixtures.

22

Fig. 1. Mortar placement with vibrating trowel in horizontal 30-in. form mould.

m· ,::: c~ t~ ~ e: 'rl ''' I ~( ! ~:1 ~tI! IF

i ~~ c ;;::

~ c:: 1.

'''': p.~

~§ t' ":;

,;;J, . :; - I~

f"I [~ ,-<. I..:; • 1= t= ~' I"" t""E; F

: ~: 1-- ~ I:f.' I'"' b f§F= t:;: ,-,- P ' Ii:. H r ... r-l' I:":

"S' I'"' f- " . 1 I ... ; - F'-

c ~ "' I.:;;. I:::~

E: I';· t,::;.!S '), ~

E' I~ !im,· ':~ I;;: I ~~ I ·· if··- :l:;~ "" ~ l!:!~

p. r ~' I-:-;~ .- ~ ~

h-I,;; 1- t;;:; H

~~ -

Fig. 2. Vertical 36-in. open frame mould.

The following materials were used:

dry bagged concrete sand, dry bagged mortar sand sharp Del r10nte silica sand (8-, 20-, 3D-mesh) Type I 'Portland cement Type II Portland cement Type III Portland cement Type V Portland cement aluminous cement water-reducing agent air-entraining agent pozzolan polyvinyl acetate emulsion

(b) Morkability

23

The workability of a mortar is commonly measured by the cone slump test (AST~'1 C143) and the flow table test (ASTM C124). Although such tests do provide a measure of the workability, the tests must be correlated to the application. Only the slump test was used in this study. The critical measure of the workability for ferrocement, however, is the ability to fully penetrate mortar into the several layers of wire mesh with a trowel.

Preliminary tests showed that a minimum slump of 3 inches was necessary for penetration into 12 layers of hexagonal mesh in a form mould. Mixes with cone slumps of only 3 inches were very stiff. These mixes readily flowed into the horizontal 30 x 3D-in. moulds when a vibrating trowel was used. However, it was impossible to obtain complete pen~tration of the 12 layers of 1/2-in. 22-ga. hexagonal mesh by hand trowelling.

In later work, in which panels were made in a 36 x 36-;n . upright open frame mould to more nearly duplicate conditions of hull mortaring, it was not possible to use the vibrating trowel. The slump of the mortar was much more critical. Slump values of 3 to 6 inches were required.

24

In the first series of tests 26· 30 x 3D-in. panels were made using various meshes, types of cements, and types of sand. Twelve of these panels contained a "s.tandard" reinforcement of 12 layers of 1/2-in. 22-ga. galvanized woven hexagonal mesh 27 x 30 in. (A 3-in. unreinforced portion was left on one side of the panel.) Various cements, viz. Types I, II, III, V, and aluminous, and three sands, viz. dry bagged concrete sand, dry bagged mortar sand, and Del f10nte silica sand (8-, 20-, 3D-mesh) were used. The water/cement ratios ranged mainly from 0.4 to 0.5 and the slumps from 5 to 6 1/2. Compressive strength specimens of 2~in. cubes, were made for 7- and 28-day tests.

The mortar workability, as measured by the difficulty of penetrating the mesh, appears 'to be not significantly affected by the type of cements or sands used ?lthough the coarser and poorly graded sand gave some difficulty in finish trowelling. The comparisons are shown in Table 2.

The effect of admixtures on workability was assessed by ten 30 x 3D-in panels reinforced with 12 layers of 1/2-in. 22-ga. galvan­ized hexagonal mesh, 27 x 3D-in. The mortar mixes for the panels contained 1 part Type II cement, 2 parts dry bagged mortar sand, a water/cement ratio of 0.4 to 0.45.

One of the following admixtures was added to each pair of mortar batches: pozzolan, 1/4 of cement replaced; water-reducing agent, 6.5 fl. oz./bag cement; air-entraining agent, 3/4 fl. oz./bag cement; and polyvinyl acetate emulsion, 1/2 of water replaced. One pair contained no addition of an admixture. Test cubes for 7- and 28-day compressive strengths were prepared. The construction details, admixtures, and a description of the ease of trowelling the mortars into the panel mesh are provided in Table 3.

The tests did not show any significant improvement in \'lOrk­ability. The optimum proportions of the admixture in the mortars may not have been realized. Additional work is needed to affirm or refute the benefits of admixtures on workability.

The workability of mortar into the mesh has been discussed in terms of the sands, cements, and admixtures. The kind of mesh being penetrated also influences the apparent workability. Five panels of various meshes, viz.: 7 layers of 3/8-in. 20-ga. welded square mesh, 12 layers of 1/2-in. 22-ga. galvanized hexagonal mesh, and 2 layers of 1/4-in. 20-ga. black fire-screening, were made. Although some low-slump mortars used in some early tests did not penetrate well into one kind of mesh reinforcement, mortar penetrated all the meshes without great difficulty. Table 4 compares the workability of mortar into the various mesh constr.uctions outlined above.

u.s. Standard Sieve

4

8

16

3D

50

100

Pan

TABLE 1. Typical Analyses of Sands Used in Ferrocement Tests. (weight retained on sieve. percent)

U.S. Bureau Dry Bagged Dry Bagged Del Monte Silica Sand of Reclam- Concrete Mortar ation * Sand Sand 8-mesh 20-mesh 30-mesh

0 1 · - - -0-5 11 · 1 . -

10-20 22 8 73 . -20-30 22 26 26 43 1

25-40 29 39 - 52 61

15-20 11 20 . 5 28

3-7 4 7 - - 10

Fineness Modulus 2.84 2.08 3.75 2.38 1.53

* Recommended for corrosion-resistant mortar linings for steel pipes • .. Proportions of a-mesh. 20-mesh. 30-mesh Del Monte silica sand

25

1 :2:1**

. -

18

28

42

10

2

2.50

TABLE 2. Workability and strength of Mortar with Various Cements. Sands. and Slumps. (Panels contain 12 layers of 1/2 in. 22-ga. galvanized hexagonal mesh in a horizontal form mould.)

Panel Cement Waterl Slull'p Water Con;pressive Modulus of Sand Cement Workability Absorption Strength. psi Rupture. psi

No. Type Ratio in: S (unreinforced) 7-dav 28-dav

5 II Mortar 0.40 1lt EISY 7.2 1125 . penetratfon 1100

6 II • 0.40 SIt • • 6.0 1'42 890

14 II • 0.40 5Is • • 7.0 6200 7500 890 . 72SO . 16 II • 0.40 6It • • 6.6 5830 9450 760

9875 820 17 I • 0.40 5 • • 7.3 5040 5875 10SO

6175 960 18 III • 0.45 4'1 Some . 5400 8325 1320

difficulty 7750 1280 19 III • 0.47 5 Easy - 51~ 8450 590

penetration 7750 560 22 III • 0.45 5 Some . 8000 7000 -

difficulty 7800 -23 Y • 0.41 5Ja Easy - 7575 10000 932

penetration 10700 843 24 Aluminous · 0.36 4'1 . · - 91 SO 7250 1028

6280 792 25 II Del 0.40 lit Tears. some - 5700 6390 635

Monte difficulty 5780 782 26 I Mortar 0.41 lit • · - 68SO 8110 855

94SO 738

26 TABLE 3. Effect of Admixtures on Workability. Absorption. and Strength of Mortars.

(MOrtar - Type II cement. dry mortar sand. cement/sand ratio 1:2) (Panels reinforced with 12 layers 1/2-in. 22-ga. galv./hexagonal mesh.)

Panel Water/ Water Compressive Modulus of Ad111xture No. Cement Slump, Workability Absorption strength. psi Rupture. psi

raUo in. S 7-dav 28-da~ (unreinforced)

1I0ne 31 0.40 21s Stiff mixes 5.2 5900 6950 1120 Penetration 5800 930

• 32 0.40 2 difficult 4300 6450 mo..

5100 6355 1025

Pozzolan replaced 33 0.42 21s Stiff mix. Penetra- 5.6 4550 7200 840 25 pe"cent of tion difficult. 7850 680 cement 34 0.45 lis More workable. 3575 6225

4975 4060 6562 760

Water-reducing 35 0.35 2 Stiff mix. Penetra- 3.9 7725 5500 1100 agent, 6.5 fl.oz. Uon difficult. 4700 1015 per bag cement

I 36 0.37 3 More workable. 5825 5875

6775 5875

1055 5485

Afr-entrainfng 37 0.40 3 Good workability 6.7 4900 6100 835 agent, 3/4 fl.oz. and easier 5100 735 per bag cement 38 0.40 3 penetration 5455 6050

7200 5175 6110 785

P01~'nYlacetate 39 0.48* 3 Stiff mixes 3500 3650 trill sion. Penetration 3775 pva/water 1:1.44 40 0.49* lis difficult. 5.8 2250 3000 850

1!QQ. 790 2875 3456 820

* includes pva

TABLE 4. Workability and Strength of Mortar in Panels Reinforced with Various Meshes. (Panels made in horizontal form mould with Type TI cement and mortar sand.)

Panel Kind of Mesh Water/ Slump. Water Compres s he Modulus of No. Reinforcement Cement in. Workability Absorption strength. psi Rupture. psi

ratio S dry basis 7-day 28-day (unreinforced)

10 3/8 in.-20 gao 0.40 &Is Easy Penetration 6.1 6050 7100 905 welded square mesh 705 not valv. 7 layers

11 1/2 1n.-19 gao 0.40 71s Easy Penetration 6.8 - 7420 1180 welded hardware 990 cloth. galv •• 9 layers

12 1/2 1n.-16 gao 0.40 7" Easy Penetration 7.2 5400 7950 840 welded square 9875 895 lllesh, ga lv •• 5 layers :

13 2.5 lb expanded 0.40 5" Easy Penetration 6.6 5950 7200 725 llletal lath. ga1v •• 7500 792 5 layers

14 1/2 i".-22 ga. 0.40 &Is Easy Penetration 7.0 6200 7600 890 hexagona 1 mesh. 7250 -galv. 12 layers

15 1/4 1n.-20 ga. 0.40 SIs Easy Penetration 7.0 5600 8150 830 fire screening, 7675 960 2 l.yers

27

(c) Mortar strength

The compressive and flexural strengths of the mortars (or mortars reinforced with a "standard" reinforcement) containing the various sands, cements, and admixtures were compared in a series of test batches and panels.

Compressive strengths were determined for the early batches by 2-i n. cube specimens (ASTf.1 Cl 09) cured for 7 and 28 days and for the later batches by both cubes and the broken halves of the 1.575 x 1.575 x 6.3-in flexure beam prisms (ASTf.1 C349).

Flexure strengths were obtained for the early batches and panels on specimens from the 3-in. wide unreinforced portion of the test panels. The specimen layout pattern is shown in Fig. 3. Mortar flexure tests for the later batches used 1.575 x 1.575 x 6.3-in. flexure beam prisms (ASTM C348). The former spec~mens were loaded at the third-points on a 10-in. span, the latter at mid-point on a 4.685-in. span. In addition, some flexure tests were performed on specimens reinforced with "standard II mesh reinforcement.

Drop-impact tests were also made, where applicable, on specimens from reinforced panels. The drop-impact strength specimens, 15 x 15-in., were cut from mesh-reinforced panels containing mortars with various sands, cements, and admixtures. The drop-impact apparatus, shown in Figs. 4 to 6, was built to approximately simulate the velocity and shock of a collision between a hull and a IIdeadhead" log at about 15 knots. The 50-1b drop tup was a round-bottom aluminum air tank loaded with steel balls. The drop height was 10 feet, giving an impact energy of 500 ft.-lb. Details of the support and cushioning with a disc of 1/4 in. plywood are shown in Fig. 4. Tests on 30-in. and 36-in. panels were performed with the same drop apparatus except that the large panels uere supported on 24 x 26-in. and 31 x 31-in. 2 x 4 'Nord frames. The drop-impact damage was assessed qualitatively and by measuring the dishing of the impacted panel specimen and the extent of cracking on the bottom "convex" surface.

The mortars made in later years were considered to be the "standard" mortar mix, viz., Type II cement/dry bagged mortar sand ratio, 0.5; water/cement ratio, 0.4 to 0.5, chromium trioxide (to inhibit a reaction between galvanized mesh and bare rods), 300 ppm. The compressive and flexural strengths of these "standard" mortars made over the five years have been statistically analyzed.

28

D

B

G

c

E Fig. 3. Layout of 30-in. panels

F

for test specimens.

A,B - drop-impact or diagonal tests C - flexure tests on unreinforced mortar O,E - flexure tests on reinforced panel,

longitudinal and transverse F,G - various test, durability, exposure,

paint, etc.

50 lb tu~, 10 ft. above specimen .

guide frame

plywood disc, 1/4 in. x 6 in. dia

foot of frame, 1/4 in. steel plate ferrocement specimen, 15 in. square plywood ring, 3/4 in. x 12 in. hole.

steel support frame

support pad, 2-in wood plank

Fig. 4. Sketch of drop-impact test guide frame.

29

Figs. 5 and 6. Drop-impact apparatus.

30

The mean values are:

Compressive strength ASTM C109, 2-in. cubes

7-day 28-day

ASTM C349, 1.575-in. prisms

5670 psi 7840 psi

28-day 10,070 psi

Flexure Strength ASTM C348, 1.575-in. prisms

28-day 1360 psi

The number of batches, the means, and the standard deviations from the means are presented in Table 5.

The flexural strength of the various mortars was also evaluated from specimens cut from panels reinforced with IIstandard mesh reinforcement ll

,

viz. 12 layers of 1/2-in. 22-ga galvanized hexagonal mesh. These flexure specimens and specimens for impact tests were cut from the 30-in. panels as shown in Fig. 3. The IImodu1us of rupture ll values were obtained.

The fibre stress formula for beams loaded in flexure, S = ~c, applies to stresses below the elastic limit, i.e. where the d,istribution of stress across the section is linear. Since the formula is not rationa1 Mc for beams loaded beyond the elastic limit, a IImodified fibre stress ll

, s1=-1 is used for beams loaded to rupture. This value of IIfibre stress ll is call~d the modulus of rupture. Throughout this report, the term IImodu1us of rupture ll has been reserved for the IIfibre stress ll calculated for :the maximum load held by the beam. The value is calculated not at the onset of first visible brittle cracking of the mortar (unless otherwise stated) but at the maximum load when mesh wires broke, rods slipped, or both.

i. The Effect of Various Sands The strengths of mortars and panels of similar reinforcement

containing either the dry bagged mortar sand or the Del Monte silica sand were compared. The average 7-day and 28-day compressive strengths for the mortar sand are 6015 and 8544 ps i, respecti ve 1y, and for the Del r10nte sand 5700 and 6100 psi, respectively. Although the Del Monte sand appears to give somewhat lower compressive strengths the values are certainly within two standard deviations, 20, calculated for all IIstandard mortar ll batches as shown in Table 5.

The average modulus of rupture values, 1~~, for unreinforced panels of the two mortars is 823 psi for the mortar sanS mortars and 709 psi for the Del Monte sand mortars. This latter value is lower than the flexure

31

strength, 869 psi, obtained on 14 mortar sand mortars. Single flexure tests on simi 1 ar1y reinforced mortars. show a·1most no di ffert;!nce between the two mortars. The specimens were obtained from panels reinforced with 12 layers of 1/2-in. 22-ga. galvanized hexagonal mesh. The beam specimens approximately 3 x 12 in. were tested in third pOint loading on a 10-in. span. The load at first visible crack in the mortar and the maximum load held by the beam specimens, oriented in both longitudinal and transverse mesh directions, were recorded. The modulus of rupture, .S~~, at maximum load was calculated.

The compressive and flexure strengths for mortars and panels containing the dry bagged mortar sand and Del Monte silica sand are presented in Tables 6 and 7 for comparison. The test results, within the limitations of replication po~sib1e, show no consistent or practical differences between the two sands used. It is concluded on the basis of these preliminary tests that it was probable that a "special" sand would not be significantly better. Therefore, it was decided to make all future panels with the dry bagged mortar sand readily available from a local source.

ii. Effect of Various Cements

A series of panels, Nos. 16,17,18,19,22,23, and 24 were made us i ng the "s tanda rd" dry mortar sand wi th Types I, II, I II, V, and aluminous cements. All cement/sand ratios were 0.5. The water/ cement ratios were 0.36 to 0.47. The reinforcement in all panels was 12 layers of 1/2-in. 22-ga. galvanized hexagonal mesh.

The compressive strengths of the mortar from 2-in. cubes at 7 and 28 days, the modulus of rupture values from flexure tests on unreinforced portions of the panels and on longitudinal and transverse reinforced specimens, and impact tests on 15-in. tiles were obtained. The results, presented in Table 8, showed no consistent superiority of mortar made with one kind of cement over that made with another kind.

-Within the replication possible, it was concluded that the type of cement used was not an important factor in the strengths of ferrocement mortars. The type may be a factor in durability, however.

iii. Effect of Admixtures

The average compressive and flexure strengths of a series of ten panels which contained no admixtu·re, pozzo1an (replacing 25 percent of the cement), a water-reducing agent (6.5 fl. oz. per bag of cement), an air-entraining agent (3/4 fl. oz. per bag of cement), and a po1yviny1-acetate emulsion (pva/water 1:1.44) are presented in Table 9. It was

32

1IILI 5. Compressive and Flexure Strength of ·Standard Mix· Mortar Batches Made Between 1969 and 1974. (-Standard Mix· is 1 part Type 11 cement. 2 parts dry bagged mortar sand - no admixtures.)

Cure NUll'ber Mean Stand. Mean Tilt Proper\), Period. of Value. DeY.a :t3CJ

days Batches psi. psi. psi.

Compressiye Strength 7 33 5666 624 3794-7538 ASTM Cl09. 2-1n. cubes 28 40 7843 898 5149-10537

CompressiYe Strength 28 14 10071 924 7299-12843 ASTM C349. 1.575 x 1.575 x

6.5 in. prisms

Flexure Strength ASTM C348. 1.575 x 1.575 x

28 14 1371 121 1008-1734

6.5 in. prisms

TABLE 6. Summary of Strength Tests on All Mortars Made with Type II Sand and Dry Mortar Sand or Del Monte Sand.

Year No. of Compressive Strength, psi Compressive Flexure Modulus of Of Kind Of Panels 2-in. cubes, C109 Strength,psi Strength, psi Rupture, psi

Test Sand (Batches) 1.575 in. prism 1.575 in. prism (unreinforced) Tested 7-day 28-day ASTM C349 ASTH C348

1969-70 Dry bagged 7 5838 8087 IIIOrtar sand (-8 mesh) 14 869

Del Monte sand 1 (8-/20-/30-mesh)

5700 6100 709

1970-71 Dry bagged 23 5505 7874 IIIOrta r sand

1972-73 Dry bagged 10 5390 7680 10,090 1350 IIIOrtar sand

11169-73 Dry bagged 4300 to 6400 to 7500 to 1120 to 705 to IIIOrtar sand 7275 9950 12.400 1730 1230

33

TABlE 7. Results of Tests on Mortars Ind Plnels Using Two Types of Sand' (Type II cement. 12 layers of 1/2-in. 22-ga. galy. hexagonal mesh.)

'anel Compressive Modulus of Panel Strength Sand Strength, psi Rupture, psi No. (unreinforced) Flexure l • psi Impact2

7-day 28-dav dishing, 1/16 in.

5 Dry blgged - - 1125 IIOrtar sand 1100

6 - - 742 890

14 6200 7600 890 longit. 2421 19. exposed 7250 - transY. 1610 mesh. broken wires

16 5830 9450 760 9875 820 -- -- --

6015 8544 904

25 Del Monte 5700 6390

I 635 10ngit. 2490

1:2:1 5780 782 trln 1660

1 Simple beam, approx. 3 x 12 in., span 10 in., third-point loading 2 SO-lb tup with round base (9-in. radius), dropped 10 ft. onto 15-in. panel specimen.

TABlE 8. Results of Tests on Mortars and Panels Using Various Types of Cement (Dry bagged mortar sand. 12 layers of 1/2-in. 22-ga. galv. hexagonal mesh.)

Compressive Modulus of Panel Strength Pinel Type of Strenqth psi Rupture, psi Ho. Cement (unreinforced) Flexure l .-. pst Impact~

7-day 28-day dishing, 1/16 in.

17 Type I 5040 5875 1050 long~t. 2910 16, exposed 6175 960 Transv. 1665 mesh. broken wires -- -- --

5040 6025 1005

14 Type II 6200 7600 890 10ngit: 2420 19. exposed 7250 - trlnsv. 1610 mesh. broken wires

16 5830 9450 760 -9875 820 -wrn- ~ m 18 Type III 6400 8325 1320 -- 1280 -19 5150 8450 590 10ngit. 2430 22. exposed

7750 560 trlnsv. 1585 mesh. broken wires 22 8000 7000 - -7800 - -

m; 1865 m 23 Type V 7575 10000 932 10ngf.t. 2960 11. exposed

10700 843 trlnsv. 1735 mesh. broken wires -- -- -7575 10350 888

24 Aluminous 9150 7250 1028 longit. 3500 18. exposed -- 6280 .m. trlnsv. 1810 mesh. broken wires 9150 6765 910

1 simple beam. approx. 3 x 12 in •• span 10 in., third-point loading I 50-lb tup with round base (9-in. rldius) dropped 10 ft. onto 15-in. panel speCimen.

observed that, except for the polyvinyl acetate emulsion which had low values of 7-day and 28-day compressive strengths, the several admixtures had little effect on the strength of the mortars. The average 7-day and 28-day compressive strengths for the admixtures (excluding the polyvinyl­acetate emulsion) were between ± 3 standard deviations of the mean for all "standard mix" mortars 1969-1974 shown in Table 5.

Although the optimum addition rate for the above admixtures in mortars is now known, the chance of significant improvements in strengths did not seem to warrant further work at this time.

(d) Water Absorption and Transmission

A few of the morta~s were tested for differences inwater absorption and transmission properties. Specimens from unreinforced panels made with Type II cement and dry mortar sand were soaked 24 hours in water. The specimens absorbed 6.0 to 7.3 percent water on an oven-dried basis. The mortars containing an admixture were also tested. The mortar containing the water-reducing agent absorbed 3.9 percent, those with the other admixtures, 5.2 to 6.7. The absorption values are given in Tables 2, 3, and 4.

It is worth mentioning that test coupons subjected to many wet/dry exposure cycles lost only about two percent of their weight after being oven-dried overnight. This suggests that the voids may become filled with a gel or become otherwise clogged by immersion in water for a long time.

Other minor tests were also performed for manifestation of the water permeability of ferrocement. A 2-ft. column of water was main­tained for one year on a mortar test coupon '3/4-in. thick. A small grey spot appeared on the bottom for a short time but no water was evident. The grey spot soon disappeared as a gelling reaction at the mortar/water interface sealed off the mortar surface. Another similar test coupon was placed on a thin polyethylene sheet. Capillary forces failed to draw moisture through the coupon at the grey spot.

It was concluded that a well-made mortar will provide a water-tight hull.

(e) Durability

The durability of concretes (and mortars) has been defined as "resistance to deteriorating influences of internal 'and external factors to which it is exposed within the duration of life expected from the structure". It follows that the requirements for a durable concrete will depend on the type of structure, the type of exposure or servic~ condition, and on the required service life. The service exposure inc1u/ weathering, chemical action, and wear.

35

Although other characteristics may be important in tropical climates, the characteristics of greatest importance to the performance of mortars in ferrocement hulls of Canadian fishing vess"els operating in Canadian waters are weather resistance and seawater resistance.

The disintegration of concretes (mortars) by weathering is caused mainly by the disruptive action of freezing and thawing and of expansion and contraction from variations in temperature and alternate wetting and drying. Although laboratory tests for durability are difficult to correlate with service performance, tests conducted over many years have shown that freeze-thaw tests can distinguish between durable and non­durable types of concrete.

Seawater is considered to be mildly corrosive to concretes (mortars) mainly because of the soluble sulphate salts in the water. It is generally recommended that concrete for use in seawater be made with Portland cements which contain not more than 8 percent tricalcium aluminate. Types II, IIA, IV, and V meet this requirement. A low water/cement ratio and entrained air are claimed to increase the resistance to attack by seawater.

Although much research and exposure testing has been under­taken over many years on structural concrete, relatively little research has been reported on the durability of ferrocement. A series of tests to determine the resistance of various ferrocement mortars to freeze-thaw and seawater exposures was therefore undertaken. The tests described herein are not comprehensive but are intended to show any drastic sho"rtcomings in the behaviour of the various mortars and ferrocement constructions used.

i. Freeze-thaw Exposure Tests

Since ferrocement vessel hulls are of relatively thin section, specimens from ferrocement panels which represent the hull in section thick­ness do not meet the specimen sizes required in ASTM specifications for testing concrete and for brick and structural clay tile, i.e. ASTM C666-73 and ASTt~ C67-73. C666 requires the specimens be subjected to 300 cycles (40F to OF) of freezing and thawing (or until its relative dynamic modulus of elasticity reaches 60 percent of its initial modulus) and C67 requires the specimens be subjected to 50 cycles of freezing and thawing.

Twelve weighed unreinforced mortar coupons, 3 x 5 x 3/4 in., containing various cements, sands, and admixtures were placed in shallow water-filled trays in an environmental chamber*. The chamber was programmed

* Environmental Chamber Model ELHH-27-MRLC-l, Associated Testing Laboratories, Inc.

36

to give six freeze-thaw cycles per 24-hour day. The water temperature (and coupon temperature) cycled from 10C to -4C and the air temperature from 25C to -12C. The cycling prpgram was continued for 350 cycles. The coupons were observed regularly. At the end of the program the coupons were dried at 200F and weighed.

The mortars tested, the visual observations, and the weight loss from spalling are recorded in Table 10. The mortar sample which contained the pozzolan addition disintegrated badly, that which contained the po1yviny1-acetate emulsion showed some spa11ing and weight loss. In general, admixtures did not confer improved resistance to freeze-thaw cycling. Fig. 7 shows four coupons, one of which has disintegrated.

It has been shown that the presence of mesh affects the freeze­thaw resistance of ferrocement. Eleven test coupons, 3 x 4 x 3/4-in., containing 12 layers of 1/2-in. 22-ga. galvanized hexagonal mesh reinforcement, were sub­jected to 76 freeze-thaw cycles in a similar program. The coupons had a top layer without reinforcement. The sawn edges of these reinforced specimens were coated to prevent ingress of water at the sawn edges.

The specimens were examined after 36 and 76 cycles. The test results are presented in Table 11. In general, the unreinforced portions of the test coupons were disintegrated, often by delamination at the reinforced/ unreinforced interface, after 76 cycles of freezing and thawing; the reinforced portions were sound. Fig. 8 shows typical specimens.

Although there were some inconsistencies in the test results, the preliminary results indicate that mesh reinforcement (e.g. 1/2-in. 22-ga. hexagonal mesh) improves the freeze-thaw durability of ferrocement mortars and the kinds of cements, sands, and admixtures used appear to have little effect on the freeze-thaw durability of ferrocement mortars.

ii. Seawater Exposure Tests

Test coupons, 3 x 4 ' in., were sawn from various panels containing various mortars and meshes. The sawn edges were coated with an epoxy compound to prevent entry of water through the sawn edges. The 24 test coupons were inserted into slots in two wheels of an exposure apparatus. The apparatus immersed the specimens in a bath of natural filtered seawater for one hour and removed them for drying in front of a fan for three hours. The tests were performed at ambient room temperature.

The condition of the test coupons after 350 cycles of seawater immersion were evaluated by visual appearance and scratch and penetration hard­ness compared with coupons not subjected to the wet-dry cycling.

Panel No.

31. 32

33. 34

35. 36

37. 38

39. 40

Pinel No.

16

17

19

23

24

25

26

31

33

35

37

4D

37

TABLE 9. Ef'ect of Admfxtures on Compressfve and Flexure Strength of Mortars. (Mortar - Type II cement. dry bagged mortar sand. cement/sand ratto 1:2) (Panels refnforced with 12 layers 1/2-in. 22-ga. galv. hexagonal mesh)

Average.Compressive Modulus of Matxture Strength. pst Rupture. pst

(unretnforced) 7-day 28-day

None 5100 6430 1025

Pozzolan-replaced 25S of cement 4060 6560 760

Water-reducing agent - 6.5 fl. oz./bag of cement 6780 5490 1060

Air-entratntng agent - 3/4 fl. oz./bag of cement 5180 6110 785

Polyvtnylacetate emulsion - pya/water is 1':1.44 2880 3460 820

TABLE 10. Freeze-thaw Durabtlity of Mortars Containing Various Cements. Sands Ind Admixtures after 350 cycles. 10C to -4C.

. Description of Mortar No. Visual Appelrance Weight loss

of of Test Coupons Dry Bisis. Cement Admixture Sand Cycles S

11 None Dry Mortar Sind

350 No significant change 0

I None • 350 • 0

III None • 350 • 0.8

V None • 350 • 0

Aluminous None • 350 • 0

11 None Del Monte sf1icl sand

350 Slight powdering 0.7

I None Dry mortar 350 No Significant chlnge 1.1 Sind

II None • 350 • 1.2

II POllohn • SO-loo Some corner crumbling 350 Crlmlbled badly. 26.2

II Water-reducing • 350 No signiftcant change 1.1 agent

II Air-entraining • 350 • 2.2 Igent

• II Polyvinyl- 100-125 Sltght surface flaking acetlte 125-150 Slight surface spalling

350 Slight surface spilltng 4.9

38

..

Fi g. 7. Condition of four unreinforced test coupons after 350 freeze-thaw cycles.

~J F-4 ... • ~ .• "" ,.! .. :~

-/( ............ '.: l.1. "7.

Fig. 8. Condition of mesh-reinforced coupons after 76 freeze-thaw cycles.

39

The description of the test coupons exposed, their visual appearance, and the penetration hardness (a Rockwell Hardness tester using a 1/8 in. steel ball and a 60 kg. load) are presented in Table 12.

The changes in visible appearance and in scratch and pene­tration hardness after 350 cycles of exposure were insignificant.

The weight loss of the test coupons on oven drying ranged from 0.7 to 2.0 percent, much lower than the normal water absorption per­centages obtained on mortars not subjected to the cyclic exposure program. It is believed that the precipitation of salts and formation of cement gels may clog the pores and voids after prolonged exposure.

It is tentatively concluded that all of the mortars tested resist attack from seawater under the ambient laboratory conditions used. The effect of various reinforcements, galvanized or baret and of seawater attack at damaged areas is considered later.

(f) Interrupted Mortaring

A large hull may tax the ability of the plastering crew to finish in one day. Interrupted mortaring or multi-stage cold-joint plastering has been used to avoid the deteriorating quality of work by an overtired crew. Several tests were performed to determine any loss of strength which may result from interrupted mortaring. Mortar was applied to one side of a panel with layers of 1/2-in. 19-9a. hardware cloth on 0.225-in. rods. The other side was wetted and plastered 24 hours later. Sectioning revealed some boundary interface sponginess in some areas, good bond in others. Flexure testing did not cause delamination. It was conc1~ded that, provided the mortar consistency was proper and the mesh penetrability was good, a satisfactory bond between the two mortar layers may be obtained.

Another panel was completely plastered from both sides except for a 12-in. wide strip at one side. The rewetted panel was finished 24 hours later. A flexure test specimen with the joint at mid-span cracked at the joint but its modulus of rupture was only slightly lower than that of specimens containing no joint.

Another panel was similarly made with a joint down the centre. Part of the joint was wetted and part was coated with a neat cement paste before remortaring 24 hours later. Flexure tests produced cracks at the joint but the flexure strengths at first visible crack were similar to those with no joints. The modulus of rupture values (at maximum load) of joint specimens are 60 to 80 percent of the modulus of the specimens with no joint.

40

TAILI 11. Freeze-Thaw Durability of Mesh-Reinforced Test Coupons of Various Cements, Sands, and Admixtures. (Reinforcement 12 layers 1/2-in. 22-ga. hexagonal mesh.)

Description of Mortar No. of Vtsual Appearance Cement Admixture Sand Cycles

Type I n11 Dry 36 No visible change. IIOrtar 76 Unreinforced layer partly disintegrated. sand Reinforced layer sound.

Type U n11 · 36 No visible change. 76 Unreinforced layer completely disintegrated.

Reinforced layer sound. Type III n11 • 36 No visible change.

76 Unreinforced layer completely disintegrated. Reinforced layer sound.

Type Y n11 · 36 No visible change. 76 Unreinforced layer partly disintegrated.

Reinforced layer sound. Ahlllfnous n11 · 36 No visible change.

Type II

Type II

Type II

Type II

Type II

76 No visible change. n11 Del Monte 36 Slight flaking top surface.

s11ica 76 Unreinforced top surface flaked slightly. Reinforced layer sound.

n11 Dry IOOrtar 36 No visible change. sand 76 · • •

POllohn » 36 • • • 76 • • •

Water- " 36 • • • reducing 76 • • • agent Air- II 36 • • • entraining 76 • • • agent

TABlE 12. Assessment of Test Coupons of Various Mortars After 350 cycles of Immersion in Seawater and Drying. (coupons contained various mesh reinforcements)

Description of Mortar No. Visual Appearance Penetration Hardness Value of of Coupons After Unex osed EXDosed

Cement Sand Admixture Coupons 350 cycles of Exposure Top Bottom Top Bottom

I DrylOOrtar n11 2 No change. 90 95 109 96 II • • 10 • 102 102 108 103 III • • 2 • 102 90 102 103 Y • • 2 • 102 105 95 103

Aluminous • • 2 • 109 109 112 113 II Del Monte • 1 • 96 91 100 105

s11ica II Dry IOOrtar • 1 • 90 - ·9S 9S II • pOllolan 1 • 89 - 99 99 II • water 1 • 103 - 105 106

reducing agent

II • air en- 1 • 85 76 111 117 training agent

II • polyvinyl 1 • 54 sa 65 62 acetate

41

It is concluded that the flexure strength of ferrocement made with interrupted mortaring will be somewhat lower than that of ferrocement with no joints. However, the difference in strength at the first visible crack does not appear to be great. Possible leakage problems at the joint have not been examined. However, it is believed that a jOint, properly bonded with cement of the proper consistency or with an epoxy interface, should not leak.

3. Evaluation of Various Reinforcements

(a) General Procedure

Tests were performed to determine the strength of the various rod and mesh reinforcements alone and as components of a steel/mortar composite material. The composites were tested mainly in flexure and impact. The mortar was generally a "standard" mix of Type II cement (1 part), dry bagged mortar sand (2 parts), water/cement ratio 0.4 to 0.5, chromic oxide Cr03 300 ppm.

(b) Rod Reinforcement

i. Kinds and Strengths

The ultimate tensile strength, the elongation (percent in 8 in.), and the reduction in area were obtained for the above rod reinforcement materials. In addition, since it is common practice for ferrocement boat builders to arc-weld some or all of the cross-over junctions of the longitudinal and transverse rods, tensile tests were also performed on specimens . of double­drawn high-tensile rods with a "typical" cross-weld. Double-drawn high-tensile A82 rods obtain their enhanced strength from cold working. Heating, as by welding, should diminish this strength.

The ultimate tensile strengths of the several rods tested were as follows:

hot-rolled black (C1020) rounds galvanized (C1020) rounds bright drawn (C1010) nail wire double-drawn high-tensile A82 double-drawn high-tensile A82 with arc weld double-drawn A82 (extra high strength) double-drawn A82 (extra high strength)

with arc weld deformed double-drawn A82

70,000 psi 50,000 psi 73,000 psi 79,000 psi 80,000 psi

101,000 psi 89,000 psi

84,000 psi

The strengths, elongations, and the reductions in area are presented in Table 13. The double-drawn A82 rod material is strongest. Its strength was not seriously diminished by a small arc weld. Excessive heat input should be avoided, . however.

42

11. Bond Strengths

Many papers have appeared in the literature showing the merits of black vs galvanized steel reinforcement for concrete construction. Building Research Digest 10916 has summarized five separate investigations into the bond strengths of steel reinforcing rods with galvanized, smooth, mill scale, or rusted surfaces. It concludes that the bond performance of galvan­ized bars is as good or better, on the average, than that of the smooth, mill scale, or rusted bars. It further points out that the protection against corrosion provided by the galvanized rods gives improved long-term bond performance over the others in a corrosive environment. Rust scaling and subsequent spa11ing of the concrete cover are avoided.

The effect of scale, ~ick1ing, drawing lubricant, rust, zinc coating, and deforming of rods on the rod/mortar bond strength in ferrocement applications was assessed in this laboratory by a series of tests. Mortar (Type II cement, dry mortar sand) was packed in moulds around hairpin-shaped rods of the several kinds to form duplicate specimens like those shown in Fig. 9. The embedded length of the arms was 6 in. The specimens were cured 28 days.

The duplicate rod/mortar specimens were tested in tensile loading. The maximum load was reached when one arm of the hairpin started to slip. Both arms of the galvanized rod appeared to slip simultaneously. The deformed double-drawn rod ·"hairpins" split the mortar blocks, presumably due to the wedging action of the dimpled surface. Two tested mortar blocks are shown in Fig. 10. The unit bond strengths were obtained by dividing the maximum load held by the embedded area of both arms of the hairpin. The bond strength of the single arm of each specimen which held was obtained after an additional period of 3 1/2 months. The results obtained in the tests after 1 month and 4 1/2 months are shown in Table 14.

The following conclusions are drawn:

- The rod/mortar bond strength increases with time (at least under non-corrosive conditions).

- The rod/mortar bond strength of rods pickled to remove mill rolling scale is similar to that of rods with the mill scale intact.

- The rod/mortar bond strength of double-drawn rods is improved by removing the drawing or protective lubricant.

- Light rusting on double-drawn rods further improves its rod/mortar bond strength.

- The dimpling process for double-drawn rods improves the rod/ mortar bond strength bu~ causes splitting of the mortar block.

- The galvanized rods had very poor bond strengths.

Fig. 9. Rod/mortar bond specimens.

Fig. 10. Rod/mortar bond specimens showing splitting of mortar block by deformed double-drawn rod.

43

TABLE 13. Tenstle Properties of Various Reinforcing Rod Materills used tn the Ferroeement Test Progrlm.

Descriptton of Rod or Rod Simple Dtameter. U.T.S. tn. psf

Hot-rolled black (C1020) rounds 0.250xO.265 70,000 (oval) 69,700

Galvanfzed (C1020) rounds 0.220xO.276 50,600 (ovll) 49,300

Bright drawn (Cl010) nafl wfre 0.250 73.400 72,700

Double-drawn high-tensfle A82 rods 0.225 78,800

Double-drawn hfgh-tensfle A82 rods - arc weld - 80,000 cross-over joint

Double-drawn high-tensile A82 rods - extra 0.225 100,000 high strength 99,000

102,000

Double-drawn high-tensile A82 rods extra - 89,000 high strength, arc weld - cross-over Joint

i1Jspecfmen broke close to or outside of gauge marks. 2 SpeCimen broke at arc-weld • J Specimen broke 1/2 in. from weld.

Elong. Red. 1n S fn 8 fn. Area.

S

23.5 67.3 24.0 66.8

24.4 71.3 25.1 69.0

(1) 63.9 8.5 64.8

10.0 63.5

7.5(2 ) 62.5

~1) 49.5 1) (1) 58.5

3.0 52.0

1.25 (3)

TABlE 14. Results of ,Rod/Mortar Bond Tests on Hairpin Specfmens of Various Refnforcing Rods.

Bond Strength, lb/sq. in. Type and Conditfon of Refnforcfng Rods of Embedded Surface Remarks

After 28 days After 4lt months

Hot rolled ,Cl020) 406 (scale fntact)

580 One arm slipped

Hot rolled (Cl020) 300 555 One arm slipped (selle removed by picklfng)

Double-drawn A82 135 280 One arm slipped (IS received with drawin9 lubricant)

Double-drawn A82 188 330 One Irm sl fpped (drawing lubrfcant removed)

Double-drawn A82 (l1ghtly rusted by few days exposure) 286 518 One arm slfpped

Deformed double-drawn A82 451 660 Mortar blocks split (clean), by wedge action

Galvanfzed (Cl020) rod 33 57 Both arms slipped (cleln) simultaneously

Old rod (reclaimed from outside panels 480 700 Rods broke, heavy submitted) corrosion and pit-

ting as fnstalled

45

It seems likely that the splitting action of the deformed (dimpled) double-drawn rod could result in delamination of ferrocement. Until it has been proven otherwise, it is recommended that this material not be used. The markedly inferior bond strengths obtained by the galvanized rod was unexpected. Building Research Digest 109 claims that the reaction between zinc and the alkaline liquid in the pores of freshly placed concrete can form bubbles of hydrogen gas which would have an unfavourable effect on the bond strength in normal reinforced concrete. Frazier 17 of the American Hot Dip Galvanizers Association cites tests which dispute the postulation of an earlier investigator that a reduced bond value may have resulted from hydrogen bubbles forming on the galvanizing which caused the adjacent concrete to become spongy. He seems to support the finding that concrete may cure more slowly in the presence of zinc and that the long-term bond strength of galvanized reinforce­ment rods will be superior. It is generally agreed that chromate-treatment of galvanized rods or the addition of chromium trioxide to the concrete (or mortar) will cure the hydrogen problem and enhance the bond strength. It has been suggested that some specifications bodies are already considering the incorporation of a requirement to chromate-treat all galvanized reinforce­ment bar. (The addition of chromium trioxide to the mortar is discussed in Section C-3-d-iv, The Hydrogen Gas Problem.)

In conclusion, it is felt that the use of galvanized rods, if properly treated, should be acceptable even in the short-term. Galvanized rods may be superior in the long term to bare steel which may be attacked by the seawater or which may be sacrificially protected by the zinc coating on the mesh. If the zinc on the mesh is consumed sacrificially to protect bare steel rods, it seems likely that the life of the mesh will be diminished. No tests or post-mortem examinations of old hulls have been made to validate this postulation.

iii. Costs

The approximate current (Feb. 1975) costs of the several rods used are presented for the purpose of comparison:

0.225-in. dia. double-drawn A82 1/4-in. hot-rolled C1020 1/4-in. galvanized C1020 1/4-1n. C1015 bright nail wire

c/1b 40 50 63 53

$/100 ft. 5.30 8.25

10.39 8.74

It will be observed that the cost of the rod material on a per 1b basis will not be a very important factor in the kind of rod chosen. The differences can be calculated for a specific hull design on the basis of the cost/100 ft. making due allowance for the difference in rod diameters.

46

(c) Mesh Reinforcement

1. Kinds and Strengths

The breaking strengths of some of the meshes were determined at various times throughout the five year program. The strengths of the dif­ferent batches purchased from various sources over the several years varied somewhat. Typical breaking strengths of mesh obtained from sing1e-, two-, three- t four-wire and folded-layer samples of mesh are as follows:

1/2-in. 16-ga. ga1yanized welded square mesh 1/2-in. 19-9a. galvanized hardware cloth 3/8-in. 20-ga. black welde; square mesh 1/2-in. 22-ga. galvanized hexagonal mesh

- longitudinal direction transverse direction

400 1b/in. width 140 1b/in. width 154 1b/in. width

60 lb/in. width 20 1 b/in. 'width

The strengths/wire obtained by the various techniques varied because of the mesh geometry as well as from difference in the strength of the steel itself. Table 15 summarizes the breaking strengths and unit tensile strengths found.

On the basis of the simple tensile strength obtained on the various meshes it is apparent that similar tensile strengths in the panels will be obtained by 2 layers of 1/2-in4 l6-ga. galvanized welded square mesh, about 6 layers of 1/2-in. 19-9a. galvanized hardware cloth, 5 layers of 3/8-in. 20-ga. black welded square mesh, and 13 layers of 1/2-in. 22-ga. galvanized hexagonal mesh (in its stronger longitudinal direction).

ii. Bond Strengths No rigorous tests to determine the mesh/mortar bond strengths

of the various meshes have been performed. Bond strength will vary with the geometry of the mesh (twisted wires, cross-welded wires), the kind of surface e.g. galvanized, unga1vanized, phosphated, chromated, rusted, scaled. One ad hoc test on 1/2-in. 16-ga. mesh with galvanized coating intact and stripped showed no significant difference in panel modulus of rupture. Each mesh was separated from the, mortar in the spec.i.mens wi th equal diffi cu1 ty. The grooves left by the separated wires show a textural difference. Those of the galvanized wire showed a spongy appearance whereas those of the stripped wire showing a smooth appearance. The spongy appearance may be due tQ a zinc-water-cement reaction.

The surface bond area per square foot of panel and the specific bond area, the ratio of the surface area of the mesh to its volume (only those portions of the wire oriented in the load stress direction) have been calculated for equal weights of mesh reinforcement, e.g. 2 layers of 1/2-in. 16-ga. galvanized square mesh, 5 layers of 1/2-in. 19-9a. galvanized welded hardware

47

cloth, 10 layers of 1/2-in. 22-ga. hexagonal me's'h (in both directions) and 6 layers of 3/8-in. 20-ga. black square mesh. These values are summarized in Table 16.

111. Specific Surface

The specific surface of reinforcement, K, the total surface of wire in contact with the mortar divided by the volume of the composite, is often used as one of the parameters to define ferrocement. Bezukladov19

claims that ferrocement must have a specific area of steel wire between 2.0 cm-1

and 3.0 cm.-1 (5.1 in.- 1 to 7.6 in.-1 ). The specific surface, K = 2TT d n where d=wire diameter, n=number of layers of mesh, a=wire spacing, at and t=thickness of panel specimen has been calculated for equal weights of the above mesh reinforcements in mortar ;,pecimens with a bare mortar cover and with 1/16-in mortar cover on each side of the mesh layer~. The values are shown in Table 17. If rods had been present, the surface area of the rods and the volume of mortar encasing the rods would have been ignored.

The specific surfaces ranged from about 2.6 to 3.9 cm- 1 for a bare cover and 1.7 to 3.20 cm.-1 for 1/16-;n. cover. It is apparent that the hexagonal mesh has the highest specific area of the three 1/2-in mesh materials examined. In practice, it is not possible to compress the layers of th~ hexagonal mesh uniformly to the "minimum" thickness and the specific surface for this "effective" thickness will be somewhat lower.

It is a1lo apparent that the 1/2-in. 16-ga. galvanized welded square mesh gives the least panel (hull) thickness for equal weight of mesh reinforcement and the 1/2-in. 22-ga. galvanized hexagonal mesh the greatest panel (hull) thickness.

1v. Workability

As shown in Table 4, the kind of mesh used, viz. 1/2-in. 16-ga. galvanized welded square mesh, 1/2-in. 19-9a galvanized hardware cloth, 3/8-in. 20-ga. black welded square mesh, 1/2-in. 22-ga. galvanized hexagonal mesh, 1/4-in. 20-ga. firescreening, and 2.5 lb/sq. yd. expanded metal lath, presented no real problems of mortar penetration when the mortar was applied into a horizontal form mould with vibration trowelling. The small holes of the expanded metal lath used would make penetration of mortar difficult or impossible where hand trowelling of a vertical panel was necessary.

v. Conformabi1ity

No formal tests on the conformability of the various meshes to compound curves have been undertaken. The hexagonal mesh, because of its

48

1/2-1n.

1/2-1n.

3/8-in.

1/2-1n.

TABLE 15. Summary of Typica' Strengths of the Several Meshes Used

Description of Wire Wire Mesh 5t -enath Diameter, lb/wire in.

16-ga. galvanized welded square mesh 0.0624 - longitudinal direction 219 - transverse direction 175

19-9a. galvanized hardware cloth 0.033 58 - longitudinal direction 64 - transverse direction 63

20-ga. black welded square mesh 0.034 58

22-ga. galvanized hexagonal mesh 0.024 - longitudinal direction of twists 27 - transverse direction 27

TABLE 16. Unit ~'eights and Bond Areas of Three Meshes as Equal Weight Reinforcements in Ferrocement Panels.

lb/in. width

418 350

116 128 126

154

60 21

Typical U. T.5., psi

65,000

70,000

64,000

60,000 60,000

Mesh Weight Bond Area Description of ~lesh

Ib/ft2 Ib/ft2 in2/ft2 in2/in 3

mesh panel of panel of mesh

1/2-1n. 16-ga. galvanized welded square mesh 0.56 (2 layers of mesh) 1.12 118 62

1/2-1n. 19-9a. galvanized hardware cloth 0.24 (5 layers of mesh) 1.20 190 96

1/2-1n. 22-ga. galvanized hexaqonal mesh 0.11 ~lO layers of mesh - longitudinal direction) 1.10 300 120 10 layers of mesh - transverse direction) 1.10 195 160

3/8-1n. 20-ga. black welded square mesh 0.200 (6 layers of mesh) 1.20 252 114

49

"soft" geometry, conforms most easily. Loose.woven wire, because of its ability to assume a diamond-shape, possesses a useful degree 'of conformability. The 1/2-1n. 16-ga. welded square mesh has least conformabi1ity but assumes the "fairest" shape on simple curves.

vi. Cost

The rapidly changing prices for steel make absolute costs of doubtful use. However, the relative costs are of interest. The local prices (Spring 1975) show that the cost of ~/2-in 16-ga. galvanized welded square mesh is about twice that of 1/2-in. 19-9a. galvanized hardware cloth and 1/2-in. 22-ga. hexagonal mesh. (cf. 44¢, 23¢, 22¢/sq. ft.) (It is interesting to compare the quoted 1971 prices of about 30¢, 12¢, and 6¢!) The difference in cost of the three mesh materials is not great on an equal weight basis (especially in 1971).

(d) Reinforcement in the Ferrocement Composite

i. Effect of Rods I

Although the strength of the rods per se is of undoubted importance the real measure of their usefulness is their performance in a ferrocement hull. Panels, although they have relatively short rod/mortar bond lengths, have been constructed to determine the contribution of rods to the drop-impact resistance and flexural strength of the ferrocement comp­osite and to assess the effect of ·the various kinds of rods and their spacing on these properties.

The effect of using rods was established by a series of panels which contained similar mesh reinforcements. The effect of the presence of rods on drop-impact resistance and flexural strength was examined in panels which contained no rods (panels 47, 48) (rods initially present to separate mesh layers, then removed immediately after mortaring) and panels which con­tained rods at 2-in. spacing (panels 42, 45), each with 1 layer of 1/2-in. 16-ga. weld mesh on the outer portions of the panel.

The drop-impact resistance and flexural strength test results presented in Tables 18 and 19 show the considerable contribution of rods to the panel strengths.

The effect of rod spacing was examined by .pane1s reinforced with 1/2-in. 19-9a. galvanized hardware cloth on 0.225 in. double-deformed high tensile A82 rods at 2-in. spacing (panels 41, 44) and 4-in. spacing (panels 54, 55). The drop-impact resistance and the flexural strengths, presented in Tables 20 and 21 show that 2-in. spacings are superior to 4-in. spacings.

50

TABLE 17. Specific Surface of Various Meshes in Theoretical Panel Specimens with Bare Mortar Cover and 1/16-1n Mortar Cover Each Side. (IPProX. equal weights of mesh reinforcement and corresponding panel thickness)

Assumed Specific Surface Specfftc Surface K

Description of Meshes Panel Wires in long. Wires in trans. Wires in both Thick. dirHtion ~ttion di rect 1 on"s. tn. in -! em. -! ;n - t"m - ~ :.t em -1

Wtth bare mortar cover

1/2-tn. 16-ga. galv. welded square mesh 1/4 3.26 1.28 3.26 1.28 6.52 2.56 (2 layers. 1.12 lb/sq.ft. panel)

1/2-1n. 19-,a. galv. hardware cloth 3/8 3.35 1.32 3.35 1.32 6.70 2.64 (5 ayers. 1.20 lb/sq.ft. panel)

1/2-1n. 22-ga. galv. hexagonal mesh 1/2 4.17 1.64 5.83 2.30 10.00 3.94 (10 l~ers. 1.10 lb/sq . ft. panel)

3/8-1n. 20-ya. black welded square mesh 3/8 4.67 1.85 4.67 1.85 9. 34 3.70 (6 ayers. 1.20 lb/sq. ft. panel)

With 1/16 in. mortar cover. both sides .

1/2-1n. 16-9a. galv. welded square mesh 3/8 2.18 0.86 2.18 0.86 4.36 1.72 (2 layers. 1.12 lb/sq. ft. panel)

1/2-1n. 19-ya. galv. hardware cloth 1/2 2.54 0.98 2.54 0.98 5.08 1.96 (5 ayers. 1.20 lb/sq. ft. panel)

1/2-1n. 22-ga. galv. hexagonal mesh 5/8 3.34 1.31 4.67 1.84 8.01 3.15 (10 layers. 1.10 lb/sq . ft . panel)

3/8-fn. 20-ga. black welded square mesh 1/2 3.51 1.~ 3.51 1.38 7.02 2:76 (6 layers, 1.20 lb/sq . ft. panel)

TABLE 18. Drop-Impact Resistance of Mesh-Reinforced Panels with and without Rod Reinforcement. (mesh reinforcement 1 layer of 1/2-in. 16 gao galvanized welded square mesh on each side)

Pinel Rod Reinforcement Dishing Max. circle Mode of Failure Ho. of cracks, in 1/16 in. in.

45 Double-drawn high-tensile 8 18 Fine radial cracks A82 rods at 2-in. spacing Fine rectilinear cracks.

48 No rods 18 32 Ffne radial cracks. One wide rectilinear cracks.

TABLE 19. Flexural Strengths of Mesh-Reinforced Panels with and without Rod Reinforcement. (mesh reinforcement 1 layer of 1/2-in. 16-ga. galvanized welded square mesh on each side)

Panel Rod Reinforcement F1rst Maximum Modulus Mode of Failure 1C0. Visible Load, lb of Rupture crack, lb psi

42A Double-drawn high-tensile 1300 2800 6050 Hain crack at a load point AB2 rods at 2 in. Rod slip noted

42B spacing 1950 3240 7000 Fine cracks at load points Rod slip noted

47A 1100 1600 2800 Several fine cracks between No rods load panels

47B 900 130D 2280 Fine cracks between load points.

A • transverse rods in tens10n side, B • lengthwise rods in tension side.

51

TABLE 20. Drop-Impact Resistance of Mesh-Reinforced Panels with Rods with 2-in. and 4-in. Spacing (Mesh reinforcements 3 layers of 1/2 in. 19-9a. galvanized hardware cloth on one side, 2 layers on other)

'Inel Dishing Max. circle Rod Reinforcement of cracks, Mode of FI11 ure No. in 1/16 in. in.

44 Double-drawn - high-tensile A82 rods 4 20 Very fine radial cracks. spaced at 2-in. centres One fine rectilinear crack.

55 Deformed double-drawn - high-tensile 10 24 Radial cracking. A82 rods spaced at 4-in. centres Fine rectilinear cracks.

Centre spall, 6-in. dia.

TABLE 21. Flexure Strength of r~esh-Reinforced Panels with Rods with 2-in. and 4-1n. Spacing (Mesh reinforcements 3 layers of 1/2 in. 19-91. galvanized hardware cloth on one side, 2 layers on other)

Pinel First Maximum Modulus of Rod Reinforcement Visible (Rupture, Hode of Failure No. Crack, lb Load, lb psi)

41A 0.225-in. double-drawn 1100 2240 3930 Main crack at load point. high-tensile A82 rods spaced No rod slip apparent.

418 at 2-in. centres 1700 2900 5080 Main crack at load point. Rod s 11 p noted.

53A As in 41A, 418 1100 1840 3230 Fine cracking. No rod slip apparent.

538 a 1900 3080 5400 Main crack at load pOint. No rod slip apparent.

54A 0.225-in. deformed A82 1000 1460 2560 Main crack at load point. rods spaced at 4-in. Fine cracking between centres load pOints.

Rod slip noted.

52

The effect of kind of rods used was examined by panels with 3 layers of 1/2-in. 19-9a. galvanized hardware cloth above and 2 layers below the following rod reinforcements spaced on 2-in. centres:

0.225 in. dia. double-drawn high-tensile A82 rods (panels 41 t 52) 0.225 in. dia. deformed double-drawn high-tensile A82 rods (panels 53, 54) 1/4 in. dia. galvanized C1020 steel rods (panel 49) 1/4 in. dia. bright C1015 nail wire rods (panel 50) 1/4 in. hot-rolled C1020 rods (panel 51)

These were compared only under flexure loadings. The results presented in Table 22 indicate a significant difference in the flexure strengths of panels made with the various kinds of rods used. The hot-rolled rods gave the best ultimate flexure strength. This would seem to be the result of better rod/mortar bond characteristics which delayed rod slippage. In an "infinitely 10ngll panel or in one in which the rods were cross-welded or held as at bow and stern, the difference is not likely to be important. Further, the diameter of the lower strength hot-rolled, galvanized, and nail wire rods is 0.25 in. Their section modulus is about 25 percent larger than that of the 0.225 in. dia. double-drawn rods. Also, the larger diameter forces the layers of mesh farther from the "neutral axis" of the panel thereby making the mesh more effective.

It is concluded that:

- rods make a significant contribution to the drop-impact resistance and flexure strength of mesh-reinforced panels.

- rods at 2-in. spacing give better drop-impact resistance and flexure strength to mesh-reinforced pane1~ than rods at 4-in. spacing.

- the kind of rods used is probably not of great importance to the strength provided that the rods can give a we11-faired hull (no kinks at cross-over points) and meet any other requirements, such as corrosion-resistance, weldabi1ity, repairability, and cost. the smaller diameter of the double-drawn high-tensile wire (for the same breaking strength), its resilience, and cost/ft. seem to favour its use.

ii. Effect of Mesh

The behaviour of the various meshes was evaluated by a series of test panels reinforced only with mesh reinforcement. No rod reinforcement was used. In the first series of tests, 30 x 30-in. panels were made in a plywood mould lined with plastic sheeting. Slightly-staggered 29 1/2 x 26 1/2-in. layers of reinforcement mesh were laid in the mould. All layers were oriented in the same direction. Layers were added until a reinforced

53

thickness of 1/2-in. was obtained. The overall, thickne~s was about 3/4 in. The mortar (Type II cement 1 part, dry mortar sand 2 parts) was carefully mixed and laid into the panel form mould with a vibrating trowel. The stripped panels were wetted regularly and cured for 28 days under plastic sheeting.

The reinforcements used in these tests were:

2.5-lb. galvanized expanded metal lath 1/2-in. l6-ga. galvanized welded square mesh 1/2-in. 22-ga. hexagonal mesh, galvanized after weaving 1/2-in. 22-ga. hexagonal mesh, galvanized before we~ving 1/4-in. 20-ga. fire screening 1/2-in. 19-9a. galvanized hardware cloth 1/2-in. l6-ga. welded square mesh, galvanized removed 3/8-in. 20-ga. welded square mesh

The number of mesh layers and weight of mesh per square foot of panel are given in Table 23.

The panels were sectioned, as shown in Fig. 3, to yield various test specimens.

. The panel specimens containing equal thicknesses of mesh were tested under drop-impact and flexure load conditions. The impact test was a 50 1b weight (9-in. bottom radius) dropped 10 feet onto a 15-in. square specimen supported on 3/4-in. plywood as described earlier and show~ in Figs. 4 - 6. The damage to the specimens was evaluated both qualitatively and quantitatively. The evaluation is presented in Table 24. The visual examinations and the measured concave deflections (dishing) 'rated the panel constructions as ,follows:

slight damage 1/2-in. l6-ga. galvanized welded square mesh 3/8-1n. 20-ga. black welded square mesh

moderate damage 1/2-in. 19-9a. galvanized hardware cloth 1/2-1n. 22-ga. galvanized hexagonal mesh

severe damage 2.5-lb expanded metal lath 1/4-in. 20-ga. fire screening

54

TAILE 22 , Flexural Strength of Mesh-Reinforced Panels with Various Kinds of Rod Reinforcement (3 layers of 1/2-1n. 19-9a.galvanized hardware cloth on one side of rods, 2 layers on other s)~

Panel First Maximum Modulus Rod Reinforcement Visible Load, of Rupture, Mode of Failure No. Crack, lb lb psi

41A 0.225-in. double-drawn high-tensile 1100 2200 3930 Main crack at load point. A82 rods spaced at 2-in. centres No rod slip apparent.

418 1700 2900 5080 Main crack at load pOint.

52A • 1300 1870 Rod slip noted.

3270 Uniform cracking.

528 2000 2050 3600 No rod slip apparent. Several fine cracks. No rod slip apparent.

54A Deformed 0.225-in. A82 rods 1000 1460 2560 Major crack at load point. Rod slip noted.

53A • 1100 1840 3230 Fine cracking.

538 1900 3080 No rod slip apparent.

5400 Main crack at load point. No rod slip apparent.

49A 1/4-in. galvanized C1020 rods 1300 1530 2680 Main crack at load point. No rod slip apparent.

498 1300 2500 4910 Several fine cracks. Rod slip noted.

50A 1/2-in. bright C1015 nail wire rods 1300 2350 4120 Main and fine cracks.

508 2320 2400 Rod sHp noted.

4210 Uniform crackinq. Rod s 11 p noted.

51A 1/4-in. hot rolled C1020 900 2900 5080 Uniform cracking. No rod slip apparent.

518 1500 3600 6310 Main crack at load point. No rod slip apparent.

A • transverse rods in tension side, S & longitudinal rods in tension side.

TABLE 23. Description of Panels Reinforced with Mesh Only and Used for Strength Evaluation of Mesh-Reinforced Panels

(All mortars Type II cement - 1 part, dry mortar sand - 2 parts)

Panel N( I Weight No. Mesh Reinforcement LIoyer:. . Mesh, 1bl

sq ft panel

3, 13 2.5 lb. expanded metal lath, oalvanized 5 1.23 4, 12 1/2-1n. 16-ga.welded square mesh, galvanized 5 2.85 5. 14 l/2-in. 22-ga.hexagonal mesh, galvanized after weaving 12 1.35 6. 16 1/2-1n. 22-ga.hexagonal mesh, galvanized before weaving 12 1.29 7. 15 1/4-in. 20-ga.fine screening, oiled, cleaned 2 1.20 8. 11 1/2-1n. 19-9a.hardware cloth, galvanized 9 1.59 9 1/2-1n. 16-ga. welded square mesh, zinc removed 5 2.85

10 i 3/8-1n. 20-ga.welded square mesh, black 7 1.59

i I

I I I

55

The f1ehJre strength, calculated as the modulus of r.upture or maximum fibre stress at ultimate failure of the beam, was determined for lengthwise and transverse 3 x 12-in". ~pecimens cut from the " panels containing various mesh reinforcements. Third-point loading on a 10-in. span was used in the manner described in ASTM C78 Flexural Strength of Concrete (using simple beam with third-point loading). The deflections under increments of loads, the load at the first visible crack, the maximum load held, and the mode of failure were reCOr?ad. The "modu1us of rupture II at the maximum load held was calculated as R = ~ where W = load, b = breadth, d = "thickness of the specimen. The ave~gge values for the lengthwise and transverse tests are summarized in Table 25. Fig. 11 shows typical load-deflection curves.

The results show the marked superiority of the 1/2-in. 16-ga., 3/8-in. 20 ga., and 1/2-in. 19-9a. welded square meshes in flexure. The hexagonal mesh and expanded metal lath are reasonably strong in the longitudinal direction but are poor in the transverse direction.

It is concluded that the square mesh reinforcements are superior to the others in both drop-impact resistance and flexure strength. Those mesh reinforcements which have very poor transverse properties, i.e. metal lath and hexagonal mesh, are deemed unsuitable except where they can be oriented so that the transverse loading is negligible or where rod-reinforcement carries these loads. Figs. 12 and 13 show the inferior crack distribution of the transverse specimens.

The major shortcoming of the square meshes and the obvious advantage of the hexagonal mesh is the conformabi1ity for compound curves. Fire screening is deemed completely unsuitable.

The relationship between the maximum flexural strengths obtained and the weight of reinforcement per square foot of panel, regardless of the kind of reinforcement, appears to be linear. Fig. 14 shows the plotted strengths.

In addition to the foregoing tests which compared strengths of panels with equal thicknesses of several mesh reinforcements, another set of panels with equal weights of the several mesh reinforcements was also tested in a similar manner. Four 30 x 30-in. panels were made with the following constructions:

3 layers of 1/2-in. 22-ga. galvanized hexagonal mesh 1 layer of 1/2-in. 16-ga. galvanized welded square mesh 2 layers of 1/2-in. 22-ga. galvanized hexagonal mesh

56

',nel 110.

4.t.12

10

8.11

6.16

3.13

7.15

'anel No.

3.13

4.9.12

5.14

6.16

7.15

8.11

10

TABLE 24. urop-Impact Resistance of Panels Reinforced with Various Meshes (All panels have lIZ-in. thickness of reinforcement mesh)

Reinforcement Dishing Description lblsq ft in Description of Mode of Failure

Pan~l 1/16 in.

1/2-in. 16-ga. galvanized 2.S5 3 No visible cracks in top surface. Some fine welded square mesh radial and rectilinear cracking to ed~es of

bottom surface. 3/S-in. 20-ga. black 1.59 6 Five ring cracks in top surface. Slightly welded ·square mesh open rectilinear and radial cracking in

bottom surface. 1/2-in. 19-9a. galvanized 1.79 9 Moderate open ring crack in top surface. hardware cloth Slightly open ring cracking in bottom

surface . 1/2-in. 22-ga. hexagonal ' 1.35 15 Large open ring cracks in top surface. mesh, galvanized after Shear spalling, open radial cracks, weaving and some broken wires in bottom surface. 2.5-lb galvanized 1.23 . 17 Open ring and transverse cracks in top expanded metal lath surface. Large diagonal cracks and

torn mesh in bottom surface. 1/4-in. 20-ga . black 1.20 22 Extremely severe major rinq cracks in top fire screening surface. Open radial cracks and mortar

crumbling in bottom surface.

TABLE 25. Flexure Strength of Panels Reinforced with Various Meshes (All panels have 1/2-in. thickness of reinforcement mesh)

Reinforcement Average Modulus lb/sq ft of Rupture, psi Mode of

Description Failure Panel Longit. Transv.

2.5-lb galvanized 1.23 3690 S50 Longit. specimens cracked expanded metal lath over wide area, trans-

verse mainly single crack. Broken mesh.

1/2-in. 16-ga. welded square mesh, 2.85 65S0 6040 Cracking at l-in . galvanized and stripped intervals on bottom.

Top ·spalling. 1/2-fn. 22-ga. hexagonal mesh, 1.35 2660 1485 Lonqit. specimens 9alvanized after weaving cracked over wide area,

transverse mainly sinqle crack.

l/2-in. 22-ga . hexagonal mesh, 1.29 3040 1275 As above. galvanized before weaving 1/4-in. 20-ga. black fire screening 1.20 1395 950 Mortar crumbled badly

in bottom surface at one or two major cracks.

1/2-in. 19-9a. galvanized 1.79 3560 3565 Both longitudinal and hardware cloth transverse specimen

cracked at 1/2-in. intervals over wide area.

3/8-in. 20-ga. black welded 1.59 5000 4460 Both lonqitudinal and square mesh transverse specimens

cracked at 3/8-in. intervals over wide span.

3000

2000

Load 1b

1000

o o O. 1

welded square mesh

1/2-in. 19-9a. hardware cloth llE

10E 3IB-in. 20-ga. welded square mesh

14D

l/2-in. 22-ga. hexagonal mesh

0.2 0.3 0.4

Def1ecti on, in.

Fig. 11. Flexure tests on mesh-reinforced beams.

57

0.5

58

.. ,

' -

.~.')l IG <J<'l.

..

r o - . ... ..., • _V I ~ C

. 1

Fig. 12. Bottom (tenston) surface of flexure specimens bent with bottom layer of mesh in transverse direction (left specimens) or longitudinal direction (right specimens).

'{

t -. )

\ ~

-I ~ If:

•

Fig. 13. Bottom (tension) surface of flexure specimens bent with bottom layer of mesh in transverse direction (left specimens) or longitudinal direction (right specimens).

7000

5000

Modulus of

Rupture psi

3000

1000

o

•

o

or. <to> ItS r-

r-ItS

<to> CIJ E "0 CIJ "0 c: ItS Q. >< CIJ

.Q • ..-U') • .

or. en CIJ E r-ItS c: 0 0'1 ItS >< CIJ

or. . ItS 0'1 • N

N

c: -• N ........ r-

1

• • •

•

. ItSClJor. O'ls.-en IItSCIJ

O::SE N CT

en . c:"O

.r- CIJ • "0

co r­........ CIJ M3: •

• •

. ItS 0'1 I

0'1 r-. c:

.r-I

N ........ r-

2

Mash Reinforcement - lb/sq.ft. panel

Fig. 14. Modulus of rupture vs. weight of mesh reinforcement in strongest direction

. ·59

.e­en CIJ E CIJ s.-10 ::s CT en "0 CIJ "0 r-

CIJ 3:

c: .r-

I N ........ r-

3

60

10 layers of 1/2-in. 22-ga. galvanized hexagonal mesh

2 layers of 1/2-in. l6-ga. galvanized square mesh

6 layers of 1/2-,;n. 20-ga. galvanized hardware cloth.

The weight of the mesh reinforcement in each panel was about 1.15 lb/sq. ft. of panel. The mortar in all panels was Type II cement 1 part, Del Monte sand 2 parts.

Specimens cut from the panels were tested as before in flexure and drop-impact. The results are tabulated in Tables 26 and 27.

The drop-impact resi~tance of the panel containing two layers of 1/2-in. 16-ga. galvanized welded square mesh was markedly superior to the panels containing other meshes. The flexure tests, performed as before, . showed the panel containing the two layers of 1/2-in. 16-ga. galvanized welded square mesh to 'be~rongest but the failure was a single bottom crack. The specimens from the panel containing six layers of 1/2-in. 19-9a. galvanized hardware cloth was considerably stronger than those from the panel containing the ten layers of 1/2-in. 22-ga. hexagonal mesh and had a somewhat superior distribution of bottom cracking. Both constructions, however, had a better crack distribution than that of the panel containing t.he 1/2-in. 16-ga. weld mesh.

Hulls are most often reinforced with rods between layers of mesh. Therefore, additional tests were undertaken to determine if rods diminished the differences between the longitudinal and transverse strengths of panels reinforced with the several kinds of meshes.

Six 36 x 36-in. panels were made in the free-standing panel moulds with 0.225 in. double-drawn high-tensile A82 rods at 2-in. spacing. The three pairs of specimens contained approximately equal weights of 1/2-in. 19-9a. galvanized hardware cloth, 1/2 in. 16-ga. galvanized welded square mesh, or 1/2-in. 22-ga. hexagonal mesh, viz.,

Panels 41,44 3 layers 1/2-in. 19-9a. galvanized hardware cloth on one side of rods, 2 layers on other side

42, 45 1 layer 1/2-in. 16-ga. galvanized welded square mesh lath on each side of rods.

43. 46 5 layers of 1/2-in. 22-ga. galvanized hexagonal mesh on each side of rods.

61

TABLE 26. Drop-Impact Resistance of Panels Reinforced with Equal Weights of Mesh

Panel Rei nforcement, No. Iblsq ft D1Shing Mode of Failure

Description Panel 1/16 in.

27 3 layers 1/2-1n. 22-ga. hexagonal mesh 1.14 14 Top - moderate r1nq crack1n~. 1 layer 1/2-in. 16-ga. welded square mesh Bottom - radial crack1nq over 2 layers 1/2-1n. 22-ga. hexagonal mesh 12-in. area, exposed mesh,

broken wires. 28 10 layers 1/3-1n. 22-ga. hexagonal mesh 1.15 16 Top - severe r1n~ cracking.

Bottom - some sheer spalling, radfal cracking over 12-1n. area, broken wires.

29 2 layers 1/2-fn. 16-ga. welded square mesh 1.14 7 Top - fine part ring crack. Bottom - moderate rectilinear crackfnq over 3-1n. area.

30 6 layers 1/2-1n. Ig-ga. har.;~re cloth 1.19 15 Top - moderate ring cracking. Bottom - radial and recti-linear cracking over 10-in. area.

TABLE 27. Flexure Strengths of Panels Reinforced with Equal Weights of Mesh

Panel Reinforcement Modulus of No. Description Ib/sq ft Rupture, ps 1 Mode of Failure

Panel long1t. Transv.

27 3 layers 1/2-in. 22-ga. hexagonal mesh 1.14 4130 3600 long1t. - bottom cracks 1 layer 1/2-1n. 16-ga. welded square mesh over 4-1n. span. 2 layers 1/2-1n. 22-ga. hexagonal mesh Transv. - bottom cracks

over 4-in. span. 28 10 layers 1/3-in. 22-ga. hexagonal mesh 1.15 2640 1650 longft. - bottom cracks

over 4-fn. span. Transv. - Single major bottom crack.

29 2 layers 1/2-1n. 16-ga. welded square mesh 1.14 5350 4520 longit. - single major bottom crack. Transv. - single major bottom crack.

30 6 layers 1/2-1n. 19-9a. hardware cloth 1.19 3460 2990 long1t. - bottom cracks over 3-fn. span. Transv. - bottom crack over 2-1n. span.

.62

Drop-impact tests were performed using a 31 x 31-in. supporting frame but the same impact load device, i.e. 50 lb dropped 10 ft. The drop­impact results, presented in Table 28, show that the panel reinforced with the 1/2-in 22-ga. galvanized hexagonal mesh on rods has a drop-impact resistance inferior to that of the panels reinforced with similar weights of either 1/2-in. 19-9a. galvanized hardware cloth or 1/2-in 16-ga. welded square mesh.

Two 12-in. wide flexure test specimens, longitudinal and trans­verse were cut from adjacent sides of the panels 41, 42, and 43 {mates to panels 44, 45, and 46,respective1y}. These flexure specimens were tested 1n third-point loading on a span of 21 inches. Mid-span deflections were measured. Loading was continued until the load dropped significantly. The loads at first visible crack and at maximum load (modulus of rupture) were recorded. The results are -presented in Table 29. The load deflection curves are shown in Figs. 15 and 16.

The following observations and conclusions may be made from these tests on panels which contain rods and approximately equal weights of three different meshes:

- the presence of rods tends to minimize the differences in flexure strengths obtained in panels containing the three meshes, viz. 1/2-in. 19-9a. hardware cloth, 1/2-in. 16-ga. welded square mesh, and 1/2-1n. 22-ga. hexagonal mesh.

- the rods diminished the difference in flexure strengths which existed in the lengthwise and transverse directions of the 1/2-in. 22-ga. hexagonal mesh.

- the flexure strength of the panels containing the 1/2-in. 22-ga. hexagonal mesh is about equal to the strength of the panel containing the 1/2-in. 19-9a. hardware cloth as tested but would still be inferior if the latter panel had had the 3 layers of mesh in the tension side and the 2 layers in the compression side.

- the flexure strength of the panels is higher when the rods in the tensile side of the specimen are in the lengthwise direction of the specimen than when they are in the transverse direction.

iii. Effect of Rod and Mesh Orientation on Flexure Strength

The effect of the orientation of the mesh and of the rod/mesh assembly with respect to the flexure stress direction has been examined in two.ways. In the first test, specimens containing either 5 layers of 1/2-in. 16-ga. galvanized welded square mesh, 12 layers of 1/2-in. 22-ga. galvanized

Pln.' No.

44

45

46

63

TABLE 28. Drop-Impact Resistance of Rod-Reinforced Panels with Equal Weights of Mesh Relnforcements

Ofshfng Circle Mesh Reinforcement on of Mode of Failure

Double-Drawn A82 Rods Spaced on 2-1n. Centres in Cracks 1/16 in. in.

2 layers 1/2-in. 19-9a. galv. hardware cloth 4 20 Very fine radial crack. 3 · • II • . • One fine rectilinear crack. 1 layer 1/2-in. 16-ga. galv. welded square mesh 8 18 Fine radlal cracks. • · • . . • . . Fine rectilinear cracks. 5 layers l/2-in. 22-ga. galv. hexagonal mesh 9 30 Radial cracking. • · • II . II •

TABLE 29. Flexural Strength of Rod-Reinforced Panels With Equal Weights of Mesh Reinforcements

Pinel Mesh Reinforcement First Maximum Modulus of No. (listed ln order from Visible load Ib Rupture Mode. of Failure

compression to tenslon sldes) Crack Ib psi

41A 3 layers 1/2-1n. 19-9a. hardware cloth 1100 2240 3930 Mafn crack at a load polnt. lengthwise rods Several fine cracks. transverse rods No rod slip apparent. 2 layers of 1/2-in. 19-9a. hardware cloth

418 3 layers 1/2-1n. 19-9a. hardware cloth 1700 2900 5080 Main cracks at load points. transverse rods Rod slip noted. lengthwl se rods 2 layers 1/2-1n. 19-9a. hardware cloth

42A 1 layer 1/2-1n. 16-ga. welded square 1300 2800 6050 Main crack at load pOint. mesh Rod slip noted. lengthwise rods transverse rods 1 layer of 1/2-1n. 16-ga. welded square mesh

428 1 layer 1/2-1n. 16-ga. welded square 1950 3240 7000 Fine cracks at load points. mesh Rod sl1p noted. transverse rods lengthwise rods 1 layer 1/2-in. 16-ga. welded square

43A 5 layers of 1/2-1n. 22-ga. hexagonal 1800 2650 4740 Main crack at a load polnt. mesh Fine crack at other polnt. lengthwlse rods No rod slip apparent. transverse rods 5 layers 1/2-1n. 22-ga. hexagonal mesh

438 5 layers of 1/2-in. 22-ga. hexagonal 1400 2700 4740 Major crack at a load polnt mesh Rod slip noted. transverse rods lengthwise rods 5 layers of 1/2-1n. 22-gl. hexagonal IIesh

3000

Load 1b

2000

1000

o

64

42A 1/2-in. 16-ga. welded square mesh

41A 1/2-in. 19-9a. hardware cloth

o

A82 rods on 2-in. centres tension side rods-transverse

Beam - 12 x 24 x 1 in. Span - 21 in. Load - third-points

0.5

Deflection, in.

Fig. 15. Flexure strength of beams with equal weights of three meshes.

1.0

3000

Load lb

2000

1000

o o

42B l/2-in. 16-ga. w~l~ed square mesh

43B 1/2-in. ?2-ga. hexagonal mesh

A82 rods on 2 in. centres tension side rods - lengthwise

Beam - 12 x 24 x 1 in. Span - 21 in. Load - third-point

0.5

Deflection, in.

Fig. 16. Flexure strength of beams with equal weights of three meshes.

65

1.0

66

hexagonal mesh, 9 layers of 1/2-in. 19-9a. galvanized hardware cloth, or 7 layers of 3/8-in. 20-ga. black welded square mesh were cut from the diagonal direction of the panels for comparison with the corresponding specimens containin~ mesh in the longitudinal and transverse directions. The flexure strength (modulus of rupture) of the diagonal specimens ranged from about 65 to 90 percent of the longitudinal and transverse specimens, except in the case of the transverse specimens from the hexagonal mesh panel which exhibits very anisotropic properties. As might be expected the strength of the diagonal specimen was appreciably higher than that of the transverse specimen. The results are shown in Table 30.

One panel was reinforced with 3 layers of 1/2-in. 19-9a. hardware cloth above and 2 layers below the 0.225 in. double-drawn rods at 2-in. spacing. The mesh layers were placed at 45 degrees to the rods. The flexure strength (modulus of rupture) of a flexure specimen oriented in line with the mesh and at 45 degrees to the rods was only about 60 percent of the strength of a longitudinal or transverse specimen cut from a similar normal panel. The strength of a specimen oriented in line with the rods and at 45 degrees to the direction of the mesh was only about 50 percent of the strength of a normal panel, as shown in Table 31.

iv. The Hydrogen Gas Problem

Two of the panels made early in the program showed an occasional blister or eruption in the mortar surface soon after mortaring was complete. These panels had, as reinforcement, only 1/2-in. 19-9a. hexagonal mesh, galvanized before weaving. The hexagonal mesh was known to have an extremely light coating of zinc. Later, the first panels with bare steel rods and various galvanized meshes showed much more severe blistering along the lines of the reinforcing rods and especially at intersections of the transverse and longitudinal rods. Christensen and Williamson 19 clearly explain how a galvanic cell is set up between the black steel rods (cathode) and the galvanized mesh (anode) in the cement mortar paste (electrolyte). The resulting galvanic reaction liberates hydrogen ions which form nascent hydrogen atoms and hence hydrogen molecules. The hydrogen gas forms blisters in the setting mortar which may lead to poor rod/mortar bond strength and,possibly, less protection of the rod against corrosion attack. The hydrogen at the rod surface may cause hydrogen embrittlementin high-tensile reinforcement. The problem seems to have been of little importance in practical boat-building but the potential seriousness warrants steps to prevent the reaction. Christensen and Williamson have suggested a number of possible solutions to the problem, viz.

- eliminate dissimilar metals by: - using ungalvanized rods and mesh - using galvanized rods and mesh

Panel No.

4

5

8

10

Panel No.

41A

41B

5eA

58B

67

TABLE 30. Effect of Mesh Orientation on Flexure Strength of Mesh-Reinforced Panels

Modulus of Rupture Mesh Reinforcement Longit. Transverse Mesh at 45 deqrees

pst pst ~si S of Longit. -: of Transv.

1/2-in. 16-ga. galvanized 59oo 6130 4700 80 77 welded square mesh, 5 layers 1/2-in. 22-ga. galvanized hexagonal 2900 1360 1950 67 143 mesh, 12 layers 1/2-in. 19-9a. galvanized hardware 3520 3530 3140 89 89 cloth, 9 layers 3/8-in. 20-ga. welded square mesh, 5000 4460 3720 75 83 7 layers

TABLE 31. Effect of Mesh and Rod Orientation on Flexure Strength (3 layers of 1/2-in. 19-9a. hardware cloth above 2 layers below 0.225 in dOuble-drawn rods oriented at 45 degrees to the mesh)

Load at Orientation of Flexure Modulus Specimen with Respect First Maximum of Rupture Mode of Failure Visible Load, lb to Direction of Reinforcement Crack, lb psi

Mesh and rods in same direction as 1100 2240 3930 Main crack under load specimen. point.

No rod slip apparent. ~lesh and rods in same direction a~ 1700 2900 5080 Main crack under load specimen. point.

Rod slip noted. Mesh at 45 degrees to and rods in 500 1220 2140 Fine cracks between direction of specimen length. load points.

Rod slip noted. Rods at 45 degrees to and mesh in 1600 180U 3150 Many cracks under load direction of specimen length. points.

Rod slip noted.

',-

- applying a protective insulating coating to the rods - chemically pa~stvating or inhibiting the galvanic cell action

As they rightly point out, ungalvanized mesh would be threatened by rapid corrosion in the marine environment, galvanic action might still occur between galvanized rods and mesh, cold-drawn high-strength rods could not be galvan­ized without some loss of strength, and the integrity of protective coatings on rods could not be guaranteed. They showed that chromium trioxide prescribed for passivating or inhibiting zinc in concrete was a simple effective cure for the galvanic cell problem in ferrocement construction. The concentrations of chromium trioxide used, 100 to 300 ppm by weight of water, effectively passivated the zinc coating. As has already been pointed out, the Building Research Station in the United Kingdom16 states that 70 ppm chromium trioxide in the cement paste (0.0035 percent in the dry cement, assuming a water/cement ratio of 0.5) will inhibit the formation of hydrggen gas. In later tests, Cornet et a1 20 showed that the mechanical properties of concrete, viz. compres­sive strength and elastic modulus, were not impaired when chromium trioxide was added to amoun~of 100, 200, and 300 ppm water.

Many normal trioxide. Others may not. galvanized steel should be are made to the mix.

Portland cements contain sufficient soluble chromium It is therefore recommended that chromate-treated

used with all cements unless chromic acid additions

As a result of the problem and of the investigations performed elsewhere, chromium trioxide (chromic oxide, Cr03) was added to the water for the mortar mix at a concentration of 300 ppm (0.3g/1 or 0.3 lb/100 Imp. gallons water) for all panels subsequently made in this laboratory.

v. Corrosion

Under most conditions Portland cement concrete is considered to provide good protection of the encased steel reinforcement against corrosion. The protection is said to be provided by the high alkalinity of the concrete. However, even under covers of two to three inches, steel reinforcement is known to have corroded where voids have allowed easy ingress of corrodents and oxygen. Thick covers of cement mortars are not possible in ferrocement boat construction. The mortar cover seldom will exceed 1/8 in. In some areas mesh may even be exposed during the fairing of the hull. Although the mortar has a low content of voids, microcracking may be present.

Many investigators have examined corrosion of reinforcement bars and r~ds in concrete. Much of the work has been directed to examining the corrosion of reinforcements in prestressed concrete water reservoirs and fixed marine structures. Although the reservoirs are considered to be concrete, a layer of less-permeable mortar is often applied to the prestressing wires by pneumatic placement to prevent corrosion of the wires. Even so, catas­trophic failures have occurred.

69

Ferrocement hulls, possibly one inch or less in thickness, with a fine steel reinforcement covered by a thin layer of rich fine mortar of relatively low permeability and intermittently wetted with seawater, present a different problem which has not been adequately examined.

The mechanisms which pertain to the corrosion and protection of steel reinforcement are briefly reviewed. Concrete or mortar normally protects embedded steel from corrosion since the steel in concrete is polarized anodically. This polarization results in the formation of a passive film of gamma iron oxide on the steel. Corrosive anions, such as chloride ions may break down this passive film in the presence of oxygen and moisture. 21 , 22 The passive film will break down when ,sufficient chloride ions have penetrated to the steel surface. Shalon and Raphae1 23 and Hausmann24 have suggested that ~ threshold concentration of chloride ions must be exceeded before corrosion occurs. Gj¢rv 25 explains that the electrochemical potential of the steel becomes more negative (anodic) as the passivity of the steel becomes partly, or completely, broken while other portions of the steel with passive potential intact act as cathode. Since moist concrete (mortar) is a good electrolyte, galvanic cells develop along the steel wires. The electromotive force in such cells depends mainly on the pH value (hydrogen ion concentration) and chloride concentration in the moisture next to the steel and on the transfer of dissolved oxygen through the concrete (mortar) cover.

Ferrocement hulls have achieved a reputation in several areas, especially in corrosion resistance and durability. The existence of a boat hull over a hundred years old is often cited as testimony. It is generally agreed that integrity of the mortar is a most important factor in preventing attack of reinforcement. Permeability is a measure of the capacity of the mortar to transmit fluids. If the pores are not connected, the permeability will be low and corrosion less likely. However, as Lewis and Copenhagen26 , 27 point out, there is ample evidence that concrete is permeable to varying degrees depending on such factors as water/cement ratio, aggregate/sand graduation, richness of the mix, compaction, and curing. Since the passivating action of concrete on steel depends on its ability to exclude inimicable ions from the steel surface, permeability is clearly of utmost importance.

Well-made ferrocement has relatively low permeability. This laboratory has shown no passage of water through a 3/4-in. section of unreinforced ferrocement mortar subjected to a hydrostatic head of three feet. Kowalski 28 cites numerous U.S.S.R. tests which maintained a hydrostatic pressure of 230 psi on ferrocement only 20 cm thick without water percolation. However, ferrocement contains microcracks and may, when damaged, contain macrocracks. Walkus,29, 30 who has performed valuable work on the state of cracking in ferrocement, defines microcracks as those cracks not exceeding 20 microns (0.02 mm). Walkus and Kowalski 31 claim that cracks between 20 and 50 microns develop during quasi-elastic deformation and that loads producing cracks up

70

to 50 microns wide are in the practical elastic working range. Further, when a crack reaches 100 microns (0.1 mm), the steel reinforcement alone carries all the tensile forces. Wa1kus and Mackiewicz 32 claim that the material is completely watertight if the width of the cracks does not exceed 20 microns (0.02 mm) and that corrosion does not occur if the width of the cracks does not exceed 100 microns (0.1 mm). No explanation or laboratory evidence to support this statement were provided in the reference although other papers by the authors which have not been obtained may indeed provide the evidence. It was considered necessary to carry out simple, practical tests under known conditions of exposure.

Several preliminary tests were undertaken early in the program period to assess the corrosion of steel reinforcements in ferrocements. The first test specimens to assess the durability of various mortars to seawater were also evaluated qualitatively for the condition of the encased reinforce­ment. The panels from which the test coupons were cut were made in a horiz­ontal panel mould lined with polyethylene sheeting. The bottom layer of mesh could be clearly seen imprinted in the bottom surface of the panel, i.e. there was only a thin film or no mortar covering the mesh wires. The specimens, of the "standard" mor.tar mix (Type II cement and dry mortar sand) contained the following meshes:

1/2-in. 16-ga. welded square mesh, galvanized 1/2-in. 16-ga. welded square mesh, zinc stripped 1/2-in. 22-ga. hexagonal mesh, galvanized after weaving 1/2-in. 22-ga. hexagonal mesh, galvanized before weaving 1/2-in. 19-9a. hardware cloth, galvanized

The specimens were immersed in seawater for 8 hours, dried at room temperature for 16 hours. Changes ' were observed during the 15 test cycles. The wires of mesh with no zinc coating produced red rust stains on the mortar surface after two cycles. The corrosion became more severe as the cycles increased. The hexagonal mesh with the light zinc coating applied before weaving showed rust stains after ten cycles. The other meshes showed no rust after 15 cycles.

Five 3 x 12 in. specimens used in flexure tests were exposed in seawater at room temperature. These specimens had suffered severe damage in the flexure test such that much of the mesh was highly exposed. Seawater could easily penetrate deep into the specimens. A copious yellow-white encrustation was quickly developed on the galvanized me$hes and severe red rust staining was observed on the wires of the 3/8-in. 19-9a. coppered or liquor-finished mesh. (This wire treatment is intended to provide only temporary corrosion protection for shipping and storage.) .

71

The effects of crack width and thickness of mortar cover on the corrosion attack of unga1vanized reinforcement wire encased in mortar were examined in an extensive program of tidal seawater exposures. The tidal seawater exposure was chosen because oDservations in the field have indicated that the most susceptib1~ parts of concrete structures are those parts most exposed to intermittent wetting and drying within the splash zone. It has been shown that if concrete becomes completely water-saturated, the corrosion becomes less severe.

A mortar specimen with a reduced section at mid-length and contai~ing one reinforcing wire was developed which could be cracked in a controlled manner to yield cracks of specific widths. Multiple-cavity moulds, which allowed 50 specimens or coupons to be made from each of eight batches of mortar mix, were constructed. The cavities had a draft allowance and removable dividers to permit easy removal of the specimens from the mould. Slots to allow embedment of the wires in the mortar to a predetermined mortar coyer were located in the ends of the moulds. The size of the specimens is ab~ut 6 cm. wide by 14 cm. long by 2 cm. thick (2 1/2 x 5 1/2 x 3/4-in.). The width at the reduced neck section is 3 cm. (1 1/4-in.).

The composition of the several mortar batches used, as in all recent work carried out in the program, is Type II cement one part, -8 mesh dry mortar sand two parts, water/cement ratio 0.45, slump 2 1/2 to 3-in. The mortar was placed in each cavity and trowelled smooth. A 10-in length of 0.105 in. dia. "cut and straightened" carbon steel · wire (breaking strength of about 900 lb.) was set into the locating grooves, pressed into the mortar coupon, and covered with small dabs of fresh mortar. The coupon was again trowelled smooth. After curing, the mortar specimen was carefully ground to a cover thickness in the necked section of 0.5, 2.0, ~r 3.5 mm. before the mid-length crack was made.

Controlling cracking of the specimens was accomplished by forcing opposing hardened steel rollers (1 1/2-in. dia.) into the notches o~ each side of the specimen, i.e. into the reduced section, until a crack of the required size was obtained. The crack widths are as follows:

o (no crack), 0.05 mm (finest crack visible to unaided eye), 0.1 mm, 0~2 mm, and 0.5 mm.

72

The crack widths were measured with a standard Brine1l hardness test microscope containing a micrometer-scale rettcule graduated in 0.1 mm. which allows measurements to be estimated to 0.05 mm. Specimens with uneven cracking, or otherwise unsuitable, were discarded. Figure 17 shows a typical set of specimens after exposure to the tidal seawater environment. Five lots, each of 45 test specimens, were prepared from the four hundred specimens moulded for exposures of 1, 2, 4, 8, and 16 months. (A sixth set of 45 was held in reserve or as a control set.) The specimens of each lot were in triplicate, i.e. three of each of the crack width/mortar cover combinations for each of the five exposure periods. The tabulation below shows · one lot of specimens for one exposure period.

Crack Width, Mortar Cover, mm. Total No. of mm. '0.5 2.0 3.5 Specimens

o (no crack) 3 3 3 9 0.05 (hairline) 3 3 3 9 0.1 3 3 3 9 0.2 3 3 3 9 0.5 3 3 .3 9

Totals 15 15 15 45

The 45 specimens comprising each lot were tied together by means of holes drilled through each specimen. The five lots were installed on December 3, 1973 at the dock of the Kitsilano (Vancouver) station of the Canadian Coast Guard, Ministry of Transport at an immersed depth five feet below high tide.

One lot of specimens was removed after 1, 2,4, and 8 months of exposure for examination and testing. The last lot has not yet been retrieved but the trend has been established.

Each specimen was visually examined, one half of the mortar was removed and the crack surface was examined for rust stains; the wire was removed and examined under the stereoscopic microscope, and the depth of pitting or ring corrosion was measured by a micrometer with pointed anvil and spindle. Finally, the breaking strengths of the wires were obtained. .

73

The visual assessment and micrometer measurements and the breaking strengths of the wires are presented in Tables 32 and 33. A set of wires after 8 months exposure is shown in Fig. 18 and graphical present­ations of the breaking strengths of the wires are shown in Figs. 19 to 21.

The following observations are made on the basis of the above tests:

- corrosion of the steel wires in mortar coupons containing cracks not wider than about 0.1 mm is not severe, even after 8 months exposure and with a mortar cover only 0.5 mm. thick.

- corrosion of the steel wires in mortar coupons containing cracks wider than about 0.1 mm. is severe after 1 to 2 months exposure, regardless of the thickness of the mortar cover, viz. 0.5, 2.0, and 3.5 mm.,

- the thickness of the mortar cover used, viz. 0.5, 2.0, and 3.5 mm. has little effect on the severity of corrosion of the steel wire if a crack is present.

- a mortar cover of 2.0 mm. substantially prevented corrosion of the steel wires in uncracked mortar coupons, at least for eight months.

- a mortar cover of 0.5 mm. failed to protect the steel wire completely for two months even in uncracked mortar coupons.

- it seems advisable to use a protective coating on the mortar cover to protect ungalvanized reinforcement from corrosion, even when no cracks are present and the mortar cover is greater than 2 mm.

- the loss of strength of unga1vanized rods which are much heavier and at greater depths in the mortar is likely to be small under crack conditions not susceptible to hull leakage. However, ungalvanized mesh nearer the surface is likely to suffer severe loss of strength from corrosion if cracks greater than about 0.1 mm. are present. Gal­vanized m~sh is therefore recommended.

4. Evaluation of a Typical Ferrocement Construction

The strength data reported so far pertain to ferrocement containing a wide variety of mortars and mesh and rod reinforcements, i.e. a wide variety of ferrocement constructions. It seemed desirable to investigate a "typica1 11 ferrocement construction in somewhat greater depth and greater replication so that data of greater reliability could be obtain~d. It was hoped that such data could ~e used later in the development of a mathematical model to aid design. .

74

Exposure No.

1

2

4

8 '

TABLE 32. Assessment of Corrosion of 0.105 in. d1a. Wires in Hortar Coupons with Cracks o to 0.5 nrn. wide and wlth 110rtar Covers of 0.5, 2.0, and 3.5 nrn. After Tidal Seawater Exposures (worst of trlpllcate exposures recorded).

Mortar Appearance of wire and depth of pits on ring groove. Cover

nrn. o (No crack) H (0.05 nrn) 0.1 nrn 0.2 nrn 0.5 nrn

0.5 no attack slight etch slight etch slight etch ring groove, pit 0.001 in. 0.002 In. deep

2.0 110 attack slight etch sllght etch slight etch rlng groove, shallow pit 0.003 ln deep

3.5 no attack no attack slight etch rlng etch ri ng groove, 0.004 In. deep

0.5 slight etch pits, rlng pits, ring plts, ring rl ng groove, 0.001 In. deep 0.001 In. deep 0.001 in. deep 0.003 in. deep

2.0 no attack pit., rlng rlng, plts, ring, pits, rlng, 0.01" in deep 0.002 In-. deep 0.002 in. deep 0.002 in. deep

3.5 no attack slight etch pits, pits, ring, ring groove, 0.001 in. deep 0.002 in. deep 0.008 in. deep

0.5 pits, plts, rlng, pits, plt, ring groove, 0.001 in. deep 0.001 In. deep 0.001 In. deep 0.005 In. deep 0.008 In. deep

2.0 slight etch pits, plts, slight etch rl ng groove, 0.001 In. deep 0.001 In. deep 0.006 in. deep

3.5 pits, pits, rlng, pits. plts. ring, ri ng groove, 0.001 in deep 0.001 in. deep 0.001 In. deep 0.001 in. deep 0.005 in. deep

0.5 pits, rlng, rlng groove. half ring, ring groove, 0.002 in. deep 0.001 In. deep 0.004 In. deep 0.020 In. deep 0.010 in. deep

2.0 no attack no attack slight etch half rlng, half ring, 0.010 in. deep 0.020 ln deep

3.5 no attack plts, 0.001 in. deep 0.001 In. deep 0.010 in. deep 0.025 In. deep

TABLE 33 Breaklng strength of 0.105 In. dia. Wires ln Mortar Coupons with Cracks a to 0.5 nrn. wide and with Mortar Covers of 0.5, 2.0, and 3.5 nrn. After Tidal Seawater Exposures (Average of triplicate values).

Hortar Average breaking strength of wire, 1b Exposure Cover,

no. nrn. a (No cracks) H (0.05 nrn.) 0.1 III!I. 0.2 nrn. 0.5 nrn.

1 0.5 893 885 908 921 911 2.0 897 892 900 886 891 3.5 867 919 912 898 877

l ~:g 91? ~OO ~g: 902 881 893 909 904 884

3.5 910 902 903 891 804 4 0.5 915 891 9Il 875 886

2.0 891 911 904 898 848 3.5 901 904 915 895 842

8 0.5 9!8 895 ~1~ U6 6?4 2.0 903 903 731 686 3.5 916 912 907 808 546

-

.'

Fig. 17. One set of specimens after exposure of 4 months. Crack size (left to right) 0, 0.05, 0.1, 0.2, and 0.5 mm. Mortar cover is 2 mm.

Fig. 18. Close-up of attack in one set of wires after exposure of 8 months. Mortar cover by groups (left to right) 0.5, 2.0, and 3.5 mm. Crack widths in each group (left to right) 0,0.05,0.1,0.2, and 0.5 mm.

75

~ r--

~

~ ~ en c v ~ ~ ~

en c .~

~ ~ v ~ co

76

1000r-----~----~------------r_------------------------~

700

600

500

200

100

. Crack width, mm.

o ~ ____ ~ ______ ~ __________________________________________ ~

o 4

Exposure, months

Fig. 19. Wire strength vs Duration of exposure in tidal seawater for various crack widths. Mortar cover 0.5 mm.

8

.0 ,.... ..

.r: +" 0'1 C

f +" V)

0'1 C .'-~ ftS Q) s-ec

77 1000

Crack width, nm.

0.1 900

800

700

600

500

200

100

a L-____ ~ ____ ~~ __________ ~~ ________________________ ~

a 1 2 4

Exposure, Months Fig. 20. Wire strength vs Duration of exposure in tidal seawater

for vari ous crack wi dths. ~1ortar cover 2.0 mm.

8

1000

900

800

700

.0 ..... ..

..c ...., 600 0'1 C

f ...., V')

0'1 C .,....

.:.l ItS 500 cu '-c:o

200

100

o

78

o 1 2 4 Exposure, Months

Crack width, mm.

o

0.1 0.05

Fig. 21. Wire strength vs Duration of exposure in tidal seawater for various crack widths. Mortar cover 3.5 mrn.

8

79

The "typical" ferrocement construction chosen contained 0.225-in. dia. double-drawn high-tensile A82 rods spaced on two-inch centres. Panels were made with two layers of 1/2-in. 19-9a. galvanized hardware cloth on each side of the rods and with three layers on each side. i.e.:

2 layers 1/2-in. 10-ga. galvanized hardware cloth 0.225 in. high-tensile A82 rods at 2-in. transverse 0.225 in. high-tensile A82 rods at 2-in. longitudinal 2 layers 1/2-in. 19-9a. galvanized hardware cloth

3 layers 1/2-in. 19-9a. galvanized hardware cloth 0.225 in. high-tensile A82 rods at 2-in. transverse 0.225 in. high-tensile A82 rods at 2-in. longitudinal 3 layers 1/2-in. 19-9a. galvanized hardware cloth

The mortar used for all the panels was Type II cement 1 part. dry mortar sand 2 parts, water/cement ratio 0.40 to 0.45, chromium trioxide 300 ppm water. slump> 3 in. Compression cubes and flexure and compression prisms were cast, cured, and tested at 7 and 28· jays.

were obtained:

Mortar

The following properties of the mortar and reinforcemen~ mat~rials

Compression Strength (C109. C349) 2-in. cubes 7-day 5400 psi

28-day 7700 psi 1.575 in. prisms 28-day 10,000 psi

Flexural Strength (C348) 1.575 in. prisms 28-day 1350 psi

Reinforcement

0.225 in. double-drawn high-tensile A82 rods Breaking strength 3,360 lb U1t.tensile strength 86,000 psi Yield strength, 0.2% 72,000 psi E10ng. % in 10 in. 6.5

1/2-in. 19-9a. galvanized Diameter, stripped Breaking strength U1t. tensile strength Yield strength, approx. Specific surface

(mesh layers only)

hardware cloth 0.038 in.

63 lb 55,000 psi 44,000 psi 7.1 in- 1 (2.80 cm.-1 )

80

(a) Strength and Elastic Modulus in Tension

Tensile tests of ferrocement specimens reinforced with mesh only present few problems. The specimens can be shaped, if necessary, and are easily gripped in the testing apparatus. Ferrocement panels or specimens containing rod reinforcement as well as mesh are difficult to test in tension. Specimens in which the rods are not cross-welded or otherwise anchored cannot develop the full strength. A considerable amount of testing failed to develop a test specimen and gripping system which adequately assessed the tensile strength of the material composite - mortar, mesh, and rods. One pair of specimens (207-3 with 4 layers of 1/2-in. 19-9a. hardware cloth and 208-3 with 6 layers) was prepared with shoulders and a reduced central portion (2 x 1 x 6-in. gauge 1ength) .by drilling and diamond sawing. Each specimen had one lengthwise rod and three tr~nsverse rods in the test section. Each specimen was fitted with a standard 2-in. linear variable . differential trans­former extensometer modi fed to 6-in. The stress-strain curves shown in Fig. 22(a) and (b) were obtained. The loads at first visible crack and the maximum loads were recorded. The single rod in the centre of the specimen began to slip as the rod/mortar bond failed. The strengths so obtained are lower than would be expected from very long specimens with very long rod/ mortar bond lengths or from specimens with rod cross-welds or rods somehow anchored into the specimen. The following test results show how the strengths developed are not much higher than the combined strength of the wires in the mesh.

Specimen 207-3 (4 layers of 1/2-in. 19-9a. hardware cloth, 2 sq. in. of ferrocement cross-section area)

Load at first visible crack Maximum load held Strength of 16 wires in mesh Rod bond (by difference)

Specimen 208-3 (6 layers of 1/2-in. 19-9a. hardware cloth,· 1 2 sq. in~ of ferrocement cross-section area)

Load at first visible crack Maximum load held Strength of 23 wires in mesh Rod bond (by difference)

1 central lengthwise rod,

1300 1b 1420 1b 1010 1b 410 1b

central lengthwise rod,

1450 1b 1900 lb 1450 1b 450 1b

The values of tangent modulus of elasticity (tangent 0 to 1000 lb load) obtained from the load/strain curves for 207-3 and 208-3 are 1.2 x 106 and 0.97 x 106 psi respectively.

CI) CI) OJ q-.,.. S-XCI) ~ Q. V)

CI) CI) OJ q- .,.. S-XCI) ~ Co. V)

M I

co 0 N

"0 c: IU

M I

r-. 0 N

CI) c: OJ E .,.. u OJ Q. CI)

OJ ,... .,... CI) c: OJ ~

S-O

I+-

CI)

OJ > S-::s u c: .,... IU S-~ CI)

"-CI) CI)

OJ S-~ til

.a

IU

N N

C'I .,... ...

82

Since the potential contribution of the rod to the strength of the ferrocement specimens has not been adequately assessed it is considered that the above values of unit strength and elastic modulus are not a proper measure of the real strength of the ferrocement composite . as used in a boat hull.

(b) Strength and Elastic Modulus in Flexure

Flexure tests, third-point loading on 18-in span, were performed on 6-in. wide test specimens from panel 207 (4 layers· of 1/2-in 19-9a. , galvan­ized hardware cloth and rods as previously described) and from panel 208 (6 layers). Pairs of 18-, 24-, and 36-in. long specimens were tested to assess the effect of specimen length, especially rod/mortar bond 1ength,on the bending behaviour. An extensometer modified to 6-in.gauge length was used to measure the tensile strain in the centre-third of the specimen. The beam deflections at midspan and third-points were recorded for increments of loads. The location of the mesh wires, both lengthwise and transverse, of each layer of mesh and rods in each specimen was carefully measured with respect to the tensile surface of the specimen for possible future use in the further development of a math­ematical model. These readings are not presented.

The values of load, strain, and deflection, shown in abridged form in Tables 34 and 35, were used to calculate:

- flexural strength at the load at first visible crack, Pfvc - flexural strength at load Pfvc t 2 - flexural strength at maximum load held, {called herein Modulus of Rupture - effective modulus of elasticity in bending at the load at first visible

crack, Pfvc, and at 400 lb (~ Pfvc t 2) based on beam curvature formula E = ~ (where R = radius of curvatur~, M = moment, I = section

I moment of inertia) - effective modulus of elasticity in bending, E = ~ at the load at first

visible crack, Pfvc, and at 400 lb (~ Pfvc t 2) based on fibre stress formula F = ~c

These values are shown in Table 36.

83

TABLE 34. Flexure Results - load Midspan Deflection D2. Difference in Midspan and Third-Point Oefle~tions, and Fibre Strain in 18-, 24-, and 36-1nch specimens from Panel 207 on la-in. span. (Abridged)

Midspan Dl;o3

' - , Load Deflection, D2 -D2 Fibre Strain. Rellllrks 1b O.ODl in. 1n./1n. 0.001 in.

Specimen 207-1 (18 in. long)

0 0 0 0 400 37 3.5 0.00053 800 98 12.5 0.00170 First visible crack

1230 213' 25.0 Max1mum'load held,

Specimen 207-4 (18 in. long)

0 0 0 0 400 45 5.5 0.00056 800 100 14.5 0.00148 First visible crack

1100 156 23.5 Maximum load held

Specimen 207-5 (24 in. long)

0 0 0 0 400 38 4.5 0.00064 800 115 17.5 0.00217 First visible crack

1000 172 27.5 Maximum load held

Specimen 207-6 (24 in. long)

0 0 0 0 400 40 1.5 0.00045

1100 166 20 0.00252 First visible crack 1400 255 33.5 Maximum load held

SpeCimen 207-7 (36 in. long)

0 0 0 0 400 47 1.5 0.00068 900 143 13.5 0.00235 First visible crack

1100 206 . Maximum load held

Specimen 207-8 (36-1n. long)

0 0 0 0 400 56 6.5 0.00088 800 110 15.0 0.00190 First visible crack

1500 280 47.5 Maximum load held

84

TABLE 35. Flexure Results - load. Midspan Deflection 02. Difference in Midspan and Third-point Deflections. and Fibre Strain in 18-. 24-. and 36-in. Specimens from Panel 208 on 18-in. span. (Abridged)

Load Midspan 0,+03 Fibre Strain. Relllarks lb Deflection. 02 --- 02 1n./in. 0.001 in. 0.001 in.

Specimen 208-1 (18-in. long)

0 0 0 0 400 42 2.5 0.00066

1000 138 12.5 0.00276 First visible crack 1200 186 17.0 Maximum load held

Specimen 208-4 (18-in. long)

0 0 0 0 400 44 2.5 0.00066

1100 143 14.5 0.00266 First visible crack 1450 230 23 Maximum load held

Specimen 208-5 (24-in. long)

0 0 0 0 400 55 4 0.00090 900 140 13 0.00282 First visible crack

1700 395 42 Maximum load held

Specimen 208-6 (24-in. long)

0 0 0 0 400 41 1 -1000 128 9 0.00060 First visible crack

1600 318 30 0.00226 Maximum load held

Specimen 208-7 (36-in. long)

0 0 0 0 400 43 0.5 0.00064 800 103 7.0 0.00152 First visible crack

1400 283 30.0 Maximum load held

Specimen 208-8 (36-in. long)

0 0 0 0 400 55 7.5 0.00080

1000 156 23.0 0.00280 First visible crack 1500 387 44 Maximum load held

Pinel Specimen

No.

207-1 -4 -5 -6 -7 -8

Av.

208-1 -4 -5 -6 -7 -8

Av.

Panel No.

210

205

85

TABlE 36. Flexure Strength and Effective Elastic Modulus at the Load .t First Visible Crack (Pfvc), 400.1b (~ Pfvct2), and Maximum Load (Pmax) (Flexural Strength only at Pmax) for Specimens from Panels 207 & 208.

Specimen Flexure Strength, psi Effective Elastic Modulus in Bending Length,

E.~ psi x 106 E·1t. CJ.-~, psi x 106 in. at P·Pfvc at P·Pfvc at Pmax c' --r P·Pfvc P"400 lb Pfvc P .. 400 lb

18 2400 1200 3700 1.38 2.95 0.88 1.19 18 2400 1200 3300 1.76 2.08 1.18 1.57 24 2400 1200 3000 1.19 2.32 0.60 1.03 24 3300 1650 4200 * * 0.82 1.34 36 2700 1350 3300 * * 0.91 1.31 36 2400 1200 4500 1.52 1.96 1.14 1.20

2600 HOO 3666 1.46 2.32 0.92 1.27

18 3000 1500 3600 1.85 3.85 0.75 1.24 18 3300 1650 4350 1.75 3.70 0.79 1.21 24 2700 1350 ~100 1.57 1.35 0.58 0.94 24 3000 1500 4800 * * 0.74 1.35 36 2400 1200 4200 * * 0.92 1.42 36 3000 1500 4500 1.27 1.95 0.66 1.31

2900 1450 4425 1.61 2.71 0.74 1.25

* Specimens kinked, bending curve not uniform, radius R very large.

TABLE 37. Number of Cycles to First Visible Crack and ~ltimate Collapse of Specimens under Unilateral Cyclic Flexure Loadings.

Load Apparent No. of Cycles to Kg Fibre First Visible Ultimate Stress

psi Crack Collapse

2 layers of 1/2-in. 19-9alvanized 380 2500 1 200 hardware cloth each side of 340 2250 5 3,000 0.225-in. double-drawn rods spaced 300 2000 12 10,000 at two inches in each direction 280 1850 - -

260 1720 50 140,000 240 1580 - -200 1320 - -

3 layers of 1/2-in. 19-9alvanized 380 2500 6 20,000 hardware cloth each side of 340 2250 13 25,000 0.225-in. double-drawn rods spaced 300 2000 1,600 55,000 at two inches in each direction 280 1850 12,000 120,000

260 1720 60,000 240,000 240 1580 so ,000 260,000 200 1320 >500,000* >500,000*

*No visible crack after 500,000 cycles.

The average values for flexure strength, deflection, and elastic modulus taken from Tables 34, 35, and 36 are as follows:

Panel 207 208

Layers of mesh on each side of rods 2 3

Modulus of rupture at Pmax, psi 3700 4400 Flexure strength, psi

at load at first visible crack, Pfvc 2600 2900 at Pfvc f 2 1300 1450

Aver. midpoint deflection, in. , at load at first visible crack Pfvc 0.13 0.12 at P400

Elastic modulus, E = ~M, psi 0.04 0.04

at load at first visible crack Pfvc 1.46 x 106 1.61 X 106 at . Pfvc t 2, i.e. P '"' 400 1b 2.32 x 106 2.71 X 106

Elastic Modulus, E = ~, ' psi at load of first isib1e crack, Pfvc 0.92 x 106 1.27 x 106 at . Pfvc t 2, i.e. P = 400 lb 0.74 x 106 1.25 X 106

(c) Behaviour Under Repeated Flexure Stresses.

It is recognized that materials in general subjected to repeated tensile stresses can fail by the development and incremental extension of a crack at stress levels well below the stress required to crack the material in a single application of. the load. On the basis of early work by C1emmer33 Older34 , and Hatt35 on repeated loading of concrete cylinders in compression and of concrete beams, both reinforced and unreinforced, in bending, it be~ame generally agreed that repeated stresses of about fifty percent of the static failure stress will cause failure by fatigue. Yoshimoto et a1.36 and Hi1lsdorf and Kes1er37 , more recently, have examined the effect of repeated loading on concrete. In 1974, Committee 215 of the American Concrete Institute discussed considerations for design of reinforced concrete subjected to fatigue 10ading. 38 Although the report applies particularly to reinforced concrete, the tests on slabs reinforced with welded wire fabric and on welded wire fabric alone are' of considerable interest in that they may provide a more macroscopic view of the location of cracking (at cross-weld joints or between them), the disturbance due to the welded intersection, and deterioration of the bond between the smooth wire and concrete which can be applied to ferrocement.

Romua1di 39 and Romua1di et al. 4o have examined the fatigue behaviour of concrete mortar reinforced with short pieces of thin steel wire. Romualdi points out that the low tensile strength of concrete is due to the

87

presence of flaws and is not an inherent property of the material. The presence of this reinforcement, randomly and uniformly closely-spaced steel wires or wire mesh, provides a crack-arrest mechanism which increases the cracking strength of the concrete or mortar. Romua1di 1 s brief review of fatigue tests showed that the endurance limit of an unreinforced concrete beam was about fifty-five percent of the static cracking strength, whereas the endurance limit (without visible cracking) of the beams reinforced with short steel wires was approximately equal to the static tensile strength.

Dinsenbacher and Brauer41 , (Naval Ship Research and Develop­ment Center, U.S. Department of the Navy), in their description of the development and evaluation of ferrocement planing boats, have presented data for NSRDC/A ferrocement construction comprising five layers of 1/2-in. rectangular unga1vanized 19 gao ste~l woven wire cloth. Their test spec­imens were tapered to give a constant stress on a six-inch portion of cantilevered specimens. The specimens were loaded on each cycle to constant displacement, so it is probable that the load decreased with time. They concluded that the endurance limit was 3,000 psi, about fifty percent of the static flexural strength. Larsen42 ran fatigue tests at maximum stresses equal to about 0.5 to 2.4 times the average cracking stress of 1320 psi obtained from static flexure tests to one million cycles.

The behaviour of ferrocement under flexure loads at both constant deflection and constant magnitude was examined.

i. Stress-Strain Hysteresis Effect-Ten Cycles

Two 6-in. wide lB-in. long specimens from Panels 207, containing 2 layers of 1/2-in. 19-9a. galvanized hardware cloth on each side of a 0.225 in. high-tensile rods, and 20B, containing 3 layers each side, were tested under repeated loadings in flexure. Mid-span deflections and the tensile side strain were measured, the latter with a modified 6-in. extensometer. The specimens were loaded to 500 1b, a load known from experience to be lower than the load at first visible crack. The load was removed and reapplied in a similar manner ten times. The repeated cycles of load vs strain on the tensile side are shown in Fig. 23 (a) and (b). After the first cycle, plastic strains of 0.0005 and 0.0003 in/in. were observed for specimens 207-2 and 20B-2 respectively. No further plastic strain was observed after ten cycles.

The effective moduli of elasticity obtained from a tangent line at the 500 1b load after the first cycle and after ten cycles are as follows:

Specimen 207-2 Specimen 20B-2

After First Load Cycle

0.B6 x 106 psi 1.41 x 106 psi

After Ten Load Cycle

1.BB x 106 psi 2.B2 x 106 psi

Load, lb.

88

ISpec i men 207-2 900

Soecimen 208-2

~r- 800

[350 ~r- 700

~,300 600

~ 500

40

3

E1cngi 'on 1 div.=0.000133 in./in. 12 1 2

a b

Fig. 23 a, b. Load/strain curves for flexure specimens 207-2 and 208-2 loaded 10 times.

89

ii. Cyclic Flexure - At Constant Deflection

An apparatus was constructed to load eight 4 x 12-in. ferro­cement specimens in flexure simultaneously. The apparatus consi-sted of four pairs of roller cam arms fixed to a rotating shaft. Each specimen was sub·· jected to thi rd-poi nt 1 oadi ng by means of a cali brated stra'i n-gauged channe 1-shaped load cell connected" to a quick-response Visicorder monitor. The deflection of the specimen under load was measured by a dial gauge in a saddle support. The number of load cycles were counted by a cam-activated electric counter. The apparatus was simple, able to test up to four pairs of specimens at four different loads but suffered the serious disadvantage of being a constant-deflection rather than a constant-load device.

Four specimens were taken from Panel 51 containing 2 layers of 1/2-in. 19-9a. hardware cloth on each side of longitudinal and transverse 1/4-in. hot rolled rod spaced at 2 in. The fibre stress in static bending at first visible crack was 2620 psi and the modulus of rupture (maximum-load) was 6310 psi. These were loaded to initial fibre stresses of 1930, 1990,2130, andJ2600 psi, i.e. loads of 75 to 100 percent of the maximum fi~re stress deve10ped at the first visible crack in a static bend test. The ' specimens were subjected to 200,000 cycles in unilateral bending. The char, cteristics curves for load (apparent fibre stress) vs Number of cycles are shL''In in Fig. 24. The apparent fibre stress of specimen 51-3,which developed fine cracks durtng the initial loading, levelled off at about 400 psi. The stress on the other specimens after 200,000 test cycles had dropped to 600 to 1000 psi.

Four 4 x 12 x 1-in. specimens were taken from a Panel 49 containing 2 layers of 1/2-in. 19-9a. galvanized hardware cloth on longitudinal and transverse 0.225-in. high-tensile rods spaced at 2-in. The flexure strength (fibre stress) at first visible crack was 2300 psi and the modulus of rupture (at maximum load) was 4900 psi. The specimens were loaded to initial fibre stresses of 1060,1340,2240, and 2550 psi, i.e. stresses from less than 50 to 100 percent of the flexural strength at first visible crack, and subjected to 300,000 load cycles of unilateral bending. Since the apparatus 1s a constant deflection device, the applied load diminished to a fairly constant value as permanent set developed. The characteristic curves, Apparent fibre stress vs Number of cycles, are shown in Fig. 25.

These initial tests suggested that ferrocement of the construction described could withstand a fibre stress of about 1000 psi under constant deflection for many thousands of cycles provided that the initial loading 1s low enough that 'cracking does not develop early in the test campaign.

.r-en Q. .. en en QJ So-..., V)

QJ S0-n -LL.

-en Q. .. en en QJ So-..., V)

QJ S0-n .r-LL.

90

3000r-----------------------------~------------------~

2000

Initial Fibre Stress, psi

1000 2600 2130 1990 1930

o ______ ..L--___ --'-____ -L-___ --L. ____ ...L.-____ ,

100,000 200,000 Number of Load Cycles

Fig. 24. Characteristic fibre stress curves for beams from Panel 51 under repeated bending.

3000r-------------------------------------------------~

2000

Initial Fibre Stress, psi

1000 49-7 1340 49-1 2550 49-2 1060 49-3 2240

O~-----~----~~----~----~-------L------~ 100,000 200,000 3.00,000

Number of Load Cycles

Fig. 25. Characteristic fibre stress curves for beams from Panel 49 under repeated bending

91

iii. Cyclic Flexure - At Constant Magnitude

Specimens, 4x12xl in. cut from Panel 210, containing 2 layers of 1/2-in. l~-ga. galvanized hardware cloth above and below 0.225 in. dia double-drawn high-tensile rods spaced at,2 in., and from Panel 205, containing 3 layers each side, had fibre strengths at first visible crack of 1660 psi and 2650 psi, respectively, and modulus of rupture values (maximum) of 3500 psi and 4250 psi, respectively. Fig. 26 shows the load-deflection curves for the specimens. It is interesting to note that the first visible crack in each specimen has occurred at a mid point deflection of 0.030 in.

Specimens 4x12xl in. from the same panels were subjected to repeated flexure in third-point loading in an Instron (Model 1130) testing machine, equipped with a 500 kg (tensile-compression) load cell and a meter-relay load cycling device. The repeated loads are unilateral loads of constant magnitude. An electric counter recorded the number of load cycles imposed. Fig 27 shows the apparatus set-up.

Cyclic loads of 440 to 835 lb (200 to 380 kg) resulting in apparent fibre stresses of 1320 to 2500 psi (93 to 176 kgf/cm2) were imposed on specimens from Panels 210 and 205. The test cycling was run to ultimate collapse of the specimen (or to 500,000 cycles in the case of the lowest load). Complete collapse quickly followed ... ,ire breakage. Fig 28 shows a collapsed specimen.

The number of cycles when the first visible crack in the mortar on the tensile side of the specimens was seen and the number of cycles when the layers of mesh on the tensile side failed (resulting in gross bending of the rods and specimen collapse) are recorded in Table 37. The number of cycles to first visible crack to ultimate collapse were plotted on semi-logarithm scale in the tradi ti ana 1 manner fOi~ endurance 1 imit curves, Fi g. 29.

The plotted curves, subject to verification by greater test replication, suggest that the ferrocement specimens from Panel 205 with three layers of mesh on each side of rods can withstand an "apparent fibre stress" of 1750 psi for about 200,000 cycles before complete and ultimate collapse and of 1320 psi for at least 500,000 cycles without visible cracking.

The broken wires and the broken mortar matrix in fractures of ferrocement specimens broken by both a single application

4200

3600

3000

Fibre stress

2400

psi

1800

1200

600

o

.92

o 20

/

40

/' /

/'

,/

~ ,/

/ /

60

Fibre stress at load of first visible crack, Pfvc

80 100

Midpoint Deflection 0.001 in. Fig. 26. Static flexure tests for specimens from Panels 210 and 205.

120

'-

, .,'

93

Fig. 27. Cyclic flexure loading at constant magnitude.

I, "

Fig. 28. Flexure specimen which broke after 1800 cycles.

2000

Fibre Stress

1500

psi

1000

500

----- ----- first visible crack ultimate collapse

~ . no failure at 500,000 cycles

O~----~~-L------~~----__ ~ __ ~ ______ ~~ ______ ~ __ ~ ____ ~~~ 1 10 100 1000 10,000 100,000 1,000,000

Fig. 29. Fatigue curves for specimens from Panels 210 and 205.

of the bending load and by repeated applications of th~ bending load 'were examined under the stereoscopic microscope a.t. magnifications to 80 times. All the wires broken in the single-load bend test

95

showed necked fractures indicative of ductile tensile failures. Most of the wires in the bending fatigue specimens showed brittle fractures, i.e. fractures with no apparent necking. Because of the fineness of the wire (0.038 in., 0.965 mm. dia), no markings characteristic of progressive fractures were able to be observed in the fatigue failures. Optical micrbscopy did reveal that most of the flat brittle fractures lay in the plane of the mortar fracture, whereas the necked fractures usually stood proud of the surface. Fig 30 and 31 show these features.

No difference in texture between the surfaces of the mortar fracture in specimens in static bending and those broken under repeated bending stress was observed.

The fracture surfaces containing necked tensile fractures and flat brittle fatigue fractures were examined under the ~canni,ng electron microscope at magnifications to 2,000 times. The necked tensile and brittle fatigue fractures are shown in Fig 32 and 32b at magnifications of 15 times. At higher magnifications, details of the fracture surfaces are clearly evident. Fig 33a shows the dimpled surface typical of steel which has broken in a ductile manner under a tensile load. Fig 33b shows the striations typical of fatigue fractures. These striations indicate the stepwise manner in which a crack progresses or propagates across the structure. Examination showed that the crack progressed from one side (the tensile side of the ferrocement specimen) completely across the wire cross-section.

A preliminary examination under the scanning electron ,microscope of the mortar fractures from specimens broken under a static single application of bending load and under repeated applic­ations has not revealed any distinct difference in appearance between the two fractures.

The fatigue tests reported herein are of a preliminary nature and require greater replication and additional tests at 1m'ler stress levels to establish the endurance limit for ferrocement of the constructions used.

The results of the tests which imposed repeated loads of constant ma~nitude show that ferrocement of the constructions tested can withstand over 500,000 cycles at an apparent fibre stress of

96

Fig. 30. Portion of surface of specimen broken in "static" bending. Note tensile nature of wire fractures. Mag. 3x.

Fig. 31. Portion of surface of specimen broken in cyclic bending. Note flat brittle nature of wire fractures. Mag. 3x.

97

a b

Fig. 32. Scanning electron microscope photographs of broken wires of (a) specimen broken in static single-cycle bending and (b) specimen broken in cyclic (fatigue) bending. Mag. l5x.

a b

Fig. 33. Scanning electron microscope photographs of broken wires showing (a) dimpled structure of wire fracture typical of tensile failure (Fig. 32a above) and (b) striated structure of wire fracture typical of fatigue failure (Fig. 32b above). Mag. 2000x.

98

1320 psi. The endurance limit at . lOG or 107 cycles has not yet been established and it i$ not yet known whether f~rrocement exhibits a true endurance limit.

The examination of the fractures under the scanninq electron microscope showed that, in general, the fractures of \'Iires in specimens that failed under repeated bending loads were in the plane of the major mortar crack or fracture, whereas those wires in specimens that failed under a single-cycle bending load stood proud ot the major mortar fracture. The broken wires in these specimens have fractures which are characteristically tensile and which show no evidence of bending. The scanning electron microscope showed that the' broken wires from specimens subjected to repeated cycl~s of bending stress have the striations uniquely characteristic of bending fatigue. The fatigue crac~s developed on the "tensile" side of the wires and progressed completely through the wire. The appearance suggests that the bond between wires that fail in fatigue and the mortar matrix is still intact (and probably with a bond stress distribution described by Kar and ~al~~~that the crack width is very small, and that the wire under the be"riding stress behaves in a "stiff" manner. ' The appearance of the "tensile" fracture in specimens broken in a single-cycle load suggests that the 'bond between wire and matrix has failed, that the mortar crack is relatively wide at failure, and that the stress in the wire at the point of fracture is almost pure tension.

5. Bolting Tests

Various brackets, bumper strips, chain plates, and marine fittings must be ,attached to the hull and decks of ferrocement boats. The bolts in those fittings which load the hull or deck as a diaphragm can generally have substantial steel washers or bearing plates to distribute the load. However, attachments which exert in-plane loads, especially near a free edge, may be needed in areas not especially reinforced. A preliminary examination of the behaviour of ferrocement It/hen steel plates or bars carrying planar loads are attached to ferrocement panel specimens has been made. The relationship between the marginal pitch (the distance of a bolt hole from the edge) and the bolt hole pitch in ferrocement panels of several constructions without special reinforcement has been considered.

The ferrocement panel specimens were prepared from one-inch thick panels of the following constructions:

1 layer of 1/2-in. l6-ga . galvanized welded square mesh on each

99

side of 0.225-in. double-drawn high strength rod spaced at 2-in. in both directions,

2 layers of 1/2-in. 19-9a. galvanized hardware cloth on one side and 3 layers on the other side of the same rods, and

5 layers of 1/2-in. 22-ga. galvanized hexagonal mesh on each side of the rods. All specimens had approximately the same weight of reinforcement per unit area.

1/2-in. bolts: The test specimens had the fo110win~ hole locations for

- Type A boH holes 2-in. from each side and end of 4 x 8-in. specimens

- Type B bolt holes 2-in. from each side and 4-in. from each end of 4 x 8-in. specimens

- Type C bolt holes 4-in. from each side and 2-in. from each end of 8 x 8-in. specimens -

- Type 0 bolt holes 4-in. from each side and from each end of 8 x 12-in. specimens.

All holes were drilled in the centre of the 2-in. space between the rods. Steel bars 5/16 in. thick x 3 in. wide were bolted to the ferrocement specimens. A 4 x 4-in. piece of 3/4-in. plywood interfaced one si~e of the specimen. Tensile loads were applied to the ends of the bars. Coplaner loads, or slightly offset loads, were therefore imposed on the ferrocement specimens. The maximum loads held are presented in Table 38. The average maximum loads held, 16 per in. width of specimen, are:

Mesh Type Types A,B Type C Type 0 2 layers 1/2-in. 16-ga. welded 840 525 750

square mesh 5 layers 1/2-in. 19-9a. hardware 760 450 710

cloth 10' layers 1/2-in. 22-ga. hexagonal 640 450 650

mesh

It is tentatively concluded that bolt loads of about 500 1b/in. width may be used in ferrocement of the constructions described if the distance of the bolt hole from the edge if more than two inches and the bolt hole pitch is about four inches. A reinforced edge and a 9reater distance between bolt hole and free edge would increase the bolt load able to be carried, possibly allowing failure of the ferrocement

100

Panel Construction

1/2-16 ga welded square mesh (2 layers)

1/2-19 ga hardware cloth (5 layers)

1/2-22 ga hexagonal lllesh

TABLE 38. Loads Held in Bolting Tests (single lIZ-in. bolts in 4 in. wide (A,B)· and 8-1n. wide (C~D) specimens)

Specimen Load at First Max. load Mode of Fail ure Type Visible Crack, lb. held, lb.

A (2400) 3300 transverse, vertical B 2600 2800 transverse B (2800) 3400 transverse · B 3000 3900 transverse C 3600 4200 vertical, transverse D 4100 6000 transverse, vertical

A (2200) 2700 transverse, vertical A 2800 3300 transverse A (2300) 2750 transverse A 2100 2600 transverse B 2800 3200 transverse B

{2600J 2800 transverse

B 3000 3850 transverse C 3200 3600 vertical, transverse C 3300 3600 vertical, transverse D (5100) 6000 transverse, vertical D 5000 5400 transverse, vertical

A* 800* 1200* transverse A 12OOO~ 2600 transverse, vertical B 1700 2500 transverse B 1800 2600 transverse C 3000 3600 transverse, vertical D 4000 5200 transverse, vertical

* tensile loading transverse to direction of mesh.

101

in compressive bearing. If offset loads which impose bending stresses are used or if the loads are cyclic, the maximum load able to be carried will be reduced.

Some preliminary tests were performed on the placement of powder-actuated 1/4-20 NC studs with 1/8-in. shanks to hold brackets. Some spalling and cracking of the panels was observed. Withdrawal loads ranged from only a few pounds to about 1000 pounds. The tests were not successful but further work appears to be warranted.

6." Design Considerations

This study has not delved deeply into the design theory for ferrocement. It is generally agreed that reinforced .­concrete analysis does not quite apply to a composite containing mortar and finely divided steel reinforcement. As part of this study, reported 1n 1-972, J. D. Smi th (4) developed a prel iminary simpl e "mathematical model" to explain the behaviour of ferrocement. His development is presented in the Appendix. .

In 1972, Bigg(44) prepared a comprehensive treatise for the Industrial Development Branch, Canada Fisheries Service, which discussed the analysis of ferrocement structures and the design criteria for these structures with a view to establishing a rational basis for design. In the study he reviewed the mechanical properties obtained from ma~y investigators of ferrocement and found gross differences due to various testing techniques and the "highly s"tatistical" nature of the prope,rties of ferrocement. He cites many of the variables responsible for this "statistical" variation. He used the work of Bezukladov(18) as a basis for his analysis of a beam. Bigg has expressed hope that in the future he will be able to extend the analysis to a stage where a designer can establish the type and placement of rod and mesh reinforcement for a given geometry and material.

7. Patching Ferrocement

Damaged ferrocement hulls must be repaired to restore a water·tight condition, the strength, and the appearance and to prevent further deterioration of the steel reinforcement from corrosion. Damage can vary in severity, e.g., surface scrapes, gouges, spalling, and cracking of the mortar matrix and extensive damage to the mortar matrix and steel reinforcement. The damaged area may be covered with oil, slimes, or other contaminants.

102

Most authors of books on ferrocement boat construction(S 1~1 extoll the ease of repairability as "one of the most endearing aspects of ferrocement hulls". Some ignore the problem. Others prescribe "knocking out the loose mortar, brushing out the dust and small particles, hammering the mesh into shape, and re-mortaring". Some prescribe applying an epoxy bonding agent to the edges of the damaged area, re-mortaring with a rich Portland cement mix or an epoxy suitably stiffened with either dry cement Ot~ fine sand. The American Concrete Institute r·1anual .of Concrete Practice, Part 2, 1967 (ACI 301-66)(~51 specifies a procedure for patching surface defects in concrete. A bonding grout of thick cream consistency (1 part cement to 1 part -30 mesh sand) is brushed onto the surface. The patch is then filled ·with a concrete of the same kind being patched. Further details are ·,Irovided. The American Concrete Institute Publication SP-21 Epoxies with Concrete(~61 discusses uses, application techniques, and characteristics of epoxy-resin compounds for concrete. Simple cracks, after thorough drying, may be injected with epoxy by various ingenious pressure techniques. Where hull damage is severe the hull must be restored to its original shape by jacks or other means. The mortar "rubble" must be cleaned out as thoroughly as possible by a·pneumatic needle chipping tool, sandblasting wire brushing, or other means. Experience in this laboratory has sho~m that it will not be possible to remove all broken pieces from the mesh. Damaged rods and mesh must be repaired by inserting pieces of rod, as necessary, and overlapping mesh.

A series of test repairs was made on specimens damaged by prior impact and flexure tests. The 30 x 3D-in. panel impact specimens, reinforced with 1/2-in. 22-ga. hexagonal mesh only, had a highly-fractured centre area and major cracks extending to the surface. No mesh had been broken. A pneumatic needle gun was found to be the most effective way to clean out fragmented mortar, to open up the cracks, and to roughen the surface. This device is an airpowered chipping and scaling tool which uses a small bundle of steel rods 2 to 3 mm in diameter. The rods easily penetrated the mesh with little damage to the wire. Cracks were opened up to expose mesh which could assist in anchoring the patch material. Another impact specimen had suffered mesh damage in the test. It was similarly cleaned out, the mesh was not repaired. Both specimens were wetted and patched with a Portland cement mortar of the kind used in the original panels. The patches were cured 21 days. Several 3 x 12-in. flexure test specimens were patched with a cement/sand mortar and several with a two-component epoxy marine patching compound, containing a filler, and with a blO-component epoxy floor-patching compound requiring a sand filler. The specimens received a minimum of preparation. The patching materials were spread on the specimens

and forced into the cracks before these specimens were straightened. When the specimens were straightened the excess epoxy squeezed out was removed. The specimens were cured 21 days for the mortar patches, 7 days for the epoxy patches.

Flexure specimens reinforced with 1/2-in. 16-ga. welded square mesh and patched with cement mortar regained about 80 percent of their original modulus of rupture values. Those reinforced with 1/2-in. 22-ga. hexagonal mesh regained 50 to 70 percent of their original strength owing to some prior damage to the wire mesh.

The several flexure specimens containing 1/2-in. 16-ga. welded square mesh, 1/2-in. E-ga. hardware 'cloth, and 3/8-in. 20-ga. welded square mesh were patched with epoxy patching components. All well-penetrated epoxy-patched specimens regained virtually all their original strengths.

It is concluded that cement/sand mortar can make a reasonably strong repair but an epoxy filler at the edges might

103

prevent spalling at the fractured edges. The epoxy materials m:~c strong repairs, virtually equal to the original strength, provided the debris was removed. The effects of contamination with oils, weathering, thermal expansion, and other factors have not been ascertained.

104

8. Protective Coatings

(a) General

Most concrete structures are not painted and there is little recorded experience available to support the claim that paint can prevent corrosion of steel in concrete structures. An investigation of 40 circular wire-wound prestressed concrete water reservoirs showed that corrosion of the steel occurred in all reservoirs except two which had been painted \t/ith a polyvinylacetate latex coating over a flood coat of raw linseed oil 47~ It was concluded that sealing the exterior wall surface reduced and equalized the oxygen supply to the wires. The only substantial reference related solely t~ ~oatings for concrete is the comprehensive guide prepared by the American Concrete Institute in 1966 48

The report identified 20 basic film-forming materials available for coatings manufacture. However, minor variations in formulations can affect the performance of the coatings. The report pointed out that surface preparation, method of application, the environmental conditions at the time of application, and the film thickness, are of prime importance. Two more recent books 49, 50 provi de a broad survey of the many conventi.ona 1 and more recently developed organic coating systems for most materials, 1ncl~ding concrete.

The several authors of books on the construction of ferrocement boats do not stress the need to paint ferrocement hulls. Whitener 13 recommends the application of finishes on hulls in sea-water and claims that the epoxy resin finishes are best and that anti-fouling paint should be applied twice a year. Jackson and Sutherland 10 state that professional New Zealand practice has been to coat the outside of the hull with an epoxy resin finish but claim that a guaranteed 0.05 in. of high quality mortar over the mesh eliminates the need for painting. Cairncross 14 feels that painting is not an absolute necessity but 1s an added safeguard and more pleasing aesthetically. He claims that epoxy paints are the most successful coatings, bonding well and giving good protection. Primers, he states, can be coal tar-epoxy, clear epoxy resin, or chlorinated rubber paint. He states that polyurethanes, vinyls, and acrylics have also been successful. Some of the factors cited as affecting the efficacy of possible coatings is the strength (e.9. epoxy coatings may be ten times as strong in tension as cement mortar), flexibility, elongation, coefficient of thermal expansion (e.g. epoxies may be much higher than cement mortar); antifouling characteristics, resistance to seawater, and changes of these with time.

105

In general, oil base paints must be avoided because the alkali in the mortar saponifies the oil-base unless the concrete (mortar) is very thoroughly dried over a long period so that the surface and inner alkalinity is neutralized. The limited resistance of oil-based paints and their permeability to moisture is said to limit their use in appli­cations where moisture behind the film can cause flaking and blistering. Latex (water emulsion) paints of the styrene-butadiene, polyvinyl acetate, and acrylic types are said to be relatively insensitive to water and to resist alkalinity well. The nature of water-based paints allows appli­cation over damp (not wet) and unaged (not uncured) mortar. Some synthetic resin coatings e.g. epoxy resins, polyesters, polyurethanes, and various synthetic rubbers have been used successfully on con~rete intended for severe service.

(b) Exposure Tests

The paint coatings evaluated in this study, on the basis of exposure to various environments, included an inorganic two-component self-curing ethyl silicate zinc-rich coating, a polyvinyl chloride-based enamel, a two-component chemical-curing polyamide resin, a chlorinated rubber-based enamel, and a highly-modified polyester resin coat in various primer and top-coat combinations.

The mortar surfaces of the 15 x 30-in. panels were prepared as follows:

- ground with flexible abrasive disc CF885F A10xite 50 Fascut resin disc) to smooth the surface and remove any cement film.

- etched by scrubbing with 200 cc of 30-percent (or 15-percent where particularly specified by paint manufacturer) muriatic acid until all bubbling ceased and re-etched for 30 seconds. Panels 13 and 14 were not etched.

- washed with much water and thoroughly dried at 100F overnight.

- dusted surface before brush application of paint according to manufacturers direction.

- paint coatings cured 14 days at normal room temperature before exposure.

The 12 paint systems used are described in Table 39.

106

TABLE 39. P.fnt Systems Applfed to Ferrocement Panels for Exposure Tests.

Pinel Descrfption of P.int System Toul Mo. Thfckness. .n,. 3A Primer-inorganic two-component self-curing ethyl silicate zinc-rfch. ,

Top-coat - same as primer coat.

6 Primer seal coat - Two-component clear epoxy finish. 4 Top coats - Two coats of vinyl resin - base ant i foulin9 paint.

7 Primer seal coat - chlorinated rubber-based paint cut with 15 percent thinner. 4 Top coats - Two coats chlorinated rubber-based paint.

9A Primer seal coat - Zinc silico-fluoride solution. 4 Top coat - A highly ~dified polyester resin vehicle with metal and metal oxide fillers.

9B Primer seal coat - none. 4 Top coat as in 9A.

llA Primer seal coat - Polyvinylchloride-based enamel cut with Top coats - Two coats polyvinylchloride-based enamel.

15 percent thinner. S

11B Primer seal coat - none. 4 Top coats - Two coats two-component pigmented epoxy-resin.

12A Primer seal coat - Inorganic two-component self-curing ethyl silicate zinc-rich. 6 Top coat - Two-component clear chemical-cured polyamiip. resin.

12B Primer seal coat - Inorganic two-component self-curing ethyl silicate zinc-rich. 6 Top coat - Polyvinyl chloride-based enamel cut with 30 percent vinyl thinner.

14 Same as 7 except that mortar surface not etched. 4

16A Primer seal coat - Two-component clear chemical-curing polyamide resin. S Top coat - Two-component clear chemical-curing polyamide resin .

16B Primer seal coat - Chlorinated rubber-based enamel cut with 1'5 percent thinner. 4 Top coats - Two coats chlorinated rubber-based enamel.

107

Specimens, ~bout 3 x 3 and 3 x,6-in. cut from the panels for the several exposure procedures, viz. ambient dry laboratory conditions (control), Weather-Ometer, laboratory wet-dry cycling in a seawater bath, and marine tidal. The specimens were assessed on the basis of visual appearance, {crazing, flaking, etc.}, ease of separating the paint coatings from the mortar substrate with a razor blade, spall-resistance when penetrated with two parallel score marks of a sharp pen-knife, and resistance to gouging-abrasion by a pointed tool.

i. Dry Laboratory Environment {Control}

The set of 3 x 3in. specimens were assessed as above after. four months in the ambient laboratory environment. The assessment is presented in Table 40.

ii. Weather-Ometer Exposure

Duplicate 3 x 6-in. specimens were exposed in a standard Weather-Ometer apparatus. Each cycle of exposure consists of 102 minutes of ultraviolet light plus 18 minutes of ultraviolet light and a water spray. The temperature is maintained at 140F. An exposure period of 250 hours is reported to be equivalent to one year of outside mid-temperature climate. The appearance of the specimens was recorded at regular intervals. The specimens were removed after 1500 hours {6 years equivalent} and rated on the above basis. The assessment is presented in Table 41.

iii. Laboratory Seawater ~Jet-Dry Cyc1 ing

Duplicate 3 x 3-in. specimens of 12 paint systems were inserted into a cyclic exposure apparatus which dipped the specimens in a bath of filtered seawater for one hour and lifted the specimens for. drying before an air fan for three hours. The specimens were observed at regular intervals and assessed, as above, after 600 cycles. An additional 2000 cycles of exposure produced no visible change. The results are shown in Table 42.

iv. Marine Tidal Exposures

Two duplicate sets 3 x 3-in. specimens of the 12 paint systems were set into shallow pans of paraffin wax and covered with a .screen cage. One set was exposed mid-February to mid-r·1ay at mean tide level at the Vancouver Kitsi1ano Station of the Canadian Coast Guard and the other at below low-low tide. The former received one or two immersion cycles per day, depending on the tides. The latter was constantly immersed. The coatings were assessed, as above, after 84 days exposure. The condition

108

Specimen No.

3 , 7

9A

98

llA

118

12A

128

14

16A

168

Specimen No.

3

, -7

9A

98

11A

llB

12A

12B

14

16A

16B

TABLE 40. Assessment of Coatings After 4 months in Room Environment (control specimens not exposed to weather or service environment)

Visual Appearance Separation Resistance (Lifting with razor blade)

Spall Resistance (Scoring with penknife)

Gouge Resistance (Pointed tool)

Fine crazing Separates eas ily. brittle flakes.

Spalls and crumbles. Fair

No defects No separation at interfaces. Spalls Fair

• • No separation at interfaces. No spalling. Good

• • No separation at interfaces. No spalling. Good

• • No separation at interface. No spal1tng. Debris tenacious. Good

• • Separates with difficl.'lty. No spalling. Debris tenacious. Good

· • Separates with difficulty. No spal1tng. Debris tenacious. Good

• • Separates fairly eaSily, Spalling. Debris tenacious. Good brittle.

• • Top coat separates from Spalls. Debris tenacious. Fair primer: Tough.

Spalls slightly. Fair • • Separates with difficulty.

• H Separates with difficulty. No spal1tng. Debris tenacious Good

• • Top coat separates from Spall ing. Debris brittle. Poor primer. Brittle.

TA8LE 41. Assessment of Coatings After 1500 Hr (6 yr) in Weather-Ometer

-- -

Visual Appearance Separation Resistance (Lifting with razor blade)

Spall Resistance (Scoring with penknife)

~uge Resistance (Pointed tool)

Fine craze cracking No separation at interface. No spalling. Debris crumbly. Good Yellow encrustation

Fine craze cracking Separates cleanly from inter- Spalls cleanly in flakes. Fair Yellow stain. face but with difficulty.

Fine craze cracking Separates easily and cleanly Spalls easily and cleanly. Poor and flaking. at interface.

Fine craze cracking No separation at interface Spalls slightly. Debris Fair Clean surface. flaking and crumbly.

Fine craze cracking No separation at interface Spalls slightly. Debris Fair Clean surface. flaking and crumbly.

Good surface. Separates readily at inter- No spal1tng. Tough fl1m. Good face in continuous film.

Good surface. Separates only with diffi-culty.

No spalling'. Tough film. Good

Fine craze cracking Separates readily at inter- Spalls easily and cleanly. Fair face with spalling.

A few craze cracks No separation at interface Spalls slightly. Debris crumbl) Fair

Fine craze cracking Separates cleanly and Spalls easily and cleanly. Poor and flaking easily at interface.

A few fine craze Separates easily and cleanly cracks. at interface.

No spalling. Tough film. Good

Craze cracking. Separates cleanly with curling, film loss. difficulty at interface.

Spalls easily and cleanly. Poor

Specimen No.

3

6

7

9A

98

llA

118

12A

128

14

16A

16B

TABlE 42. Assessment of Coatings After 2600 cycles in Seawater. (1 hr immersed - 3 hr dr,ying in moving air)

Visual Appearance

Heavy brown bloom. No surface defects.

No surface defects. Yellow stain. *

• •

• •

• •

• •

• •

•

Separation Resistance (Lifting with razor blade)

No separation at interfaces.

No separation at interfaces.

No separation at interfaces.

No separation at interfaces.

No separation at fnterface.

Easy separation at mortar interface.

Separates with difficulty.

Separates fairly easily. Brittle.

Coating lifted at Top coat separates from one corner primer as tough film.

No surface defects. Separates wfth difficulty.

No surface defects. Separates with difficulty.

No surface defects. Top coat separates from primer.

Spall Resistance (Scoring with penknife)

No spalling. Debris crumbly

Spalls. Debris slightly cruq,ly.

No spalling. Debris slightly crumbly.

No spalling. Debris tenacious.

No spalling. Debris tenacious.

Spalling. Debris tenacious.

·No ·spalling. Debris tenacious.

Spalling. Debris tenaciou~

No spalling. Debris tenacious.

Spalls slightly. Debris tenacious.

No spalling. Debris tenacious.

Spalling. Debris brittle.

* All specimens exhibited yellow stair.ing.

109

Gouge Resistance (Pointed tool)

Good

Fafr

Fair

Fair

Fafr

Fair

Fafr

Fafr

Poor

Poor

Fair

Poor-spa 11s.

110

of the specimens except for a slime coating appeared to have changed little. The results are reported in Table 43.

I The two lots of specimens were returned to the sea from the end of May and to the end of October. Examination after this additional 150 days of exposure showed that the barnacles had attached themselves to all of the specimens except those two which had the inorganic two-component self-curing ethyl silicate zinc-rich paint primer and top coat, (specimen 3) and those having the two-component clear epoxy finish primer with two top coats of vinyl resin-base antifouling paint (specimen 6).

" The specimens were scraped free of barnacles and reexamined. Scraping easily removed the barnacl~ shells but their bare plates remained attached to the substrate. Close inspection revealed that the plates had removed the paint to bare mortar on those specimens coated with the highly-modified polyester resin vehicle containing metal and metal oxide fillers. The barnacles did not att~ck the other coatings but scraping to remove the base plates of the barnacles, as would be necessary on a hull, caused some damage. The results are found in Table 44.

(c) Discussion and Conclusions

On the basis of the visual and physical assessment of the specimens subjected to the above exposure tests the most satisfactory coatings are deemed to be:

System on Panel 3A Primer - inorganic ethyl-silicate zinc-rich paint Topcoat - inorganic ethyl-silicate zinc-rich paint

System on Panel 6 Primer - two-component clear epoxy finish

"Topcoat - two coats of vinyl resin-base anti-fouling paint

System on Panel 118 Primer - two-component pigmented epoxy resin Topcoat - two-component pigmented epoxy resin.

System on Panel 11A Primer - polyvinyl chloride-based enamel Topcoat - two coats of po1yvinylch1oride-based enamel.

The other systems tested were considered less acceptable. It is considered that barnacle-free, freshwater exposures may result in a different rating order. Thermal expansion, aesthetics of colour, and other factors have not been considered in the rating system.

Specimen No.

3

, 7

9A

98

llA

118

12A

128

14

16A

168

111

TABLE 43. Assessment of Coatings After 84 days Marfne Exposure at Mean Tide (Vancouver - Kitsilano)

Visral Appearance Separation Resistance (Lifting with razor blade)

Slime layer - otherwise No separation at interface. clean as origfnal.

• • •

• •

•

• •

•

•

Spalls with dffficulty.

No separation at interface.

• •

Separates as tough film.

Separates only with difficulty

Spalls at interface.

Top coat separates from primer as tough film.

No separation

Spalls readily.

• •

Spall Resistance (Scoring with penknife'

Slight spalling. Debris crumbly.

Spalls. Debrfs slightly crumbly.

No spalling. Debris slightly crumly.

• Slight spalling. Debris slightl) crumbl_y.

Slight separation. Debris tenacious.

• Spalls fairly readily

Spalls fairly readily. Debris crumbly.

Slight separation. Debris tenacious.

Spalls readily.

• •

~ouge Resistance (Painted tool)

Good

Fair

Good

Good

Good

Good

Good

Good

Fair

Fair

Good

Poor

112

TAILE 44. Conditions of Specimens After Second Period of Marine Tidal Exposure - Total 234 Days at low-low Tfde

Specimen Pafnt System Used Cond1Uon No.

3 Prime and top coat - 1i\organic two-component self-curing ethyl silicate zinc-rich paint.

No barnacles.

6 Primer - two-component clear epoxy finish. 110 barnacles. Top coat - two coats of vinyl resin base antj-fouling paint.

7 Prfmer - thinned chlorfnated rubber-based paint. Bases of barnacles did not damage ~op coat - two coats of chlorinated rubber-based paint. paint but are dffficult to scrape

off without paint damage.

9A Primer - sealed with zinc s1l1co-fluoride solution. Barnacles completely dissolved paint Top coat - a highly ·modified polyester resin/metal/oxfde. around base and partly under base.

98 Primer - no seal coat. As in 9A. Top coat - as in 9A.

llA Primer - thinned polyvinyl chloride-based enamel. As in 7. Top coat - two coats polyvinyl chloride-based enamel.

118 Primer - none. As in 7. Top coat - two coats of two-component pigmented epoxy resin.

12A Primer - inorganiC two-component self-curing ethyl silicate Bases did not damage paint and could zinc-rich primer. be scraped off with little damage to Top coat - two-component clear chemical curing polyamide resin. paint.

128 Primer - as in 12A. As in 7. Top coat - thinned polyvinyl chloride-based enamel.

14 Primer - thinned chlorinated rubber-based paint. As in 7. Top coat - two coats of chlorinated rubber-based paint.

16A Primer - clear chemical curing polyamide resin. As in 12A. Top coat - two-component clear chemical curing polyamide resin.

168 Primer - thinned chlorinated rubber-based enamel. As in 7. Top coat - two coats of chlorinated rubber-based enamel. -

9. gyality Assurance

Many areas of construction must be controlled if the ferrocement hull is to be of good quality. Various tests to verify the strength of the mortar and reinforcement and that of the resul-

113

tant composite have already been outlined. Sands and cements of recognized quality are readily obtainable. Controls, such as cement/ sand and water/cement ratios, slump, compressive, and flexure tests for the mortar are strai ghtfor'lJard. Tests for the strength of the steel reinforcements are also straightforward. It is important that the details of mix, placement procedure, and properties of the mortar be adequately specified. The kinds and lay-up configurations of the steel reinforcements used are important. Specimens to determine the strength and performance of the ferrocement composite must realistically represent the properties of the hull.

It is very desirable that non-destructive tests be developed td......assist in quality assurance. It has been eVident in the five-year program that it is quite possible to w.ake substandard ferrocement even when the panels are simple and made in the favourable environment of the laboratory. Sectioning revealed unsoundness in panels of good outward appearance. The construction of hulls with extra layers of mesh and rod reinforcement in thick sections at the keel, ribs, bow, and stern poses serious problems of mortar penetration. Our preliminary test using ultrasonic techniques failed to detect unsoundness in a plane specimen. It seems likely that tapping with a hammer may be the most effective way to test plane sections at the present time. Heavy T-rib and keel sections pose a different problem.

8igg 44 has outlined many of the important points requiring attention in a quality control program. He has outlined problem areas, and suggested parameters for judging its character.

The certifying bodies, viz. Marine Services Canada Ministry of Transport and American Bureau of Shipping,nave not had to deal with many requests for certification. Each body laid down certain general regulations, requirements, and guidelines for the construction of ferrocement vessels {generally available in mimeo only) ca 1968 when interest in ferrocement construction was high. 51,52,53. For convemence these are presented in the Appendix.

114

D. BIBLIOGRAPHY OF FERROCEI,1ENT LITERATIIRF

Much of the literature on ferrocement, or related to ferrocement, has been collected and annotated in a continuing bibliographic listing during the several program years. Many of the items were of technical significance but some of the early items were "news i terns II •

The bibliography, presented in the Appendix of this report, has been stripped of the "news " items but those of technical and historical significance have been retained. Undoubtedly many worthwhile contributions to the ferrvcement technology are not found in the list. Some of these may be present in the annotated pa~ers, many of which have a good bibliography.

Most of the items listed are on file at B.C. Research but interested persons should, \'/here possible, try to obtain articles from the original source. Notification and receipt of articles on the subject are welcomed for inclusion into any future reprintings of the report.

115

E. ACKNOWLEDGEMENTS

B.C. Research thanks the Fisheries and Marine Services. Environment Canada. for the privilege of undertaking this work for it during the past six years. It particularly appreciates the cooperation enjoyed with Mr. L.S. Bradbury, Director of the Industrial Development Branch. Mr. H.A. Shenker. Chief of the Vessels and Engineering Division of the Branch. and Mr. G.M. Sylvester', Vessel Technologist and Project Officer of the Division.

It is felt that the program, although it has not exhaustively explored any of the properties of ferrocement, has provided a much better "feel" for a wide range of properties of the material which will facilitate design and construction of fishing and other vessels. However, much work is required to bring the ferrocement to the same level of technology as that of the other common construction materials.

~~ /'

A. W. Greenius Division of Engineering Physics

Head, Physics

116

f. REFERENCES

1. Kelly, A.M. and W.N. English, Ferro-Cement as a Fishing Vessel Construction Material, B.C. Research report to Industrial Development Service, Canada Department of Fisheries, 1968, published in Project Report No. 42, Ferro-Cement for Canadian Fishing Vessels, W.G. Scott, Edit., Industrial Development Branch, Fisheries Service, Canada Department of the Environment, Ottawa, Aug. 1971, pp. 11.

2. Kelly, A.M. and T.W. Mouat, Ferro~Cement as a Fishing Vessel Construction Material, Proc. of a Conference on Fishing Vessel Construction Materials, Montreal, Canada, Oct. 1-3, 1968. (Also published in Project Report No. 42, Ferrocement for Canadian Fishing Vessels, W.G. Scott, Edit., Industrial Development Branch, Canada Department of the Environment, Ottawa, Aug. 1971, pp. 42 incl. Appendix and Reference List.)

3. Greenius, A.W., The Development of Ferro-Cement for Fishing Vessel Construction, Project Report No. 42, Ferro-Cement for Canadian Fishing Vessels, W.G. Scott, Edit., Industrial Development Branch, Fisheries Service, Canada Department of the Environment, Ottawa, August 1971, pp. 61 and Technical Supplement, pp. 58.

4. Greenius, A.W., Ferro-Cement for Canadian Fishing Vessels, Vol. 2, and Smith, J.D., Part II - Development of a Mathematical Model, Project Report No. 48, Industrial Development Branch, Fisheries Service, Can~da Department

----------------------40uf~th~e~Eunv~'w·r~ownmme~n~t~, ~~~7~2~,~pwph.~92~a~n~d~2~1~~------------f

5 •. Greenius, A.W., Ferro-Cement for Canadian Fishing Vessels, Vol. 3, Project Report No. 55, Industrial Development Branch, Fisheries Service, Canada Department of the Environment, Ottawa, August 1972, pp. 55.

6. Greenius, A.W., Ferro-Cement for Canadian Fishinq Vessels, Vol. 4, Technical Report No. 64, Industrial Jeve10pment Branch, Fisheries and Marine Service, Canada Department of the Environment, Ottawa, 1973, pp. 57.

7. Greenius, A.W., Ferro-Cement for Canadian Fishing Vessels, B.C. Research report to Industrial Development Branch, Fisheries and ~1arine Servi ce, Canada Department of the Environment, Ottawa, Oct. 1974, pp. 50. (Not pub­lished for general distribution.)

8. Hartley, R., Boatbuilding with Hartley, Boughb/ood Printing House, Auckland, New Zealand, 1967, 33-50.

9. Samson, J. and G. Wellens, How to Build a Ferro-Cement Boat, Samson Marine Design Enterprises Ltd., Vancouver, Canada, 1968, pp. 120.

10. Jackson, G.W. and W.M. Sutherland, Concrete Boatbuilding, Allen and Unwin, London, 1969, pp. 106.

11. Benford, J.B. and H. Husen, Practical Ferro-Cement Boatbuilding, International Marine Publishing Co. Camden, ~~e., 1970, pp. 176.

117

12. Roberts, W.H., Guide to Ferrocement Sail and Power Boats and Design, Rapid .Blue Print Limited, Hamilton, Canada, 1970.

13. Whitener, J.L., Ferrocement Boat Construction, Cornell Maritime Press Inc., Cambridge, t.1d., 1971, pp. 128.

14. Cairncross, C., Ferrocement Boat Construction, Inter­national Marine Publishing Co., Camden, Me., 1972, pp. 192.

15. Dinsenbacher, A.L., and F.E. Brauer, Material Development, Design, Construction, and Evaluation of a Ferrocement Planning Boat, Marine Technology, 11(3} July 1974, 277-296.

16. Building Research Station Digest 109, Zinc-coated Reinforcement for Concrete, Building Research Station, Garston, Watford, U.K., Sept. 1974, pp. 8.

17. Frazier, K.S., The Protection of Reinforcing Steel in Concrete, Paper presented at Second Annual Offshore Technology Conference, Houston, Texas, April 1970, pp. 8.

118

18. Bezuk1adov, V.F., Ship Hulls Made of Reinto·rced Concrete, Shipbuilding Publishing House, Leningrad, 1968, Trans. Navships Trans. 1148, CFSTI AD680042, 1968, pp. 187.

19. Christensen, K.A. and R.B. Williamson, Solvi~g the Galvanic Cell Problem in Ferro-Cement, Report No. UC SESM 71-14, University of California, Berkeley, July 1971, pp. 58.

20. Cornet, I.,.R.B. Williamson, B. Bresler, S. Nagarajan, and K.A. Christensen, Chromate Admixture to Improve Performance of Galvanized Steel in'Concrete Sea Structures, Proc. FIP Symposium Concrete Sea Structures, Tbilisi, Sept. 1972, published by Federation Internationale de la Precontrainte Terminal House, London, SWIOWAU, April 1973, 159-163.

21. Robinson, R~C., Design of Reinforced Concrete Structures for Corrosive Environments, Materials Protection and Performance, Vol. 11, No.3, March 1972,15-19.

22. Hausmann, D.A., · Steel Corrosion in Concrete, Material Protection, Vol. 6, No. 11, November 1967, 19-23.

23. Sha 1 on, ·R. and t1. Raphael, Inf1 uence of Sea Water on Corrosion of Reinforcements, Proc. ACI Journal, Vol. 55, 1959, 1251~1268.

24. Hausmann, D.A., Electrochemical Behaviour of Steel in Concrete, Proc. ACI Journal, V.ol. 61~ 1964, 171-188.

25. Gj~rv, O. E"., Durabil i ty of Concrete Structures· in the Ocean Environment, Proc. of the FIP Symposium Concrete Sea Structures, Tbi1isi, Sept. 1972, published by the Federation Internationa1e de la Precontrainte, . Terminal House, London, SWIWOAU, April 1973, 141-145.

26. Lewis, D.A.·and W.J. Copenhagen, The. Corrosion of Reinforcing Steel in Concrete in Marine Atmospheres,. the South African Industrial Chemist, Oct. 1957, 207-219.

27. Lewis, D.A. and W.J. Copenhagen, Corrosion of Reinforcing Steel in Concrete in Marine Atmospheres, Corrosion, Vol. l~, No.7, July 1959, 382t-388t.

119

28. Kowalski, T.G., Ferrocement in Hong Kong, Far East Builder, July 1971, 29-35.

29. Walkus, R.; State of Cracking and Elongation of Ferrocement Under Axial Tensile Load (I), Bul. Inst. Po1it. Din lasi, XIV(XVIII), 3-4, 1968, 653-664.

30. Wa 1 kus, R., ·Sta te of Cracking and El onga ti on of Ferrocement Under 'Axial Tension (II), Bul. Inst. Pol it. Din lasi, XVI(XX), 3-4, 1970, 53-60.

31. Walkus, R. and T.G. Kowals~i, Ferrocement: a survey, Concrete, 5 (2), Feb. 1971,48-53.

32. Walkus, B.R. and A. Mackiewicz, Application of Ferrocement Shells in Marine Structures, mimeo, published at Symposium on Industrialized Spatial and Shell Structures, Kielce, Poland, June 18-23, 1973, 385-398.

~3. Clemmer, H.F., The Fatigue of Concrete, Proc. American Society for Testing t~aterials, Vol. 22,1922, 408-419.

34. Older, G., Highway Research i.n Illinois, Trans. American Society of Civil Engineers, Vol. LXXXVII, 1924, 1180-1224, esp. 1196.

35. Hatt, W.K., Researches in Concrete, Engi-neering Bulletin of Purdue University, 24, Nov. 1925.

36. Yoshimoto, A., S. Ogino, and M. Kawakami, Micr0cracking Effect on Flexural Strength of Concrete after Repeated Loading, ACI Journal, Proc. Vol. 69, No.4, April 1972, 233-240.

37. Hilsdorf, H.K. and C.E. Kesler, Fatigue Strength of Concrete under Varying Flexural Stresses, .ACI Journal, Proc. Vol. 63, No. 10, Oct. 1966, 1059-1076.

38. ACI Committee 215, Considerations for Design of Concrete Structures Subject to Fatigue Loading, ACI Journal, Proc. Vol. 71, No.3, March 1974, 97-121.

120

39. Romualdi, J.P., The Static Cracking Stress and Fatigue Strength of Concrete Reinforced with Short Pieces of Thin Steel Wire, The Structure of Concrete (and its behaviour under load), Proc. International Conference, London, Sept. 1965, Edit., A.E. Brooks and K. Newman.

40. Romualdi, J.P., M. Ramey, and S.C. Sanday, Prevention and Control of Cracking by Use of Short Random Fibers, Paper No. 10, Causes, Mechanism, and Control of Cracking in Concrete, American Concrete Institute Publication SP-20, American Concrete Institute, Detroit, Michigan, 1968, 179-203.

41. Dinsenbacher, A.L. and F.E~ Brauer, Material Development, Design, Construction, and Evaluation of a Ferro-Cement Planing Boat, Marine Technology, Vol. 11, No.3, July 1974, 277-296.

42. Larsen, H.J., Jr. (John A. Blume & Associates, San Francisco, Ca.), Study and Evaluation of Ferro-cement for Use in Wind Tunnel Construction, prepared for National Aeronautics and Space Administration, Ames Research Center, Moffatt Field, California, NASA-CR-114501, JABE-ARC-07, July 1972, pp. 155.

43. Kar, J.N. and A.K. Pal, Strength of Fiber-Reinforced Concrete, J. Structural Division, Proc. American Society of Civil Engineers, Vol. 98, ST5, May 1972, 1053-1068.

44. Bigg, G.W., An Introduction to Design for Ferrocement Vessels, Project Report No. 52, Industrial Development Branch, Fisheries Service, Canada Department of the Environment, Jan. 1972, pp. 224.

45. Manual of Concrete Practice, Part 2, The American Concrete Institute, 1967, (AeI 301-66), 32.

46. Epoxies with Concrete, Publication SP-21 , The American Concrete Institute, 1968, pp. 140.

47. Westerback, A.E~ and L.B. Hertzberg, Testing Corrosion of Reservoirs, Materials Protection, 6 (6), June 1967, 58-62.

48. Guide for the Protection of Concrete Against Chemi.ca1 Attack by Means of Coatings and Other Corrosion­Resistant Materials, ACI Committee 515, J. American Concrete Institute, 63(12), Dec. 1966, 1305-1391.

49. Paints and Protective Coatings, Technical Manual No. TM5-618, U.S. Dept. of the Army, Navy, and Airforce, Washington, D.C., 1969.

50. Roberts, A.G., Organic Coatings - Properties, Selection, and Use, Building Science Series 7, U.S. Dept. of Commerce, National Bureau of Standards, Washington, D. C ., 1968, pp. 187.

51. Bonn, W.E., Regulatory Aspects of Traditional and New Construction Materials, (esp. Part 6 - Requirements Applicable .to Vessels Constructed of Ferro-cement), paper presented to Conference On Fishing Vessel Construction Materials, Montreal, Canada Oct. l-3, 1968, Canadian Fisheries Reports No. 12, June 1969, 73-90.

52. Anon, Tentative Requirements for the Application of Ferrocement to the Construction of Yachts and Small Craft, lloyd ' s Register of Shipping, london, pp. 15, and Tech. Note: FC/REQ/1 Tentative Requirements for the Construction of Yachts and Small Craft to Ferro­cement, Jan. 2, 1967, pp. 10.

121

53. Anon, Guidelines for the Construction of Ferro-Cement Vessels, American Bureau of Shipping, ca. 1969, pp. 12.

122

G. APPENDIX

1. Development of Mathematical Model - J. O. Smith

2. Regulations for Constructio~ of Ferrocement Boats -Canada Transport Ministry.

3. Guidelines for the Construction of Ferro-cement Vessels -American Bureau of Shipping.

4. Bibliography of Ferrocement Literature.

Appendix 1. Development of a Mathematical Model (by John D. Smith, P. Eng.*)

A. INTRODUCTION.

123

The available literature on ferro-cement boat building mainly concentrates on construction techniques developed through experience for specific types of reinforcement, with little information on design methods to aid the naval architect. Architects with experience in ferro-cement design tend to regard their methods as trade secrets. The more technical articles on ferro-cement are often qualitative comparisons of results of· tests in which various strengths of mortar, mesh sizes and types, percentages of steel, and reinforcing rods were used. Also, most investigators emphasize the ultimate strengths achieved. It is only with great difficulty that the naval architect can find design information in a form useful to him.

The naval architect needs to know:

1. What working stress can be used for designing under tension, compression, shear, and bending and what is the effect of combined loading.

2. What deflection will be produced by a given load. At times the most significant criteria will be deflection rather than stress.

3. What type of failure will occur from accidents such as grounding (possible high local loads), or hitting a rock or log (impact loads). If the damage will seriously affect the water-tight integrity of the hull, he may want to allow extra material to compensate.

One approach to determining the required design informa­tion is to make and test a sufficient number of panels covering the range of likely reinforcement combinations under various load conditions. Since test results for reinforced concrete typically show a wide spread, the number of specimens of each type must be large enough to define perform­ance adequately and to allow the range of deviations to be determined. It should be kept in mind that a small defect in a small specimen will have a greater effect than the same defect in a large panel. Therefore, a greater number of small specimens may be required.

It is evident that this approach will be lengthy and expensive. This method could lead to greater confidence in an acceptance of ferro-cement as a boatbuilding material but it could also retard the evolution of new and better reinforcing materials and combinations.

*Mr. John D. Smith was formerly associated with B.C. Research but is now at Defence Research Establishment Pacific, Esquimalt, B.C.

124

An alternative approach is to develop a mathematical model for the behaviour of ferro-cement. This model could then be proven or improved by the results of a limited number of test specimens. If successful, this approach could effect a considerable saving in time and money and allow new combinations of reinforcement materials to be cheeked out on paper. Only the most promising combination need then be chosen for experimental verification.

Experimental methods would still be required to investi­gate such factors as labour requirements, the effect of joints (hull to deck, frames to hull, etc.), ease of fabrication, and behaviour under impact loads.

The object is to develop the simplest model for the behaviour of ferro-cement which will give results agreeing fairly well with observed experimental results. Since the loading conditions to be experienced by a vessel during its lifetime can only be guessed at and since there can be large variations in actual strength due to workman­ship, it is doubtful that a large increase in complication to achieve a small increase in accuracy is justified. The model and its application methods should also indicate the effects of changes due to increasing mortar strength and in the type, quantity, and distribution of the reinforcement.

The development of a mathematical model can be divided into four convenient stages:

1. A linear model in which both the mortar and steel are assumed to behave in a linear fashion. The linear model should result in the 'least complicated solutions. Since working loads will be considerably lower than ultimate loads, it is probable that non-linear effects will not be significant and that a linear model will be adequate in this region. The analysis of natural frequencies and resonances will be much simpler if a suitable linear model can be used.

2. The linear model is extended to account for t4e non-linearities of the mortar. The steel is still assumed to behave linearly.

3. The loads and deformations where yielding of the steel or limited compressive failure of the concrete occurs is investi­gated. It is important to know when permanent deformation occurs and what the properties will be after a partial failure .• With suitable assumptions it is probable that a linear model can be used to describe the behaviour of the section under low loads after some permanent deformation has occurred.

125

4. The analysis of ultimate failure and prediction of the mode of failure would be investigated.

In the following sections, only the first two stages will be investigated.

B.. DEVELOPHENT OF THE MODEL.

Muhlert(l) at the University of Michigan has applied methods used in the design of reinforced concrete beams to an analysis of ferro-cement bend test specimens. His results have been fairly consistent but conservative. Mowat(2) at the University of Calgary attempted to predict the performance of ferro-cement through a non­linear analysis. Most of his calculations were to obtain ultimate loads, and he used the ratio of actual moment at failure to the predicted moment as a measure of the efficiency of the reinforcement. One criticism of his results is that in calculating his ultimate loads he has assumed that the mortar at the compression face has reached the maximum strain before compression failure occurs. He also computes the height of the neutral axis and the steel strains on this basis. Therefore, if the steel fails in tension before this occurs the efficiency calculated will be low. A better criteria would be the ratio between the percentage of effective steel and the ultimate load.

Both Muhlert and Mowat used relatively simple computer programs to perform the calculations using successive approximations. However, in this study graphical methods will be used as much as possible to make it easier to visualize the effects of changing mortar strengths and reinforcement quantities.

Linearized model.

All loads and s~resses are calculated as a-function of the total strain (the sum of the absolute values of the strains at the tension and compression faces) since the ratio of thickness to the total strain is equal to the radius of curvature and proportional to the deflection.

(1) Muhlert, H.F., Analysis of Ferro-cement in Bending, The University of Michigan, Paper No. 043, January 1970.

(2) Mowat, D.L., Flexural Testing of Ferro-cement Planks, Thesis for M.Sc. in Civil Engineering, University of Calgary, Calgary, Canada, January 1970.

126

It will be assumed that the mortar can exert only a compressive force. Shah(3) has reported that once cracking has occurred, the modulus of elasticity in tp.nsion of ferro-cement is close to that determined from the steel alone. ' Since fine surface cracks have been observed on new hulls (possibly due to settling during curing or to shrinkage stress) it is reasonable to assume the cracked condition.

y

e t a strain at tension face

e t e .. strain at compression c & a total strain

h = thickness h

c .. height of neutral axis 1 ! above compression face c I y = height of any element

above compression face

At any point the strain is given by:

& e = (y - c) h' taking elongation as positive.

Also define the following dimensionless parameters:

yaY... h

Therefore

. ,

e = (Y - C)&

face

To achieve equilibrium the sum of the forces in the steel, Fs, and in the mortar, Fm, must equal zero for pure bending.

(3) Shah, S.P., Ferro Cement as a New Engineering Material, College of Engineering Report No. 70-11, University of Illinois, Dec. 1970.

127

Linear steel.

For one layer of steel reinforcement:

I i The force on the layer is given by

and the net steel force is

where Ai a area/inch width

Yi D height of layer

E a modulus of elasticity s

n (Yi - c) Fs a it h EAiEs b f 1 n anum er 0 ayers

&E s F a __

s h

However,

Z a

Define

where z • height of the centroid of the steel

128

The moment for the steel is given by:

2 (Yi - c)

Ms - I h Ai£Es

x moment of the steel about the neutral axis of the beam.

If 1 s - moment of the steel about the centroid of the steel

Linear mortar.

£E M - [1 + (z - C)2A ] s s s s h

The mortar is assumed to exert a force only in compression and the force is assumed to be linear with strain.

The stress at the compressive face S is given by: c

s - - .£. £E m h m

where E - modulus of elasticity in m compression for the mortar.

129

The mortar force is then

F c C D _

(h tEm) m 2

C2tE h m -... 2

and the moment for the mortar is

M 2 .. F (- - c) m c 3

C3E th2

M m D

m 3

For equilibrium the sum of the steel and mortar forces must equal zero

or

F a [Z - C] tE A s s s

C2 tE h F • __ --:._m_ m 2

dividing both by (th) and equating

F F Z - C E A C2E

....!.+...!!.= m 0 --2- = th th h s s

Z - C E A C2E m =--h s s 2

We can then solve for C by plotting both sides of the equation as a function of C.

It should be noted that at this stage no account has been made of the concrete displaced by the steel on the compression side of the neutral axis. The effect of this will be investigated with an example later.

130

The moment equations obtained were:

1 e)2 A ] M

s (Z -- [-+ eE h 8 h2 s s

and e3E eh2

M m • m 3

Dividing both by 2 eh we get

1 A [ -.!. + (Z - e) 2 -..!. ] E

h3 h s

and

As an example it would be convenient to use Mowat's results for his Series 3 Plank 9. This plank contained 13 layers of 1/2" x 1/2" welded mesh and was strain-gauged top and bottom. The gauges remained intact for the full range of loads allowing us to find both the total strain and the height of the neutral axis for each bending moment.

Table 1 presents Mowat's data and the derived total strains and heights for the neutral axis. These are also plotted in Fig. LA.

To calculate the height of the neutral axis we must have a value of Modulus of Elasticity for the mortar.

Mowat used a stress strain relationship.

e - e f .. f [1 _ ( cu e)A]

e eu e eu

where: f .. mortar stress e

f .. ultimate mortar stress eu e .. ultimate mortar strain eu e .. mortar strain e

). 25 ..

1.25 + f (psi) e

·d f Taking E c ___ c_

m de c e - 0 c

Howat used a value of 0.38% for e • For cu

f - 5000 psi, we get cu

E a 5.26 X 106 psi. m

131

Since the steel is symmetrically arranged Z a 0.50 and

Z E A : 8 T 0.539 x 106

C2E Z - C m The functions h EsAs and -2-- are plotted in the top

half of Fig. 2A. The curves intersect at C = 0.293.

The curves for

and each part of H s - -£h

are also plotted. Taking the values from the curves

~ - (0.045 + 0.077 + 0.045) x 106

£h2

6 - 0.167 x 10

for £ a 0.2% and h = 1.0 in.

M - 0.167 (0.002)(1)2 x 106

- 334 in.-lb/in.

132

This corresponds to a load of 365 lb which is much lower than the value of 530 lb taken from Fig. LA. However, if the load vs strain for the linear model is drawn on Fig. LA it will be seen that the calculated strain curve is offset from the experimental load/ strain curve but nearly parallel to it.

Before commenting further, the effect of the concrete displaced by the steel on the compression side of the neutral axis should be considered. This can be done by replacing the area

E - E Ai by .....;..s~E--m- Ai for those layers.

s

For this case the corrected A = 0.033 sq in. s

Z a 0.518 A

The corrected line for (Z - C) Es: is shown in Fig. 2A by a dashed line.

moment is:

4 The corrected I = 0.00229 in. lin. and the corrected s

M a 326 in.-lb/in. for € = 0.2%

This is a change of 5.4%, which is small compared to the extra work involved.

Non-linear mortar.

It will be assumed that the steel behaves linearly as in the last section. However, the effect of a non-linear stress/ strain relationship for the mortar will be investigated.

The mortar force will be given by:

Fma-af C cu

F "'!!c:-af C Eh cu

a .. a stress block factor defined as the ratio of the average mortar stress to the ultimate stress f • cu

This is

III

The stress strain relationship

e fe f cu

- 1 - (1 - R». where R - ~ will be used. e eu plotted in Fig. 3A.

l.~--------r-----~-,

o ~~~~~------+----o R 1.0

For a given R f

a - average value of ~ between 0 and R. cu

shaded area -.;;..;,;==~~;;;,.

R

1 - (1 - R». + 1 This gives a = 1 - (A + 1) R and is plotted in Fig. 4A.

Now e c

R a --- and e - C £ e c cu

F Therefore ~ = - A f C is now a function of £ as well as £h cu

C and a separate curve can be plotted for each value of £. This is done for £ = 0.01%, 0.2% and 0.4% in Fig. SA. It can be seen that the height of the neutral axis increases as the total strain increases, which is opposite to the trend shown in Fig. 1A for Mowat's specimen 3.9.

Improved linear mortar model.

Previously it was assumed that the mortar could only exert a force in compression. If we now assume that the mortar has a limited tensile strength and characterize this by an ultimate tensile

134

strain etu • The mortar force now becomes

E m --2

and the mortar moment becomes

M m

eh2

E m

a-3

e 2 E (tu) ~

& 2

]

When & » etu the force and moment approach those for

the previous linear model. The height of the neutral axis now decreases for increasing strain, approaching the value given by the earlier linear model. This is demonstrated in Fig. 6A.

c. DISCUSSION ..

The linear model resulted in relatively simple expressions for forces and moments. ~e graphical method employed (Fig. 2A) in solving for the height of the neutral axis and moments clearly shows the effect of varying parameters such as steel area, mortar modulus of elasticity and beam thickness.

Using Mowat's Series 3 Plank 9 as an example gave calculated moments lower than the experimental results. However, the calculated load/strain curve was roughly parallel to the experimental. It appeared that the calculated values could be improved by choosing a higher value for the modulus of elasticity for the mortar. This would also lower the calculated neutral axis height, as well as increasing the calculated moment.

The non-linear model indicated that the height of the neutral axis above the compression face would increase with increasing strain as long as the steel did not yield. This result was inconsistent with the experimental result.

135

Compared to the linear model, the non-linear mortar approximation gave a greater neutral axis height and would give a lower bending moment, thus resulting in an even poorer agreement with the experiment.

The improved linear model which accounted for some tensile strength in the mortar correctly forecast the trend for decreased neutral axis height with increasing strain and gave a higher mortar moment than the previous models. It is felt that with a suitable adjustment of the parameters Em and etu a good fit with the experimental result could be attained.

No attempt was made to fit the experimental curves more closely since this should be done using the results of many tests rather than one isolated example, and the values chosen were adequate to illustrate trends.

The correction of the linear model for the volume of concrete displaced by the steel in the compression zone did not result in a large change in neutral axis height or calculated moment.

D. CONCLUSIONS AND RECOMMENDATIONS.

Either the linear or the improved linear model promises to· be a satisfactory basis for a design procedure for ferro-cement in the working stress range. Further development of the method will require the elimination of appropriate constants by comparison with experimental results.

Strain measurements on both tension and compression faces are an essential requirement to determine the behaviour of the test specimens. The effects of cracking at the tension face on the strain gauge readings must be considered.

There exists enough experimental data and information on standard practices to establish a standard mortar to be used for design purposes. This would be the first step in establishing an approved design procedure. Design charts and standards could then be developed for this standard mortar. When advances in cement technology permit mortars of higher properties to be produced consisten~ly, a second standard mortar could then be established.

Using the standard mortar for test specimens, efperimengal results could be used to establish points on the curves for -- and ~.

Eh Eh~

136

Initially the points could be fitted to a C2 function for mortar forces and a C3 function for moment. As the experimental data increased, empirical curves could be established and values of Es to be used with basic types of reinforcement could be determined. The final stage would be to determine whether an improved linear mortar model would be an improvement. It is likely that the experimental data will show a great enough spread that a more complicated model would not be justified.

Rather than establishing working stresses for design purposes, the possibility of determining strain limits. for tension and compressive strains under design loads should be investigated.

Most of the available data gives load/strain or load/ deflection curves for specimens loaded progressively to failure. Since boat hulls will occasionally experience high loads and the effects ~ay be cumulative, it is essential to monitor specimens through repeated load cycles to higb loads and througv cycles of alternating loads. A design procedure must consider the strains and strengths of the material after many years of service, not just for the new condition.

137

TABLE 1. Mowat's Data for Series 3 Plank 9.

13 layers 1/2" x 1/2" welded mesh - assumed evenly distributed.

Wire dia - 0.042 in.

-Thickness 1 in.

Width

Length

6 in.

33 in.

Total longitudinal wire = 0.00276 sq in./in./layer

a 0.0359 sq in./in.

Moment of steel about steel centroid I -s Mortar compressive strength = 4830 psi.

Compressive Tension Load Defl. Strain Strain (lb) (in. ) (in./in. ) (in./in. )

150 .035 0.010 0.02

300 .129 0.027 0.06

450 .260 0.045 0.114

600 .385 0.061 0.176

750 .529 0.080 0.241

900 .719 0.107 0.950

1050 1.19 0.157 0.642

1090 Failure

4 0.00257 in. lin.

Total Strain Neutral Axis (in./in. ) height/thickness

0.030 0.30

0.087 0.31

0.159 0.283

0.237 0.257

0.320 0.250

0.457 0.234

0.819 0.192

138

0.50 1000

· 0.40 800 c:s '" ..

"Load for Linear Hodel u II)

oM ~ .0 lIS 0.30 r-I 600

.-4 .. X lIS -t:S

"""- C for Linear Hodel ~ lIS .&J 0 ::s H Q)

c:s 'H 0

\c .&J 0.20 400 ,d 00

'" Q)

~

0.10 200

o

Fig. lA.

o o 0.20 0.40 0.60 0.80

Strain, percent

The derived height of neutral axis, C = c/h and derived loads at various strain levels compared with measured values by Mowat (Series 3, Plank 9)*

~owat, D.L., Flexural Testing of Ferro-cement Planks, Thesis for Master of Science in Civil Engineering, University of Calgary, Calgary, Canada, Jan. 1, 1970.

1.00

.05

• .!t _<'01

~ s:i I ~ .10 . ~ -\0 I o .-4 - .15

.20

Fig. 2A.

.2-c

C a -h

h

.3

Plot of modulus functions vs strain to obtain the value of C and hence location of neutral axis.

140

III) III) .. 1.0 ... 41 III)

~ ... a .. 0.8 41

! 41 rot =' ...... CD CD U ... 0.6 41 CD

... • 41 ... a 0 .... 0.4 41

~ •

'W u u~='

0.2.

o o

Fig. 3A.

fc R -r- vs

cu

f III 5000 psi c

(). III 4)

0.2 0.4 0.6 0.8

e R" ~ III Ratio mortar ' strain/ultimate mortar strain. e cu

Stress Ratio vs Strain Ratio R.

1.0

III III ., ... U III ., U

] u .... ::J ....... III III ., ... U III

... CIS u ... g ., 00 CIS ... OJ

~ 0

ori u :! • cs

141

1.0

0.8

0.6

0.4

A D 4

0.2

o~------~--------~------~~------~------~ o

Fig. 4A.

0.2 0.4 0.6 0.8

e R D ~ = Ratio mortar strain/ultimate mortar strain

e cu

Stress ratio a vs strain ratio R.

1.0

\0 I

142

1.0

0.8

0.6

~ 0.4 tC

0.2

A (Z - C)E s s­

h

& a 0.01%

Ol~~~~ ______ ~ ______ ~ ______ ~ ____ ~ __ __

0.1 O.~

F

C Ca­h

0.3

Fig. SA. &~ vs C for Non-linear Mortar.

0.4 0.5

0.8

Assumed etu ~ 0.02% £» etu

0.6 £ a 0.2%

0.2

o

F

A s (Z - C)E -

s h

c 0.3

Fig. 6A. £: vs C for Improved Linear Model.

0.4

143

144

Appendix 2. Extract from Regulatory Aspects of Traditional and New Construction Materi a 1 s, Harren E. Bonn, r·1arine Regul ati ons Branch, Canada Tra'nsport Ministry. (Ref. 51.)

Part 1 - General Requirements Applicable To All Fishing Vessels

. Notification of Pr0~osed Construction

The owner or the builder 'of the vessel should advise the Steamship Inspection Service of the proposed construction, size of vessel, nature of service, type of material of which it is to be built and the extent of the voyages for which it is required.

Submission of Plans

Prior to commencement of construction the plans and information (required by Small Fishing Vessel Inspection Regulations and Large Fishing Vessel Inspection Regulations of Canada Shipping Act) should be submitted to the nearest Steamship Inspection Service Office for approval and should the owner or .builder require any particular information relative to requirements for the type of construction he is proposing the Board will be pleased to provide all possible advice and assistance within their jurisdiction.

Inspection During Construction

During construction a Steamship Inspector will carry out regular inspections to check that the vessel is being built in

·accordance with the approved plans and that the materials and workmanship are to the required standards. In addition to the hull construction he will witness all necessary hose testing and tank testing and will examine and test the machinery installation, piping installations and steering arrangements. He will also check the lifesaving, firefighting and navigating appliances and other statutory requirements.

Sea Trials

On completion of construction the Steamship Inspector shall be present during the sea trials to ensure that the machinery and all essential services are functioning properly and that the vessel is operating in a safe and satisfactory manner.

Certification

On completion of the "First Inspection" the Steamship Inspector will issue an appropriate Inspection Certificate for the voyages on which the vessel will be engaged. The period of validity of the certificate will normally be

145

i) one year for vessels of more than 150 gross tons, ii) one year for vessels that are steam driven,

regardless of their tonnage, or iii) four years for vessels that are not steam

driven and not more than 150 gross tons.

Periodical Inspection and Certification

Periodical inspections will be carried out by a Steamship Inspector when renewal of an Inspection Certificate is required and in accordance with the requirements of the Large and Small Fishing Vessel Inspection Regulations.

It should always be remembered that it is the respon­sibility of the owner, operator or master to have his vessel inspected and certificated in accordance with the requirements of the Canada Shipping Act. That is to say he should advise the local Steamship Inspection Office when the vessel is due and ready for inspection and in the case of new construction, the builder should advise when he wants any particular inspection or test etc. carried out.

Shipbuilder

Part 6 - Requirements Applicable to Vessels Constructed of Ferro-Cement

Construction should be carried out at an approved builders, where the personnel are properly trained and familiar with the type of work which they are to perform.

Strength

The modulus of the midship section and the stresses in the structural members should be acceptable to· the Board. Calculations for the reinforcements should be made from first principles.

146

Care should be taken to ensure that the reinforcements form continuous strength members and that discontinuities and local high stress areas are avoided.

Materials

The strength of the ferro-cement hull is obtained from the homogeneous qualities of the cement and the grid re-inforcements which bind together to form a solid structure. The requirements for the materials are as follows:

Connections

(a) Cement - The cement although contributing to the strength of the vessel·s hull has the primary function of giving rigidity to the re-inforcements. For the cement the Board stipulates the following requirements:

(i) it should be of the Portland or equivalent type, should be recommended by the manu­facturer for marine use and should be approved by the Board.

(ii) the water used for mixing should be clean fresh water and free of impurities and chemicals that may effect the concrete mix,

(iii) the aggregate of the mix should be of a suitable type and as recommended by the manufacturer and approved by the Board. The water/cement ratio should be controlled as low as poss i b 1 e to g.i ve a good qua 1 ity and workable material.

(b) Reinforcements - The reinforcing pipes, rods, bars and wire mesh used are to be of an approved grade of steel for which certificates should be available. The steel should be clean and free of scale, oil, grease or other similar contamination.

Welding, lacing and clipping of all main hull re­inforcements should be carried out with care and completed to the satisfaction of the Steamship Inspector.

Construction of Tanks

Tanks for oil or water may be constructed of steel or ferro-cement that has been treated with a suitable sealer.

way of all possible. reduce the

Adequate supporting structure should be provided in tanks and through bolting should be avoided wherever Longitudinal divisions shall be fitted in wide tanks to effect of free surface liquids.

Machinery Seatings

Due to induced stres~es from the vibrations and weight of the machinery special attention should be given to the design and construction of machinery seatings. Care should be taken that hard .notches and corners are eliminated and the continuity of strength maintained.

Insl ~ction Procedures

During the construction regular inspections will be car' 'ied out by a Steamship Inspector with particular attention being given to the following stages:

147

(a) when the steelwork re-inforcement is half complete, (b) when the steelwork re-inforcement is complete,

Testing Procedures

(c) during the application of the cement mixture, (d) at the removal of forms or moulds, (e) at completion of the hull prior to curing, (f) at completion of the hull after curing, and (g) on completion of the vessel and during the

running of the sea trials.

At the present· time the Board of Steamship Inspection is participating in a research program, instituted by the Industrial Dev­elopment Service of the federal Department of Fisheries and being undertaken by the British Columbia Research Council, to determine the qualities and suitability of ferro-cement as a shipbuilding material. ~/e hope that results will be forthcoming from this program in the near future that will provide clear guidelines into the construction, testing and inspection procedures which we should follow.

148

However, pending the completion of the above mentioned research program the Board has decided that the following testing procedures should be adopted:

(a) During the course of construction the Steamship Inspector will carry out standard slump tests on the concrete mix to ensure that the mixture is a good quality and workable material.

(b) There should be prepared, concurrent with the hull plastering, test specimens of the main hull structures, the preparation of which should be witnessed by the Steamship Inspector.

(c) Tests will t:~ required for tensile, compressive, flexural and impact strengths. These tests should be carried out at a recognized laboratory and witnessed by the Steamship Inspector. For vessels built in Canada to date these tests have been carried out at the Department of Public Works testing laboratories in Ottawa.

(d) The number of test specimens will be decided upon by the Board for individual vessels generally depending upon their size, type of construction and whether the vessel is of a prototype design.

Provisional Requirements for Periodical Inspections and Certification

Special attention will be given to a vessel of ferro­cement construction for the first four years of operation and provisional inspection and certification will be as follows:

(a) the vessel wi 11 be 1 imi ted to Home Trade Class III Voyages - i.e. not more than 20 miles' off shore and not more than 100 miles between ports of refuge,

(b) inspection will be made of the vessel afloat every six months, and

(c) underwater inspection will be carried out annually.

Following the first four-year period and provided the vessel is found in satisfactory condition, the normal inspections will be carried out in accordance with the Large or Small Fishing Vessel Inspection Regulations as applicable.

Appendix 3 GUIDELINES ~nR CONSTRUCTION OF FERRO-CEME~T VESSELS (AMERICAN BUREAU OF SHIPPING)

1. General Conditions

1.1 Classification

149

Vessels which have been wholly or primarily built of ferro-cement, and which have been built under the special supervision of the Surveyors to the Bureau, in accordance with these Guidelines, or their equivalent and other relevant sections of the Rules, will be consiaered for classification, and where approved by the Committee, distinguished in the Record by the symbols + Al "Annual Survey. II The type of construction "Ferro-Cement" will be noted in the Record.

1.2 Workmanship

The Surveyor is to satisfy himself that all operators employed in the construction of vessels to be considered for classification, are properly qualified in the type of work proposed, and that equipment and other facilities are such, that acceptable standards can be obtained for the construction of the hull, superstructures and appendages thereto, and for the installation of equipment, machinery, piping and the electrical system.

1.3 Construction Surveys

The builder is to maintain a schedule of systematic "inspections at regular intervals during the construction of the vessel, and records thereof, made by qualified personnel of the yard, are to be made available for inspection by the Surveyor. The Surveyor is to be present at the completion of all the major stages of construction. Additional visits will depend on the" size of the vessel, and requests of the owner or builder.

1.4 Surveys after Construction

The hull is to be subject to an Annual Survey on drydock, equivalent to a Special Survey. The hull is to be examined internally and externally, and all framing, appendages, deck houses, bulkheads etc. are to be examined. These Annual Surveys are to continue, until sufficient experience has been acquired to determine that surveys at longer intervals are reasonable and proper.

150

1.5 Submission of Plans

Plans showing the particulars 9 arrangements and details of the principal parts of the hull structure of each vessel to be built under Special Survey are to be submitted and approved before the work of construction is commenced. These plans are to indicate clearly the particu1ars 9 as well as the details and arrangements of the reinforcements of the hull. A construction schedule, giving details of materials, mixes, reinforcements, mortar application and curing procedures, is also to be submitted. Plans should generally be submitted in triplicate.

1.6 talcu1ations

The designer is to prepare strength calculations to justify the strength of the hull and its components. These calculations are to be based on the values obtained from the testing procedure, as prescribed in Section 4, and are to be submitted with the plans, as required by 1.5

2. Particulars and Construction

2.1 Definitions

The definition of a hull or structure built in Ferro-Cement is as follows:

2.2 Reinforcements

A thin, highly reinforced shell of concrete, in which the steel reinforcement is distributed widely throughout the concrete, so that the material, under stress, acts approximately as homogeneous material. The strength properties of the material are to be determined by testing a significant number of samples of representative panels, according to Section 4. If a similar approval is obtained from -a recognized authority, the Bureau may waive these requirements, upon review of the previous tests and such check tests as may be deemed necessary.

The steel content of the Ferro-Cement should be as high as practicable, and arranged in such a manner as to allow adequate

151

pen~tration of the mortar, and thereby result in a void-free material. The reinforcing rods, pipes and wire mesh are to be evenly distributed and shaped to form. Transverse frames or bulkheads are to be fitted to provide adequate transverse strength. The ·reinforcement network should be securely welded or otherwise fastened together, so that" it remains in its original position during the application of the mortar.

Structural steel sections may be inco~porated into the Ferro-Cement structures as longitudinal strength members, floors etc., but care must be taken to ensure penetration of the mortar, and a proper bonding between the framework and the mesh.

The reinforcements may be tapered towards the ends of the structure, where the hull form becomes "finerll, but care is to be taken to avoid discontinuities in the strength of the reinforcements, and ends of members are to be faired into the adjoining structure. The overlaps of the mesh layers at the keel, transom edges, etc. are to be staggered to allow even distribution of reinforcement in those areas, and to ensure satisfactory penetration of the mortar. Butts in reinforcement are to be suitably staggered, to avoid discontinuities.

2.3 Formwork

In methods of construction where internal or external forms are employed, satisfactory penetration of the mortar must be ensured, and the reinforcements are to be secured so that distortion is minimized on application of mortar. The formwork is to have a smo~th surface, and is to be thoroughly cleaned before applying the mortar.

2.4 Concrete

The methods employed for the mixing, handling, compacting and curing of the concrete are to be consistent and result in high quality material. The mortar should be applied as soon as possible after mixing, and constant agitation of the mix is to be provided during the waiting period. If any separation of water from the mix is observed durinq the waiting period, the mortar is to be remixed before application. Containers used to transport the mortar are to be clean. Care must be taken during the application of the mortar, so that no void spaces remain adjacent to the reinforcements or in corners. Vibrators, and/or hand rodding, are to be used to compact the mortar at thicker sections. A complete coverage of the reinforcement is to be ensured, although the thickness of coating should be kept at a minimum, and an excessive buildup of cement is to be avoided. Ferro-Cement structures

152

ere to be cured in a satisfactory manner. Various methods of curing are acceptable, depending on ambient conditions, but in general, the curing should be done by water spraying, by steam curing under a hood, or by membrane curing. Curing should normally not commence until about three to four hours after the mortar application, or when the mortar has taken its first set. This period may be longer in association with low atmospheric temperatures. The temperature during the curing period is to be kept approximately constant. Where a form is employed, it shall be kept in position for as long as practicable during curing.

3. Material s

3.1 Cement

The cement shall be ordinary Portfand Cement, in accordance with a suitable approved specification, such as ASTM C 535-67T. Other cements will also be considered providing they offer adequate water-tightness and uniform consistency. Cement should be stored under dry conditions, and if the application of the mortar is done in stages, a suitable turnover of. cement stock is to be arranged to ensure consistent freshness. Any presence of lumps in the cement renders it q~estionab1e for use, and it is to be sieved before mixing.

3.2 Aggregate

Aggregates are to have suitable strength and durability, and are to be free of foreign materials, including chemical salts. The aggregate is to normally include clean washed sand of a silicious nature. The aggregate is·to comply with a suitable specification, such as ASTM C 330-68T.

3.3 Water

Water is to be free from foreign materials that may im­pair the strength and resistance of the mortar. It is to be free of salts.

3.4 Mixing

Mixing is to be done in such proportions as to consistently give the required strength, as determined by Section 4. The proportions of the mix are to be by weight. The water-cement ratio is to be controlled as low as possible to give the material a consistent quality

153

and workability. Initially this is to be judged by a slump test and practicable workability under the existing conditions. Once this criterion is established, the mortar is to be held to a consistent slump test standard.

3.5 Reinforcements

Reinforcements (rods, pipes, expanded metal, wire mesh) are to have sufficient tensile and yield strength and ductility, and other properties essential for good construction. The reinforcements are to comply with a suitable specification, such as ASTM A 615-68, 185-64 and A 390-66. The reinforcements are to be free frommillscale, grease and any other contamination. Light corrosion is not objectionable, but should be brushed to remove free oxide. Black or galvanized reinforcements are acceptable.

4. Testing

4.1 Mechanical Properties Testing

The mechanical properties tests, as listed below, are to be performed on representative samples. Prior to commencement of construction, preliminary tests are to be carried out on standard test pieces, as described below, in order to determine that the proportions of the mortar mixes and properties and arrangements of the reinforcements will satisfy the deSign strength requirements of the vessel. The preliminary test pieces are to be in accordance with a suitable specification such as ASTM C 192-68, although curing may be done at an accelerated rate. Preliminary tests are to be carried out satisfactorily before construction is begun. During construction, test pieces, as described below, are to be made from the same mortar batches used in the actual hull construction, and the following tests are to be carried out.

For each 50 cubic feet or fraction thereof, a minimum of one each of the following tests: direct tensile, compressive, flexural and impact tests" are to be made. At least three of each of these tests are to be made for each.hull or structure. Hhere 1 arger unit hulls or structures are being built and large identical mixes of mortar are used, one set of tests per batch of 10 cubic yards (7.65 m3 ) or fraction thereof shall be carried out. A minimum of six sets of tests are to be made for each unit of construction. These

154

tests are to be carried out in a manner that will yield reliable values of the tensile and co~pressive strength at both cracking and failure, as well as the modulus of rupture and elasticity and impact strength of the reinforced samples. In the construction tests, the curing is to be in accordance with a suitable specification such as ASTM C 31-66.

a) Compressive Test

The compressive test is.to be carried out on un-reinforced samples, which are to measure 4 inches in diameter and 8 inches long. The compressive test is to conform to a suitable specification, such as ASn., C 39-66, and the test report is to conform thereto.

b) The tensile strength is to be determined by the "split cylinder" test, using similar testing apparatus as in the compressive test above. ASTM C 496-66 specification described the procedure for this test, and offers the formula to determine the "splitting tensile strength". The test pieces are to be unreinforced and of the same size as those in the compressive test. However, it should be noted that the true tensile strength of the specimen lies between 50 and 70% of the "sp1itting tensile strength".

c) Flexural Test

The flexural tests are to be carried out on slabs of concrete approximately 4 feet long and 12 inches wide and of the same thickness as the hull. The test pieces are to be reinforced and should have the same pattern of reinforcement as the actual hull. The flexural test is to conform to a suitable specification, such as ASTM C 293-68 and ASTM C 78-64, but care must be taken to ensure that the load application and support blocks to provide a uniform load across the test piece. Furthermore, readings are to be .taken at both cracking and failure.

d) Impact Test

An impact test is to be performed on representative reinforced panels. The thicknesses and reinforcement ·.of the test panels are to follow the same patterns as those of the actual hull. The panel is to be flat and should measure about 2 feet x 2 feet, and is to have two mutually perpendicular vee notches 1/25" (1 mm.) wide and 1/12" (2 mm.) deep across the centroid of test panel. The notches are to be at right angles to the edges. A drop weight type test is

155

to be employed. Failure occurs when the test panel develops a leak, and this is to be determined by a water-hose test er equivalent. The test report is to include, the following:

4~11 Identification Number.

All dimensions of the specimen. Applied load that causes failure. Curing history, and moisture condition of specimen at testing.

65) Qefects of specimen and age.

) Ambient conditions.

156

..,..tx: '4 libl10graphy Of ferracement Literature

AUTItOR. ORGANIZATION

Z Bezukladov. Y.F. et • 1

3 Canby. C.B.

4 AdaIllS. R. (T.Y. Lin and Associates)

8 Harper. R.

t Hartley. R.T.

10 Jackson. G.W. and W.M. Sutherland

11 fIowat. D.N.

12 Muhlert. H.F.

13 Samson. J. and G. Wellens

17 Anon.

37

40

41

42

43

Anon.

Anon. Cement 10 Concrete Association f Australia.

and

ibson. P.

agenbach. T.M.

Hurd. H.K.

Anon. Kaiser Cement Co •• Oakland. CA.

Kelly. A.M. and T.W. Mouat

Krfstinsson. G.E.

Lachance. L. and P. Fugere

TITLE CITATlOII

Ship Hulls Made of Refnforced Shipbufldfnq Publishing House. xxxxxx Concrete (ferrocement). Lenfn9rad. 1968. Navshfps Trans •

(1148) AD680042. pp 187

Ferro-cement - with Particullr,No. 014. The Department of Haval x x x Reference to Marine Applicat- IIArchitecture and Marine Engineering. toni. The University of Michigan. Ann

Arbor. Mfch. March 1969. pp 64.

IFerro Cement Panels. Yol 1. ,CR 69.008 Naval Civil Engineering x x x

l'Experimental evaluation and ,Laboratory. Port Hueneme. CA. protective potential. /AD850630.

IBoltbuilding fn Ferro-cement. ;Book. The authors. Vancouver. B.C •• x

lea 1.67. pp 36. mimeo.

x

x x

,x

X

x

x

Boatbuildfng with Hartley. ,Book. Hartley's Boat Plans Ltd.. x I'X x :x I IAuckllnd. N.Z. 1967. 33-50. ! 'Concrete Boatbuilding. ;Book. Allen and Unwin. London. 1969. x xlxlx x x x

iPP 106. ' ,

:Flexural Tes~ing of Ferro- iM.Se. Thesis. Dept. Civil Engineeringx xlxi ,x x x ;cement Planks. j'UniV. of Calgary. Calgary. Alta. " II"" I ,1'70. I

!AnalYSis of Ferro-cement ,in :No. 043. The Department of Naval ,x x:x ,x ~x I xi

IIBendtng• :Architecture and Marine Enqineering. : i I 'I! I

jThe Untversity of t';chigan. Ann ! iii" :Arbor. Hich. Jan. 1970. pp 86. ! I " ! I . ,

"'BHoaOWtt.o Build a Ferro-Cement 'Book. Samson. Marine Design IX x 'I ,x IX I::X ,'II I :Enterprises Ltd •• Vancouver. B.C. p.68. pp 136. I

struction of an 18m Ferro- 'Kung-ch'eng Chien-she (Engineering Ix x ~x I ix I" '

nt Hyperbolic Shell. 'Construction) Peiping. No.9. 15 I! ' I :May 1960. Trans, OTS U.S, Dept. II', I I,:, I jCommerce. Washington 25. D.C ••

'Ferro Cement boats. I

I tontrol of cracking in concrete.

~PRS:4167. 8 Nov. 1960. pp 7. I I : i i;;~f~~~ Monthly. Sept. 1967. r r r I

~f. C.39. Cement 10 Concrete 'x I saciatton of Australia. ca 1968. : ; I

PP •• I I ! ! I

,Battelle Technical Review 17. 'x jX I jSePt/Oct 19~8. 3-9 ,; !

erro-cement construction for :Fishing News International. April , 'x hhin, vessels. :1.68. 51-55. May 1968. 39-43. 'i!,', I "

~une 1968. 30-32.

hhboats in Ferro-Cement ~stem Fisheries. Jan. 1968. ,:!X'ix ~4.26.28.

erro-Cement Boats ~roc. Conf. on Fishing Vessel' x:,';XIX

Ferro-Cement Boats.

;Ferro-Cement Sea-going ,"httO<t"" "",,,to. Ferro-cement as a Fishing ivessel Construction lolaterialo

,The Growing Acceptance of Ferrocement as a First-class Boatbuilding Material.

Construction of a Ferro-shotcrete Motor-sailer Hull.

tonstruction Materials. Montreal. I Pet. 1-3. 1968. Canadian Fisheries l :, I

~port No. 12. June 1969. 365-371.

J. Amerfcan Concrete Institute. i!X I x' March 1968. ~02-204. I I !Speci.l Report T-l9. Concrete Trends.x : iKaiser Cement Co •• Oakland. CA. 'I

IPP 8. I ;Canadfan Fisheries Report No. 12. IX :June 1969. 135-162. I iSla Harvest 10 Ocean Sciences. !Dec. 1 969/Jan. 1970. 32-34.

L'1ngenfeur. March. 1970.

x x

X X x x x

43 Lachance, L

46 Morgan, R.G.

47 Morgan, R. G.

48 Nervi, P.L.

50 Nervi, P.L.

51 Nervi, P.L.

52 Nervi, P.L.

53 Oberti, G.

54 ,Oberti, G.

62 Collen, L.D.G. and R.W. Kirwan

63 Collen, L.D.G.

65 Anon. Portland Cement Association, Skokie, 111.

66 Samson, J.

67 Fraser, D.J.

68 Hedges, L. and E. Perry

69 Gardner, J.

71 Daranandana, H. et al

74 Collins, J.F. and J.S. Claman

n Benford, J.R. and H. Husen

78 Romualdi, J.P.

Ferro-shotcrete: a promising Ocean Industry, Nov. 1970. x IIIlteria 1. 60-62.

~derwater Concrete.

Concrete as a Shipbuilding Material.

Underwater Science and Technology ,x, x Journal. June 1970, 74-80. I International ~larine and Shipping :x Conference, London. June 1969, Sect-j ,

157

x x

x x

x x x

Ferro~cement: Its Charact­eristics and Potentialities.

ton II. Materials, 9-14. " L'Jngegnere. No.1. 1951 ANIAI. x x x x Italy. (English Transl.) pp 17. I'

Chap. 4, Ferro-cement.

!Precast Concrete Offers New Possibilities for Design of Shell Structures.

Thin Reinforced Concrete Members form Twin Exhibition Hulls.

The Penstock of Castelbell0

Some Conclusions about Deformability and Resistance

lin Tension of Ferro-cement.

Book. Structures. McGraw-Hill, x x 1956, 50-62. I J. American Concrete Institute, XI x Feb. 1953. Title No. 49-37, " 537-548.

,Civil Engineering, V.83, Jan. 1951, xl 2~~. I Energia Electrica. 8rochure No.5. x'x, Vol XXX, 1953, (English Transl.) I: ,' PP 18. I

, Source unknown. Milan, Dec. 1949. Ix x! i (English Transl.) pp 13. II Feb. 1959, 195-196.

x

x

, XI i

II x

ISome Notes on the Charact­leristics of Ferro-Cement.

Isome Experiments in Design and Construction with Ferro­Cement.

I Civil Engineering and Public Works 1'1: XI:' !;I x I x'I',. XIII Review, Vol. 54, No. 632.

The Institution of Civil Engineers !X!X;X IXtx! x

: ~:n~1~~3~'3~~~~~" Vol. 86. No.2, II,' I I i I'

;Ferro-cement 80ats. CR OlO.OlG, Portland Cement Assoc- !x,: xIx x tatton, Skokie, Ill. 1969, pp 13. i II I

Ferro-Cement 80at Construction Proc. Conf. on Fishing Vessel Con- IXI ix x ! struction Materials, Montreal. ' ,! I

I ! I 'I Oct. 1-3, 19f9, Canadian Fisheries I,' I' ,I Report No. 12, June 1964, 267-279.

Estimate Hull Work and ibid., 305-311. Material Content for 100 Combination Fishing Vessel in Different Materials.

IFerro-cement Fishing Vessels.

,Consultant Finds Ferro-Cement ;Has Limitation.

!Ferro-cement for Construction

I::·F:~""' """' ..... "

!Ferro-cement for Marine 'Applications - an Engineer­ing Evaluation.

Practical Ferro-cement 8oatbuilding.

ibid., 427-429

National Fisherman, Feb. 1970, 4-B, 5-B, 16-B.

Research Report No. 21/14. Dept. 'of Fisheries. rlinistry of Agricul t­ure, 8angkok, Thailand, 1969, PP 27.

Presented to·New England section. The Society of Naval Architects and Marine Engineers. Boston, Mass. March 1969, pp 68.

Book, International ~arine Pub­lishing Co., Camden, role., 1970, pp 176.

The Static Crackinq Stress and Proc. International Conference, The Fatigue Strength of Concrete Structure of Concrete, Sept. 1965, Reinforced with Short Pieces London, Cement and Concrete or Thin Steel Wire. AsSOCiation, 190-201.

x x x x x

x

IX ,x

x x x 'XiX x

x

i II L" ,11" : i " I ' ,

x x x x: x x

"" I,

158

79 Whitener, J.R.

80 Shah, S.P. and W.H. Key, Jr.

81 Naaman. A.E. and S.P. Shah

82 Walkus. R.

831 Walkus. R.

84 Jagtianie. M.K.

I 85 IKar, J.N. and I A.K. Pal.

86 ,Shah. S.P. and B.V. Rangan

87 Lessard. Y.

88 ITurner. D.R.

89 Anon. American Concrete Institute

90 Christensen. K.A. and R.B. Williamson

91 Tancreto, J.E. and H.H. Haynes

92 Bi99, G.W.

93 Sutherland. W.M.

Ferro-Cement Boat Construction.

Book. Cornell Maritime Press, Inc., x x xl lxlx x Cambridge, Maryland, 1971, pp 128. I'

I I Impact Resistance of Ferro­cement.

J. Structural Division, Proc. American SO,ciety of Civil Engineers. Jan. 1972. 111-123.

xxx'xxx x

,Tensile Tests of Ferrocement American Concrete Institute J., Title No. 68-58, Sept. \971, 693-698.

I x x xI x

I x

I I

State of Cracking and Bul. Inst. Polito Din lasi. x x Xi X x, x Elongation of Ferrocement I XIV(XVIII), 3-4. 1968, 653-664. \ I

,Under Axial Tensile Load (1) I I :State of Cracking and ibid. x x XI X X x

I~~~~~a~!~~l o~e~~~~~C~~~~\II) I XVI(XX). 3-4. 1970, 53-60. i I I iConcrete Boats, Barges, and ! Journal not identified, from :xix x: !X'X X x

I:ShiPS. I GaRlllon India Ltd .• Bombay 25, India" I 'i I!

1972. PP 19. I : I ,Strength of Hber-Reinforced I J. Structural Division, Proc. XIX x. !xl ,x ;Concrete. American SOCiety of Civil Engineers, ; I 'I i i May 1972. 1053-1067. Iii i I t I I t I I ~ Fiber Reinforced Concrete ! American Concrete Institute J., IX;X!Xi Ix: I 'x :Properties. 'Title No. 68-14, Feb. 1971, I' I . I II' I I 1126-135. I i I IProprietes et Applications du I M.S. Thesis. Facule des Sciences, IX'X x: X!X~ ix ~Ferro-shotcrete. I Universite Laval, Quebec, P.Q. II .. ; I I ; I I Hay 1971, pp 196. I I iii : ',An Investigation into the M.E. Thesis. Faculty of Engineering'ix;xix' 'x'xi ix Tensile Strength of Ferro Sir George Williams University, ; I , : I ! ; I Icement. Ioklntreal, Que., April 1971, pp 71. I '\ ! , ! i , 'State-of-the-Art Report. ACI Committee 544, American Concretelx:x x: jX ! !x t iber Reinforced c~ncrete. I Institute, Nov. 1971. pp 56. I iii I j ! ! 'Solving the Galvanlc Cell Report tlo. UC SE SM 71-14. ,X!X',x: x:x! Ix Problem in Ferro-cement. Structural Engineering Laboratory, !; i '! i

I, University of Cal ifornia, Berkeley, I: I I"!

CA •• July 1971, pp 59. I ii, I I ! I I I

:Flexural Strength of Ferro- Technical Report R772, Naval Civil ',XiX xl X!x\ IX ,cement Panels. Engineering Laboratory. Port I I I : I'

I Huenema. CA., Aug. 1972. pp 332. I I' I

An Introduction to Design for Project Report No. 52. Industrial :xlx Xllxix! x

IFerrocement Vessels. Development Bra;lch, Fisheries I, I . I I. I

Service, Canada Department of the I I

Environment, Jan. 1972. pp 224. II i I I ' I!

,Boats from Ferro-cement. Utilization of ShipbuildinQ and IX!x xl x xlxlx Repair Facilities. Series No. I, i" 'i I i I I' I United Nations Industrial Dev- I e10pment Organizations. Vienna. I i I United Nations, New York, 1972, iii

I \ 94 Anon. National Acad- 'Ferrocement: Applications

pp 123. , I ' in National Academy of Sciences. Ix x x 'x XIX

I Washington, D.C., Feb. 1973, pp 89.,; , : I' I emy of Sciences. Developing Countries.

Washington. D.C.

95 Anon. The Society of References on Ferro-cement Naval Architects and the Marine Environment. Marine Engineers.

in Technical and Research Report R-14, i I ,x Task Group H. S. -6-4 (Ferro-Cement) I . I

New York. N.Y.

96 Greeniu5, A.W. and J.D. Smith

'The Development of Ferro­'~ement for FishinQ Vessel Construction, llarch 31, 1970,

P 61 and Technical upplement. llay 31 1970,

pp 53.

The Society of Naval Architects and' Marine Engineers, New York, N.Y., Oct. 1972. pp 32.

Ferro-Cement for Canadian Fishing Vessels, edit. W.G. Scott, Proj. Report No. 42. Industrial Dev­elopment Branch. Fisheries Service, Department of the Environment. Ottawa. AU!1. 1971, pp 119.

,

I x x x XiX

! x

I

I

17 Greenius. A.W. and J.D. Smith

IS Greenius. A.W.

19 Greenius. A.W.

10"1' ..... "'. R.G.

101 Morgan. R.G.

102IGj-'rv.0.E.

,.,1 .... ,.". T.G.

104 Cornet.!.. R. B. W111iamson. S. Nogarajan, and K.A. I Chri s tensen

10S'Haynes, H.H.

106 Kudzfs. A.

107 Kowalskf. T.G. and B.R. Walkus '

108 Walkus. B.R. and T.G. Kowalski

109 Kowalskf. T.G.

110 Walkus. B.R. and A. Macldewicz

111 Walkus. B.R .• M. Kaminska and E. Szejko~lski

112 Dinsenbacher, A.L. and F. Eo Brauer

113 ibid.

114 Calrncross. C.

115 Eyres. D.J.

The Development of Ferro­cement for Fishing Vessel Construction-II, 'lay 31, 1971 pp 113.

Ferrocement for Fishing Vessel Construction-III, une 1972, pp 54.

Ferrocement for Fishing Vessel Construction-IV. une 1973. pp 57.

Concrete Floating and Sub­rged Structures.

Concrete Ships.

I

Durability of Concrete Structures in An Ocean Environment.

,Ferrocement Marine Mixes in a Iwarm and Humid Environment.

:Chromate Admixture to Improve Performance of Galvanized 'Steel in Concrete Sea Structures.

!ReSearCh and Development of IDeep-SUbmergence Structures.

I,pre-stressed Polymer-cement for Sea Structures.

.Concrete Technology in the ~uality Control of Ferro­Lement Vessels.

,Ferrocement: a survey.

Ferrocement in Hong Kong.

Ferro-cement for Canadian Fishfng Vessels, Vol. 2. Project Report No. 48. Industrial Development Branch. Fisheries Service. Dept. of the EnVironment., Ottawa. Jan. 1972. pp 113.

159

x x x

ibid., Vol. 3, Project Report No. 55 x x x, I'X x x Aug. 1972. pp 54.

ibid •• Vol. 4. Technical Report. X.X x: !x x .x No. 64. Industrial Development I i I

i I

'I Branch. Fisheries and r1arine Service I' ,',"! ,. Environment Canada. Ottawa, 1973. pp 57.

: The Concrete Society. Terminal x:,,' "x::! ':i·· x, xl x 'House. Grosvenor Gardens, London

SWIW OAJ. pp 56 and plates. I " I

Proc. FIP Symposium Concrete Sea Ix.xix Ixi ~x:x StrUctures, Tbilisi, Sept. 1972, Iii" i I Published by Federation Internat- 'i i I lonale de la Precontrainte, I ! i I, Terminal House. Grosvenor Gardens, london. April 1973, pp 114-119. 125. I

ibid •• pp 141-145.

ibid •• pp 150-158.

I ibid .• pp 159-163.

i

I ibid .• pp 180-185.

ibid •• pp 164-165.

ibid •• pp 246-251.

Concrete (London), Vol. 5. No.2. Feb. 1971. pp 48-52.

Far East Builder, July 1971. pp 29-35.

x , I' Ie X x ix

I x x x Ix

x x· x

x

x

x

i x I

I x' x x

x

IX

I !x I

x

x

x

x

I !

x I,x 1. x x ( ~Application of Ferrocement Symposium on Industrial Spatial and x XIX !x'x X:X :Shel1s in Marine Structures. Shell Structures, Kielce, Poland, !! I I ; , June 15-23. 1973. mimeo. pp 385-398. i,' i 'Mechanized r~ethod of Manu- fbfd., mimeo. pp 399-410. x x x· !x x !x ;facture of Prefabricated ; I I i (She 11 s . ! I I I I I! Material Development. Design, I Presented at Chesapeake Section x x x ~ :x X Ix ~x ,Construction, and Evaluation !Meeting, Society of Naval Architects I ':.'.! ,i

[

' a Ferrocement Planing Boat. and I"arine Enqineers, mimeo, Naval Shfp Research and Development I Center. Bethesda. Md •• U.S,A. pp 77. !! I

I i ibid. Harine Technolooy, Vol. II, No.3, x x xi XIX xix \ July 1974. pp 277-296. I Ferrocement Boat Constructfon Book, International Marine Pub1ish- x x x'x x

ing Company, Camden, Me., U.S.A., I Survey of Ferro-Cement Fish­ing Boats Built in New Zeal­and. mimeo, pp 30.

1972. pp 192. I Seminar on the Desfgn and Construc- JX X, x X X tion of Ferro-Cement Fishing Vessels ' I Wellington. New Zealand, Oct. 9-13. 1972, F.A.O. of United Nations.

160

116 Larsen. H.J .• Jr. Study and Evaluation of Ferro~ Prepared by J. Blume & Associates x x x x x x x cement for Use in Wind Tunnel for National Aeronautics and Space Construction. Administration, Ames Research

Center. Moffatt Field. Ca., NASA-CR-l14501. JABE-ARC-07. July 1972. pp 155.

117 Anon. The Concrete Ferroeement Vessel~ ~ A Naval Architect. No.4 (1973), Oct •• p 115 Socfety Prelfmfnary Report 'of The

Concrete Society Workfng Party.

118 Greenius. A.W.

119 Johnston, C.D. and D.N. Mowat

IFerrocement for Fishing IVessel Construction, V, 10ct. 1974,-pp--.5J1.

I iFerrocement - Material 'Behaviour in Flexure.

Not yet publish~d for distribution by Industrial 9velopment Branch, Fisheries and r rine Service, Envtronment Can da. Ottawa.

x

x x x

1

I i

I x

I IX xix x

t I

I

120' Roberts. W.H. I Guide to Ferrocement Sail &

tProc. American /Society of Civil Engineers, J. of the Structural Division. V.100 No. St 10, October 1974. 2053-2069.

Book, Baycrete Marine, Hamilton

1

xxi

I

j I ! X i IX x x

1211Smith. R.B.L.

I I l221Greenius, A.W.

123 Surya Kumar, G.V.

I 124! Raj ase ka ran. S.,

let &1

1,1251 Rajagopolan, K. and 'V.S. Parameswaran

Ipower Boats and Design.

I :A Rationale for the Use and ,Development of Ferrocement. I :Behaviour of Ferrocement !Under Repeated Stresses. i 'An Investigation into the Flexural Behaviour of :Ferrocement.

:Behaviour of Ferrocement ;specimens in Bending and

lont. (Rapid Blue Print Limited, :Hamilton, Ont.) 1970, pp llC .

' J. of Structural Engineering (Roorkee) Vol. 2, No.4, Jan. 1975,

1125-128. I

I ibid •• 129-136. i i ! ibid., 137-144.

i i i ! ibid., 145-154.

ICOmpression. , [ i ,Analysis of Ferrocement Beams. ; ibid., 155-164.

i i

,I I x i

i

, X X X X x:

I

x X x

II )xx

x x x x t

11261 Basavarajaiah, B.S., I H.V. Venkatakrishna, I and U.R. Raghotham

'Experimental Study of the 1 ibid., 193-197. x x x x x Applicability of Ferrocement i ;for Precast Folded Plate i IElements. I 'The Design and Construction ! ibid., 199-202. of Two Ferrocement Canoes. ;

1127 Troitsky. M.S. and D.R. Turner

x x

128ISo".'. P.G. The Impact Resistanc~ of !M.SC. Thesis, Naval Architecture x x x

I 129, Snyder. P.G. et al

Mo('lfied Ferrocement Panels. :and Marine Engineering, !Massachusetts Institute of Tech­jnology, Sept. 1973, pp 77. ,

The Impact Resistance of 'Report No. MITSG 74-18. Modified Ferro-cement Panels • . Massachusetts Institute of Tech-

Inology, Mar. 31, 1974, pp 74.

x x x

1301,,"", W.E., (,,", .. Dept. of Transport. Ottawa.?

Regulatory Aspects of Traditio~ Conf. on Fishing Vessel Constructio X :nal and New Construction ; Materials, Montreal, Canada, Oct, ' ~terials esp.Part 6. Require- ~ 1-3. 1968. Canadian Fisheries Report~ ~ts applicable to Vessels : No.12 June 1969. 73-90 ronstructed of Ferrocement. '

1131 Anon •• Lloyd's 'Tentative Requirements for the mimeo, 1971, Register of Shipping, Application of Ferrocement to . pp.13 London ~'the Construction of Yachts and!

Small Craft Hull Requirements ' j .

132 Anon •• American ; uidel ines for the Construction mimeo. 1969. Bureau of Shipping 'of Ferrocement Vessels. pp.12

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