116490 Ferrocement for Canadian Vessels

8/3/2019 116490 Ferrocement for Canadian Vessels

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This publication is number 86in the Technical Report Seriesof the Industrial Developrtlent Branch

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C!? -:3 / ~ - .

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

CANADIAN FISHING VESSELS

- A S u m m a r y a n d I n t e r p r e t a t i o nof Te s t R e s u l t s - 1 9 6 9 - 1 9 7 4

prepared byArnold W. Greenius

B.C. ResearchVancouver, Canada

forVessels and Engineering Division

Industrial Development BranchFisheries and Marine Service

Environment Canada

Project Officer

G.M. Sylvester

Division ChiefH.A. Shenker

March 1975

Opinions expressed and conclusions reachedby the author are not necessarily endorsed

by the sponsors of this project


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ABSTRACT

This report summarizes, integrates, and interprets thetest results obtained at B.C. Research on the properties of ferrocementfor fishing vessel construction during the five program years, 1969 to1974. 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 reinforcingmeshes on workability, strength, and durability. I t has also examinedpatching, bolting, painting and other factors affecting performance.

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


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TABLE OF CONTENTS

A. I NTRODUCTI ON

1. Objectives2. Historical Background3. Scope of the Test Work 1969-19744. Applicability of the Test Results

B. DIGEST OF TEST RESULTS AND C O N C L U S I O N ~

1. Mortars

2. Reinforcements3. The Reinforced Mortar Composite4. Bibliography

C. TEST PROCEDURES AND RESULTS

1. The Component Materials - Mortars

Page

1

1134

6

6

81115

16

and Steel Reinforcements 162. Evaluation of Various Mortars 213. Evaluation of Various Reinforcements 414. Evaluation of a Typical Ferrocement Construction 735. Bolting Tests 986. Design Considerations 1017. Patching Ferrocement 1018. Protective Coatings 1049. Quality Assurance 113

D. BIBLIOGRAPHY OF FERROCEMENT LITERATURE

E. ACKNOWLEDGEMENTS

F. REFERENCES

G. APPENDIX

1. Development of Mathematical Model -J . D.

Smith2. Regulations for Construction of Ferrocement Boats- Canada Transport Ministry

3. Guidelines for the Construction of Ferro-cementVessels - American Bureau of Shipping

4. Bibliography of Ferrocement Literature

114

115

116

122


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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 Fisheriesand Marine Services, E n v i r o n m e n ~Canada has funded a series of programsat B.C. Research, Vancouver, B.C., to evaluate some of the propertiesof ferrocement for fishing vessel construction. The objectives vf thisreport are to summarize and interpret the findings obtained and documentedin five major reports during the last five years. This report proidessome measure of the strengths and shortcomings of the test data obtainedfrom 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 mortarshell highly reinforced with fine w i d e l y - d i ~ t r i b u t e dreinforcement.This definition is general enough to include the most common compositesof steel mesh and rods in a matrix of Portland cement mortar, those whichcontain short steel fibres or no reinforcing rods, and those which havea matrix of polymer mortars. In i ts present state of practical development for fishing vessels, ferrocement is a Portland cement mortar

containing a widely-distributed reinforcement ofsteel

mesh of variouskinds generally with steel rods.

Various a d v a n ~ a g e shave been stated for ferrocement as amaterial of boat construction, e.g. good sound insulation, good thermalinsulation, fire-resistance, resistance to marine borers, ease of fabrication, ease of repair, low cost, good abrasion resistance, good impactstrength, good corrosion resistance, and others. Some of these areundoubtedly questionable.

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


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years of relative inactivity, a ferrocement renaissance in New Zealandand England in 1961 started a world-wide adoption of the ferrocementmethod of building boats. Although pleasure sailboats were of prime1rtterest in 1961, China, Cuba, and many developing countries are nowbuilding ferrocement fishing boats, work and harbour boats, and shelterboats in great numbers.

In 1968, the activities of amateur and professional boatbuilders, especially on Canada1s Pacific Coast, interested the FisheriesService, Canada Department of Fisheries. These builders were constructingboth pleasure and work boats. The Industrial Deve1pment Branch of theFisheries Service commissioned B.C. Research to undertake a study offerrocement as a construction material for fishing vessels. The statedaims of the f i rs t study were: l} to collect and collate the availabledata on ferrocement for boatbuilding, and 2} to undertake a limitedtest program to determine the properties of conventional ferrocement.

This work was reported in 1968 by Kelly and Englishl

to the FisheriesService and by Kelly and Mouat2 to the Conference on Fishing VesselConstruction Materials, Montreal, Canada, October 1-3, 1968.

As a result of this f i rs t program of collecting andcollating SOffie of the available data and of performing some tests, theIndustrial Development Branch embarked on the funding of the f i rs t offive annual programs at B.C. Research to evaluate ferrocement for fishingvessel construction.

Since ferrocement is a non-homogeneous composite materialof great variety, i t was realized that the available fundtng would allowonly a very general assessment of the properties and performance offerrocement. I t was hoped, however, that patently unsuitable materialsand procedures would be identified and that a set of guidelines to aidpersons wishing to make a f2rrocement boat and persons charged with theresponsibility for certifying ferrocement boats would be developed. Infact, the five reports 3 - 7 of the work submitted to the Industrial Development Branch over the past five years have recorded the results of testscovering a very broad range of properties. The engineering and performance data obtained are not the results of in-depth investigations of afew properties but are rather the preliminary results of tests on abroad front. The reports were reproduced verbatim by the Branch fo rgeneral distribution even though the complete documentation of thetest results diminished the usefulness of the results to a prospective

builder. Therefore, at the end of the fifth program, the Branchcontracted with B.C. Research to summarize and interpret all the testresults obtained so that prospective builders might more readily usethem.


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This summary has attempted to consolidate the findingson 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 ignoredsome results which now appear to be of l i t t le significance and has"gleaned" some useful information, not formerly appreciated, from someof the tests performed. And finally, i t should be stated that thisis not a "How-to-build-it" book, an aspect well covered in severalpractical guides. S- 14

3. Scope of the Test \ ~ o r k1969-1974

The programs undertaken in the five annual contracts1969-1970 to 1973-1974 are briefly summarized as follows:

1969-1970 - The mortar mix - various mixes of sands, cements, andwater/cement ratios were tested in standard compressiontests and tested as t i les reinforced with "standard llmesh reinforcements in bending, impact, and freezethaw and seawater exposure tests.

- The mesh reinforcement - various meshes were testedin t i les with "standard ll mortar mix in bending andimpact.

- Repair - the use of mortar and polymers fo r patchingwas examined.

1970-1971 - The mortar mix - the use of admixtures was examinedfor improvements to workability, strength, and durabilityof mortar.

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

- The effect of interrupted mortaring on strength wasobserved.

- The attachment of fittings by powder-activated toolswas examined.

- The preliminary development of a mathematical modelfo r the behaviour of ferrocement was considered.


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

- The bolting strength of ferrocement was tested.

- Ceatings fo r ferrocement were evaluated in laboratoryand marine exposure tests.

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

- Additional seawater exposure tests on painted f ~ r r o -cement specimens.

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

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

- Additional tests on interrupted or multi-stage mortaringwere undertaken.

The programs over the five-year period also involved theup-dating of a bibliographic listing and maintaining a f i le of ferrocementliterature at B.C. Research, advice to specific technical enquiries from

persons interested in ferrocement construction, and various miscellaneoustests 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 oranticipated a subsequent contract. Each year's work was planned to becomplete in i tself and to provide information over as broad a range ofvariables as possible within the imposed limits of time and funding.No exhaustive in-depth study of any property was intended or undertakenand no attempt has been made to obtain an "optimum ferrocement construction".

Materials which have seemed unsuitable in the tests reportedherein may prove acceptable when treated in a different manner. Forexample, expanded metal lath appeared unsuitable because of itsanisotropic properties. I t was also difficult to get good penetration


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of the mortar into several layers of the mesh by trowelling .. However,one manufacturer uses expanded metal lath successfully by embedding i tlayer by layer into successive layers of mortar sprayed into a female

mould. The potential innovative builder, therefore, will experimentwith and evaluate the available materials in terms of his proposedconstruction techniques.

Although the more common relatively homogeneous materialsare not always adequately characterized by the standard test specimensand procedures available, a reasonable correlation exists between thebehaviour of a component and the results obtained from a standard testspecimen of the material in the component. However, standard tests andprocedures are not available for ferrocement in i ts present state oftechnical development. Each investigator of ferrocement properties hasused such specimens fo r strength, flexure, and impact as suits his ferro-cement construction facilities and techniques and his testing equipment.I t is unwise to try to quantitatively correlate the results presentedherein with those of another investigator. The results are best used tocompare ferrocement constructions in which one variable is changed, egokind of mesh reinforcement. Satisfactory repl ication of tests has notbeen possible. The results presented apply only to the ferrocementconstructions used in the tests. Much more work needs to be undertakenbefore a mathematical model can be developed which will enable test resultsobtained 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 variouspreliminary tests, often insufficiently replicated, performed on severalconstructions of ferrocement. I t is believed that the test results providea good "feel" for many of the properties of ferrocement, typical of theconstructions which have been and will be used by the amateur and semi-professional builder of a ferrocement boat.


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B. DIGEST OF TEST RESULTS AND CONCLUSIONS

Some of the test results and the conclusions drawn arebriefly presented in this digest. The reader should refer to the pertinentsections 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 onthe results and conclusions obtained from a tes t program which has notalways allowed sufficient replication.

1. Mortars

Mortars of several sands, cements, and admixtures have beenexamined for the effect of the various components on workability (penetrationof 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 thetests:

- dry bagged concrete sand (some plus 8-mesh)- dry bagged mortar sand (no plus 8-mesh)- sharp Del r1onte 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 wereplaced with vibrating trowels into the horizontal form moulds containingthe mesh layers. The ease of placing the mortar and the penetration into

the mesh layers were evaluated qualitatively. All mortars tested gaveadequate penetration provided the cone slump value was greater than 3 in .The mortars containing sands with some plus 8-mesh material were moredifficult to trowel smoothly. The various cements and admixtures appearedto g i v ~no significant improvements.


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The 36-in. panels made in the upright open frame mouldswere somewhat more difficult

to mortar.The

vibrating trowel couldnot be used. Higher slumps (3 to 6 in.) were necessary for good penetration.

(b) Strength

Compressive strengths of the various mortars were obtainedfrom 7-day and 28-day 2-in. cube specimens. The flexure strengths wereobtained from unreinforced portions of the panels made. No importantdifferences in strength were observed in the mortars made with the severalsands, cements, and admixtures.

(c) Absorption

Specimens were soaked in water and subsequently driedto determine the voids. They absorbed about 7 percent water. The differencesin water absorption for mortars of various sands and cements were notsignificant. The water-reducing agent appeared to reduce the absorptionto about 4 percent.

(d) The Hydrogen Gas Problem

Gas bubbles in the form of blisters were encountered onpanels which contained both rods and galvanized mesh. A galvanic reactionbetween the two kinds of reinforcement in the presence of the cementmortar causes hydrogen to evolve. Chromium trioxide was added to themortar 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 noapparent effect on the freeze-thaw durability. No significant deteriorationwas observed after 350 cycles. Admixtures did not improve the durability.The upper unreinforced layer of coupons reinforced with wire mesh delaminatedor disintegrated badly in a test of 76 cycles of freezing and thawing. I t isconcluded that differential expansion between the reinforced and unreinforcedlayers of the test coupons aggravated the stresses from freezing and thawing.I t 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 ~ / e t - d r yseawater cycles. No changes invisual appearance and hardness of the mortar were observed. I t is concluded that all have good resistance to seawater.


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(f) Conclusions

The tests of mortars with various sands, cements, andadmixtures showed, in general, no real advantage for one type of sand orcement over another and no real improvement from the addition of admixtures.I t appeared best to avoid coarse sands, to use a cement with at least somesulphate resistance, and to avoid the use of admixtures. I t was thereforedecided 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 usedwith ungalvanized rod reinforcement.

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

Comrressive Strength:ASTMC109, 2-in. cubes7-day

28-day5670 psi7840 psi

ASTMC349,1.575-in. prisms28-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 testedalone and as components in a matrix of "standard" mortar, i .e. ina ferrocement composite.

The following tensile strengths of the six kinds of rodsused were obtained:


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hot-rolled black C1020galvanized C1020bright drawn C1010 nail wiredouble-drawn high-tensile A82double-drawn extra high-strength A82deformed double-drawn A8 2

70,000 psi50,000 psi73,000 psi79,000 psi

101,000 psi84,000 psi

9

I t was observed that a "cross weld" with minimum heat imputdid not seriously impair the strength of the double-drawn wire although i tis possible that "kinking" at the joint may occur in hull areas with greatercurvature.

The following breaking strengths of several of the meshesused were obtained:

1/2-in. 16-ga. galv. welded square mesh1/2-in. 19-9a. galv. hardware cloth3/8-in. 20-ga. black welded square mesh1/2-in. 22-ga. galv. hexagonal mesh

- longitudinal directiontransverse direction

2.5 1b expanded metal1/4-in. coil 20-ga. fire screening

400 lb/in. width140 1b/in. width154 lb/in. width

60 lb/in. width20 lb/in. width

not donenot done

Panels containing mesh only were tested in flexure. Theresults indicated tbat the flexure strength is essentially proportional tothe 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. hexagonalmesh and expanded metal tested in transverse direction.

(b) Bond Strength

The bond strength of rods was determined from "hair pin" rodspecimens encased in mortar. Black hot-rolled, pickled hot-rolled, andcleaned and lightly rusted double-drawn high-tensile rods gave similarbond strengths. Bright rods, especially with the drawing lubricant (or rustpreventing), and galvanized rods gave lower bond strengths even after 4 1/2 monthsThe deformed douole-drawn rod had high bond strength but spli t the mortarcoupons.

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


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I t is concluded that cracks >0.1 mm cannot be tolerated

and that a mortar cover of at least 2mm

should be used. I t seems advisableto 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 kindand spacing of rods to the flexure and impact strengths of panels of theferrocement composite. The presence of rods is very important, as is theirspacing. However, the kind of rods used, viz. hot-rolled, galvanized, ordouble-drawn high-tensi le rods appears to have only a small ef&ect on thestrength of the panels. Other considerations such as "kinkingll over stiffenernodes and attachment to stern and bow may be of some importance.

Tests \'Jere performed to compare the f1 exure and impactstrengths of ferrocement panels containing approximately equal thicknessesof the several kinds of mesh reinforcement. The flexure strength of thespecimens containing 1/2-in. 16-oa. welded square mesh was superior tothat of specimens containing t h e ~ l i g h t e rgauge welded square meshes (1/2-in.22-ga. and 3/8-in. 20-ga.) and markedly superior to that of specimens containingthe 1/2-in. 22-ga. hexagonal mesh. I t should be mentioned, however, that t h ~differences were almost eliminated when rods were also present.

The drop-impact performance of panels reinforced with1/2-1n. 22-ga. hexagonal mesh when rods were also present was st i l lsomewhat poorer than that of comparable panels of the welded square meshes.

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

I t was also observed that the flexure strengths of specimenswith the rods, mesh, or both oriented at 45 degrees to the specimen lengthwere 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 somewhatgreater detail. The "typical" ferrocements considered here had a mortar


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matrix of Type II cement and dry mortar sand reinforced with 0.225-in. double-drawnhigh-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. galvanizedhardware cloth.

A single tensile specimen prepared from each panel was testedbut each specimen held a load only equal to the sum of combined strength ofthe mesh wires and the rod/mortar bond strength. (Tensile tes t specimensfrom 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 modulusobtained were obtained: 207 20S

No. of layers of meshNo. of wires in sectionArea of section, sq.in.Load at f i rs t visible crack, lb.Max. load held, lb.Modulus of elasticity, psi x 106

4

162

13001420

1.1

6232

14501900

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 thetensile strain in the centre portion of the span between the third-pointloads. The beam deflections at the third-points and at mid-length 'weremeasured. The location of the mesh wires and the rods relative to thespecimen beam surface were obtained at the third-points and mid-lengthfo r future work.

The flexure strengths at load of f irst visible crack, P fvcat Pfvc f2, and at maximum load held (modulus of rupture) and the elastic mOdulusvalues from beam curvature and elastic formulas at the load of f irst visiblecrack, Pfvc' and at Pfvcf2 were calculated for si x specimens from each plate.

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

No. of layers of mesh 4 6Flexure strength, psi, at Pfvc 2600 2900at PpVCf2 l300 1450Modulus of rupture, psi at ma x 3700 4400Elastic modulus, psi x 106

E = ~ Mat Pfvc 1.5 1.6

at Pfvcf2 2.3 2.7


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~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 on4 x 12 x 1 in. specimens from several panels. The f i rs t tests used

13

an apparatus which loaded the specimens to constant deflection. Thelater tests used an apparatus which loaded the specimens in third-pointloading 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 at1320 psi fibre stress withstood 500,000 cycles without visible cracking.

The work needs greater replication and tests at lower fibrestress levels to obtain an endurance limit. A true endurance limit may notexist for f e ~ r o c e m e n t(as for many other materials) but the values obtainedgive a "feel ll for the probable behaviour of "typical ll ferrocement constructionunder repeated bending loads.

The fracture surfaces of mesh wires in the specimens brokenunder a simple single bending load and under the repeated loadings wereexamined by means of the scanning electron microscope. The photomicro-graph of the single load fracture shows the "dimpled" appearance typical of atensile failure \'/hereas that of the repeated load fracture shows the "striated llappearance typical of a bending fatigue failure.

(d) Bolted Strength

Preliminary tests were undertaken to determine the boltedstrength of ferrocement. Specimens 4 and 8 in . wide were cut from one-inchthick panels with 0.225-in. dia. rods spaced at 2 in . and 2 layers of1/2-in. 16-ga. welded square mesh, 5 layers of 1/2-in. 19-9a. hardwarecloth, or 10 layers of 1/2-in. 22-ga. hexagonal mesh. The 4-in. wide

specimenscarried

a co-planer load, transmitted by a single1/2-in. bolt,

of about 500 lb/in. width when the single bolt hole was 2 in . from thefree edge and the "equivalent bolt hole pitch" was 4 in. A reinforced edgeand a greater distance between bolt hole and free edge would allow the boltjoint to possibly fail in compressive bearing.


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(e) Design Considerations

The use of the mechanical properties developed in the programfor design has not been pursued. Readers are referred to the excellentreview - An Introduction to Design for Ferrocement Vessels by G.W. Biggfo r the Industrial Development Branch, Fisheries Service, Canada Departmentof the Environment in 1972.

The preliminary mathematical model prepared by J.D. Smithearly 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 flexurestrength with either cement/sand mortars or with filled epoxy-resin patchingcompounds. Ferrocement with some broken mesh regained 50 to 80 percentof i ts original strength. A m u 1 t i ~ n e e d 1 epneumatic chipping and scalingtool was effective in breaking up most of the loose mortar debris and inopening up cracks without seriously damaging the mesh. The behaviour ofthe patch under weathering and conditions of thermal expansion has not beenascertained.

(g) Protective Coatings

The question of coatings has received considerable attention.Twelve coating systems of various materials for primers and topcoats weresubjected to dry laboratory environment (control) , Weather-Ometer, laboratorywet-dry cycling in s ~ a w a t e r ,and marine tidal exposures.

The most satisfactory performance was obtained from thefollowing 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 ferrocementcomposite and of the composite i t se l f . The importance of the cement/sandand water/cement ratios, slump, compressive and flexure tests, strength ofthe reinforcement materials, reinforcements and layup, and mortar placementprocedures is stressed. Testing of ferrocement specimens must realisticallyrepresent the properties of the hull. Non-destructive testing of the hullis not well developed. Tentative guidelines for construction of ferrocementhulls have been issued by the certifying inspection bodies, viz. CanadaTransport Ministry, Lloyd's Register of Shipping, and American Bureau ofShipping.

4. Bibliography

The bibliographic l isting of articles pertinent to ferrocementvessel construction has been maintained and is presented in the Appendix.


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c. TEST PROCEDURES AND RESULTS

1.The Component ~ 1 a t e r i

a1s -~ 1 0 r t a r s

and SteelRei

nforcements(a) General

The two main components of the ferrocement composite arethe mortar and the steel reinforcement. The steel reinforcement,generally rods and wire mesh, provides the skeleton on which the mortaris applied. I t resists the tensile loadings. The function of themortar in a ferrocement vessel is to keep water out and to providecompressive strength to the mortar/mesh composite. In addition,mortar must resist chemical attack by seawater and disintegrationfrom 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 ormore admixtures added to give special properties. I t is generally agreedthat 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. curingconditions. The number of possible combinations is great. I t wasnecessary to limit the number of tests by maintaining some variablesconstant. For example. i t was assumed that many amateur and semiprofessional builders would not be able to adequately steam-cure a newlyplastered boat. Effective steam-curing requires that the surroundingatmosphere be raised to 130F fo r at least 48 hours. Most builders willcover their hull with polyethylene sheeting and hose i t down regularlyfor about a month. Our test panels were done in this manner. r10rtartest specimens were wetted, wrapped in paper towels. placed in a plasticbag 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, wasused throughout the programs. The water/cement ratio was held as closeto 0.4 as possible since a low water/cement ratio favours high strength.The water/cement ratio was adjusted to allow penetration of the mortarthrough the several layers of mesh reinforcement. The mortar variationsassessed were restricted to several types of sands and cements and to

a few admixtures. The mortars have been evaluated as an unreinforcedmaterial and as a reinforced mortar/steel composite.


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Tests were performed to determine significant differences

in the performance of ferrocement mortars made with the several cements.Admixtures fulf i l l 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 workabilityimprovers. The Division of Building Research, National Research Council,Canada has pointed out that any benefits are contingent on proper use anda knowledge of any possible harmful side-effects. The admixtures areoften proprietary and specific formulations may not be generally available across the country.

I t was decided ~ h a tunless admixtures showed a substantialimprovement in the mortar i t was best to avoid their use. A pozzolan,a water-reducing agent, an air-entraining agent, and a polyvinylacetateemulsion were evaluated in a limited tes t program.

Pozzolans are described as siliceous or siliceous andaluminous materials, possessing l i t t l e or no cementitious value,which, in finely divided form and in the presence of moisture,will react chemically with calcium hydroxide at ordinary temp-eratures to form compounds with cementitious properties inconcrete. No recommendations for the optimum proportions ofpozzolans in mortar have been found.

Water-reducing agents are considered to lower themix water requirement which results in an increased compressivestrength. I t should be possible to reduce the cement contentfo r a given strength. The basic ingredient of the commonwater-reducing admixtures is either salts of lignosulphonicacid or hydroxycarboxylic acids. The water-reducing agentused in this study is described as nan aqueous solution ofmetallic salts of lignin sulfonic acids which contains acatalyst to counteract the hydration-retarding actionn.

Air-entraining agents have a reputation fo r producingconcretes which can resist damage by frequent wetting and bycycles of freezing and thawing. ~ 4 a n yspecifications requireconcretes which contain about six percent entrained air. The

agents are generally formulated from wood resins, sulphonatedhydrocarbons, and synthetic detergents. The agent used inthis study is described as lIan aqueous solution of purifiedand modified triethylamine salts of a sulfonated hydrocarbonand which contains a catalyst to promote more rapid andcomplete hydration of the Portland cement ll


25/166


26/166

20

The following readily available kinds of reinforcing rodmaterial were obtained fo r testing purposes:

hot-rolled black (C1020) 1/4-in. roundsgalvanized (C1020) 1/4-in. roundsbr1ght drawn (C1010) 1/4-in. nail wiredouble-drawn, high-tensile ASTt1 A82 0.225-in. roddouble-drawn, high-tensile ASTI1 A82 0.225-in. rod,

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

defonned by passing through dimpling rolls.

The kinds of IIfinely divided steel reinforcement ll are~ l m o s tlimitless. The reinforcement may be steel rods of many kinds,

chopped wire or fibre, slit ted and expanded mesh, woven or welded mesh.The material may be of various mesh sizes and geometrics, e.g. hexagonalmesh, and link mesh. The wires may be hard drawn, oil-tempered, annealed,bright,black, galvanized, plated or coppered.

Many kinds of IImeshesll have been used by tne ferrocementboatbu11der'. Many, such as welded wire fabric and hardware cloth, hex-agonal mesh IIchicken ll wire, expanded metal lath, and woven screeningare 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, weldedsquare mesh, hardware cloth, or combinations of these. Expanded metallath has been successfully used, at least in part of the structure, byFibersteel Company and i ts licensees. High tensile woven mesh has beensuccessfully used by the U.S. Department of the Navy.IS

I t became evident in the early work of this program thatonly a few of the several varieties of mesh available locally could beexamined. Various tests were undertaken with a view to ruling outpatently unsuitable kinds. The following kinds, mainly 1/2-in. mesh,were chosen fo r examination:

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

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

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

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

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

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.


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21

A few other meshes, only slightly different from thoselisted, were also examined in a preliminary way but are not worthy ofrecord. I t was not possible to purchase loose-woven 1/2-in. mesh

screening locally at the time of the tests. Some high tensile drawnand oil-tempered woven screens were available but these seemed toos t i ff and too expensive to warrant testing at the time.

2. Evaluation of Various Mortars

(a) General Procedure

Tests were performed to evaluate the workability, compres-sive strength, flexure strength, impact strength, porosity (permeability),and durability (resistance to disintegration in freeze-thaw and seawaterenvironments) of mortars made with several kinds of sand, cement, andadmixtures. The mortar was tested alone and in combination with steelreinforcement as ferrocement test panels.

All batches of ferrocement mortars were prepared in ahorizontal-arm mixer which was able to mix 120 lb. of dry cement andsand 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 from3 to 5 in. Compressive strength test specimens, 2-in. cubes (ASTt1 C109),were made from each batch. In later work, compressive strengths ( A S T ~ 1C349) were also determined from broken flexure prism specimens, 1.575 x1.575 x 6.3 in., cast in steel moulds. Flexure strengths of the mortarswere determined from unreinforced portions of the test panels and, inlater 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 strengthsobtained from the broken flexure prisms were generally higher than thosefrom the 2-in cubes. This is considered to be partly due to bettergeometry of the moulds used.

The firs t test panels were made in a horizontal 30 x 3D-in.plywood mould lined with 5 mil plastic sheeting. Later panels were madein an open 36 x 36-in. frame mould in an upright position to m o' ~ e nearlysimulate conditions encountered in. mortaring a hull. The mould and mouldframe 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.


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22

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

m ::: c ~ t ~ ~e : 'l' ' ' I ~ ( ! ~ : 1~t I ! IF

i ~ ~ c ;;: :

~c:: 1.

' ' ' ': p . ~~

t' ":;,;;J, . : ; - I ~

f"I [ ~, -


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The following materials were used:

dry bagged concrete sand,dry bagged mortar sandsharp Del r10nte silica sand (8-, 20-, 3D-mesh)Type I 'Portland cementType II Portland cementType III Portland cementType V Portland cementaluminous cementwater-reducing agentair-entraining agentpozzolanpolyvinyl acetate emulsion

(b) Morkability

23

The workability of a mortar is commonly measured by thecone slump test ( A S T ~'1 C143) and the flow table test (ASTM C124).Although such tests do provide a measure of the workability, the testsmust be correlated to the application. Only the slump test was usedin 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 incheswas necessary for penetration into 12 layers of hexagonal mesh in a formmould. Mixes with cone slumps of only 3 inches were very st i ff . Thesemixes readily flowed into the horizontal 30 x 3D-in. moulds when avibrating trowel was used. However, i t was impossible to obtain completep e n ~ t r a t i o nof the 12 layers of 1/2-in. 22-ga. hexagonal mesh by handtrowelling.

In later work, in which panels were made in a 36 x 36-;n .upright open frame mould to more nearly duplicate conditions of hullmortaring, i t was not possible to use the vibrating trowel. The slumpof the mortar was much more cri t ical . Slump values of 3 to 6 incheswere required.


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24

In the f i rs t series of tests 26 30 x 3D-in. panels weremade using various meshes, types of cements, and types of sand. Twelveof these panels contained a "s.tandard" reinforcement of 12 layers of1/2-in. 22-ga. galvanized woven hexagonal mesh 27 x 30 in . (A 3-in.unreinforced portion was lef t on one side of the panel.) Various cements,viz. Types I, II , III , V, and aluminous, and three sands, viz. dry baggedconcrete sand, dry bagged mortar sand, and Del f10nte silica sand (8-,20-, 3D-mesh) were used. The water/cement ratios ranged mainly from0.4 to 0.5 and the slumps from 5 to 6 1/2. Compressive strength specimensof 2 ~ i n .cubes, were made for 7- and 28-day tests.

The mortar workability, as measured by the difficulty ofpenetrating the mesh, appears 'to be not significantly affected by thetype of cements or sands used ?lthough the coarser and poorly gradedsand gave some difficulty in finish trowelling. The comparisons areshown in Table 2.

The effect of admixtures on workability was assessed byten 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 contained1 part Type II cement, 2 parts dry bagged mortar sand, a water/cement ratioof 0.4 to 0.45.

One of the following admixtures was added to each pairof mortar batches: pozzolan, 1/4 of cement replaced; water-reducingagent, 6.5 f l. oz./bag cement; air-entraining agent, 3/4 f l . oz./bagcement; and polyvinyl acetate emulsion, 1/2 of water replaced. One paircontained 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 panelmesh 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 nothave been realized. Additional work is needed to affirm or refu te thebenefits of admixtures on workability.

The workability of mortar into the mesh has been discussedin terms of the sands, cements, and admixtures. The kind of mesh beingpenetrated also influences the apparent workability. Five panels ofvarious 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 of1/4-in. 20-ga. black fire-screening, were made. Although some low-slumpmortars used in some early tests did not penetrate well into one kindof mesh reinforcement, mortar penetrated all the meshes without greatdifficulty. Table 4 compares the workability of mortar into the variousmesh constr.uctions outlined above.


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u.s.StandardSieve

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 Sandof Reclam- Concrete Mortaration * 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 6115-20 11 20 . 5 28

3-7 4 7 - - 10Fineness Modulus 2.84 2.08 3.75 2.38 1.53

* Recommended for corrosion-resis tant 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 WaterCon;pressive Modulus of

Sand Cement Workability Absorption Strength. psi Rupture. psiNo. Type Ratio in: S (unreinforced)7-dav 28-dav

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

6 I I 0.40 SIt 6.0 1'42890

14 I I 0.40 5Is 7.0 6200 7500 890.72SO .

16 I I 0.40 6It 6.6 5830 9450 7609875 820

17 I 0.40 5 7.3 5040 5875 10SO6175 960

18 I I I 0.45 4'1 Some. 5400 8325 1320

difficulty 7750 1280

19 II I 0.47 5 Easy

-5 1 ~ 8450 590

penetration 7750 56022 II I 0.45 5 Some

. 8000 7000 -difficulty 7800 -

23 Y 0.41 5Ja Easy - 7575 10000 932penetration 10700 843

24 Aluminous 0.36 4'1 . - 91SO 7250 10286280 79225 I I Del 0.40 lit Tears. some - 5700 6390 635Monte difficulty 5780 78226 I Mortar 0.41 lit - 68SO 8110 85594SO 738


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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. psiRupture. psi

raUo in . S 7-dav 2 8 - d a ~(unreinforced)

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

32 0.40 2 difficult 4300 6450mo..

5100 6355 1025

Pozzolan replaced 33 0.42 21s Stiff mix. Penetra- 5.6 4550 7200 84025 pe"cent of tion difficult . 7850 680cement 34 0.45 lis More workable. 3575 6225

49754060 6562 760

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

I

6 0.37 3 More workable. 5825 5875

6775

5875

1055485Afr-entrainfng 37 0.40 3 Good workability 6.7 4900 6100 835agent, 3/4 fl.oz. and easier 5100 735per bag cement 38 0.40 3 penetration 5455 6050

72005175 6110 785

P 0 1 ~ ' n Y l a c e t a t e39 0.48* 3 Stiff mixes 3500 3650trill sion. Penetration 3775pva/water 1:1.44 40 0.49* lis difficult . 5.8 2250 3000 850

1!QQ. 7902875 3456 820

* includes pva

TABLE4. 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 Compress he Modulus ofNo. Reinforcement Cement in. Workability Absorption st rength . 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 905welded square mesh 705not valv. 7 layers

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

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

13 2.5 lb expanded 0.40 5" Easy Penetration 6.6 5950 7200 725llletal lath. ga1v 7500 7925 layers

14 1/2 i".-22 ga. 0.40 &Is Easy Penetration 7.0 6200 7600 890hexagona1 mesh. 7250 -galv. 12 layers

15 1/4 1n.-20 ga. 0.40 SIs Easy Penetration 7.0 5600 8150 830fire screening, 7675 9602 l.yers


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27

(c) Mortar strength

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

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

Flexure strengths were obtained fo r the early batches andpanels on specimens from the 3-in. wide unreinforced portion of the testpanels. 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 beamprisms (ASTM C348). The former s p e c ~ m e n swere loaded at the third-pointson a 10-in. span, the lat ter at mid-point on a 4.685-in. span. Inaddition, some flexure tests were performed on specimens reinforced with"standard I mesh reinforcement.

Drop-impact tests were also made, where applicable, onspecimens from reinforced panels. The drop-impact strength specimens,15 x 15-in., were cut from mesh-reinforced panels containing mortarswith various sands, cements, and admixtures. The drop-impact apparatus,shown in Figs. 4 to 6, was built to approximately simulate the velocityand shock of a collision between a hull and a IIdeadhead" log at about15 knots. The 50-1b drop tup was a round-bottom aluminum air tankloaded with steel balls. The drop height was 10 feet, giving an impactenergy of 500 ft.-lb. Details of the support and cushioning with a discof 1/4 in. plywood are shown in Fig. 4. Tests on 30-in. and 36-in. panelswere performed with the same drop apparatus except that the large panelsuere supported on 24 x 26-in. and 31 x 31-in. 2 x 4 'Nord frames. Thedrop-impact damage was assessed qualitatively and by measuring thedishing of the impacted panel specimen and the extent of cracking onthe bottom "convex" surface.

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


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28

D

BG

c

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

F

for test specimens.

A,B - drop-impact or diagonal testsC - flexure tests on unreinforced mortarO,E - flexure tests on reinforced panel,

longitudinal and transverseF,G - various test, durability, exposure,

paint, etc.

50 lb t u ~ , 10 ft. above specimen .

guide frame

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

foot of frame, 1/4 in. steel plateferrocement specimen, 15 in. squareplywood 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.


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29

Figs. 5 and 6. Drop-impact apparatus.


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30

The mean values are:

Compressive strengthASTM C109, 2-in. cubes7-day

28-day

ASTM C349, 1.575-in. prisms

5670 psi7840 psi

28-day 10,070 psi

Flexure StrengthASTM C348, 1.575-in. prisms

28-day 1360 psi

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

The flexural strength of the various mortars was also evaluatedfrom specimens cut from panels reinforced with IIstandard mesh reinforcement ll ,viz. 12 layers of 1/2-in. 22-ga galvanized hexagonal mesh. These flexurespecimens and specimens for impact tests were cut from the 30-in. panelsas shown in Fig. 3. The IImo du1us 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 ,istributionof stress across the section is linear. Since the formula is not rationa1 Mcfor beams loaded beyond the elastic limit, a IImodified fibre stress ll , s 1 = - 1is used for beams loaded to rupture. This value of IIfibre stress ll isc a l l ~ dthe modulus of rupture. Throughout this report, the term IImo du1usof rupture ll has been reserved for the IIfibre stress ll calculated for :themaximum load held by the beam. The value is calculated not at the onset off i rs t visible bri t t le cracking of the mortar (unless otherwise stated) butat the maximum load when mesh wires broke, rods slipped, or both.

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

containing either the dry bagged mortar sand or the Del Monte silica sandwere compared. The average 7-day and 28-day compressive strengths for themortar sand are 6015 and 8544 ps i , respecti ve1y, and for the Del r10nte sand

5700 and 6100 psi, respectively. Although the Del Monte sand appears to givesomewhat lower compressive strengths the values are certainly within twostandard deviations, 20, calculated for all IIstandard mortar ll batches asshown in Table 5.

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


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31

strength, 869 psi, obtained on 14 mortar sand mortars. Single flexuretests on simi 1ar1y reinforced mortars. show a1most no di ffert;!nce between thetwo mortars. The specimens were obtained from panels reinforced with 12layers of 1/2-in. 22-ga. galvanized hexagonal mesh. The beam specimensapproximately 3 x 12 in . were tested in third pOint loading on a 10-in.span. The load at f i rs t visible crack in the mortar and the maximum loadheld by the beam specimens, oriented in both longitudinal and transversemesh directions, were recorded. The modulus of rupture, . S ~ ~ ,at maximumload was calculated.

The compressive and flexure strengths for mortars andpanels containing the dry bagged mortar sand and Del Monte silica sandare presented in Tables 6 and 7 for comparison. The test results, withinthe limitations of replication p o ~ s i b 1 e ,show no consistent or practicaldifferences between the two sands used. I t is concluded on the basis of

these preliminary tests thati t

was probable that a "special" sand wouldnot be significantly better. Therefore, i t was decided to make all futurepanels with the dry bagged mortar sand readily available from a localsource.

i i . Effect of Various Cements

A series of panels, Nos. 1 6 ,1 7 ,1 8 ,1 9 ,2 2 ,2 3 , and 24were 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 12layers of 1/2-in. 22-ga. galvanized hexagonal mesh.

The compressive strengths of the mortar from 2-in. cubesat 7 and 28 days, the modulus of rupture values from flexure tests onunreinforced portions of the panels and on longitudinal and transversereinforced specimens, and impact tests on 15-in. t i les were obtained.The results, presented in Table 8, showed no consistent superiority ofmortar made with one kind of cement over that made with another kind.

-Within the replication possible, i t was concluded thatthe type of cement used was not an important factor in the strengths offerrocement mortars. The type may be a factor in durability, however.

i i i . Effect of Admixtures

The average compressive and flexure strengths of a seriesof ten panels which contained no admixture, pozzo1an (replacing 25 percentof the cement), a water-reducing agent (6.5 f l . oz. per bag of cement), anair-entraining agent (3/4 f l . oz. per bag of cement), and a po1yviny1-acetate emulsion (pva/water 1:1.44) are presented in Table 9. I t was


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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. MeanTilt Proper\), Period. of Value. DeY.a :t3CJdays Batches psi. psi. psi.

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

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

6.5 in. prisms

Flexure StrengthASTM 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 ofOf 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 7874IIIOrtar sand

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

11169-73 Dry bagged 4300 to 6400 to 7500 to 1120 to 705 to

IIIOrtar sand 7275 9950 12.400 1730 1230


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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.)

'anelCompressive Modulus of Panel Strength

Sand Strength, psi Rupture, psiNo. (unreinforced) Flexure l psi Impact27-day 28-dav dishing, 1/16 in .

5 Dry blgged - - 1125IIOrtar sand 11006 - - 742890

14 6200 7600 890 longit. 2421 19. exposed7250 - transY. 1610 mesh. broken wires16 5830 9450 7609875 820- - - - - -

6015 8544 904

25 Del Monte 5700 6390

I

635 10ngit. 24901:2:1 5780 782 trln 1660

1 Simple beam, approx. 3 x 12 in . , span 10 in . , third-point loading2 SO-lb tup with round base (9-in. radius), dropped 10 f t . 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 StrengthPinel Type of Strenqth psi Rupture, psiHo. Cement (unreinforced) Flexure l .- . pst

I m p a c t ~

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

17 Type I 5040 5875 1050 l o n g ~ t .2910 16, exposed6175 960 Transv. 1665 mesh. broken wires

- - - - - -5040 6025 1005

14 Type II 6200 7600 890 10ngit: 2420 19. exposed7250 - trlnsv. 1610 mesh. broken wires16 5830 9450 760 -875 820 -rn- ~ m

18 Type II I 6400 8325 1320 -- 1280 -19 5150 8450 590 10ngit. 2430 22. exposed7750 560 trlnsv. 1585 mesh. broken wires

22 8000 7000 - -7800 - -m ; 1865 m

23 Type V 7575 10000 932 10ngf.t. 2960 11. exposed10700 843 trlnsv. 1735 mesh. broken wires- - -- -7575 10350 888

24 Aluminous 9150 7250 1028 longit. 3500 18. exposed- -

6280 .m. trlnsv. 1810 mesh. broken wires9150 6765 910

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


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observed that, except fo r the polyvinyl acetate emulsion which had lowvalues of 7-day and 28-day compressive strengths, the several admixtureshad l i t t le effect on the strength of the mortars. The average 7-day and28-day compressive strengths for the admixtures (excluding the polyvinylacetate emulsion) were between 3 standard deviations of the mean forall "standard mix" mortars 1969-1974 shown in Table 5.

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

(d) Water Absorption and Transmission

A few of the m o r t a ~ swere tested for differences inwaterabsorption and transmission properties. Specimens from unreinforced panelsmade 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 containingthe 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.

I t is worth mentioning that test coupons subjected to manywet/dry exposure cycles lost only about two percent of their weight afterbeing oven-dried overnight. This suggests that the voids may become filledwith a gel or become otherwise clogged by immersion in water for a long time.

Other minor tests were also performed fo r manifestationof the water permeability of ferrocement. A 2-ft. column of water was main

tained for one year on a mortar test coupon '3/4-in. thick. A small greyspot 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/waterinterface sealed off the mortar surface. Another similar test coupon wasplaced on a thin polyethylene sheet . Capillary forces failed to drawmoisture through the coupon at the grey spot.

I t was concluded that a well-made mortar will provide awater-tight hull.

(e) Durability

The durability of concretes (and mortars) has been defined

as "resistance to deteriorating influences of internal 'and external factorsto which i t is exposed within the duration of l i fe expected from thestructure". I t follows that the requirements for a durable concrete willdepend on the type of structure, the type of exposure or s e r v i c ~condition,and on the required service l i fe. The service exposure inc1u/ weathering,chemical action, and wear.


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Although other characteristics may be important in tropical

climates, the characteristics of greatest importance to the performanceof mortars in ferrocement hulls of Canadian fishing vess"els operating inCanadian waters are weather resistance and seawater resistance.

The disintegration of concretes (mortars) by weatheringis caused mainly by the disruptive action of freezing and thawing and ofexpansion and contraction from variations in temperature and alternatewetting and drying. Although laboratory tests for durability are difficultto correlate with service performance, tests conducted over many years haveshown 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. I tis generally recommended that concrete for use in seawater be made withPortland cements which contain not more than 8 percent tricalcium aluminate.Types II , IIA, IV, and V meet this requirement. A low water/cement ratioand entrained air are claimed to increase the resistance to attack byseawater.

Although much research and exposure testing has been undertaken over many years on structural concrete, relatively l i t t le researchhas been reported on the durability of ferrocement. A series of tests todetermine the resistance of various ferrocement mortars to freeze-thaw andseawater exposures was therefore undertaken. The tests described hereinare not comprehensive but are intended to show any drastic sho"tcomings inthe 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 fortesting concrete and fo r brick and structural clay t i le , i .e . ASTM C666-73and A S T t ~C67-73. C666 requires the specimens be subjected to 300 cycles(40F to OF) of freezing and thawing (or until i ts relative dynamic modulusof elasticity reaches 60 percent of i ts initial modulus) and C67 requiresthe 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 shallowwater-filled trays in an environmental chamber*. The chamber was programmed

*

Environmental Chamber Model ELHH-27-MRLC-l, Associated TestingLaboratories, Inc.


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to give si x freeze-thaw cycles per 24-hour day. The water temperature (andcoupon temperature) cycled from 10C to -4C and the air temperature from25C to -12C. The cycling prpgram was continued for 350 cycles. The couponswere observed regularly. At the end of the program the coupons were driedat 200F and weighed.

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

I t has been shown that the presence of mesh affects the freeze

thaw resistance of ferrocement. Eleven test coupons, 3 x 4 x 3/4-in., containing12 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 toplayer without reinforcement. The sawn edges of these reinforced specimenswere coated to prevent ingress of water at the sawn edges.

The specimens were examined after 36 and 76 cycles. The testresults are presented in Table 11. In general, the unreinforced portions ofthe test coupons were disintegrated, often by delamination at the reinforced/unreinforced interface, after 76 cycles of freezing and thawing; the reinforcedportions 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 andthe kinds of cements, sands, and admixtures used appear to have l i t t le effecton the freeze-thaw durability of ferrocement mortars.

i i . Seawater Exposure Tests

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

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


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PanelNo.

31. 32

33. 34

35. 36

37. 38

39. 40

PinelNo.

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 I I cement. dry bagged mortar sand. cement/sand ratto 1:2)(Panels refnforced with 12 layers 1/2-in. 22-ga. galv. hexagonal mesh)

Average.CompressiveModulus

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 lossof of Test Coupons Dry Bisis.

Cement Admixture Sand Cycles S

11 None Dry Mortar

Sind

350 No significant change 0I None 350 0I I I None 350 0.8V None 350 0

Aluminous None 350 011 None Del Monte

sf1icl sand350 Slight powdering 0.7

I None Dry mortar 350 No Significant chlnge 1.1Sind

I I None 350 1.2I I POllohn SO-loo Some corner crumbling

350 Crlmlbled badly. 26.2I I Water-reducing 350 No signiftcant change 1.1

agentI I Air-entraining 350 2.2

Igent I Polyvinyl- 100-125 Sltght surface flakingacet l te 125-150 Slight surface spalling

350 Slight surface spilltng 4. 9


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The description of the test coupons exposed, their visualappearance, and the penetration hardness (a Rockwell Hardness tester usinga 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 rangedfrom 0.7 to 2.0 percent, much lower than the normal water absorption percentages obtained on mortars not subjected to the cyclic exposure program.I t is believed that the precipitation of salts and formation of cement gelsmay clog the pores and voids after prolonged exposure.

I t is tentatively concluded that all of the mortars testedresist

attack from seawater under the ambient laboratory conditions used.The effect of various reinforcements, galvanized or baret and of seawaterattack at damaged areas is considered later.

(f) Interrupted Mortaring

A large hull may tax the ability of the plastering crew tofinish in one day. Interrupted mortaring or multi-stage cold-joint plasteringhas been used to avoid the deteriorating quality of work by an overtired crew.Several tests were performed to determine any loss of strength which mayresult from interrupted mortaring. Mortar was applied to one side of apanel with layers of 1/2-in. 19-9a. hardware cloth on 0.225-in. rods. Theother 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. I t was c o n c 1 ~ d e dthat, providedthe mortar consistency was proper and the mesh penetrability was good, asatisfactory bond between the two mortar layers may be obtained.

Another panel was completely plastered from both sides exceptfor a 12-in. wide strip at one side. The rewetted panel was finished 24hours later. A flexure test specimen with the joint at mid-span cracked atthe joint but i ts modulus of rupture was only slightly lower than that ofspecimens 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 pastebefore remortaring 24 hours later. Flexure tests produced cracks at the jointbut the flexure strengths at f irst visible crack were similar to those withno joints. The modulus of rupture values (a t maximum load) of joint specimensare 60 to 80 percent of the modulus of the specimens with no joint.


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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 II I 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 IIType 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 agentAir- II 36 entraining 76 agent

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

Description of Mortar No. Visual Appearance Penetration Hardness Valueof of Coupons After Unex osed EXDosedCement Sand Admixture Coupons 350 cycles of Exposure Top Bottom Top Bottom

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

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

s11icaI I Dry IOOrtar 1 90 - 9S 9SI I pOllolan 1 89 - 99 99I I water 1 103 - 105 106

reducingagentI I ai r en- 1 85 76 111 117

trainingagent

I I polyvinyl 1 54 sa 65 62acetate


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I t is concluded that the flexure strength of ferrocement made

with interrupted mortaring will be somewhat lower than that of ferrocementwith no joints. However, the difference in strength at the f i rs t visiblecrack does not appear to be great . Possible leakage problems at the jointhave not been examined. However, i t is believed that a jOint, properly bondedwith cement of the proper consistency or with an epoxy interface, shouldnot leak.

3. Evaluation of Various Reinforcements

(a) General Procedure

Tests were performed to determine the strength of the variousrod and mesh reinforcements alone and as components of a steel/mortar compositematerial. The composites were tested mainly in flexure and impact. The mortarwas generally a "standard" mix of Type II cement (1 part), dry bagged mortarsand (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 in8 in.) , and the reduction in area were obtained for the above rod reinforcementmaterials. In addition, since i t is common practice for ferrocement boatbuilders to arc-weld some or all of the cross-over junctions of the longitudinaland transverse rods, tensile tests were also performed on specimens . of doubledrawn high-tensile rods with a "typical" cross-weld. Double-drawn high-tensileA82 rods obtain their enhanced strength from cold working. Heating, as bywelding, should diminish this strength.

The ultimate tensile strengths of the several rods tested wereas follows:

hot-rolled black (C1020) roundsgalvanized (C1020) roundsbright drawn (C1010) nail wiredouble-drawn high-tensile A82double-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 psi50,000 psi73,000 psi79,000 psi80,000 psi

101,000 psi89,000 psi

84,000 psi

The strengths, elongations, and the reductions in area arepresented in Table 13. The double-drawn A82 rod material is strongest. Itsstrength was not seriously diminished by a small arc weld. Excessive heatinput should be avoided, . however.


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11. Bond Strengths

Manypapers have appeared in the literature showing themerits of black vs galvanized steel reinforcement for concrete construction.

Building Research Digest 10916 has summarized five separate investigations intothe bond strengths of steel reinforcing rods with galvanized, smooth, millscale, or rusted surfaces. I t concludes that the bond performance of galvanized bars is as good or better, on the average, than that of the smooth, millscale, or rusted bars. I t further points out that the protection againstcorrosion provided by the galvanized rods gives improved long-term bondperformance over the others in a corrosive environment. Rust scaling andsubsequent spa11ing of the concrete cover are avoided.

The effect of scale, ~ i c k 1 i n g ,drawing lubricant, rust, zinccoating, 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-shapedrods of the several kinds to form duplicate specimens like those shown inFig. 9. The embedded length of the arms was 6 in. The specimens were cured28 days.

The duplicate rod/mortar specimens were tested in tensileloading. The maximum load was reached when one arm of the hairpin started toslip. Both arms of the galvanized rod appeared to slip simultaneously. Thedeformed double-drawn rod "hairpins" spli t the mortar blocks, presumably dueto the wedging action of the dimpled surface. Two tested mortar blocks areshown in Fig. 10. The unit bond strengths were obtained by dividing themaximum load held by the embedded area of both arms of the hairpin. The bondstrength of the single arm of each specimen which held was obtained after anadditional period of 3 1/2 months. The results obtained in the tests after1 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 leastunder non-corrosive conditions).

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

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

- Light rusting on double-drawn rods further improves i tsrod/mortar bond strength.

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

- The galvanized rods had very poor bond strengths.


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Fig. 9. Rod/mortar bond specimens.

Fig. 10. Rod/mortar bond specimens showingsplitting of mortar block by deformeddouble-drawn rod.

43


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TABLE 13. Tenstle Properties of Various Reinforcing Rod Materillsused 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 73.40072,700

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

Double-drawn hfgh-tensfle A82 rods - arc weld - 80,000cross-over jointDouble-drawn high-tensile A82 rods - extra 0.225 100,000

high strength 99,000102,000

Double-drawn high-tensile A82 rods extra - 89,000high 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. 1nS fn 8 fn. Area.

S

23.5 67.324.0 66.8

24.4 71.325.1 69.0

(1) 63.98.5 64.8

10.0 63.5

7.5(2 ) 62.5

~ 1 ) 49.51) (1 ) 58.53.0 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(I S 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 slfppedDeformed double-drawn A82 451 660 Mortar blocks split

(clean), by wedge actionGalvanfzed (Cl020) rod 33 57 Both arms slipped

(cleln) simultaneouslyOld rod (reclaimed from outside panels 480 700 Rods broke, heavy

submitted) corrosion and pit-ting as fnstalled


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I t seems likely that the splitting action of the deformed(dimpled) double-drawn rod could result in delamination of ferrocement. Untili t has been proven otherwise, i t is recommended that this material not beused. The markedly inferior bond strengths obtained by the galvanized rodwas unexpected. Building Research Digest 109 claims that the reaction betweenzinc and the alkaline liquid in the pores of freshly placed concrete can formbubbles of hydrogen gas which would have an unfavourable effect on the bondstrength in normal reinforced concrete. Frazier 17 of the American Hot DipGalvanizers Association cites tests which dispute the postulation of an earlierinvestigator that a reduced bond value may have resulted from hydrogen bubblesforming on the galvanizing which caused the adjacent concrete to become spongy.He seems to support the finding that concrete may cure more slowly in thepresence of zinc and that the long-term bond strength of galvanized reinforcement rods will be superior. I t is generally agreed that chromate-treatmentof

galvanized rods or the addition ofchromium

trioxide to the concrete (ormortar) will cure the hydrogen problem and enhance the bond strength.I t has been suggested that some specifications bodies are already consideringthe incorporation of a requirement to chromate-treat all galvanized reinforcement bar. (The addition of chromium trioxide to the mortar is discussed inSection C-3-d-iv, The Hydrogen Gas Problem.)

In conclusion, i t is fe l t that the use of galvanized rods, i fproperly treated, should be acceptable even in the short-term. Galvanizedrods may be superior in the long term to bare steel which may be attacked bythe seawater or which may be sacrificially protected by the zinc coating onthe mesh. If the zinc on the mesh is consumed sacrificially to protect baresteel rods, i t seems likely that the l ife of the mesh will be diminished. No

tests or post-mortem examinations of old hulls have been made to validate thispostulation.

i i i . Costs

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

0.225-in. dia. double-drawn A821/4-in. hot-rolled C10201/4-in. galvanized C10201/4-1n. C1015 bright nail wire

c/1b40506353

$/100 f t .5.308.25

10.398.74

I t will be observed that the cost of the rod material on a per1b basis will not be a very important factor in the kind of rod chosen. Thedifferences can be calculated for a specific hull design on the basis ofthe cost/100 f t. making due allowance for the difference in rod diameters.


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(c) Mesh Reinforcement

1. Kinds and Strengths

The breaking strengths of some of the meshes were determinedat various times throughout the five year program. The strengths of the different batches purchased from various sources over the several years variedsomewhat. 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 mesh1/2-in. 19-9a. galvanized hardware cloth3/8-in. 20-ga. black welde; square mesh1/2-in. 22-ga. galvanized hexagonal mesh

- longitudinal directiontransverse direction

400 1b/in. width140 1b/in. width154 1b/in. width

60 lb/in. width20 1b/in. 'width

The strengths/wire obtained by the various techniques variedbecause of the mesh geometry as well as from difference in the strength ofthe steel i tself . Table 15 summarizes the breaking strengths and unit tensilestrengths found.

On the basis of the simple tensile strength obtained on thevarious meshes i t is apparent that similar tensile strengths in the panels willbe obtained by 2 layers of 1/2-in4 l6-ga. galvanized welded square mesh, about6 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. galvanizedhexagonal mesh (in its stronger longitudinal direction).

i i . Bond StrengthsNo rigorous tests to determine the mesh/mortar bond strengths

of the various meshes have been performed. Bond strength will vary with thegeometry of the mesh (twisted wires, cross-welded wires), the kind of surfacee.g. galvanized, unga1vanized, phosphated, chromated, rusted, scaled. One adhoc test on 1/2-in. 16-ga. mesh with galvanized coating intact and strippedshowed no significant difference in panel modulus of rupture. Each mesh wasseparated from the, mortar in the spec.i.mens wi th equal diffi cu1 ty. The groovesle f t by the separated wires show a textural difference. Those of the galvanizedwire showed a spongy appearance whereas those of the stripped wire showinga smooth appearance. The spongy appearance may be due tQ a zinc-water-cementreaction.

The surface bond area per square foot of panel and the specificbond area, the ratio of the surface area of the mesh to i ts volume (only thoseportions of the wire oriented in the load stress direction) have been calcul

116490 Ferrocement for Canadian Vessels

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