ACI 549.1R-93

Guide for the Design, Construction, (Reapproved 1999)

and Repair of Ferrocement

Reported by ACI Committee 549

Gordon B. Batson*Chairman

Colin D. JohnstAntoine E. NaaJames P. RomuSurendra P. Sh

Ronald F. Zollo*

on

* Principal authorsThe following associate members of Committee 549 contributed to t Nanni, Ricardo

P. Pama, P. Paramasivam, Sherwood P. Prawel, and Andrei M. Reinhorn

Members of the Committee voting on the 1993 revision

P.N. BalaguruChairman

M. ArockiasamyNemkumar BanthiaGordon B. BatsonJose O. CastroJames I. DanielDavid M. GaleAntonio J. Guerra

Martin E. IornsColin D. JohnstonMohammad ManJohn L MulderAntoine E. NaamAntonio NanniD.V. Reddy

made in the Project Documents. If items found in thesedocuments are dements, they shoulincorporated into

All rights reserved including rights of reproduction and use in any form or bysired to be a part of the Project Docu-d be phrased in mandatory language andthe Project Documents.

any means, including the making of copies by any photo process, or by any elec-tronic or mechanical device, printed, written, or oral, or recording for sound orvisual reproduction or for use in any knowledge or retrieval system or device,unless permission in writing is obtained from the copyright proprietors.Lloyd Hackman James P. Romualdi

This guide supplements two earlier publications (ACI 549R, State-of-the-Art Report of Ferrocement, and SP-61, Ferrocement-Materials andApplications). It provides technical information on materials and materialselection, design criteria and approaches, construction methods, main-tenance and repair procedures, and testing. The objectives are to promotethe more effective use of ferrocement in terrestrial structures, providearchitects and engineers with the necessary tools to specify, and use ferro-cement, and provide owners or their representutives with a reference docu-ment to check the acceptability of ferrocement alternative in a given ap-plication.

Keywords: admixtures; cements; composite materials; construction; constructionmaterials; ferrocement; fibers; flexural strength, maintenance; metals; modulus ofelasticity; reinforced concrete; reinforcing materials; repairs; structural design;tension tests; welded wire fabric.

CONTENTS

Chapter l-General, pg. 549.1R-2

ACI Committee Reports, Guides, Standard Practices, andCommentaries are intended for guidance in designing, plan-ning, executing, or inspecting construction and in preparingspecifications. References to these documents shall not be

Rogerio C. Zubieta

l . l-Scope1.2-Approval to use procedures

Chapter 2-Terminology, pg. 549.lR-22.1-Reinforcement parameters2.2-Notation2.3-Definitions

Chapter 3-Materials, pg. 549.1R-43.1-Matrix3.2-Reinforcement

Chapter 4-Design, pg. 549.1R.84.1-Design methods4.2-Strength requirements4.3-Service load design4.4-Serviceability4.5-Particular design parameters

ACI 549.lR-93 supersedes ACI 549.1R-88 and became effective November 1,1993.Copyright 0 1988, American Concrete Institute.Perumalsamy N. Balaguru*Jose O. CastroAntonio J. GuerraMartin E. Iorns*549onmanaldiah

Secretary

(former Chairman) *Narayan SwamyBen L.TilsenRobert B. WilliamsRogerio C. Zubieta

he preparation of this report: Shuaib H. Ahmad, Douglas Alexander, Antonio .

s:

sur

an

Parviz SoroushianSecretary

Surendra P. ShahNarayan SwamyBen L. TilsenMethi WecharatanaRobert B. WilliamsonRobert C. ZellersRonald F. Zollo.1R-l

Eift

t

c

m

r small-ncapsul-

forcementd organic,ith metal-teel rein-.speciallylf-help orts anding units,g sheets,

.

ed in thisr govern-ect.

acterizing the vol-ent, and

olume ofomposite

ns- of rein-

lor area ofr) dividedithe volume meshes,l

ted from:

rein-

en is549.1R-2 ACI COMMITT

4.6-Examples4.7-Design aids

Chapter 5-Fabrication, pg. 549.1R-115.1-General requirements5.2-Construction methods

Chapter 6-Maintenance and repair, pg. 549.lR-156.1-Introduction6.2-Blemish and stain removal6.3-Protective surface treatments6.4-Damage repair6.5-Repair materials6.6-Repair procedure

Chapter 7-Testing, pg. 549.lR-207.1-Test methods

Chapter 8-References, pg. 549.1R-228.1-Recommended references8.2-Cited references

Appendix A-Calculation of volume fraction of rein-forcement, pg. 549.1R-25

Appendix B-Flexural strength analysis of ferrocementsections, pg. 549.1R-25

Appendix C-SimpIified design aids, pg. 549,1R-28

Appendix D-Surface treatment for ferrocement struc-tures attacked by commonly used chemicals, pg. 549.1R-29

CHAPTER l-GENERAL

l.l-ScopeThis guide is based on technical informat

sembled by ACI Committee 549, Ferrocement, rent practice, developments, and advances in ferrocement around the world. It represents asupplement to the state-of-the-art report (ACI 549R)published earlier by the committee. The guidmaterials for ferrocement, materials selection,dards; design criteria and approaches; construcods; maintenance and repair procedures; and

The objectives of this guide are to promote tive use of ferrocement in terrestrial structurearchitects and engineers with the necessary tocify and use ferrocement, and provide owners opresentatives with a reference document to acceptability of a ferrocement alternative inapplication. This guide is consistent with ACI BuildingCode Requirements for Reinforced Concrete (ACI 318)except for the special characteristics of ferroceas reinforcement cover and limits on deflectionFerrocement is a form of reinforced concreE REPORT

on as-rom cur-he field of practical

e coversand stan-tion meth-testing.he effec-s, provideols to spe-r their re-heck thea given

ent, such.

closely spaced multiple layers of mesh and/odiameter rods completely infiltrated with, or eated, in mortar. The most common type of reinis steel mesh. Other materials such as selectenatural, or synthetic fibers may be combined wlic mesh. This guide addresses only the use of sforcement in a hydraulic cement mortar matrix

Applications of ferrocement are numerous, ein structures or structural components where selow levels of skills are required. Besides boamarine structures, ferrocement is used for houswater tanks, grain silos, flat or corrugated roofinirrigation channels, and the like (see ACI 549R)

1.2-Approval for use in design and constructionUse of ferrocement and the procedures cover

guide may require approval by the authority omental agency having jurisdiction over the proj

CHAPTER 2-TERMINOLOGY

2.1-Reinforcing parametersThree parameters are commonly used in char

the reinforcement in ferrocement applications:ume fraction, the specific surface of reinforcemthe effective modulus of the reinforcement.2.1.1 Volume fraction of reinforcement Vf-Vf is the

total volume of reinforcement divided by the vcomposite (reinforcement and matrix). For a creinforced with meshes with square openings, Vf is equal-ly divided into Vfl and Vft for the longitudinal and traverse directions, respectively. For other typesforcement, such as expanded metal, Vfl and Vft may beunequal. Examples of computation ofVf are shown inAppendix A.2.1.2 Specific surface of reinforcement Sr-Sr is the tota

bonded area of reinforcement (interface area the steel that comes in contact with the mortaby the volume of composite. Sr is not to be confused wthe surface area of reinforcement divided by thof reinforcement. For a composite using squareSr is divided equally into Srl and Srt in the longitudinaand transverse directions, respectively.

For a ferrocement plate of width b and depth h, thespecific surface of reinforcement can be compu

cS 0=7t bh (2-1)

in which x0 is the total surface area of bondedforcement per unit length.2.1.3 Relation between Sr and Vf-The relation betwe

Sr and Vf when square-grid wire meshes are used

4 vS f=-te usingf db

549.1R-3

h

go

e

m

ede

e

m

f

i

f

tr

or rein-

sistance

e longi-

e trans-

e longi-

r stress

rein-nsile-

ppliede mesh

esh re-ent

pplied

(gener-

ment =

cement

lding of

y do notnology,ement.skeletalat.ger(see

idely support forwhere db is the diameter of the wire. For other types oreinforcement, such as expanded metal, Srl and Srt maybe unequal.2.1.3 Effective modulus of the reinforcement-Although

the definitions of most ferrocement propertiesame as for reinforced concrete, one propertybe different is the effective modulus of the resystem Er. This is because the elastic modulus of(steel or other) is not necessarily the same as modulus of the filament (wire or other) from wmade. In a woven steel mesh, weaving impartsating profile to the wires. When tested in tenwoven mesh made from these wires stretches a similar welded mesh made from identical straiHence, the woven mesh behaves as if it has a ltic modulus than that of the steel wires from wmade.

In addition, when a woven mesh is embeddmortar matrix and tends to straighten under tmatrix resists the straightening, leading to atension stiffening. A similar behavior occurs wexpanded metal mesh (lath) and hexagonal account for the above effects, the term effective of the reinforcing system Er is used. For welded stmeshes, Er may be taken equal to the elastic mothe steel wires; for other meshes, Er may be determinfrom tensile tests on the ferrocement composplained in Chapter 7. Design values for common mused in ferrocement are recommended in Chapter 4.

2.2-NotationAc =A =S

Asi -

b =c =

d" =db =

di =

cross-sectional area of ferrocement cototal effective cross-sectional area oforcement in the direction considered

A, = f: Asii=l

effective cross-sectional area of reinforof mesh layer i in the direction consideredwidth of ferrocement sectiondistance from extreme compression neutral axisclear cover of mortar over first layer odiameter or equivalent diameter of rement useddistance from extreme compression centroid of reinforcing layer ielastic modulus of mortar matrixelastic modulus of cracked ferrocementsion (slope of the stress-strain curvecracked elastic state)effective modulus of the reinforcing syelastic modulus of steel reinforcemenspecified compressive strength of mostress in reinforcing layer istrength of mesh reinforcement or rein

barsFERROCEMENT

f

s are the that mayinforcinga meshthe elasticich it is

an undul-sion, themore thanht wires.wer elas-hich it is

ed in ansion, the form ofithesh. To

moduluselulus ofd

ite as ex-shes

positef rein-

cement

iber to

f meshnforce-

iber to

in ten-in the

stem

tar

forcing

f =Y

hM =nN =n N =nr =s =Sr =Srl =

S =rt

V =fVfi =

V =fl

V =ft

PI =

rl =

772 =

rlt =

rl@ =

c =cu

l . =CZ

Ey =

I:0 -

Q =

o- =cu

yield strength of mesh reinforcementforcing barsthickness of ferrocement sectionnominal moment strengthnominal tensile strengthnumber of layers of mesh; nominal remodular ratio of reinforcementmesh opening or sizespecific surface of reinforcementspecific surface of reinforcement in thtudinal directionspecific surface of reinforcement in thverse directionvolumevolume

fractionfraction

of reinforcementof reinforcement for mesh

layer ivolume fraction of reinforcement in thtudinal directionvolume fractionverse direction

of reinforcement in the trans-

factor defining depth of rectangulablock (ACI 318, Section 10.2.7.3)global efficiency factor of embeddedforcement in resisting tension or tebending loadsvalue of q when the load or stress is aalong the longitudinal direction of thsystem or rod reinforcementvalue of q when the load or stress isS appliedalong the transverse direction of the minforcement system or rod reinforcemvalue of 7 when the load or stress is aalong a direction forming an angle 0 with thelongitudinal directionultimate compressive strain of mortarally assumed to be 0.003)strain of mesh reinforcement at layer i

J

nominal yield strain of mesh reinforce

VEtotal surface area of bonded reinforper unit lengthstress in ferrocement composite at yiethe reinforcementstress in ferrocement composite at ultimatestrength in tension

2.3-DefinitionsThe following terms are defined because the

appear in ACI 116R, Cement and Concrete Termior have another meaning as applied to ferroc

Armature-The total reinforcement system or reinforcement and mesh for a ferrocement bo

Longitudinal direction-The roll direction (londirection) of the mesh as produced in plant Fig.2.1).

Skeletal reinforcement-A planar framework of wspaced tied steel bars that provides shape and

layers of mesh or fabric attached to either side.

ere

tsh

necc

s sizer,o te a

s lessesistant tot whicht.crete and

ed to sul-

pend on classifiedsed struc-r tanks canen in con-

he use ofI or Type

ronments to specifys present inwell-graded fine aggregate (sand) that passen ASTMNo. 8 (2.36 mm) sieve. If permitted by the mesh openings and the distance between layf meshsmall-size coarse aggregate may be added t

The mortar matrix usually comprises morn 95percent of the ferrocement volume and hasype II cement wasance in a sea environ-rosion than Type V. Iferal admixture that im-vailable, a rich mortaran be used with a pro-

ming to ASTM C 595r IP-A can also be

igher in ferrocementral admixtures, such ase slag, may be used tofine filler material. should comply with to their possible im-terials also benefitortar permeability, andfluence on the behavior of the final product. Hence,great care should be exercised in choosing the constituentmaterials, namely cement, mineral admixtures, and fineaggregates, and in mixing and placing the mortar. Thechemical composition of the cement, the nature of theaggregate, the aggregate-cement ratio, and the water-cement ratio are the major parameters governing theproperties of the mortar. The importance of these para-meters is discussed in detail in ACI 549R and in Refer-ences 1 through 4. The following sections give a briefsummary of the material requirements.3 . 1 . 1 Cement-The cement should comply with ASTM

C 150, ASTM C 595, or an equivalent standard. The ce-ment should be fresh, of uniform consistency, and free oflumps and foreign matter. It should be stored under dryconditions for as short a duration as possible.

Detailed information regarding the types of cements,chemical and mineral admixtures, sampling, testing, and

sea water. ACI 357R reports that Tfound adequate for sulfate resistment and better for resisting corsulfate-resistant cement or a minproves sulfate resistance is not amix with normal cement (Type I) ctective surface coating (see Section 6.3).

Blended hydraulic cement conforType I (PM), IS, I (SM), IS-A, IP, oused.

Cement factors are normally hthan in reinforced concrete. Minefly ash, silica fumes, or blast furnacmaintain a high volume fraction of When used, mineral admixturesASTM C 618 and C 989. In additionprovement of flowability, these malong-term strength gain, lower mFig. 2.1-Assumed longitudinal and transverse dirf

Spritzing-Spraying or squirting a mortar onto aface.

Transverse direction-Direction of mesh normal to ilongitudinal direction; also width direction of mesproduced in plant (see Fig. 2.1).

CHAPTER 3-MATERIALS REQUIREMENTS

3.1-MatrixThe matrix used in ferrocement primarily co

mortar made with portland cement, water, and aggrA mineral admixture may be blended with the special applications. Normally, the aggregate corrosion can be found in ACI 225R and in Reference 2.The most commonly used cement type is designated actions oinforcement

sur-

as

sists ofgate.ement foronsists ofae of thes ohe sand.tha great in-

Type I in ASTM C 150. Type II cement generateheat during hydration and is also moderately rsulfates. Type III is a rapid-hardening cemenacquires early strength more rapidly than Type I cemenType IV is a low-heat cement used for mass conis seldom considered for ferrocement. Type V is a sul-fate-resisting cement used in structures exposfate.

The choice of a particular cement should dethe service conditions. Service conditions can beas electrochemically passive or active. Land-batures such as ferrocement silos, bins, and watebe considered as passive structures, except whtact with sulfate-bearing soils, in which case tsulfate-resistant cement, such as ASTM Type IV, may be necessary.

For structures in electrochemically active envisuch as boats and barges, it may be necessarysulfate-resistant cement because of the sulfatesin some cases improved resistance to sulfates and chlor-ides.5

Dac(esogbr

cpe

hl

oUgr

et

p

delam

bga

forcement

admix- C 494.s an in-ength or a

rge weather

ent ratios limitedatings

8) canand dura-can beciably re- mortars,duce ce-

es to im-

measur-me isgth, per-

cent. Plas-t of silica

C 260and thaw-thawing, require-

ing anybility. In

ser-

ards areASTM C 33; however, the maximum particle sizbe controlled by construction constraints sucsize and distance between layers. It is generathat a maximum particle size passing sieve Nmm) is appropriate in most applications. grading is desirable to achieve a workable himortar mix, but trial-tested gap-graded mortabe used.6,7

Aggregates that react with the alkalis in cembe avoided. When aggregates may be reacshould be tested in accordance with ASTM Cproven reactive, the use of a pozzolan to sureactivity should be considered and evaluateddance with ASTM C 441.

Lightweight fine aggregates can also be user fer-rocement. They should comply with the requirfine aggregate given in ASTM C 330. Volcanic ash, bfurnace slag, expanded shale fines, perlite, pumiculite, and inert alkali-resistant plastics may as lightweight aggregates. The use of lightweigates instead of normal weight aggregates le

duction in the strength of the mortar. Hence c

cfrd

t

t

r-applica-

2.5, andigher theontent tous of thetio should

in ferro-content.ortant toding adjustments may be needed in the structu3 . 1 3 Water-The mixing water should be fresh,

and potable. The water should be relatively organic matter, silt, oil, sugar, chloride, anmaterial. Ittion in the

shouldhaveapHr 7 to minimize thepH of the mortar slurry. Salt water

reduc-

acceptable, but chlorinated drinking water can beused.3.1.4 Admixtures-Chemical admixtures used in ferro-

is not

cement servereduction, whbility; improvement in impermeability; air entrainmen

one of the following four purposes: waich increases strength and reduces permea-DESIGN, CONSTRUCTION, AN

Table 3.1-Guidelines for grading of sand

Sieve size, U.S.standard square mesh

No. 8 (2.36 mm)No. 16 (1.18 mm)No. 30 (0.60 mm)No. 50 (0.30 mm)No. 100 (0.15 mm)

Percent passing byweight

80-10050-8525-6010-302-10

3.1.2 Aggregates-Normal-weight fine aggregate (sis the most common aggregate used in ferroshould comply with ASTM C 33 requirements aggregate) or an equivalent standard. It should binert, freeof organic matter and deleterious suband relatively free of silt and clay. Hard, strsharp silica aggregates achieve the best strenSharp sand may, however, cause pumping promay outweigh the slight gain in strength ovegrains.

The grading of fine aggregate should be in awith the guidelines of Table 3.1, which are adawhich increases resistance to freezing and thawing; and REPAIR OF FERROCEMENT 549.1R-5

nd)ement. Itfor fine clean,tances,ng, andth results.lems that rounded

cordanceted from should

as meshly agreed. 16 (1.18niform

h-densitys can also

nt shouldive, they227. Ifpress thein accor-

foments forstice, ver-

e suitableht aggre-ds to a re-orrespon-ral design.lean,ee from acidic

,

er

suppression of reaction between galvanized reinand cement.1

Conventional and high-range water-reducingtures (superplasticizers) should conform to ASTMThe use of water-reducing admixtures permitcrease in sand content for the same design strdecrease in water content creases in water content

for the same workability. De-result in lower shrinkage and

less surface crazing. Retarders are used in latime-consuming plastering projects, especially in hotconditions.

If watertightness is important, such as in water-- orliquid-retaining structures, special precautions must betaken. To achieve watertightness, the water-cemshould preferably be kept below 0.4, crack width(see Chapter 4) and, if necessary, waterproofing coapplied8 (see Section 6.3.3).

Mineral admixtures such as fly ash (ASTM C 61be added to the cement to increase workability bility. Normally, 15 percent of the cement replaced with mineral admixtures without appreducing the strength. Unlike conventional cementthe pozzolanic admixtures are not added to rement but to replace part of the fine aggregatprove plasticity. The tendency for some natural poz-zolans to absorb water and thus adversely affect hydra-tion of the cement phase should be checked bying the water of absorption. Adding silica fureported to reduce porosity and improve strenmeability, and durability;5 however, little experienexists so far in using silica fumes in ferrocemetering may be hindered by an excessive amounfume, which may render the mix stickier.

Air-entraining admixtures conforming to ASTM can be used to increase resistance to freezing ing. To insure good resistance to freezing and the air content should be consistent with thements of ACI 201.2R.

A quality matrix can be obtained without usadmixtures if experience has shown its applicaspecial exposure situations, admixtures (Section 6.5.2) orcoatings (Section 6.3.3) should be used to improve viceability.

Other admixtures not covered in ASTM standnot recommended.3 . 1 . 5 Mix proportioning-The ranges of mix propo

tions recommended for common ferrocement tions are: sand-cement ratio by weight, 1.5 towater-cement ratio by weight, 0.35 to 0.5. The hsand content, the higher the required water cmaintain the same workability. Fineness modulsand, water-cement ratio, and sand-cement rabe determined fromtrial batches to insure a mix that caninfiltrate (encapsulate)) the mesh and develop a strongand dense matrix. Shrinkage is not a problem cement because of the high reinforcement Instead, in ferrocement mortars it is most imp

maintain plasticity as a design criterion.

TT

in weldede out oftransverseual to twogitudinalDependingckness mayeshes havehan woven the initialven-wire with than wire and

her threeg a meshe mesh is

, only onelternatingables the

e.ed form. strength.cing bars549.1R-6 ACI C OMMIawd

t

ec

eEsg

anwfe

always oriented in the directions of the principimum) stresses. However, they are very flexible

may react to produce hydrogen gas. Atomic hydrogenrogen gasd concreteal (max-Fig. 3.1-Types of wire mesh reinforcement usedment

The moisture content of the aggregate shouldsidered in the calculation of required water. Qumaterials should preferably be determined by

The mix should be as stiff as possible, providenot prevent full penetration of the mesh. Normslump of fresh mortar should not exceed 2 in. (50 mm).For most applications, the 28-day compressive s3 by 6-m. (75 by 150-mm) moist-cured cylinders shonot be less than 5000 psi (35 MPa).

3.2-ReinforcementThe reinforcement should be clean and fre

deleterious materials such as dust, loose rust, paint, oil, or similar substances.

Wire mesh with closely spaced wires is thcommonly used reinforcement in ferrocement. metal, welded-wire fabric, wires or rods, pretendons and discontinuous fibers are also beinspecial applications or for reasons of performeconomy.3.2.1 Wire mesh--Common wire meshes have hex

al or square openings (Fig. 3.1). Meshes with hexagoopenings are sometimes referred to as chicken or aviary mesh. They are not structurally as efmeshes with square openings because the wir it doesally the

rength ofuld

fromoating of

mostxpandedtressiug used in

ance or

gon-alire mesh

icient ass are notEE REPORT

be used in doubly curved elements.Meshes with square openings are available

or woven form. Welded-wire mesh is madstraight wires in both the longitudinal and directions. Thus welded-mesh thickness is eqwire diameters. Woven mesh is made of lonwires woven around straight transverse wires. on the tightness of the weave, woven-mesh thibe up to three wire diameters. Welded-wire ma higher modulus and hence higher stiffness tmeshes; they lead to smaller crack widths inportion of the load-deformation curve. Womeshes are more flexible and easier to workwelded meshes. However, welding anneals thereduces its tensile strength.9

A three-dimensional mesh is also available (Fig. 3.2).A crimped keeper wire frictionally locks togetalternating layers of straight wire, thus forminwith a total thickness of five wire diameters. Thsufficiently thick so that, in some applicationslayer is required. The frictional locking of the alayers of wire causes little springback and enmesh to be easily formed into a desired shap

Wire meshes are also available in galvanizGalvanizing, like welding, reduces the tensileGalvanized meshes used with regular reinfor inferroce-

be con-ntities ofeight.

may embrittle the steel reinforcement. Hydbubbles permeate freely through the hardene and canFig. 3.2-Schematic of three-dimensional mesh

DESIGN, CONSTRUCTION, AND REPAIR OF FERROCEMENT

ess

ported

ed-wireeir normal

al (LWDifferhis tends

loading.xcellent

expandedlications.

are

al is costshoul

e

y

tby weight of mortar. However, a substantiallproportion may be sufficient to prevent hydrogtion.1 Epoxy-coated mesh may be substituted foized mesh.

Reinforcing meshes for use in ferrocement sevaluated for their susceptibility to take and has well as for their strength performance in the composite system. Common types and sizes of steel used in ferrocement are described in Table 3.2.

Standards for the mechanical properties meshes commonly used in ferrocement are noSome design information on yield strengths amodulus of meshes available in the United Stafound in Chapter 4. Suggested tests and test procThe most cost effective type of expanded metal is

o a widthngths for

metalsf differentusedills, and

to derive relevant mechanical properties of ferrocement

that ex-hach layerred, as is

s recom-

times usedplaster lath expanded from a 9-in. (229-mm) strip of 24gauge [0.023-in. (0.58-mm)] cold-rolled steel tof 27 in. (0.68 m) and cut into 8-ft (2.43-m) lethe building trades. This lath weighs 3.4 lb/yd2 (1.84kg/m2). A lighter gauge lath weighing 2.5 lb/yd2 (1.35kg/m2) is also widely available. Other expandedare specialty items manufactured in a variety ogauges, dimensions, and mesh openings, which are for such purposes as machinery guards, grgradings.

and ferrocement meshes are given in Chapter 7.3 . 2 . 2 Welded-wire fabric-The major differences be-

tween welded-wire mesh and welded-wire fabric are thesize and spacing of the wires. Welded-wire fabric nor-mally contains larger diameter wires [0.08 in. (2 mm) ormore] spaced at 1 in. (25 mm) or more.

Welded-wire fabric could be used in combination withwire mesh to minimize the cost of reinforcement. Thefabric should conform to ASTM A 496 and A 497. Theminimum yield strength of the wire measured at a strainof 0.035 should be 60,000 psi (414 MPa).3.2.3 Expanded metal mesh reinforcement-Expanded

mesh reinforcement (metal lath) is formed by slittingthin-gauge steel sheets and expanding them in a directionperpendicular to the slits (Fig. 3.3). Punched or otherwiseperforated sheet products are also available. Expandedmesh is suitable for hulls and tanks if proper constructionprocedures are used.

In structural applications, it must be noted panded metals are much weaker in the direction in whicthe expansion took place. The orientation of ein the ferrocement composite must be considedone with plywood. The global efficiency factormended in Chapter 4 can be used in design.3.2.4 Bars, wires, and prestressing strands-Reinforcing

bars and prestressing wires or strands are someTable 3.2-Common types and sizes of steel meshes used in ferrocement

Designation,gage*FabricationShape

% x % No. 16 2 x 2 No. 19 3 x 3 No. 22 4 x 4 No. 23

Woven orweldedSquare

Wire mesh

Welded 1 x 1 No. 14

Rectangular Welded 2 x 1 No. 14

1 No. 181 No. 20

l% No. 22TwisteddHexagonal

Expanded metalmesh

3.4 lb/ydGage No. 18Gage No. 20

Diamond Slit and drawn

* American wire gage

and may have an adverse effect on the matrix strenand permeability particularly at the interface oforcement. As suggested in Reference 10, this reactioncan be passivated by adding chromium trioxidmixing water in proportion of about 300 parts pThe use of expanded metal mesh was first s549.1R-7

Wire spacing Wire diameter or sheet thickn

in. I mm in. I mm

0.75 19.0 0.0630 1.600.50 13.0 0.0410 1.000.33 8.5 0.0286 0.720.25 6.4 0.0250 0.64

1.00I

25.0 0.0800I

2.00

2 x 1 I 50 x 25 0.0800 I 2.000

1.00 25.0 0.0475 1.201.00 25.0 0.0348 0.88

lY2 13.0 0.0286 0.72

0.0230 0.580.0400 1.000.0300 0.76

Collen in 1960.9 Further research findings were reby Byrne and Wright11 Johnston and Mowat,12 andIorns. l3 The general conclusions were:12,13

- Expanded mesh reinforcement and weldmesh offer approximately equal strength in thorientation.- Expanded mesh reinforcement in its norm

direction shown in Fig. 3.3) orientation results in a stcomposite when compared with welded mesh. Tto minimize crack widths in the early stages of- Expanded mesh reinforcement provides e

impact resistance and excellent crack control.Despite the aforementioned advantages,

metal meshes are not suitable for some appLacking flexibility except in lighter gages, they difficult to use in construction involving sharp curvesexcept in cut strips. However, expanded meteffective compared to wire reinforcement and d beconsidered as an alternative.

gthf the rein-

to theer million smalleren evolu-r galvan-

hould beold shape-meshes

of steel available.nd elastictes can beedurestudied byin combination with wire meshes in relatively thick ferro-

Ti y

AG,,t

oncrete

rs shoulddance with-

designedd stresses

fy service-f

nt will be at serviceand close

bers shouldequal to thead combin-

.2,

cross sec-hear force,h calculatedions or -3.2.5 Discontinuous fibers and nonmetallic reinforcement-Addition of fibers to ferrocement may enhance theproperties of the matrix considerably.14 The addition offibers retards crack growth and also permits the use ofmuch heavier gauge wire mesh. The various types of steelfibers and their specific use are discussed in ACI 544.3Rand in ASTM A 820.

Another type of fiber reinforcement consists of irreg-ularly arranged continuous filaments of synthetic or nat-ural organic fibers such as jute and bamboo.15-19 If or-ganic materials are used, care should be taken to conductappropriate investigations to insure the strength anddurability of the finished ferrocement product.

C H A P T E R 4 - D E S I G N C R I T E R I A

4.1-Design methodsThe analysis of a ferrocement cross section subjected

to either bending, or bending and axial load, whetherbased on strength or working stresses, is similar to theanalysis of a reinforced concrete beam or column havingseveral layers of steel (Fig. 4.1). The following guidelines

chapter.All members should also be designed to satis

ability criteria in accordance with provisions oSection4.4 of this chapter.

The width and spacing of cracks in ferrocemeless than for conventional reinforced concreteloads because of the high specific surface spacing of the layers of mesh reinforcement.

4.2-Strength requirementsFerrocement structures and structural mem

have a design strength at all sections at least required strengths for the factored load and loations stipulated in ACI 318.

Required strength U to resist dead load D and liveload L should be determined using ACI 318, Section 9Required Strength.

Design strength provided by a member or tion in terms of axial load, bending moment, sor stress shall be taken as the nominal strengtin accordance with requirements and assumptf ACI318, multiplied by the strength reduction facto# to satisfy the general relationship549.1R-8 ACI COMMIT

I Ilsq

/ LWD*

Flattened Mesh

Fig. 3.3-Typical expanded metal mesh; LWD = longituddiamond

cement elements or in the ribs of ribbed or T-shapelements.

Reinforcing bars should conform to ASTM A 616, or A 617. Usually reinforcing bars are steel with a minimum yield strength of 60(414 MPa) and a tensile strength of about 90(621 MPa). Prestressing wires and strands, wher pre-stressed or not, should conform to ASTM A 4A 416, respectively.are normally used for the design of ferrocemetures. When special provisions are not cited, EE REPORT

I/

Regular Mesh

nal or long-way diamond, SWD = transverse or short-wa

ed

615,rade 60000 psi000 psihe21 and

Building Code Requirements for Reinforced C(ACI 318) should govern.

In design of ferrocement structures, membebe proportioned for adequate strength in accorprovisions of this guide using load factors and strengthreduction factors specified in ACI 318.

Alternatively, ferrocement members may beusing service loads and permissible service-loain accordance with the provisions of Section 4.3 of thisnt struc-the ACI Us+N (4-l)

DESIGN, CONSTRUCTION, AN

-

tee

where U is the factored load (equal to the minim,

hoc

em

eo

t

ould befaction of

ncrete) distance

te) com-3. yieldre

ed in Sec-aterntequal hall be

ompres-train mayalent rec- Sectionquired design strength), N is the nominal resistance4 is a strength-reduction factor defined in Section 9.3 oACI 318, Design Strength.

Design strength for the mesh reinforcementbased on the yield strength fy of the reinforcement should not exceed 100,000 psi (690 MPa). Such a higlimit on yield strength is justifiable for ferrbecause of its high reinforcement content, duvery small crack widths that results from the higsurface Sr and close spacing of the reinforcemcommended design yield strengths of various forcement representative of meshes available are given in Table 4.1.20) These could be used for din lieu of test data. When tests for determinatistrength are needed, they should be conductedance with Sections 7.1.3 and 7.1.4 of this guide.4.2.1 Flexure20-23-As shown in Fig. 4.1, the strain

distribution at nominal moment resistance is abe linear, and a rectangular stress block may computing the resultant compressive force acconcrete. considered effective toed ferrocement section

(4-2)

ement for mesh layer

f mesh reinforcementconsideredforcement for mesh

a of mortar (concrete)Table 4.1-Minimum values of yield strength andeffective modulus for steel meshes and bars re-commended for design

reinforcement per layer of meshresist tensile stresses in a crackcan be determined as follows20

W o v e n W e l d e d Hexa- Expan- Longi-square square gonal de-d metal tudinalmesh mesh mesh mesh b a r s where:

Yield f v , k s is t r e n g t h ( M P a )

0%~~.103 ksi

E f f e c - (Id MPa)t i v e .modulus Q%WU.

lo3 ksi(103 M P a )

6 5 6 5 4 5 4 5 6 0( 4 5 0 ) ( 4 5 0 ) ( 3 1 0 ) ( 3 1 0 ) ( 4 1 4 ) A Si =

2 0 2 9 1 5 2 0 2 9

( 1 3 8 ) (200) (104) (138) (200) r7 =

2 4 2 9 1 0 1 0 - V =F( 1 6 5 ) ( 2 0 0 ) (69) (69) -

Ac =

Ad = tl vfl A,

effective area of reinforciglobal efficiency factor oin the loading direction volume fraction of reinlayer igross cross sectional areh

= 4/dCL- dFig. 4.1-Strain and force distribution at ultimaa fD REPAIR OF FERROCEMENT 549.1R-9

,003

t-i.85fk-4

_ -I-----__

. .

ccF CS,Ts2---tTs3

>Ts4

-

in rrocement section under bending

um re- andf

should bebut

cementtility, andh specificnt. Re-esh rein-

in the U.S.signn of yieldd in accor-

ssumed tobe used ining on the

4 . 2 . 1 . 1 Assumptions-Strength design of ferroce-ment members for flexure and axial loads shbased on the following assumptions and on satisequilibrium and compatibility of strains.

a. Strain in reinforcement and mortar (coshould be assumed directly proportional to thefrom the neutral axis.

b. Maximum strain at extreme mortar (concrepression fiber should be assumed equal to 0.00

c. Stress in reinforcement below specifiedstrength fy should be taken as Er times steel strain wheEr is defined in Table 4.1 and Section 2.1.3. Er could alsobe determined from tests such as those describtions 7.1.3 and 7.1.4 of this guide. For strains grethan that corresponding to fy, stress in reinforcemeshall be considered independent of strain and fy.

d. Tensile strength of mortar (concrete) sneglected in flexural strength calculations.

e. Relationship between mortar (concrete) csive stress distribution and mortar (concrete) sbe considered satisfied by the use of the equivtangular concrete stress distribution defined in10.2 of ACI 318.

4 . 2 . 1 . 2 Effective area of reinforcement-The area ofsection

ti ehhg

nd trgnbi

e,

s l skia

sh layer

nom-e-carrying) matrix

ortar ma-reinforce-square orded meshtof

g capacity strength,

hearre.

rvicesed with

om the

rete) andor equal to

ar (con-

loading,he effec-

should belare andign values ised con-in References 12, 24, and 25. In lieu of the values rived from tests for a particular mesh system,of 7 given in Table 4.220 for common types of reinfoment and loading directions can be used. The ciency factor applies whether the reinforcemetension or the compression zones of the memitions of reinforcement directions are illustrated Fig.2.1

Note that the value of vt = 0.2 for expanded mmesh (Table 4.2) may not always be conservativecularly in thicker sections in flexure with thoriented in the SWD (short way diamond).26 The valuein Table 4.2 should be used for sections 2 in. (50less in thickness, and tests conducted for globavalues for sections of 2 in. (50 mm) in thickne4.2.2 Tension 27-29-The nominal resistance of crac

ferrocement elements subjected to pure tenscan be approximated by the load-carrying capmesh reinforcement alone in the direction ofThe following procedure may be usedir

r

econditions

ates and

sile stressn to in-ck-width

measurements on a model test indicate that a higherNn= syAf (4-3)

N =n nominal tensile load resistance in dconsidered

A =s effective cross-sectional area of reinfoin direction considered

fy = yield stress of mesh reinforcement

The value of As is given by

I3*549.1R-10

T a b l e 4 . 2 - R e c o m m e n d e d d e s i g n v a l u e s o f t h e g l o b a l e f -ficiency factor 77 of reinforcement for a member in uni-axial tension or bending

L o n g i t u d i n a l 0.50 0.50 0.45 0.65 1G l o b a l qIeffi-ciency Transverse q1 0.50 0.50 0.30 0.20 0

factor A t 4 5 d e g , 70 0.35 0.35 0.30 0.30 0.70

The global efficiency factor q, when multiplied by volume fraction of reinforcement, gives the evolume fraction (or equivalent reinforcement ratthe loading direction considered. In effect, it leadsequivalent (effective) area of reinforcement pmesh in that loading direction. For square mes 71 isequal to 0.5 when loading is applied in one of tpal directions. For a reinforcing bar loaded alon77 = 1.

Some information on the derivations of r) and onother concepts concerning efficiency factors ca= _ Asii = 1 (4-4)hequivalento) into anr layer ofes,e princi- its axis,

be founde-he valuesce-lobal effi-t is in theer. Defin-n

tal parti-e mesh

mm) orefficiencys.edle loadingcity of theloading.

ection

cement

where

N =Asi =

number of mesh layerseffective area of reinforcement for mei (Eq. 4-2)

4.2.3 Compression-As a first approximation, the inal resistance of ferrocement sections subjectd to uni-axial compression can be derived from the loadcapacity of the unreinforced mortar (concreteassuming a uniform stress distribution of 0.85 fc, wherefc is the design compressive strength of the mtrix. However, the transverse component of the ment can contribute additional strength when rectangular wire meshes are used, while expancontributes virtually no strengtheningachieved by the mortar alone.12

beyond thaSlenderness effects

thin sections, which can reduce the load-carryinbelow that based on the design compressiveshould be considered.4 . 2 . 4 Shear-No test data are available on the s

capacity of ferrocement slabs or beams in flexu

4.3-Service load design4.3.1 Flexure-for investigation of stresses at se

loads, straight-line theory (for flexure) shall be uthe following assumptions.

a. Strains vary linearly with the distance frneutral axis.

b. Stress-strain relationships of mortar (concreinforcement are linear for stresses less than permissible service load stresses.

c. Mortar (concrete) resists no tension.d. Perfect bond exists between steel and mort

crete).To compute stresses and strains for a given

the cracked transformed section can be used. Ttive area of each layer of mesh reinforcement determined from Eq. (4-2). The same value of moduratio, nr,= Er/Ec, is commonly used for both tensilcompressive reinforcement. Recommended desof Er are given in Table 4.1. Once that neutral axisdetermined, the analysis proceeds as for reinforccrete beams or columns having several layers of steel andsubjected to pure bending.

4 . 3 . 1 . 1 Allowable tensile stress-The allowable tensilstress in the mesh reinforcement under service may generally be taken as 0.60 fy where fy is the yieldstrength. Values of fy given in Table 4.1 are representa-tive of steel meshes available in the United Stmay be used for design. Tests to determine fy for a par-ticular mesh system are described in Chapter 7. Forliquid retaining and sanitary structures (refer to ACI350R), it is preferable to limit the allowable tento 30 ksi (207 MPa). Consideration can be givecreasing the allowable tensile stresses if crastress will not impair performance.

.avice load

ee

t

b

n

u

os

reinforce-

n letal rein-f the thick-

nt, better terms of

orcementcifico

layers of mesh would be acceptable, the advantages ofthan two

erro-proce-Appendix

ngth of

Following

sion-rength of

in Fig.rtar covero 0.06 in.nsidered

he appli-of

on andChapter 3, placing,construc-

any has to behis may

require a large number of workers involved in plasteringDESIGN, CONSTRUCTION, AN

4.3.1.2 Allowable compressive stress-The allowablecompressive stress in either the mortar (concrferrocement composite may be taken as 0.45 fc where6is the specified compressive strength of the mosurements of the mortar compressive strength mtained from tests on 3 x 6-in. (76 x 152-mm) cylinders

4 . 4 - S e r v i c e a b i l i t yFerrocement members and structures should

imum meet the intent of the serviceability reqof ACI 318 except for the concrete cover.4.4.1 Crack-width limitations-It is recommended th

the maximum value of crack width under serconditions be less than 0.004 in. (0.10 mm) for non-corrosive environments and 0.002 in. (0.05 mmrosive environments and/or water-retaining structures.23,30It should be noted that the recommended craare smaller for ferrocement than values suggesty ACI318. Crack widths may be measured from modtheir values may be estimated using acceptableequations such as those recommended in ACI 549R orReference 31.4 . 4 . 2 Fatigue stress range-For ferrocement struc

to sustain a minimum fatigue life of two millionthe stress range in the reinforcement must be30 ksi (207 MPa). A stress range of 36 ksi (348 MPa)may be used for one million cycles.32 Higher values mabe considered if justified by tests.4.4.3 Corrosion durability-Particular care should

taken to insure a durable mortar matrix and opparameters that reduce the risk of corrosion (seeSection 3.1.4 of this report).4 . 4 . 4 Deflection limitation-Because ferrocement i

thin sections is very flexible and its design is veto be controlled by criteria other than deflecparticular deflection limitation is recommended

4.5-Particular design parametersa. The cover of the reinforcement should b

twice the diameter of the mesh wire or thicknesreinforcement used. However, a smaller cover table provided the reinforcement is not suscerapid corrosion, the surface is protected by apriate coating, and the crack width is limited to(0.05 mm). For ferrocement elements of thickthan one in. (25 mm), a cover of the order of(2 mm) has given satisfactory results.

b. For a given ferrocement cross section thickness h, the recommended mesh openings shobe larger than h.

c. For nonprestressed water-retaining structures thetotal volume fraction of reinforcement should nthan about 3.5 percent and the total specific reinforcement should not be less than 4 in.2/in.3(0.16 mm2/mm3).

d. In computing the specific surface of the rement, the contribution of fibers added to the m

be considered while the fiber contribution ma) for cor-

ck widthsd bl tests orprediction

ures cycles,limited to

y

etimize the also

ry likelytion, no.

e abouts of otheris accep-ptible ton appro-0.002 in.ness less0.08 in.

of totalld not

t be lessurface of

inforce-atrix may

ferrocement are mostly realized when more layers are used.

4.6-ExamplesTypical examples for the analysis and design of f

cement flexural elements in accordance with the dures described in this chapter are provided in B.

4.7-Design aidsThe computation of the nominal moment stre

ferrocement sections (as illustrated in Appendix B) canbe time-consuming unless a computer is used. an extensive cornuterized parametric evaluation, Naa-man and Homrich20 derived the following nondimenal equation to predict the nominal moment stferrocement beams subjected to pure bending

A design graph representing Eq. (4-5) is given4.2. In developing these design aids the net moto the first layer of mesh was assumed equal t(1.5 mm), a minimum of two mesh layers was cothroughout, and when more than two layers of meshwere used they were assumed equally spaced. Tcation of Eq. (4-5) and Fig. 4.2 to the examples Appendix B is illustrated in Appendix C.

CHAPTER 5 - F A B R I C A T I O N

5.1-General requirementsThe materials used in ferrocement producti

their selection have already been discussed in of this report. This chapter discusses the mixingand handling of materials used in ferrocement tion.5 . 1 . 1 Planning-It is generally believed that for

fabrication method with ferrocement, plasteringcontinuous through the completion of the job. TD REPAIR OF FERROCEMENT 549.1R-11

ete) or the

rtar. Mea-ay be ob-

as a min-uirements

t

nored in computing the volume fraction of ment.

e. If skeletal reinforcement (see definition iSection5.2.1) is used, it is recommended that the skeforcement not occupy more than 50 percent oness of the ferrocement composite.

f. For a given volume fraction of reinforcemeperformance-not in terms of strength, but incrack widths, water-tightness, and ductility-can beachieved by uniformly distributing the reinfthroughout the thickness33,34 and by increasing its spesurface. While for certain applications, a minimum of twy be ig-

rAh.e

le

mt

t

aat-aioevbeitertdeth, bts grl-sar ia(s

be shothods are

sure surfaceoating ist recom-

anicallyechanicalched withause cor-surface.ay leave

an-cid is re-th speci- can betial

osphoric producte tmay be be taken

r-cement for large

s, and thehould beesrable. Aethylenentinuoushe likeatex usedssists theasonable

ment. Allteria to layers of concrete

most ap- nature oflability ofthe skill factoryount of

aration isquality.

urrent stater projectadjusted to provide a fluid mix for initial penthe armature followed by a stiffer, more heamix at the finish. Mortar should be mixed in that mortar is plastered within an hour aftRetempering of the mortar should be prohibing will reduce the waste of mortar due to pa

In designing the mortar mix, a recommendure used with plaster-type mixers is to put first, then the cement and pozzolan, if usedslurry. Then enough aggregate is added to osired mix consistency. Rotating-drum mixerconventional concrete depend on coarse agefficient mixing and are not, therefore, welferrocement mortars. They may be used if cto assure complete mixing by adding the drygradually. The final desired consistency will vwhat with the construction method selected 5.2)549.1R-12

0.4

0.3F

yr:a

b 0.2E

E

0.1

0 0.2 0.4 0.6 0.8 1.0 1.2

Fig. 4.2-Chart for strength design of ferrocemebending

and in maintaining a constant supply of matework, most often in confined work spaces. bond at cold joints may be achieved througroughness or treatment with bonding agentsmay be useful in large time-consuming plastjects, especially in hot weather conditions.5 . 1 . 2 Mixing-Mixing of the mortar-like materia

ferrocement may be accomplished in a plastmixer with a spiral blade or paddles inside a drum or in a pan-type mixer. To provide uniforthe use of rotating drum mixers with fins affixed to sides is discouraged. Any method, including hanwhich assures a homogeneous mixture of ingredienshould be satisfactory. Mix ingredients shouldfully batched by weight, including the water, or charged in the mixer so that there is no cwater should be accurately weighed so that e watercement ratio is controlled. The water-cement rbe as low as possible but the sand-cement rat5.1.3 Mortar placement-Mortar is generally place byhand plastering. In this process, the mortar

genuity ofnt in

ials duringdequate surface

Retardersring pro-

s forr (mortar)stationary

mixes,hed mixing,s be care-nd addedking. Mixhtio should should be

tration ofily sandedatches sor mixing.d. Batch-ial setting.d proce-e water into form aain the de-used foregates foruited fore is takenngredientsry some-ee Section

d

through the mesh. Alternately the mortar maythrough a spray-gun device. Construction metdiscussed in greater detail in Section 5.2.5.1.4 Finishing-Surfaces must be finished to as

the proper cover to the last mesh layer. Thefinish should be slightly roughened if a surface cto be bonded later. A steel trowel is generally nomended for finishing boat hulls.

Surfaces that are too smooth may be mechabraded by sandblasting or other means of mabrasion. Alternatively, such surfaces may be etphosphoric acid. The use of muriatic acid can crosion of reinforcement which lies close to the Phosphoric acid is preferable in this regard but ma residue which is insoluble in water and therefore cnot be readily washed away. Thus phosphoric acommended if such residue will not interfere wified finishes and mild solutions of muriatic acidapplied with proper attention to corrosion poten. ACI201.2R, however, reports that the reaction of phacid with concrete produces a non-water-solublethat cannot be washed away as easily as that duo muri-atic acid. Hence a mild solution of muriatic acid preferable in some cases. Additional care mustwhen plastering around openings.5 . 1 . 5 Curing-Moist or wet curing is essential forfer-

rocement concrete construction. The low wateratio and high cement factors create a demandquantities of free water in the hydration procesamount permitted to evaporate into the air skept to an absolute minimum. The use of fogging devicunder a moisture-retaining enclosure is desidouble layer of soaked burlap covered with polyor a soaker hose are also good procedures. Cowetting of the surface or of wet burlap or trequires constant attention to avoid dry spots. Lin the surface mortar holds in moisture in and acuring process. Curing should start within a retime after application of the finishing layer.

5.2-Construction methodsThere are several means of producing ferroce

methods require high-level quality-control criachieve the complete encapsulation of severalreinforcing mesh by a well-compacted mortar ormatrix with a minimum of entrapped air. The propriate fabrication technique depends on thethe particular ferrocement application; the avaimixing, handling, and placing machinery; and and cost of available labor. However, field andexperience has shown that only a modest amtraining, production standardization, and preprequired to produce ferrocement of consistent

A number of procedures for the production of ferro-cement are discussed here and represent the cof the art. The procedure used on a particulashould be based on the experience and the inis forcedthe builders and the judgment of the engineer.

v

t

nmused in the

m; MESH LAYERS

nd areas

bedment

or rods.zed mesh

uired to pressures

uired on

difficult internal

lyf relativelythe matrixontributingoidstering pro-strated a

tio whereficulty of achieving a uniform matrix impregnarebound materials and mesh layers are presenshotcrete, with air added to the mix only at thcreate the spray, is the preferred shotcrete msystem is suitable for all types of ferrocememortar volumes justify the setup of needed machinery.

Each of the generic fabrication systems listare discussed separately. Some of the cautioommendations applicable to a particular systeapply to the others, depending of the particcation. All systems have been successfully uconstruction of ferrocement structures, the vain marine applications, i.e., boats, barges, bpiers, and docks.

In most ferrocement fabrication, the mesh sheeshould be staggered or the ends lap-spliced at mesh openings to insure continuity of the stnating the direction of the principal axis of smesh layers by 90 deg to achieve continuity amay be desirable.5.2.1 Armature system-The armature system is a

framework of tied reinforcing bars (skeletal which layers of reinforcing mesh are attacheside. Mortar is then applied from one side athrough the mesh layers towards the other side, ain Fig. 5.1.

The skeletal steel can assume any shape. Dthe steel bars depends on the size of the struetal steel is cut to specified lengths, bent to profile, and tied in proper sequence. Sufficienment lengths should be provided to ensure For bar sizes commonly used in ferrocement (#2 or less)lap lengths from 9 to 12 in. (230 to 300 mm) are usuasufficient. The required number of layers of mesh aretied to each side of the skeletal steel frame.

A list of advantages and disadvantages in usystem is summarized below. For a particular applicaeven one advantage may outweigh all listed disadvatages.

5.2.1.1 Advantagesa. Good mesh infiltration if mortar is pushed throu

the mesh.

b. No form material is required other than st majorityulkheads,

tsleast twoeel. Alter-uccessivend isotropy

steel) tod on eachnd forceds shown

iameter ofcture. Skel-the propert embed-

continuity.,lly

sing thistionn-

gh

[] MORTAR

Fig. 5.1-Armature system

needed to support the armature.c. Repairs may proceed from both sides, a

requiring touchup are visible.5 . 2 . 1 . 2 Disadvantages

a. Reduced performance associated with emof reinforcement (see Section 5.2.1.3).

b. Added weight associated with use of bars c. Possible galvanic corrosion between galvani

and steel framework.d. Time-consuming tying and bracing are req

stabilize framework and mesh layers under theof plastering and the weight of mortar.

e. Two or more layers of mesh may be reqeach side of the rod framework.

f. Application of mortar from one side may befor thick or dense mesh systems, resulting invoids.

5.2.1.3 Discussion-Performanceemay be adverseaffected by three primary factors: (1) the use olarge-diameter, rigid bars in a thin section; (2) in the space formed by the armature system cto weight but not to flexural strength; and (3) air vtrapped within the ferrocement during the plascess. U.S. Naval Laboratory tests have demonremarkable increase in strength-to-weight raonly mesh is used.35-37DESIGN, CONSTRUCTION, AN

The objective of all construction methods isoughly encapsulate a layered mesh system with a plasticportland cement matrix. This is satisfied to degrees, depending on the particular applicatuse of four principal application procedures: ature system, closed-mold system, integral-moand open-mold system. Within these four gec fer-rocement molding systems, mortar may be applievariety of production techniques, including ditering and shotcreting. Variations of these basmay be engineered to incorporate factory produtechniques, such as flat-bed vibrocasting anextraction.

Of the possible machine-assisted procedureof dry-mix shotcrete is not recommended dueD REPAIR OF FERROCEMENT 549.1R-13

to thor-

aryingion, by thethe arm-ld system,nerid by arect plas-ic systemsctiond vacuum

s, the useto the dif-ion whent. Wet-mixe nozzle toethod. Thisnt where

ed aboves and rec- may also

lar appli-

FORCE PLASTE R TOFULLY IMPREGNATE

PLASTER FROMARMATURE

1BOTH SIDES

J

SKELETAL STEELTIED TOGETHERAT INTERSECT IONS

LAYERS OF MESHEACH SIDE OFAND TIED TOSKELETAL STEEL

SKELETAL STEEL

$$ :tthatA certain amount of inefficiency is associated with the

ACI COMMITTE

iently to

tentedmesh isaced in the

for one-

e difficultold.

orcement,the mesh

ying facili-d provides

esh layersin mortart dry out,d the firstlly aboutideal for

inexpen-P L A S T E R F R O M T H I S SIDE

M U L T I P L E L A Y E R SO F M E S H

I M P E R M E A B L E

B O N D B R E A K EA T I N T E R F A C E

M E T H O D I : P L A S T E R F R O MO N E S I D E O V E R M E S H

M E T H O D II: L A Y M E S H L A Y E R I N T O M O R T A R B E D

( P L A S T E R E D O R P N E U M A T I C A L L Y A P P L I E D )

M O L D ( F O R M )l

th

eh

e

omq, os

aubte it

to

te or twominimumar setting,hich fur-rtar are

mold mayh as poly-

in, refersocement,tact withwood fin-ice material.e case ofement orers to pre-layers ofweigh

s when

lements.-mqc_cs M E S H

I MORT

L A Y E R S

A R

Fig. 5.2-Closed-mold system

armature system since a high percentage of the total steeused is located at or near the midsection of thcross section. Thus, weight is added to the strucout significant increase in strength. Further, tthickness of ferrocement sections produced inplastered procedure is increased due to the usture bars in the form of a grid and tied togetfew bars or rods are used and are not tied at anumber of intersections, bulging may occur dutering pressures or simply the weight of theOften the weight of the framework and wet mcause enough local and general distortion frosired geometry that substantial shoring is reprevent bulging. Bulging may result in thickunder-reinforced mesh sections that may later crack5.2.2 Closed-mold system-Themortar is applied fr

one side through several layers of mesh or mecombinations that have been stapled or otherwiseheld inposition against the surface of a closedmold, i.e., a malemold or a female mold. The mold may remain manent part of the finished ferrocement strremoved, treatment with release agents may

The use of the closed-mold system represenFig.5.2 tends to eliminate the use of rods or bars,mitting an essentially all-mesh reinforcement; 549.1R-14 that plastering be done from one side.5 . 2 . 2 . 1 Advantages

ides ofe bendingure with-e overall the fully of arma-

er. If too sufficient to plas-

mortar.rtar can the de-uired to

and spall.mh and rod

s a per-cture. Ife needed.d in

thus per- requires

excellent mesh encapsulation. To assure that mdo not pop out against the closed mold, a thcover layer is placed and allowed to set, but noprior to application of a second mortar layer anmesh layer. This first mortar layer is general/s in. (3 mm) thick. The closed mold system is factory production.

Rolling in layers of mesh is aided by using an sive and simply fabricated tool which is similar a four-bladed disk harrow.33,345.23 Integral-mold system-An integral mold is firs

constructed by application of mortar from onsides onto a semi-rigid framework made with a number of mesh layers. This forms, after morta rigid but low-quality ferrocement mold onto wther application of reinforcing mesh and moapplied on both sides. Alternately, the integral be formed using rigid insulation materials, sucstyrene or polyurethane, as the core. A schematicdescription of this system is shown in Fig. 5.3.

The integral-mold system, as described hereto any mold system which is left inside the ferror in which the mold is left permanently in conthe ferrocement, such as to obtain an interior ish, or to core-type construction systems in whh ferro-cement layers are applied to each side of a corThe core may be rigid foam insulation or, in thclosed molds, it may consist of either a ferrocnear-ferrocement material. The term near refcast products having a minimum number of reinforcement, perhaps only two, and using lightt orlow-quality mortar to produce a rigid core.

5 . 2 . 3 . 1 Advantagesa. Excellent rigidity and insulating propertie

insulating core is used.b. A rigid mold can be formed using precast e

No wood or other mold materials would then be required.

c. The layup method may be applied to both sE REPORT

a. Molds are reusable.b. The molds reinforce the structure suffic

allow moving it or reorienting it for curing.c. The system is especially well suited for the pa

layup method of mortar application, whereby placed in the mortar rather than the mortar plmesh.32,33

5 . 2 . 2 . 2 Disadvantagesa. Large and costly molds are uneconomical

time applications.b. Depending on the mold material, it may b

to keep the mesh together and close to the mc. In plastering onto and through mesh reinf

internal voids and incomplete penetration of cannot be detected.

5.2.2.3 Discussion-The patented method of lasuccessive mesh layers in a bed of fresh mortar istated by spray application of mortar layers anthe integral mold.

D r

eg

l

na

ieil

m

trsmn

u

r

E T

least untilpart of theed, wherepregnation

but with

onstruc-

gs.ld

ble.

riorationt precipi- are at-Environ-lso affectdures. filling

ive coat-s. Noete sur-Fig 5.3-Integral-mold system

d. The layup method may be used against amold, covered by the core materials, which alaid up with another ferrocement layer.

e. If rods must be used to form or reinforccast core, their thickness can be filled with liconcrete mortar.

f. The precast core generally requires muchthan, for example, the armature system.

5.2.3.2 Disadvantagesa. May require special details for shear co

between rigid ferrocement layers, especially sulating cores.

5.2.3.3 Discussion-This method is ideal for foperations. The possible variations are unlimvided adequate attention is paid to structurarequirements that assure the completed systetion as a composite.5 . 2 . 4 Open-mold system-In the open-mold sys

mortar is applied from one side through layeor mesh and rods attached to an open mold lattice of wood strips (ribbands) and statiocommon to boat building. The form, shown in Fig. 5.4, iscoated with a release agent or entirely coveredethylene sheeting (thereby forming a closed band transparent mold) to facilitate mold rempermit repair and observation during the moPLASTER FROM EACH SIDE O RLAYUP F R O M E A C H SUE

EMENT O RI S E ) T OI N S I D E

INTEGRAL MOLD

MES H L A Y E R S

MORTARcation process.This system is similar to the closed-mold sy the pre-htweight

ess tying

nectioncross in-

ldted, pro- detailing will func-

em, of meshade of a

frames

with poly-t nonrigidoval andtar appli-

far better control of the quality of the resulting ferroce-ment product.

b. Uses traditional boat-building methods of ction.

5 . 2 . 4 . 2 Disadvantagesa . Requires finishing both sides, i.e., includin

mold side, after removal of open-mold elementb. Requires construction of an extensive mo

shoring system which may or may not be reusa

CHAPTER 6-MAINTENANCE AND REPAIR

6 . 1 - I n t r o d u c t i o n

the

and

Terrestrial structures are susceptible to detefrom pollutants in ground water and those thatate from the air (acid rain). Marine structurestacked by sulfates and chlorides in seawater. mental temperature and humidity variations aferrocement durability and maintenance proce

Maintenance primarily involves detecting andvoids, replacing spalled cover, providing protectings, and cosmetic treatment of surface blemishet allof the usual methods to treat conventional concrDESIGN, CONSTRUCTION, AN REPAIR OF FERROCEMENT 549.1R-15

closede in turn

P O L Y E T H Y L E N E S H E( O P T I O N A L )

7

L A Y E R S O FM E S H /

S T A T I O NF R A M E

M O L D ( F O R M )

lzll$y..&

,v_v M E S H L A Y E R S

I M O R T A R

Fig. 5.4-Open-mold system

which the mortar is applied from one side, at the mold can be removed. It enables at least underside of the mold to be viewed and repairnecessary, to assure complete and thorough imof the mesh.

5.2.4.1 Advantagesa. Similar to those of the closed-mold systemstem infaces can be applied to ferrocement. For example, due tothe thin cover in ferrocement, muriatic acid (hydrochloric

h

m

s

mf

ed

ar

oear

n

ue to thecal, careource and

loride org.cover sur-

urface ap- a darker

, causing surface.be Thoroughsh and

fective, aphoric ortreatmentlution of calciument makesion.o be re-ubbing, aultice is

into theor moreid with ad lime, ore is spread dry. Aor paperthan oneeeded for

ve stainsontact andhould first materialppear at a

ratel result in is termed concrete

ade withd is wellay fillence willter gained

, as withvoid withent grout.

6.3-Protective s u r f a c e t r e a t m e n t s549.1R-16 ACI COMMITTE

acid) should be used with extreme caution. Pacid and other nonchloride cleaners should befied alternative (see Section 5.1.4).

Repairs seldom involve large quantities of and are usually accomplished by hand. Emphabe placed on ability of the repair material to the mesh cage, to fully coat the reinforcing to inhibit cor-rosion, and to bond to the substrate. Rapidstrength gain may be overriding considerationsgency repairs. Protective coatings must bond walkali tolerant, thermally compatible, and reenvironmental pollutants and ultraviolet radexposed.

Some useful information can be derived froture on bridge deck repair in the Guide for Repair oConcrete Bridge Superstructures by ACI Committee 54Terrestrial ferrocement structures are seldom the severe conditions encountered by bridge the recommendations and procedures reportey Tut-hill38 and other references listed in Referencetoration of deteriorated concrete provide a understanding many repair methods that are to ferrocement.

Available literature that details the methodsof ferrocement is generally nontechnical and wrepair of boat hulls. The most complete repoinformation on ferrocement maintenance is locInternational Ferrocement Information CenteAsian Institute of Technology, in Bangkok, ThIFIC publishes the Journal of Ferrocement, which is de-voted to research and applications of ferrocem

This chapter is intended to provide informatimost common generic compounds that are usprietary patching materials. Proprietary materibe reviewed before using them to patch ferMany materials have been tested by governmcies, and over 300 are listed in the Patching Msection of SPEL, Special Product Evaluation List.39

6.2-Blemish and stain removal6 . 2 . 1 General-Because ferrocement is usually

porous than conventional concrete, stains do trate very deeply in the mortar matrix. The thimortar over ferrocement reinforcement also mgreater care must be taken when preparing th

Reference 40 discusses stain removal for cBulletins on the subject41,422 are based on the resultscooperative investigation by the U.S. Bureau dards and the National Association of Marble D

All sources agree that even weak acids, suchcarbonic, and acetic, may etch concrete if thefor extended lengths of time and not neutralizepletely flushed off.6.2.2 Construction blemishes-Construction blemishes

are often caused by improper selection or useials, faulty workmanship, uneven evaporation, ancuring. Other causes include:1. Cement from different mills will cause coloE REPORT

osphoricthe speci-

aterialssis shouldpenetrate

set and for emer-ell and beistant toiation, if

litera-

6.xposed toecks, but

d b on res-basis forapplicable

for repairritten forsitory ofted at the (IFIC),ailand.

ent.n on thed in pro-ls should

ocement.ent agen-aterials

lessnot pene- cover ofeans thate surface.oncrete. of aof Stan-ealers.as oxalic,y are leftd or com-

of mater-d uneven

tion, although most of the color in mortar is dsand component. Where appearance is critishould be taken to obtain sand from a single shave it thoroughly washed.

2. Mottling results from the use of calcium chhigh-alkali cement combined with uneven curin

3. The use of polyethylene sheet material to faces promotes uneven curing.

4. The water-cement ratio affects tone and spearance. Low water-cement ratios will result inappearance.

5. Hard steel troweling densifies the surfacemore rapid drying and also leaving a darkened6 . 2 . 3 Stain removal-Treatment of stains should

done promptly after the discoloration appears.flushing and brushing with a stiff bristle brudetergent is the first approach. If this is inefdilute (about three percent) solution of phosacetic acid can be applied. Another chemical considered safe and effective is a 20 to 30 sodiammonium citrate, a mild acid which attackscarbonates and calcium hydroxide. This treatmthe surface more porous and promotes hydrat

When a stain has penetrated too deeply tmoved by surface chemical application and scrpoultice or a bandage may be needed. A pointended to dissolve the stain and absorb itpoultice. The poultice is made by mixing one chemicals such as a solution of phosphoric acfine inert powder such as talc, whiting, hydratediatomaceous earth to form a paste. The pastin a thick layer over the stain and allowed tobandage may consist of a few layers of cloth toweling soaked in a chemical solution. More application of a poultice or bandage may be nstubborn stains.

Caution: Most of the chemicals used to remoare toxic and require safeguards against skin cinhalation. Whenever acids are used, surfaces sbe saturated with water or the dissolved stainmay migrate deeper into the concrete and realater date as efflorescence.6.2.4 Efflorescence-When water-bearing salts mig

to exposed surfaces of concrete, evaporation wilthe deposit of salts on the surface. This processefflorescence. It occurs most readily in porousso it should not be a problem for ferrocement ma water-cement ratio of not more than 0.4 ancompacted to be free of voids. Voids, if present, mwith water (in certain applications) and efflorescappear on surfaces around the place where waentrance to the void.

Treatment consists of breaking into the voida hammer, and replastering, or drilling into the a masonry bit and injecting a nonshrinking cemr varia-6 . 3 . 1 General-Good-quality mortar has excellent re-

Dter

f a

lfeg.

s

t

o

t

oardt

a

ea

n el

s. with anicone ande of water

eeneakage andr resinsave poor

preferred.s lamin- am-ortar sur-ials, may

tion ino removepe, and re-

how re-der water.n the

ght to bege and

pairedresistanceevels wellortar. Allowed to

e in lam-g bacminationunder im-he interiorn tapped

may also

m-f the rein-ter, mostction.

ed from ar, by pres-re referredtely

t.DESIGN, CONSTRUCTION, AN

sistance to weathering. General construction usuanot require any protective surface treatment. the application of protective surface treatmenim-prove the performance of ferrocement and exuseful service life. Surface treatments can bimprove appearance, harden the surface, and meability, thus guarding against the corrosiveacids, alkaline salts, and organic substances.

Appendix D of this report, and ACI Committereport, A Guide to the Use of Waterproofing, Dampprooing, Protective, and Decorative Barrier Systems forprovide an extensive list of substances that mcontact with ferrocement and recommend pmeasures for those which may be deleterious.6.3.2 Hardeners-The most commonly available

ener often recommended is sodium silicate, awater glass. It is quite viscous and must be diwater to achieve penetration. The amount odepends on the quality of the silicate and thbility of the concrete. Silicate of about 42.5 deBaume gravity diluted in the proportion of 1 galof silicate with 4 gal. (15.12 1) of water usuallygood solution for the first application. A ssolution can be used for succeeding coats. Emust be completely dry before the next coat i

Other hardeners which seal and prepare thfor application of oil-base paints are magnesium fluo-silicate and zinc fluosilicate.43 The treatment consistwo or more applications. A solution containinglb. (0.45 kg) of fluosilicate crystals per gal. should be used for the first application; and acontaining 2 lb/gal. (0.24 kg/l) should be usedsequent applications. After the last applicationthe surface should be brushed and washed wiremove any crystals that may have formed.6.3.3 Coatings-Epoxy and polyurethane comp

are the most widely mentioned protective coconcrete. They have excellent adhesion to femortar and are alkali resistant. Some compoununder exposure to ultraviolet (UV) rays, become briwith age, and have a much higher coefficient sion than concrete. They have not performed wfaces exposed to sunlight or subjected to widvariation. A thick epoxy coating is stronger thn thecement substrate and very likely will shear bbondline of surfaces exposed to wide tempchanges such as boat decks. As the sealing characteristics of epoxies are desirable, a sadeck finish can consist of one or two thin coatsfollowed by one or more coats of polyurethaneing a UV inhibitor.

Polyurethanes, especially those furnished inmixtures, are considered to offer the best resabrasion among the commonly available coatithose formulated from acrylics provide the bestto sunlight and weathering. An example can bReference 44. Acrylic latex house paints are wide

on ferrocement and have the advantage of being water REPAIR OF FERROCEMENT 549.1R-17

lly doesHowever,ts can end its used toeduce per- action of

e 515s-Concrete,y come inreventive

hard-lso calleduted with dilution permea-ree

(3.78 1) makes atrongerach coat applied.e surface

s of about 1f water solution for sub-has dried,h water to

undstings forrocements degrade

tleof expan-ell on sur-e thermal

elow theraturend bondtisfactoryof epoxy, contain-

two-partistance togs, whileresistance found iny used

based so they can be applied to damp surfaceFor any surface opposite a surface sealed

impermeable coating, an acrylic coating (or silsilane coating) formulated to allow the escapvapor should be specified.6 . 3 . 4 Sheathing-Fiberglass laminates often have b

used on boat hulls to seal the surface against limprove impact resistance; however, the polyesteused in the fiberglass boat building industry hadhesion to ferrocement, so epoxy resins are

Not all applications of epoxy-based fiberglasates have been successful.45 Several factors, such asbient temperature during sheathing, soiled mface, or thermal incompatibility of the matercontribute to failure of the sheathing.

6.4-Damage repair6 . 4 . 1 General-Repairs have received little atten

ferrocement literature beyond instructions tloose mortar, push the armature back into shaplaster.

Hagenbach45 reports on several cases and tellspairs were made, including one repair made unDonovan and Baugh46 cover several case studies ogrouting and repair of ferrocement hulls. Bowen47reports on the reconstruction of a boat thoubeyond repair. Watkins484describes extensive damarepair to a 53 ft (16.15 m) fishing vessel.

Biggs49 points out that damage must be requickly because, while ferrocement has good to a single impact, repeated impacts at load lbelow the initial impact will pulverize the msimilar danger exists when major cracks are aexpand under cyclic loading.6.4.2 Common types of damage6 . 4 . 2 . 1 Delaminations-Delaminations occur when

ferrocement splits between layers which may binated construction. This may be due to springink orbridging of the mesh during construction. Delasometimes occurs at or near the neutral axis pact or flexure when there are many voids in tlayers. Such areas give off a hollow sound whewith a hammer or stroked with a steel bar.

Pressure from expansive corrosion products cause delamination. The Guide for Repair of ConcreteBridge Superstructures, by ACI Committee 546 recomends tests to determine whether corrosion oforcement is active, but as a practical matferrocement can be opened up for visual inspe

6 . 4 . 2 . 2 Spalls-A spall is defined in ACI 116R as adepression resulting when a fragment is detachlarger mass by a blow, by the action of weathesure, or by expansion within the mass. Spalls ato as large when their size exceeds approxima% in.(19 mm) in depth or 6 in. (152 mm) in any dimension.

Spalls are usually caused by corrosion of steel, whichcauses an expansive pressure within the ferrocemen-Chlorides in the concrete greatly increase the potential

TEE REPORT

ions, con-so

thr

nthu

ristoen

e,ai

c

o ra d

let.g

m.o

face sealant, but the presence of the leak indicates thato moisture,y also

, and thet that need

structure;or air; and

perature, or chlor-einforcing it may be

ty) to re-e originalr removedete recon-tion, meshextensive.ng with aface, or bytening forterioratedroduce a hammer

moveated withwhich theougher theding.

, unsound, hammerse foompletely

mmeringr crackedeinforcing

edlerocement,ace. Thisling tools,.esh need

o interfere from the

moved by methods.to brushthe repair549.1R-18 ACI COMMIT

for corrosion of the steel. Under such condittinued spalling is likely and the repair of local spalI areamay even promote the deterioration of the ccause of the presence of dissimilar materials.

An area of steel corrosion and chloride-conconcrete may be considerably larger than tspalled concrete, and if only the spall area is continuing repair program will probably be req

6.4.2.3 Scaling-Scaling is defined as local flakipeeling away of material near the surface of It is caused by the generation of internal pressfreezing of water trapped in saturated voids.

6 . 4 . 2 . 4 Fire damage-No definitive study of firesistance has yet been published, although sombeen done under the direction of Williamson.50 It hasbeen hypothesized that ferrocement might beceptible to fire damage than conventionalbecause of the thin cover, but preliminaryindicate otherwise.

It is possible that the mortar protects the fereinforcing, which in turn distributes and dissheat evenly with little damage to the compocontributing to fire resistance may be the fact typical ferrocement mortar is relatively nonpcontains little water to generate steam prheating. The absence of large aggregate havithermal characteristics may also contribute tofire resistance.

If the fire were intense enough to release thof chemically bound water in the cement, dbond between the cement and the aggregatethe reinforcement, the surface would be chspalled so that the damage could be easily Full-scale removal and repair is then required. Benford*and Iorns51 have reported instances where ferroboats survived fires which would have destroboats.

6.4.2.5 Cracks and local fractures-Hairline cracksand crazing due to temperature changes or dryage in the cover coat do not require repair. Cwet curing will cause autogenous healing, andcoating will conceal the crack from view. If ccaused by continuing overloads or are due tosettlement and the cause cannot be removement or a structural overlay will be required. Cto occasional impact or overload are repairab

Local fractures are cracks in which displacthe section has occurred as a result of impac6 . 4 . 3 Evaluation and testing-Evaluation of dama

must take into consideration its extent, calikelihood of the cause still being active. The mrepair will be dictated by the type of damavailability of special equipment and repair and the level of skill of the workers employed

Economic factors may influence the decisiwhether the repair should be extensive and p

or limited in scope in response to an immediateA leak in a tank or boat hull may be stopped wa sur-ncrete be-

aminatede area ofepaired, auired.g ore mortar.res during

re-e work has

more sus-concretefindings

rocementpates theite. Alsohat therous andssure ong varyingincreasing

e amountstroy the or oxidizerred anddentified.

ementyed steel

ing shrink-ntinuous

a flexiblecks arestructural, replace-

racks duee.ment of

euse, andethod of

age, theaterials,

n as toermanent,

the interior reinforcement has been exposed toxygen, and possibly other corrosive agents. It maindicate poor workmanship during fabricationstrong possibility that other voids are presento be located and repaired.

Repair materials should bond to the original resist pollutants in the surrounding soil, water respond in the same way to changes in temmoisture, and loads. Removal of deterioratedide-contaminated mortar trapped within the rmesh requires a large amount of hand labor, soeconomical (and better for long-term durabiliconstruct or replace an entire area using thstructure as a form which can be left in place oafter the overlaid structure has cured. Complstruction is advisable when chloride contaminacorrosion, and deterioration of the mortar are

Testing ferrocement is usually done by tappihammer to break into any voids under the surdrawing a metal bar over the surface and lissounds indicating voids or the presence of deconcrete. A high-quality ferrocement should pbell-like sound and resist moderately severeblows without damage.6.4.4 Surface preparation6.4.4.1 General-The primary objective is to re

any deteriorated mortar or mortar contamincorrosive agents and to provide a surface to repair materials can be bonded properly. The rsurface, the greater the area available for bon

6 . 4 . 4 . 2 Removal of deteriorated concrete-The firststep in any repair is to remove all disintegratedand contaminated mortar. Saws and chippingused for conventional concrete are unsuitablr fer-rocement unless large sections are to be cremoved.

Small areas are quickly prepared by hand hajust hard enough to pulverize deteriorated omortar, but not to the point of damaging the rmesh.

Scott and Greenius52 found that a pneumatic negun is very effective for cleaning out broken feropening out cracks, and roughening the surfdevice is similar to airpowered chipping and scabut uses a bundle of small-diameter steel rods

Particles of sound mortar embedded in the mnot be removed if they are small enough not twith the penetration of new mortar or projectfinished surface.

6 . 4 . 4 . 3 Reinforcement-Any loose, scaly corrosionrevealed on cleaning out the mortar must be resandblasting, water jet, airblasting, or vacuum

An alternate method for removing rust is naval jelly or spray dilute phosphoric acid over problem.ith

l Benford, J., personal communication to M.E. Iorns about a fire at the Peter-son Boatyard, Tacoma, Washington.

D

t ro

srtei

oiotp

ho

o

filgn

o

nw

o

sad

a

the waterer cracks thertar.moted forte andents.ne, whichhich U.S.

chation andin the pro- pontoons.e bonding

ar the tensileited as the

the poresve agents.h evapor- hydrationome

ghtly lessa range ofused as then be ap-e allowed

ater.re-oven-driedd so must

n any areapackaged handled

ailable in tempera-

nt and can

ners useded in their

yed where chloridee acceler-articularlyis

utty con- chloride.

so ind or in a hole,irg mater-DESIGN, CONSTRUCTION, AN

area and flush thoroughly.Where the mesh cage has been displaced but

tact, it is pushed or jacked back in place and susecurely to withstand the pressure of applying thmaterial. Where the reinforcing has been torn,mesh may need to be laced back to close the

The rods supporting the mesh cage are ofdistorted by impact but seldom sheared off. Ifbe spliced, a 15-diameter overlap of the partner rusually sufficient; otherwise hooks can be used

6.4.4.4 Cleaning-Loose particles and dust refrom hammering or sandblasting should be aivacuum cleaned if epoxy or methymethacrylais the repair material. Water jetting is an optrepair is to be made with hydraulic cementmodified mortar.

If an air jet is used, the compressor shequipped with an oil trap to prevent contamthe surface. Surface oil or dirt can be remtrisodium phosphate or other strong detergen

6.4.4.5 Cracks-Cleaning cracks presents a sproblem since ferrocement is seldom used forflat surfaces which can be filled by gravity flusually simpler to hammer out the mortar onof the crack and replaster with latex mortar.

If opening the crack is not feasible, epoxy injection systems may be attempted in accordthe product directions. Generally the crack is cleaned with oil-free compressed air, and small/sin. (2 to 3 mm)] drill holes are made at the hilowest points in the crack. The surface betweeis sealed with strong coatings or a pressure plyzed epoxy or MMA is injected at the lower hit comes out at the upper hole.

If a latex-cement grout is to be used, the ithe crack must be thoroughly saturated with allowed to drain.

6.5-Repair materials6.5.1 Portland cement-Portland cement (see ACI

225R) is usually the most readily available andpensive repair material. Its characteristics are wand compatible with the ferrocement in terms and moisture variations. Some recommendatioment selection can be found in Section 3.1.1 of thisguide.

Sand matching that used in the original conis suitable unless the need for the repair arosereactive or contaminated sand.

Neat portland or blended cement paste is usedsmall cracks, and a mortar with fine sand is ularger cracks or voids. Both are used in combinlatex for thin patches and overlays. The chief tage of paste is that it shrinks as it dries. Shrinkagedisturbs the bond and necessitates repeated ato achieve the original level. Otherwise, the p

be overfilled and ground down. REPAIR OF