CHAPTER 6CONSTtiUCTlON - FABRICATION

OF FERROCEMENT

Summary: The four most commonly encountered methods of ferrocement construction aredescribed and their advantages and disadvantages are discussed. Some specialmanufacturing techniques are also presented. Noteworthy suggestions about goodconstruction practice are provided. A brief section addresses the composition, quality, andworkability of the mortar matrix followed by a description of protective surface treatments afterhardening. Currently known daring ferrocement structures using forward ideas and extendingthe concept of ferrocement are briefly reviewed.

6.1 INTRODUCTION

The materials used in ferrocement production and their selection have alreadybeen discussed in Chapters 1 and 2. This chapter discusses construction detailsthat directly affect planning, mixing, placing, handling, and the quality of thefinished ferrocement product. Much of the information found in Section 6.3 of thischapter is taken from the ACI Guide for the Design, Construction, and Repair ofFerrocement, which was developed by ACI Committee 549 while the author wasChair of the committee.

The ranges of mix proportions recommended for common ferrocementapplications are (Table 1.1): sand-cement ratio by weight 1.5 to 2.5, water-cementratio by weight 0.35 to 0.6. Typical mix proportions and corresponding compressivestrengths are given in Table 1.2. The higher the sand content, the higher therequired water content to maintain equal workability. Fineness modulus of thesand, water-cement ratio, and sand-cement ratio should be carefully balanced tomaintain the quality of the matrix. The addition of fly ash, such as about 20 percentreplacement of cement, is beneficial in improving the consistency of the fresh mixand reducing porosity. The fineness of the sand particles in the mortar should beevaluated in terms of the ferrocement reinforcing cage to be encapsulated.Clearly, a large number of mesh layers of small openings in the section is muchharder to fully penetrate and encapsulate than a section with only two layers ofmesh. Shrinkage is not a problem in ferrocement because of the highreinforcement content and because the large surface area of the aggregatesdemands high cement factors. Instead, in mortars for ferrocement it is mostimportant to maintain plasticity as a mix design criterion. The moisture content ofthe aggregate should be considered in the calculation of the required water.Quantities of material should preferably be determined by weight.

The mix should be as stiff as possible (except when closed molds are used),provided it does not prevent full penetration of the mesh. Normally the slump offresh mortar should not exceed 50 mm (2 in.). For most applications with normalweight concrete and steel meshes, the 28-day compression strength of 75 x 150 m-n

181

182 Naaman- FERROCEMENT AND LAMINATED CEMENTITIOUS COMPOSITES

(3 by 6 in.) moist cured cylinders should be not less than 35 MPa (5000 psi).

The reinforcement should be clean and free from deleterious materials such asdust, loose rust, coating of paint, oil or similar substances.

Wire mesh with closely spaced wires is the most commonly used reinforcementin ferrocement. Expanded metal, welded wire fabric, reinforcing wires or rods,prestressing tendons, and discontinuous fibers are also used in specialapplications or for reasons of performance or economy. Figure 6.1 shows typicalsections of ferrocement with different configurations such as with a number oflayers of mesh only, with a combination of mesh and skeletal steel, and with acombination of mesh and discontinuous fibers. The type of section to be built willinfluence to a certain extent the selection of the construction method and thecomposition of the mortar mix.

\ \No Skeletal Steel \ Skeletal Steel in One Direction ’

-ISkeletal Steel in Two Directions

Combination of Mesh and Discontinuous Fibers

Figure 6.1 Typical cross sections of ferrocement (see also hybrid composites inChapter 10).

6.2 MORTAR PLACEMENT

Mortar is generally placed by hand plastering. In this process, the mortar is forcedthrough the mesh. Alternatively the mortar may be shot through a spray gun device(shot-creting). A proprietary technique, called the lay-up technique (or laminating

Chapter 6 -CONSTRUCTION - FABRICATION OF FERROCEMENT 183

process) was developed by Martin lorns of California. It involves placing the meshin the mortar rather than the mortar in the mesh. In this technique, successivelayers of mesh are placed in layers of freshly sprayed, or manually placed, mortar.To assure that mesh layers do not pop out, a thin mortar cover layer is placed firstand allowed to set, but not dry completely, prior to application of a second mortarlayer and the first mesh layer. This first mortar layer is generally about 3 mm (l/8in.) thick. The process can use any type of mesh; however, lorns recommendsexpanded metal plaster lath weighing 3.4 pounds per square yard as the most costeffective. A major advantage of the lay-up technique is that each layer of mesh isplaced under full visual control; any gap in the mortar is immediately apparent andinstantly corrected. This technique was shown to provide excellent meshencapsulation.

From a modern perspective, it is possible to assume that industrializedtechniques of production, such as utilized for extruded or pultruded sheets, areapplicable to ferrocement. In the case of extrusion, for instance, the mortar matrixwill be very stiff (zero slump), but high vibration and compaction in the productionprocess would take care of full penetration.

6.3 CONSTRUCTION METHODS

There are several means of producing ferrocement. All methods (except the lay-upmethod described in Section 6.2) require high level quality control criteria toachieve the complete encapsulation of several layers of reinforcing mesh with awell compacted mortar or concrete matrix with a minimum of entrapped air. Indeed,air voids trapped within the ferrocement during the plastering process can besources of leaks, especially serious in water retaining or water-tight structures.

Four methods of fabrication are described next: 1) the skeletal armaturemethod, 2) the closed mold method, 3) the integral mold method, and 4) the openmold method. These methods have been successfully used in the construction offerrocement structures, the vast majority in marine applications, that is, boats,barges, bulkheads, piers, and docks. In these four generic ferrocement moldingmethods, mortar may be applied by a variety of techniques, including directplastering and wet shotcreting. Variations of these basic methods may beengineered to incorporate factory production techniques, such as flat-bed vibro-casting and vacuum extraction. Extrusion and pultrusion of simple linear shapes,or the use of a closed mold system where the matrix is poured as in conventionalreinforced concrete, are other possible alternatives which require a higher initialinvestment in set-up and equipment.

In most ferrocement fabrication, the mesh layers should be staggered, or theends lap-spliced at least four mesh openings to insure continuity of thereinforcement. For design, alternating the direction of the principal axis ofsuccessive mesh layers by 900 to achieve continuity and isotropy may bedesirable, especially in shell type structures subjected to biaxial loading.

Each of the generic fabrication methods listed above is discussed separately.In all, besides construction requirements, structural design controls the number oflayers of wire mesh and skeletal reinforcement used.

184 Naaman- FERROCEMENT AND LAMINATED CEMENTITIOUS COMPOSITES

6.3.1 Skeletal Armature Method

The armature method is a framework of tied reinforcing bars (skeletal steel), wiresor strands, to which layers of reinforcing mesh are attached on each side (Fig. 6.2).Mortar is then applied, preferably from one side, and forced through the meshlayers until a slight excess appears on the other side. This excess is then pressedback through the armature and struck off.

(W),

/. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

Construction Notes:1. Skeletal steel must be tied together at intersections unless a

welded fabric is used.2. Layers of mesh must be tied to skeletal steel and/or together.3. Force plaster, preferably from one side, to fully encapsualte armature;4. Finishing preferably from both sides.

Advantages:1. No forms.2. Good penetration.3. Easy to patch up all areas

from both sides.

Disadvantages:1. Time consuming.2. Skeletal steel not as performant

as mesh.3. Possible galvanic corrosion

between galvanized mesh andnon-galvanized skeletal steel.

Figure 6.2 Skeletal armature method of ferrocement construct ion.

The skeletal steel framework can assume any shape. The diameter of the steelbars depends on the size of the structure. It is generally recommended that theskeletal reinforcement, if used, not occupy more than 50 percent of the depth of thesection. Skeletal steel is cut to specified lengths and bent to proper profiles; it istied in proper sequence to represent as precisely as possible the shape of thestructure. If too few bars or rods are used and are not tied at a sufficient number ofintersections, bulging may later occur due to plastering pressures or simply theweight of the mortar. The weight of the framework and wet mortar can causesufficient local and general distortion from the desired geometry to warrant someshoring. Bulging may result in thick, unreinforced mesh sections which may latercrack and spall, especially in applications involving temperature or moisturevariations, fatigue, impact or dynamic loading.

Chapter 6 - CONSTRUCTION - FABRICATION OF FERROCEMENT 185

Sufficient splice lengths should be provided to ensure continuity of steel. Forbar sizes commonly used in ferrocement (less than about 6 mm (0.25 in.) indiameter), lap lengths from 230 to 300 mm (9 to 12 in.) seem to be sufficient. Localcodes for reinforced concrete could also be used to insure proper lap lengths.

The main advantages of the skeletal armature method are: 1) no form materialis required other than that needed to support the armature; 2) encapsulation isgenerally good if mortar is pushed through the mesh; and 3) repairs may proceedfrom both sides, and areas requiring touch-up are visible.

Disadvantages include: 1) time-consuming tying and bracing are required tostabilize skeletal steel and mesh layers in view of the pressures of plastering andthe weight of mortar; 2) application of mortar from one side may be difficult for thickor dense mesh systems, resulting in internal air voids; 3) galvanic corrosionbetween galvanized mesh and skeletal steel may develop; 4) the embedment ofskeletal reinforcement near the center of the section leads to a reducedperformance in bending; and 5) two or more layers of mesh may be required oneach side of the skeletal steel framework.

If strength to weight ratio is an issue, the performance of the structure maysuffer from replacing the mesh by skeletal reinforcement. This is due to the doublethickness of relatively large diameter (compared to mesh wires) skeletal bars thatmust form a grid and be tied together. However, the opening between the mainbars of the skeletal reinforcement may be filled by a lightweight core (polystyreneor similar material) allowing the section to act as a sandwich panel. In such cases,care should be taken to insure proper shear transfer between the two skin layers ofthe panel (see also integral mold method).

Figure 6.3 illustrates the application of the skeletal armature mold method ofconstruction in building a ferrocement hyperbolic paraboloid shell.

6.3.2 Closed Mold Method

In this method, several layers of mesh or mesh and rod combinations are stapled orheld in position against the surface of a closed mold; that is, a male mold or afemale mold (Fig. 6.4). The mortar is then applied from one side. The mold mayeither remain as a permanent part of the finished ferrocement structure, or beremoved for future use. However, if the mold is to be removed, pre-treatment withrelease agents may be necessary prior to laying the reinforcing mesh.

The selection of a closed mold tends to eliminate the use of skeletal rods orbars, thus permitting an essentially all-mesh reinforcement; it requires thatplastering be done from one side.

The closed mold method has several advantages, namely: 1) it is ideal forfactory production, since it permits reusable molds; and 2) the molds reinforce thestructure sufficiently to allow moving it or reorienting it for curing. The closed moldmethod is especially well suited to the lay-up technique of mortar application thatwas developed by Martin lorns of California and used extensively with expandedmetal mesh for marine applications in the US [Refs. 6.11 to 6.14 in Appendix C]. Inthe lay-up technique, a thin layer of mortar is first placed in the mold and allowed tosettle; then a layer of mesh is pushed in the mortar and fully encapsulated; a

Figure 6.3 Hyperbolic paraboloid ferrocement shell built by the skeletal armaturemold method of construction.

A ferrocement hyperbolic paraboloid shell was started in 1976 by the student chapter of the AmericanSociety of Civil Engineers at the University of Illinois in Chicago to commemorate the bicentennialanniversary of the United States. The author served as the ASCE Student Chapter Faculty Advisor.The structure was meant to serve as a site for information on campus activities. It was completed in1977. It is made of four connected hyperbolic paraboloid shells covering an area of about 40 squaremeters and rising 7 meters above ground. ‘The construction procedure followed was the armaturemethod of construction. A skeleton of the structure was formed using square steel tubes; steelstrands, l/8 inch in diameter (3 mm), were attached between the sides of the tubes in two oppositedirections forming agrid with openings of about 300x300 mm. This grid represented the skeletalsteel Two layers of l/4 inch opening wire mesh (6.3 mm opening and 0.62 mm in diameter) were thensuccessively attached on each side of the skeletal structure. The mortar was placed by shotcreting.Although the design thickness of the shell was supposed to be around 20 mm, actual thicknesscould not be controlled during shotcreting. The structure is still in excellent condition after more than20 years in the harsh Chicago weather.

Figure 6.3 (continued) Hyperbolic paraboloid ferrocement shell built by the skeletalarmature mold method of construction.

Counter-clockwise from top left: placing the skeletal steel; attaching the mesh; applying the mortarmatrix by shotcreting; and finishing the surface.

1 8 8 Naaman- FERROCEMENT AND LAMINATED CEMENTITIOUS COMPOSITES

second layer of mortar is then placed and the procedure is repeated until thedesired number of layers is placed. The procedure is also suitable for wet-mixshotcreting (dry-mix shotcrete, commonly called gunite, is more difficult to control),thus allowing increased efficiency and savings on labor cost.

The closed mold method also has some disadvantages, namely: 1) large andcostly molds are not economical for one-time application; 2) depending on themold material, it may be difficult to keep the mesh layers together and close to themold unless the mesh can be stapled to the mold; and 3) in plastering onto andthrough the mesh reinforcement, internal voids, and incomplete penetration of themesh cannot be detected.

Mortar from this sideI

/BondI

Breaker at Interface (optional)

Construction Notes:1. In one method, plastering can be applied from one side while mesh

layers are stapled to or held in position against the mold.2. In another method, mesh layers are successively layed into a

preplaced mortar bed.3. The mold may remain as a permanent part of the ferrocement

structure.

Advantages:1. Molds may be reused.2. No skeletal reinforcement.3. Suitable for patented

layup method.

Disadvantages:1. Mold is costly for one time use.2. Internal voids more difficult to

avoid and detect.3. Complete penetration from one

side more difficult to guarantee.

Figure 6.4 Closed mold method ,of ferrocement construction.

6.3.3 Integral Mold Method

An integral mold is first constructed by application of mortar from one or two sidesonto a semi-rigid framework made with a minimum number of mesh layers, or acoarser mesh. This forms, after mortar setting, a rigid but low quality ferrocementmold onto which further application of reinforcing mesh and mortar are applied onboth sides. Lightweight mortar may be used. Alternatively, the integral mold maybe formed using rigid foam insulation materials, such as polystyrene orpolyurethane, as the core. A schematic description of this method is shown in Fig.6.5.

Chapter 6 -CONSTRUCTION - FABRICATION OF FERROCEMENT 189

The integral mold method implies primarily that the mold is left inside theferrocement. It could also imply that the mold is left permanently in contact (on oneside) with the ferrocement, such as to obtain an interior wood finish. In that case,the method becomes similar to the closed mold method except that the integralmold is designed to remain as part of the finished structure.

Advantages of the integral mold method include: 1) excellent rigidity andinsulating properties when an insulating core is used, and 2) if rods must be usedto form or reinforce the core, their thickness can be filled with lightweight mortar, orrigid foam insulating materials.

The main disadvantage is that special details are required for adequate shearconnections between rigid ferrocement layers, especially across insulating cores.

The integral mold method can be ideal for field operations. The possiblevariations are unlimited provided adequate attention is paid to structural detailingrequirements to guarantee that the final structure will function as a true composite.

Mortar~ (ii&z&E)

I I

CJ v 0 0 0 0 v 0 0 0 0 0 I

u 0 01

0 0 0 u 0 0 0 0 0. . . . . ..*.......................*.......................................... . . . . . . . . . . . . . . . . . . . . . . . .

Mortar f

Construction Notes:1. Plastering or lay-up from both sides to penetrate layers of mesh

stapled or held against permanent mold.2. The integral mold may be made of ferrocement or other material.3. Generally the skin layer on each side of the mold is thinner and

easier to penetrate than other methods.

Advantages:1. Integral mold may be designed

to provide good insulation.2. Integral mold provides good

rigidity.3. May provide good water

tightness.

Disadvantages:1. Special detailing is needed

for bonding to and sheartransfer across the core.

2. Finishing is needed onboth sides.

Figure 6.5 Integral mold method of ferrocement construction.

190 Naaman - FERROCEMENT AND LAMINATED CEMENTITIOUS COMPOSITES

6.3.4 Open Mold Method

The open mold method is a traditional boat-building construction method. An openmold is made of a lattice of wood strips or other suitable material and stiffened byframing ribs or by shoring (Fig. 6.6). Mortar is applied from one side through layersof mesh or mesh and rods attached to the open mold. To facilitate mold removal,the mold is coated with a release agent and/or entirely covered with polyethylenesheeting, thereby forming a closed, transparent, but non-rigid surface. Thetransparent sheeting permits observation and fixing during the mortar applicationprocess. It also catches excess mortar that must be pushed back and struck off onthe outside.

Plaster or lay-up from this side

I. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

/ Polyethylene Sheet (or equivalent)

(wood strips or equivalent)

Construction Notes:1. Plastering is applied from one side while mesh layers are stapled to

or held in position against the ribbands or framing.2. The polyethylene sheeting allows observation to facilitate full

mortar penetration and patch up.3. The mold may remain as a permanent part of the ferrocement

structure.

Advantages: Disadvantages:1. Better control of finish than 1. Framing and shoring systems

closed mold method. are costly.2. No skeletal reinforcement 2. Finishing may be needed on

needed. both sides.3. Uses traditional boat building 3. Complete penetration from one

methods. side more difficult to guarantee.

Figure 6.6 Open mold method of ferrocement construct ion.

The open mold method is similar to the closed mold method, in which themortar is also applied from one side, at least until the mold can be removed.However, it enables part of the underside of the mold to be viewed and repaired,where necessary, to assure complete and thorough impregnation of the mesh.

Chapter 6 -CONSTRUCTION - FABRICATION OF FERROCEMENT 191

Advantages of the open mold method are similar to those of the closed moldmethod but with far better control of the quality of the resulting ferrocement product.Disadvantages include: 1) it requires finishing both sides, that is, including moldside, after removal of open mold elements, and 2) it requires construction of anextensive mold and shoring system which may or may not be reusable. In boatbuilding, the open mold is often designed to remain part of the structure. Leavingthe mold in place provides space for insulation and a means for attaching theinterior finish material.

Figure 6.7 illustrates the application of the open mold method of construction inbuilding a ferrocement boat.

6.4 SPECIAL MANUFACTURING TECHNIQUES

There are other construction methods for ferrocement that do not fit exactly into theabove mentioned categories. For instance, in forming the shape of a ferrocementelement, the armature system can be preshaped using different techniques such asdescribed above, or by lifting (to create a funicular shape), or by pressing such asin pressure molding, or by explosion to give a three-dimensional spherical likeshape.

Raichvarger and Tatsa [Ref. 6.20 in Appendix C] described severalmanufacturing technologies for fabricating singly and doubly curved ferrocementelements from flat ferrocement sheets. In one method, a ferrocement sheet isinitially cast on a flat mold and then bent to produce a U-shaped section (Fig. 6.8a).The bending must be done while the mortar matrix is still plastic and not yethardened. Also the mold must be properly designed to allow a smooth operation.In another method, a flat ferrocement panel is cast while having at its periphery arigid frame (Fig. 6.8b). The frame is later lifted slightly, while the matrix is stillplastic; as the panel tends to deform under its own weight, it forms a curved shelllike element. Different panel shapes can be obtained such as square, rectangular,triangular or round. These panels will generally have a double curvature. Thesame principle can be applied to develop panels with single curvature, includingshallow cylindrical sections. A similar technique was used by Douglas Alexander[Refs. 6.1 and 6.2 in Appendix C] in New Zealand to produce the walls of cylindricalwater tanks (Fig. 6.8~). In that technique, a freshly made ferrocement sheet isrolled over a cylindrical drum or a large roller. While, during bending, some cracksform in the plastic matrix, they tend to heal upon curing. For all the abovementioned techniques to be successful, the cementitious matrix mixture must beproperly designed and carefully tested to determine the proper timing of forming.

Figure 6.9 describes another manufacturing technique for mass production ofsmall elements. In that technique a strong molding press is used to shape theelement into the desired form. The mesh reinforcement could be prepared eitherflat as for flat sheets, or roughly preshaped for the final product. Here also, it isessential to have good control of the matrix composition in order to insurepenetration of the mesh.

Wainshtok Rivas [Ref. 6.21 in Appendix C] describes a technique for producingU-shaped, V-shaped, or W-shaped roofing panels from flat panels (Fig. 6.10). Thetechnique involves pouring the mortar matrix over a series of parallel flat panels,

Figure 6.7 Ferrocement boat built by the open mold method of construction(courtesy Alain Dupuis and Renee Lepee, France).

The sequence of photos shown on this page and the following two pages illustrates: a) inside and outsideview of open mold framing; b) attaching the mesh; c) applying the mortar matrix to the deck; d) completedhull; and e) finished boat in sea water. The boat described was built by Alain Dupuis and Renee Lepeefrom France. A detailed account of their work can be found in the French publication: ‘Tout ce que vousdevez savoir sur la construction des bateaux en Ferrociment,” Loisirs Naufiques, Numero Hors Serie 17,December 1983.289 oaoes.

w

Figure 6.7 (continued).

Chapter 6 - CONSTRUCTION - FABRICATION OF FERROCEMENT 1%

Ferrocement platek

Shaping plate prior to hardening

_ Ferrocement

Plastic

rame

‘Inside mold notconnected to frame

Lifting theframe before

(c)

Figure 6.8 Production of different shapes of ferrocement elements using flatsheets: a) U-shaped section; b) shell shaped elements; and c) cylindrical element.

196 Naaman - FERROCEMENT AND LAMINATED CEMENTITIOUS COMPOSITES

leaving strips of mesh between them without mortar. These strips act as jointstraversed by mesh reinforcement. After hardening of the mortar, the panels arelifted to proper position and the joints are filled with new fresh mortar. Thistechnique is essentially inspired by the origami concept of paper folding andshould be applicable, in principle, to many other shapes.

I Vibrating Tayi

Figure 6.9 Pressing technique for mass production of small ferrocement elements.

(b) /

Figure 6.10 Typical production of ferrocement W-shaped elements from f latsheets .

Today the mortar matrix can be made very stiff or very fluid or more plastic inthe fresh state, to be better adapted to a particular application. Conceptually, thinferrocement panels could be built like reinforced concrete panels, that is, where thearmature reinforcement is encased in molds, then encapsulated by a cementmatrix, in this case a very fluid matrix similar to a cement slurry. It is alsoconceivable, for instance, to apply extrusion or pultrusion techniques to buildferrocement sheets or shapes for which a very stiff matrix is needed. Extrusion hasbeen applied to prestressed concrete hollow cored slabs, and to thin fiberreinforced plastic sheets. Pultrusion has been applied to all types of structuralshapes using fiber reinforced plastics such as glass fibers and polymeric matrices.It is likely that such techniques will be applied to ferrocement production in thefuture, especially when fiber reinforced plastic (FRP) meshes become more readilyavailable (see Chapter 10).

Chapter 6 -CONSTRUCTION - FABRICATION OF FERROCEMENT 197

Vibrator

Compactor

Glass fiber

Cutter

Figure 6.11 Manufacturing techniques for large scale production of cementsheets: a) process adaptable to extrusion or pultrusion, b) the Reticem process,and c) process developed by USG corporation.

Figure 6.11 illustrates three different techniques currently used for the production ofcement composite sheets. These were developed as alternatives to the Hatscheckprocess, which was widely utilized for asbestos cement products until the mid-

198 A’aaman - FERROCEMENT AND LAMINATED CEMENTITIOUS COMPOSITES

1980’s. Figure 6.1 la shows a very simple technique requiring little investment. Itcan be adapted to extrusion or pultrusion. Either a belt can be used to move thesheet as produced, or the entire set-up can move with respect to a long bed. Thismethod can be adapted to small or large scale production. Figure 6.11 b illustratesthe Reticem process (developed in England and used in Italy), in which thereinforcement consists of a large number of layers of polypropylene slit film (PPnetwork). This process suggests that a ferrocement type composite can indeed bemanufactured provided the reinforcement is flexible enough (such as FRPmeshes). Figure 6.11~ describes a technique used by USG (US Gypsum)Corporation to produce continuous surface reinforced cement based sheets, trade-named Durock, used as cement boards for interior, exterior or underlaymentapplications.

Sandwich panels have been built with a lightweight core, made frompolystyrene or other lightweight material, sandwiched between two ferrocementskins, Ties or shear connectors are generally necessary between the two skins toinsure shear transfer and composite action. The method of construction ofsandwich panels is similar to the integral mold system but can also bemechanized. Sandwich construction offers numerous advantages includingimproved isolation from noise and temperature and better structural efficiency (seeSection 9.4).

6.5 FERROCEMENT ELEMENT VERSUS STRUCTURE

The methods described in the preceding sections apply primarily to manufacturingferrocement composite material elements from which a structure is to be built. I nthe case of a boat, the shell element becomes the boat hull itself, although it can beargued that the boat is made of different components such as the hull, the deck, thekeel, etc. Generally, methods used in building reinforced concrete structures applyto ferrocement as well. They include cast in place construction, prefabrication, andin some instances prestressing. In any case, joining the different elements offerrocement together, either by cast in place joints or by other jointing techniques,such as bolting (see Chapter 9), is an important part of the construction process.The reader is referred to specialized publications where these subjects arecovered in more details.

6.6 PROTECTIVE SURFACE TREATMENTS

Like other concrete materials, ferrocement can be made to perform satisfactorilywhen exposed to severe weather conditions, to water and soil containingchemicals, and to many common chemicals. The ACI Guide for Design,Construction, and Repair of Ferrocement (AC1549.1 R) [Ref. 5.2 in Appendix C] hasan excellent chapter on “Maintenance and Repair” and an Appendix on SurfaceTreatments. Most of the following information is taken from that document.

Protective coatings, when used, must bond well, be alkali tolerant, thermallycompatible, and resistant to environmental pollutants and ultraviolet radiation, ifexposed.

Generally, good quality mortar has excellent resistance to weathering. For

Chapter 6 -CONSTRUCTION - FABRICATION OF FERROCEMENT 199

general construction purposes it does not require any protective surface treatment.However, the application of protective surface treatments can improve theperformance of ferrocement and extend its service life. Surface treatments can beused to improve appearance, harden the surface, and reduce permeability, thusguarding against the corrosive action of acids, alkaline salts and organicsubstances. Protective surface treatments take the form of hardeners, polymericcoatings, oils, or sheathing.

The most commonly available hardener is sodium silicate, also calledwaterglass. It is quite viscous and must be diluted with water to achievepenetration. A stronger solution can be used for succeeding coats. Each coat mustbe thoroughly dry before the next coat is applied. Other hardeners, which seal andprepare the surface for application of oil based paints, are magnesium fluosilicateand zinc fluosilicate. The treatment consists of two or more applications.

Epoxy and polyurethane compounds are the most widely mentioned protectivecoatings for concrete. They have excellent adhesion to ferrocement mortar and arealkali-resistant; however, some degrade under exposure to ultraviolet (UV) rays,become brittle with age, and have a much higher coefficient of thermal expansionthan concrete. It should be noted that because hardened epoxy is brittle, has acoefficient of thermal expansion different from ferrocement, and is generallystronger than the mortar substrate, multiple coats (or a thick coat) should not beused on a surface subjected to large diurnal changes in temperature such as aboat deck. The difference in thermal expansion creates large interlaminar shearstresses between the coating and the mortar. In comparison, acrylic coatings retaintheir flexibility longer than epoxy coatings and are highly resistant to ultravioletrays.

Bituminous based compounds, in the form of coatings, emulsions, tar, enamel,and plastics, applied in plain layers, or reinforced, provide good resistance againststrong acids, oxidizing solutions, or salt solutions. Acrylic paints and coatingsincluding chlorinated rubber, or varnishes using china wood oil, phenolic resins,and the like, give good protection against acetic, lactic, and carbonic acids, causticsoda, fluorides, light oils, gasoline, phenols, grains, milk, molasses, and vinegar.

Diluted, raw, or boiled oils, such as wood oil, tung oil, soybean oil, and linseedoil, if applied with brushes, penetrate in concrete and ferrocement and provide,upon drying, good protection for acid waters, phosphoric acid, chlorides, fluorides,sulfates, gasoline, and heavier oils.

Fiberglass laminates have been often used on boat hulls to seal the surfaceagainst leakage and improve impact resistance; epoxy resins are preferred forsuch application. Several factors such as temperature when sheathing, soiledmortar surface, and thermal incompatibility must be considered to developsuccessful sheathing.

6.7 CURRENT REACHES WITH AND NOTABLE STRUCTURES OFFERROCEMENT

As with any other structural materials, the design of ferrocement structures iscontrolled by a number of design criteria, which may test the limits of the material.

200 Naaman- FERROCEMENT AND LAMINATED CEMENTITIOUS COMPOSITES

So it may be informative to review, in addition to what has been covered so far inthis and other chapters, the size and type of some structures or structural elementsbuilt with ferrocement in order to provide an idea of what can be achieved.Following are some examples:

1 .

2 .

3 .

4 .

5 .

6 .

7 .

8 .

9 .

Boats of up to 33 meters in length (China, New Zealand); boats usingcombined ferrocement and reinforced concrete of up to 90 meters in China.

Double cantilever V shaped roofing beams spanning 33 m and having athickness of only 50 mm (reported by de Hanai in Brazil).

Structural shell elements spanning 16 m, such as for the group of “coupolas”built by V. Barberio, to house a fish farm in Abruzzo, Italy.

A 55 meter long by 15.9 m wide oil tanker to carry up to 1100 tons of fuel(Pertaminal Fuel Oil Barge) built in Indonesia by Douglas Alexander of NewZealand (Fig. 1.7).

A series of domes built for the mausoleum of Queen Alia in Amman, Jordan, thelargest having a diameter of 16 m with a 10 m height (Fig. 6.12) as reported byJennings.

Ribbed precast ferrocement coffers (3.6 x 3.6 m and 50 mm thick) used aspermanent formwork for the reinforced concrete roof of the Schlumbergerlaboratories in Cambridge, England.

Lining for an Olympic size swimming pool in Cuba, reported by WainshtokRivas.

Thinnest ferrocement shell built at the University of Sidney for their ferrocementcanoe (Aurora Australis); it had a thickness of about 2 mm and used theconcept of an origami folded structure.

A six meters span hollow cored box section bridge built for one way traffic andlight trucks weighting up to 8 tons in Mexico, reported by Fernandez.

10. A 150 ms elevated water tank in Brazil, reported by de Hanai.

11. Prefabricated water tanks, 3.6 m in diameter and 16 ms in capacity, developedin Singapore by Paramasivam (Fig. 9.21).

12. Sunscreen L shaped elements 5 m long and 40 mm thick also developed inSingapore by Paramasivam and Mansur (Fig. 9.22).

Some of the most daring structures using ferrocement were built by D.Alexander in New Zealand. He combined the concepts of ferrocement, fiberreinforced concrete, and prestressing with high strength wires to build relativelylarge scale oil barges and wharves at competitive cost (Fig. 1.7). In particular, hecombined the use of high tensile wires and fibers with wire mesh reinforcement toimprove crack distribution, crack width, and overall mechanical properties. In asimilar manner, another engineer from Hong Kong and Australia, Peter Allen, built

Figure 6.12 Queen Alia’s Mausoleum near Amman in Jordan used ferrocementdomes built by the skeletal armature method of construction; the lower left photoshows the armature of the dome during construction and the lower right photoshows the details of the ribbed interior surface (courtesy P. Jennings, U.K.).

202 Naaman - FERROCEMENT AND LAMINATED CEMENTITIOUS COMPOSITES

large scale roofing elements (hangars) of up to 30 m in span, using ferrocement,high strength steel wires, and prestressing. He also built a 22 m long ocean racingyacht, the He/s&, using ferrocement and post-tensioning. Helsal received severalline honors and held several records in Australia. Curved wing like external wallpanels, 9 m long and 3 m wide, were built as part of the Technical Building for theYambu Cement Company in Saudi Arabia (Fig. 6.13). Martin lorns designed anintegral ferrocement floating mold, estimated to cost about $20 per square yard(1998), which can be used to build any size concrete platform directly on the water.Also, in US Patent No. 5,024,557 of June 18, 1991, lorns describes a method forforming a hollow column of ferrocement on a floating offshore platform by applyingsuccessive layers of mortar and reinforcing mesh to a single surface slip-formwhich outlines the inner or outer contour of the column. The column is lowered bymeans of gravity under the control of embedded (skeletal) cables, and can reachgreat depths to the seabed. Primary applications include cold water pipes forOcean Energy Thermal Conversion (OTEC), access tunnels to undersea habitat, orto gas and oil well equipment.

A new generation of engineers and architects is discovering the benefits,versatility, and unique characteristics of ferrocement in special applications. Acase in point is the main gate to the Yambu Cement Company, which resembles apiece of fabric blowing in the wind, to form the roofing structure, which finishes atone end by a ribbon-like ferrocement that undergoes a steep rotation and becomesthe tower of the structure as if to provide a veil for it (Fig. 6.14). Another recentexample reported by R. Alexander is the use of ferrocement for building a 7.3 mdiameter prototype diffuser augmented wind turbine for generating electricity fromwind (see photo at end of Chapter 11). These accomplishments should beconsidered at the boundaries of today’s ferrocement technology. It is hoped thatthey will become widely utilized in the future, while new daring frontiers will beattained.

%ngineering is the art andscience offinding solutions, even ifthat seemsimpossibk ”

Figure 6.13 Main gate (ferrocement shell) and technical building (ferrocement sunshadepanels) of the Yambu Cement Company in Saudi Arabia (courtesy D. Angelotti, Studio 65,Italy).

Figure 6.14 Main gate to the Yambu Cement Company in Saudi Arabia showing theferrocement ribbon like roof that ends wrapping around the tower (courtesy D. Angelotti,Studio 65, Italy).