Glass Fiber Reinforced Concrete Products

Glass Fiber ReinforcedConcrete ProductsProperties and Applications

John Jones Thomas P. LutzAssistant General Manager Engineering ManagerCem-Fil Corporation Cem-Fil CorporationNashville, Tennessee Nashville, Tennessee

Presents a state-of-the-art report on the productiontechniques, properties, applications (with designand erection suggestions) and economics of alkaliresistant glass fiber reinforced concrete productsmanufactured by the spray-up process.The advantages, limitations and cost of thematerial, especially in regard to producingarchitectural precast panels, are fully discussed.

F fibers as a reinforcing mediumhave been used for many cen-

turies. The prime objective of usingnatural fibers—such as straw inbrickmaking—has always been to alterand improve the properties of the brit-tle matrix.

The largest commercial use of fibershas been in the asbestos cement in-dustry as it has developed for the last60 years. Asbestos is also a naturalfiber and the search for man-made fi-bers whose properties can be con-trolled and used for the reinforcement

80

of matrices has been continuing sincethe beginning of the century.

The potential of using glass fiberreinforced cement (GRC) systems*was recognized in the very early daysof glass reinforced plastic develop-ment; and, in fact, the Russiansstarted as early as 1941 to developmethods of using glass fiber to rein-force concrete.

The definitive work on Russian ex-perience was published in 1964; thiswas all based on alumina cements andnot portland cement because the fi-bers then available were not able towithstand the alkalinity generated inthe cement paste.

The major breakthrough in the de-velopment of GRC systems took placewhen Dr. A. J. Majumdar of the Build-ing Research Establishment in En-gland conceived a glass compositionwhich gave the fibers a far greater re-sistance to the alkali attack of portlandcements.

Pilkington Brothers Limited of En-gland took a license for this glass andtheir research and development led toa commercially available glass fibercalled Cem-Fil. Processes for produc-ing GRC as well as an understandingof the behavior of the material havebeen under development now for 8years.l"

References 1 through 12 give themost significant work done so far onGRC and its related products.

As a further step forward in the de-velopment of this new material in theUnited States, the Prestressed Con-crete Institute has recently estab-lished a special committee whose ob-jective is "to further usage of fiberreinforced precast panels through thedevelopment of production informa-tion, design criteria and promotionalactivities."

The purpose of this paper is to pre-sent a state-of-the-art report onspray-up GRC products. The discus-sion is restricted to GRC manufac-

tured by the spray-up process (de-scribed later). The paper does notcover the use of glass fibers in moreconventional concrete mixes or its usein surface bonding materials.

Both these materials are substan-tially different from spray-up GRCboth in properties and the role playedby the glass fibers in the compositeand their construction is beyond thescope of this particular paper.

What is GRC?

GRC is a composite material madeup of a matrix of cement (or cementplus sand) and water, reinforced withglass fibers.

It is important to appreciate that thematerial is a total composite in thatthe reinforcing elements are dis-tributed throughout the matrix—unlike reinforced concrete where thereinforcing steel is placed in particu-lar zones.

Manufacture of GRC

Currently, the spray-up process isthe most widely used method of pro-ducing GRC products. In this paper, itwill be assumed that the products de-scribed are manufactured using thisprocess.

Nevertheless, at the end of this sec-tion brief mention will be made ofsome other manufacturing techniques.

*The proprietary term "glass fiber reinforced cement"(GBC) has been in long-standing usage. In this article themore generic engineering term "glass fiber reinforcedconcrete" is intended.

tIn 1975, Cem-Fil Corporation, a joint venture of FerroCorporation (USA) and Pilkington Brothers Limited, wasformed to market alkali resistant glass fiber and thetechnology of producing glass fiber reinforced concreteproducts in the United States.

Pilkington Brothers Limited has granted licenses toproduce their patented glass formulations for alkali resis-tant glass fiber to Ferro Corporation and Owens CorningFiberglass Corporation in the United States and AsahiGlass Company in Japan.

PCI JOURNAL/May-June 1977 81

Spray-up processIn the spray-up process a specially

designed hand-held gun is usedwhich sprays a cement slurry onto thegiven form and at the same time chopsa continuous glass roving into pre-determined lengths which are sprayedat random in the plane of the surface.

The advantages of this process arethat the equipment is relatively inex-pensive and products of almost anyshape can be produced.

The unit shown in Fig. 1 has beenspecifically designed for manualspraying of GRC. It comprises a mixerwhich feeds slurry directly to a pumpwhich in turn transports the slurry tothe spray nozzle. Coupled to the noz-zle is a glass fiber chopping gunwhere the continuous roving (Fig. 2)is converted to the required strandlength (usually 1 1/z in.).

Both the slurry delivery rate and theglass delivery rate are adjustable toenable the correct glass fiber contentto be achieved which is typically setat 5 percent of the total compositeweight.

The spray rate is usually set to de-liver between 24 to 30 lbs per minuteof wet composite. Much faster rates ofspray make it difficult for the operatorto control thickness. Actual daily out-put will vary considerably dependingon the product complexity, amount ofrepetition, and other factors, but for acustom panel operation it should bepossible to produce over 4000 lbs ofGRC per 8-hour day from one spray-up unit.

For most manual operations onespray-up unit will require a four-manteam (comprising one sprayer andthree others to handle mix prepara-tion, mold preparation, product de-mold, etc.) The capital requirementis about $10,000 for a spray unit.

The very minimum factory spaceneeded for correct and efficient pro-duction from one spray-up unit isabout 10,000 sq ft; this includes areasfor spraying, mold preparation andde-molding, product curing, raw ma-terial storage, and a quality controlsection.

Proper curing of GRC is vitally im-

Fig. 1. Spray-up unit for manufacturing GRC.

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Fig. 2. Glass fiber roving.

portant and sufficient space must beavailable for holding at least 7 daysproduction under high humidity androom temperature conditions.

The use of steam curing is being in-vestigated to reduce this time.

Strict quality control is also essen-tial and usually comprises:

1. Regular checks on material sprayrates.

2. Thickness of product is checkedduring spraying to insure ab-sence of "thin spots."

3. Test boards are made periodi-cally during production fromwhich glass fiber content ischecked. Coupons cut from thesetest boards can be used forstrength testing.

Where sufficient product volumeand standardization exists it is possi-ble to automate the spray-up process.There are many ways of achieving thedesired degree of automation but onewell-developed process involves thespray deposition of a flat sheet on to avacuum dewatering bed. The slurry

Fig. 3. Semi-automatic spray dewatering plant for flat sheet manufacture.

PCi JOURNAUMay-June 1977 83

Fig. 4. 5 x 10-ft insulated panels usedto construct walls and roof of a man-ufacturing warehouse and officebuilding in Bridgeport, Connecticut.

used in such a process has an excesswater content. The excess water iswithdrawn from the deposited flatsheet through the dewatering bed bya suction-vacuum process.

The resulting flat sheet has suffi-cient integrity to enable it to bemolded, while in the "green" state, toproduce the required product shape.The automated spray-dewatering pro-cess usually provides material withmaximum density, the best mechan-ical properties and the most consistentquality.

The wide range of possibilities forautomated spray-up plant makes itimpossible to give meaningful rep-resentative data on capital cost andoutput capacity; but the simplest autospray-dewatering plant, as shown inFig. 3, would cost around $70,000.

Other manufacturingprocesses

Although production processesbased on the spray method are almostuniversally used, other methods areunder development. It is not possiblein this paper to go into any detail be-cause these processes are still underdevelopment and as yet some way

Fig. 5. 30-in. diameter GRC concretepipes manufactured in England usingcentrifugal spinning process.

from being proven, or they are subjectto patent applications.

In the United States, Maso-ThermCorp. of Bridgeport, Connecticut, hasdeveloped a continuous process formanufacturing GRC panels in whichthe GRC totally encapsulates apolyurethane core. Fig. 4 shows oneof the first projects to use thesepanels.

Amey Roadstone Corporation inEngland has developed a centrifugalspinning process for the manufactureof GRC pipes (Fig. 5) which they havejust put into production. Initially,their pipes will be confined to lowpressure, sewerage and drainage ap-plications; but the process may lenditself in the future to the production ofpressure pipes and other tubularproducts.

Several other companies are inves-tigating processes that use premixedfibers and slurry which can be cast,pressed, extruded or processed onmodified asbestos cement machinery.

84

So far it has not been possible to pro-duce premixed GRC that matchessprayed GRC either in mechanicalproperties or consistency; but a mostpromising process, which is based ona modified extrusion concept, is beingdeveloped in England by BanburyBuildings Limited.

Undoubtedly, other processes willcome into use; but at the moment, al-most all commercial application andmuch of the technical data relates tothe spray-up process and the remain-der of this paper will deal exclusivelywith this process.

Mechanical Propertiesof GRC

All the test data given in this paperhas been developed by PilkingtonBrothers Limited and the BuildingResearch Establishment in England.It is based on composite materialcomprising 5 percent by weight of

11/2 -in. chopped strands of Cem-Fil al-kali resistant glass fiber and neat port-land cement paste with a water-cement ratio of 0.28 to 0.33. Exceptwhere specifically stated the test datarelates to material tested at 28 daysold.

The test material was manufacturedby the spray-dewatering processwhich produces a composite with fi-bers that are distributed in a two-dimensional array in the plane of theboard. The test specimens were nom-inally 6 x 2 x 3/8 in.

Some reference, however, will bemade to the properties of non-dewatered material and the effect ofthe addition of sand in the composite.

Stress-strain behaviorof GRC

Fig. 6 shows a detailed tensilestress-strain curve giving the four re-gions that the material passes throughbefore failure. In Region I the mate-rial behaves elastically, with Young's

2500

2000

0_, 1500

U)U)wF 1000U)

Region I—Elastic behaviorRegion II—Bend-over rangeRegion III—Multiple crackingRegion IV—Crack opening

0.25 0.5 0.75STRAIN , PERCENT

Fig. 6. Stress-strain behavior of GRC in direct tension.

IV

III

500

1.0


8000

6000

U)0

U) 4000

F-U)

2000

0\

0.25 0.5 0.75 1.0

STRAIN , PERCENT

Fig. 7. General stress-strain behavior of GRC subject to compression, bendingand tension.

modulus of elasticity given by themixture law:

E,=E,Vf+E.VmRegion II (A-B) is a transition zone

where microcracking starts. Point A isusually referred to as the Bend-overPoint (BOP). Region III (B-C) is theregion in which multiple crackingtakes place. At Point C, crack de-velopment has been completed andthe specimen is covered with finetransverse cracks.

Finally, Region IV corresponds tocrack opening with the fibers bridgingthe cracks. The final failure is initi-ated by a combination of fiber pull-outand fiber breakage, the ultimate ten-sile strength (UTS) being defined byPoint D on the curve.

Fig. 7 shows representative stress-strain behavior of GRC in direct ten-sion, bending, and compression.

In bending, the material passesthrough the same four stages as de-scribed above for the tensile test. Theprincipal difference is that departurefrom linearity, or the limit of propor-tionality (LOP), and the ultimate fail-

lire point, or modulus of rupture(MOR) both occur at higher stresslevels than the BOP and UTS in thetensile test. Theory predicts that theMOR should be about two and one-half times UTS and this relation hasbeen verified by the test results.

Shear strengthBecause GRC components made by

the spray-up method have the fibersrandomly distributed in the plane ofthe section, shear values thereforevary with the type of load application.

(a) Inter-laminar shearThe fibers play no part in resist-ing this shear, the value of shearstrength is therefore that of thematrix and is about 300 psi.

(b) In-plane shearShear is resisted by the matrixand the components of the fi-bers at right angles to the line ofload. The value is about 1200psi.

(e) Punch-through shearIn punch-through shear the fi-bers are fully utilized and the

86

8000

7000

6000

500C

Q 400C

3000F

2000

IOOC

0

100

150 NZ

:00J

Z50

I-C-)

Q.00

10

-, 0 0 IV I.G IY

FIBER CONTENT, PERCENT

Fig. 8. Effect of fiber content on modulus of rupture (MOR), ultimate tensilestrength (UTS), and impact strength of GRC.

value is therefore fiber-controlled. It has been mea-sured at about 5100 psi.

Impact strengthThe impact strength of GRC has

been measured using the Izod testand values around 120 in.-lb/in ,2 aretypical. As a point of reference, asbes-tos cement is typically around 25 in.-lb/in 2.

In addition to having much higherimpact resistance, GRC has a com-pletely different failure characteristicthan either asbestos cement or con-crete. Typically, asbestos cement andconcrete, being brittle materials, failin impact by cracking or shattering;GRC on the other hand exhibits apseudo-ductile characteristic anddamage due to impact is usually con-fined to the area of impact withoutany evidence of cracks propagatingbeyond this area.

The high work to failure charac-teristic of GRC has clear benefits ofabuse resistance, particularly where a

product may be handled many timesbefore installation.

Effect of various parameters onGRID properties

The principal determinants of theproperties of GRC are fiber content,composite density, inert filler content(e.g., sand), fiber orientation, andcondition of cure. Other parameters,such as water-cement ratio and degreeof compaction, have an indirect effectonly because they affect density.

Fiber content primarily affects UTS,MOR, and impact strength; and therelation with these properties isshown in Fig. 8. The leveling off ofthe strength curves is caused by thefact that the higher fiber contents tendto entrap air into the composite andthus reduce density.

Composite density affects matrixdependent properties such as LOP,BOP, and Young's modulus, thehigher the density the higher theproperty. Fig. 9 shows a typical den-sity effect on Young's modulus. Fiber

PCI JOURNALJMay-June 1977 87

00—4

x

0

U 3

J

00

2

c7ZZ)01

140 130 IZO 110 100 90 80

DENSITY, LB./FT.3

Fig. 9. Effect of density on Young'smodulus of elasticity of GRC.

content has little effect on Young'smodulus because of the low percent-age of fiber used in composites.

Low density also reduces MOR andUTS because at lower densities moreair is entrained in the concrete whichhas the effect of reducing the bondbetween the fibers and the concrete.

The lower density of non-de-watered material as compared withdewatered material is the primary rea-son for the difference in the prop-erties of these two composites asshown in Table 1.

Inadequate cure usually means thatthe concrete is not fully hydrated andso a poor bond develops between theconcrete and the fibers. This leads tolow MOR, UTS, and impact strength.It will also mean that the matrix de-pendent properties, such as LOP andYoung's modulus, will be low.

GRC based on neat cement pasteexhibits fairly high shrinkage. Ulti-

mate initial drying shrinkage can beup to 0.3 percent at 122 F and 30 per-cent relative humidity. This shrinkagecan be reduced by incorporating aninert filler such as silica sand. Fig. 10shows the relation between sand con-tent and shrinkage.

Although the incorporation of sandbenefits shrinkage there is an increas-ing loss in mechanical properties withincreasing sand content as shown inFig. 11. Point A in Fig. 11 is usuallytaken as the maximum desirable sandcontent.

Long-term propertiesMany properties of GRC change

with time depending on environmen-tal conditions. In the context of thisreview paper it is not possible to dis-cuss durability in detail. This topic iswell covered in Reference 12, andTable 2 summarizes the results of thedurability testing program carried out

88

SAND /CEMENT RATIO0.1 0.5 1.0

0.35

0.3

I-ZW00.250:Wa-

Iii0 0.2

Z

2C/) 0.15wI-

l— 0.1J

0.5

20 40 60 80 100SAND CONTENT, PERCENT BY WEIGHT OF TOTAL MIX

Fig. 10. Ultimate shrinkage at 120 F against sand content forspray-dewatered GRC.

Table 1. Typical properties of GRC products at 28 days.

Properties Spray-Up Spray-Up Dewatered

Limit of Proportionality (psi) 1000-1600 1450-2300

Modulus of Rupture (psi) 3000-4000 4000-6000

Ultimate Tensile Strength (psi) 1150-1600 1450-2500

Impact Strength (in.-lb./in.2) 57- 143 85- 170

Compressive Strength (psi) 7300-11400 8700-14500

Young's Modulus (psi) 1.5-3x106 2.2-3.6x106


soon

500

Na- 400

U)NW

E- 300U)

ZaZ 20WM

100

A

a

0-

4)

0-

00

0 LOP

0 n *Sz nc n7F In 5

SAND / CEMENT RATIO

Fig. 11. Effect of sand additions on modulus of rupture (MOR) and limit ofproportionality (LOP) on GRC.

Table 2. Strength properties of spray-dewatered GRC at various ages using 5percent glass fiber (BRE data).

Properties

Total Rangefor Air and

Water StorageConditions

1 Year 5 Years 20 Years(estimated)

Air* Water** Weathering Air* Water** Weathering Air* Water**at 28 Days

Bending 5075-7250 5075-5800 3200-3600 4350-5200 4350-5075 3050-3600 3050-3350 3775-4900 2900-3000NOR (psi)

LOP (psi) 2000-2550 1300-1900 2300-2800 2000-2500 1450-1750 2300-2800 2175-2610 1200-1450 2300-2610

Tensile 2000-2550 2000-2300 1300-1750 1600-2000 1900-2175 1300-1750 1000-1200 1750-2175 1200-1600UTS (psi)

80P (psi) 1300-1450 1000-1200 1300-1600 1300-1450. 1000-1200 1000-1300 1000-1200 1000-1200 1200-1600

Young's Modulus 2.9-3.6 2.9-3.6 4.0-5.0 2.9-3.6 2.9-3.6 4.0-5.0 3.6-4.6 2.9-3.6 4.0-5.0(Psi 0106)

Impact Strength 85-155 90-125 40-50 65-80 90-105 20-30 20-35 70-100 20-35(Izod)

(in-lb/in.2)

*At 40 percent relative humidity and 68 F. on: NOMoR -- Modulus of rupture. 015 -- Ultimate tensile strength.

Notati

**At 64 to 68 F. LOP -- Limit of proportionality. BOP -- Bend-over point.

Although GRC is a relatively newconstruction material, it has alreadybeen used fairly extensively. Manyapplications of the material are eitherin existence or are under develop-ment.

The predominant initial use of GRCin most countries has been in ar-chitectural panels and Figs. 12 and 13show two of the most ambitious so far.The advantages GRC offers in this Fig. 12. The new Credit Lyonnais

type of use include: building in London, the first buildingof its kind in the world is clad inter-

(a) Very few restrictions on shape nally and externally with sculptured,or size of the product (the lightweight GRC.

Fig. 13. Double skin window and mullion panels on office block developmentat Kingston on Thames, England.

by Pilkington Brothers Limited andthe Building Research Establishmentover the past 7 years.

The weathering program is continu-ing in Great Britain; and in addition,weathering sites have been estab-lished in several other countries, in-cluding Canada, Nigeria, India andAustralia, which is providing durabil-ity data under a wide variety of differ-ent climatic conditions.

Applications of GRC

PCI JOURNAL/May-.tune 1977 91

Fig. 14. Ribbing detail for 10 x 4-ft panel shown in Fig. 20.

largest panels manufactured sofar are the ground floor units onthe Credit Lyonnais building,measuring approximately 24 x10 ft).

(b) The product's high impactstrength provides resistance todamage during handling anderection.

(c) The product being non-combustible, it does not con-tribute to the fire load of thebuilding and further it is possi-ble to design panels with over 2hours fire resistance.

(d) The panels are relatively light-weight, particularly when com-pared with concrete (typicallybetween one-quarter to one-tenth the weight).

(e) A wide range of surface finishesare possible, including as-molded exposed aggregate, andas-molded cement color with

plain, textured, or featured fin-ishes.

Two basic approaches are possiblein the design of GRC panels, namely,single skin and sandwich construc-tion. Typically, single skin panels arenominally % in. thick, but design con-siderations may require extra thick-ness or the incorporation of stiffeningribs in the panel. These are usuallymanufactured by over-spraying lostrib formers located in the appropriateplaces on the back of the panel whileit is still "green."

Fig. 14 shows the ribbing on theback of a 10 x 4-ft fascia panel inwhich the horizontal rib was formedby over-spraying a strip of polystyrenefoam. The vertical ribs were formedby spraying against removable steelformers which were fastened to theedges of the mold.

Sandwich panels usually comprisetwo skins of GRC, 1/4 or 3/s in. thick,

92

Fig. 16. Highway noise barrier constructed on M4 highway, London, England.System comprises steel posts and 3/8 in. thick GRC panels 2 x 8 ft.

Localized crushing of the CRC by thefasteners should also be avoided byuse of large washers or compressiblewashers.

Jointing between panels also pre-sents no unusual features in that buttjoints with caulking, gaskets, anddrain joints are all possible, and theprinciples observed with precast con-crete are applicable to GRC.

Although architectural panels is thepredominant application at the mo-ment, GRC has many other uses. Figs.15 and 16 show two applicationswhere GRC has been used for acous-

tic control. GRC follows the acceptedmass law for sound reduction and soits relatively high density (125 lbs percu ft) offers good attenuation charac-teristics.

A 3/s-in. sheet of GRC at 4 lbs per sqft yields a sound reduction index of22dB at 350 Hz rising to 39 dB at 4000Hz.

The use of GRC formwork for con-crete is an application to which thematerial is well suited. Being cementbased it is compatible with the con-crete and because it is strong in thinsection, non-rotting, and can be pro-

Fig. 17. Permanent GRC bridge deck formwork for road bridge.

94

Fig. 18. Permanent GRC forms for waffle floors in Trumans Brewery, London,England.

duced in a variety of shapes and tex-tures, it is most often used as lost orpermanent formwork, although with asuitable surface sealant and mold re-lease agent it has been used for reus-able formwork.

An added benefit of GRC perma-nent forms is that they can substan-tially upgrade the fire performance ofthe concrete structure. Tests in En-gland on GRC column forms showedthat a column cast in a permanentGRC form had fire rating almost onehour Ionger than a column of exactlysimilar overall dimensions and coverto the reinforcement steel but cast in aremovable timber form.

Fig. 17 shows GRC panels being in-stalled as permanent formwork for aroad bridge deck. The bridge spanneda river which made it difficult to pro-vide support for removable formworkand permanent GRC formwork provedto be the most cost effective solution.The unsupported span was 4 ft 6 in.,the load due to wet concrete and liveloads was taken as being 140 lbs persq ft and the deflection limitation was'zs times the span. The GRC panel

PCI JOURNAL/May-June 1977

used was s/s in. thick with 2 x 3-in, ribsat 18-in. centers.

Fig. 18 shows GRC waffle panswhich were used to form the fivefloors of a brewery building in Lon-don. Each of the 5500 units requiredfor the job was 4.75 x 4.75 x 3.75 ftwith '/2-in, wall thickness andweighed 396 lbs.

Most of the commercial applicationsof GRC shown up to now have oc-curred in Great Britain. However, inthe last few years some noteworthystructures have been built in theUnited States using CRC panels (seeFigs. 19 through 28).

Fig. 19. Single skin aggregate facedpanels on Marshall Street Educa-tional Center, Hagerstown, Maryland.(Courtesy: Cem-Fit Corporation.)

Fig. 20. Single skin panels in buff concrete on Ivey's Store, Volusia Mall,Daytona, Florida. (Courtesy: Lake Manufacturing Company.)

Fig. 21. A fascia panel used at the U.S. Post Office, Ketchikan, Alaska, weighsonly 450 lb. (Courtesy: Olympian Stone Company.)

96

Fig. 22. Fascia panels are lifted into place on to wood framing at U.S. PostOffice construction site. (Courtesy: Olympian Stone Company.)

Fig. 23. Single skin Cem-Lite panels with raised aggregate finish on completedKetchikan Post Office. (Courtesy: Olympian Stone Company.)


Fig, 24, Finished panels are located on a truck ready for shipment to the RCAAlascom Headquarters Building In Anchorage, Alaska, by roll.on.roli-off ship.(Courtesy: Olympian Stone Company.)

Fig. 25. Panels at RCA job site being readied for placement on building.Panels were insulated at producer's plant for a "U" factor of 0.05. Typicalpanels are 20 ft x 9 ft 6 in. x 2 ft deep and weigh 2800 Ibs, (Courtesy: OlympianStone Company.)

98

Fig. 26. Large spandrel panels with 2-ft returns top and bottom provide set-back for windows in energy saving design at Alascom Headquarters Building.(Courtesy: Olympian Stone Company.)

Fig. 27. Typical sunshade stored in producer's yard for University of Washing-ton Health Science Modification, Seattle, Washington. One inch of styrofoaminsulation was applied to the back of these panels prior to shipping to the jobsite. Typical panel size was 13 ft x 4 ft 1 in. with sunshade projection of 1 ft 4in. (Courtesy: Olympian Stone Company.)


several years before fully structuralGRC uses will be advocated.

Many of the problems that havebeen encountered with GRC were as-sociated with the relatively high dry-ing shrinkage of GRC based on neatcement slurry. The incorporation ofsand, as is now standard practice, hasreduced the amount of shrinkage; butnonetheless, it is still significantlygreater than that exhibited by precastconcrete because of the much highercement content of GRC.

Shrinkage derived problems man-ifest themselves in the usual ways ofbowing and distortion. Although thiscan usually be kept to within a toler-ance of less than 1/360 the span, de-signers should be mindful that stiffen-ing ribs or some other method of re-straint may be necessary. A particularcase is where the product is to befaced with a material which shrinkssignificantly less than GRC, such asexposed aggregate mix, or which pre-vents the GRC drying out through theface of the product, such as tiles orimpermeable paints.

Shrinkage cracking should not be aproblem with GRC, even where thecomposite does not contain sand; butit can occur where there is a low fibercontent or fiber orientation. Crackscan run in the direction of the orienta-tion because there are not enough fi-bers to resist the propagation of thecrack.

The temptation to use steel rein-forcement in GRC should be avoidedbecause the higher shrinkage of GRCcan cause severe distortion and prob-ably cracking. The use of molded-insteel in GRC products should be con-fined to the fastening devices and anysupporting steel should be kept exter-nal to the GRC.

Like all materials GRC has to beproduced according to recommendedprocedures; and, if it is not, suspect orfaulty products will be produced.GRC produced by the manual spray

process has the added feature that ma-terial quality is dependent on theoperator. This means that GRC pro-ducers must operate strict quality con-trol procedures to insure maintenanceof material quality and specifiers ofGRC products should check that theGRC manufacturers they purchasefrom are operating a satisfactory qual-ity control program.

Economics of GRCArchitectural Panels

GRC hand spray is a labor intensiveprocess and alkali resistant glass fiberis a relatively expensive raw material,both of which mean that GRC cannotbe considered to be a cheap buildingmaterial. The precise economics willdepend substantially on the manufac-turer's labor utilization and materialwastage, particularly from oversprayand unnecessary over-thickness.

Well-trained spray operators are es-sential to control material usage effi-ciency and careful planning and ex-perience is necessary to insure thatplant layout and work organizationmaximizes labor utilization.

Economically priced CRC can onlybe produced by manufacturers withwell-trained operators and who havewell organized plants. Where theserequirements are not met, GRC canonly be produced at competitiveprices by skimping on quality and ma-terial thickness.

The basic raw material cost for GRCcomposites depends largely on thetype of cement and the glass contentbut typically it will be around 35 to 40cents per sq. ft. for a composite con-taining 5 percent glass fiber and 3/s in.thick and not allowing for materialwasted.

The finished product price will ob-viously depend on the type of prod-uct, labor force, production volume,mold cost, type of manufacture, treat-


ment of overhead, and other factors.However, by way of example, theprice of architectural custom-made ar-chitectural GRC panels ranges from$2.50 to $8.00 per sq. ft.

In the case of architectural panelsthe factory or delivered price shouldnot be looked at in isolation but ratherGRC often provides cost savingswhen the effect on the total cost of aproject is considered.

These corollary savings can derivefrom:

(a) Panels are relatively lightweight,particularly when compared to con-crete or masonry walls (typically lessthan one-quarter the weight of anequivalent concrete panel) which canprovide cost savings in transportation,.site handling, and a lighter structuralframe.

(b) When constructed in sandwichpanel form, high insulation values canbe obtained with thin wall panels(e.g., a wall of 6 in. overall thicknesswill have, a "U" better than 0.06),which provides developers with moreusable floor space for the given totalground area covered by the building.

(c) Being "non-combustible" andbeing able to design GRC panelswhich meet most required full fire re-sistance ratings GRC does not con-tribute to the fire load of a building.Therefore, special fire protectionmeasures are not necessary.

(d) There is very restriction onshape or size of panels which, in par-ticular, offers the opportunity toachieve savings in installation costs.

(e) Its good impact strength pro-vides resistance to damage duringhandling and erection, but evenwhere damage may occur it is oftenrepairable on site.

(f) A wide range of surface finishesare possible, many of which aremaintenance free.

In many other product areas thesame is true, namely, that theeconomic justification for its use is not

necessarily in the factory cost of theGRC product but rather it can stemfrom technical advantages and costsavings which CRC offers elsewhere.

Conclusion

GRC is just at the start of its de-velopment in North America, but theextent of its use in Europe after only 6years of commercial developmentleaves little doubt that similar growthin its use will be seen here and otherparts of the world.

Its good impact strength andflexural strength together with itsgood fire properties, flexibility inshape and size, maintenance-free sur-face finishes, and relative lightweightcompared to concrete makes it aneminently suitable material for theconstruction industry.

Although these characteristics arewell utilized in building panels, itsuse is not confined to this application,but rather it is anticipated that manyother applications will become just asimportant.

Further, they will not be confinedto the construction industry as GRChas benefits to offer other areas, par-ticularly products used for publicworks, (e.g., pipes and products atpresent made in cast iron), in noiseabatement and control. The productalso offers a ready solution to thosesituations where a replacement for as-bestos cement is being sought toovercome the health hazard problemof handling asbestos-containing prod-ucts.

References

1. Ali, M. A., Majumdar, A. J., Singh, B.,"Properties of Glass Fiber Cement—The Effect of Fiber Length and Con-tent," Journal of Materials Science,V.10, 1975, pp. 1732-1740.

2. Majumdar, A. J., Nurse, R. W., "Glass

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Fiber Reinforced Cement," MaterialsScience and Engineering, V. 15, Nos.2-3, Aug./Sept. 1974, pp. 107-127.

3. Proctor, B. A., "Glass Fiber ReinforcedCement," Physics in Technology,1975, pp. 28-32,

4. Ferry, R., "Glass Fiber ReinforcedCement," Concrete Construction,April 1975, pp. 137-139.

5. Proctor, B. A., Oakley, D. R., Wiecher,W., "Tensile Stress/Strain Characteris-tics of Glass Fiber Reinforced Ce-ments," Composite-Standards, Test-ing, and Design 1974 Conference, IPCScience and Technology Press, pp.106-107.

6. Hoff, G. C., "Research and Develop-ment of Fiber Reinforced Concrete inNorth America," (U.S. Army EngineersWaterways Experiment Station,Vicksburg), Symposium on ConcreteResearch and Development 1970 -1973,Sydney, Australia, 1973, pp. 1-4.

7. Ironman, R., "Stronger Market Seenfor Glass Fiber Concrete," ConcreteProducts, January 1976.

8. ACI Committee 544, Symposium onFiber Reinforced Concrete, SpecialPublication, SP-44, American ConcreteInstitute, Detroit, 1974, 554 pp.

9a. Nair, N.G., "Mechanics of Glass FiberReinforced Cement," Rilem Sym-posium 1975 on Fibre Reinforced Ce-inent and Concrete, pp. 81-94. (Avail-able through Concrete ConstructionPublications, Inc., 329 Interstate Road,Addison, Illinois 60101).

9b. Jaras, A. C., and Litherland, K. L.,"Microstructural Features in GlassFibre Reinforced Cement Compos-ites," Rilem Symposium 1975 on FibreReinforced Cement and Concrete, pp.327-334.

9c. Soane, A. J. M., and Williams, J. R.,"The Design of Glass Fiber Rein-forced Cement Cladding Panels,"Rilem Symposium on Fibre ReinforcedCement and Concrete, pp. 445-452.

10. Steele, B. R., "Prospects for FiberReinforced Construction Materials,"Conference Proceedings, InternationalBuilding Exhibition, London, 1971,BRS Current Paper No. CP 17/72.

11. "Developments in Fiber Composite,"Precast Concrete, October, 1975.

12. "A Study of the Properties of Cern-Fil/OPC Composites," Building Re-search Establishment Current PaperCP38176. Copies available from Gem-Fit Corporation.

Discussion of this paper is invited.Please forward your discussion to PCIHeadquarters by November 1, 1977,


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Glass Fiber Reinforced Concrete Products