De e p - p rofile precast panels two stories tall and10 feet(1)† wide provide a curtain wall facing forthe Lu t h e ran Social Se rvices office building ad-dition built in Minneapolis during 1975.

T h e y ’re unusual: each panel weighs only 2000 pounds.( 2 )

A typical precast concrete panel in this design we i g h sabout 14,000 pounds.(3)

The high flexural strength of glass fiber re i n f o rc e dc o n c rete (GFRC)‡ made the dramatic weight saving pos-s i b l e. The panels are impre s s i vely strong despite the factthat ave rage thickness is only 3⁄4 i n c h .( 4 ) New on the con-s t ruction scene and still in the development stage, GFRCis described by one British re s e a rcher as “without doubtone of the major new material deve l o p m e n t s, if not themost important, to be re a l i zed during the past 40 to 50ye a r s.”

Mo re than 100 firms now manufacture the pro d u c tt h roughout the world. Most are in the U.S., Great Bri t a i nand Japan. Products now made commercially ra n g ef rom large building panels to livestock watering tro u g h s.So far, the two producers of alkali-resistant glass fiberswho license or control fiber sales to end-product manu-f a c t u rers are limiting recommended uses to modest,n o n s t ru c t u ral and semistru c t u ral applications. The twofiber producers are Owe n s - Co rning Fi b e rglas Co r p o ra-tion, To l e d o, Oh i o, and Pilkington Brothers Limited,England. Pilkington’s fibers are distributed in the Un i t-ed States by Ce m - Fil Co r p o ration, Na s h v i l l e, Te n n e s s e e(jointly owned by Pilkington and Fe r ro Co r p o ra t i o n ,C l e veland, Oh i o ) .

These two firms are conducting tests on the effectson GFRC of aging and we a t h e ring in va rious parts of theworld. Re s u l t s, as some test installations move into theirsixth and seventh ye a r s, are encouraging. Glass fiber en-gineers are likely to broaden recommendations to in-clude more demanding applications before too long;

Glass fiber reinforced concrete (GFRC)A new composite for construction

BY WALLACE NEAL*

FIBER REINFORCEMENT RESEARCH

Reinforcing a matrix with fibers isn’t new. Naturehas a good head start on us—beavers pack mud intointertwined branches to build their amazingly stronghouses and dams. Barn swallows, robins and otherbirds build sturdy little mud nests reinforced withstraw or twigs. Early man may have noted these bene-fits of reinforcement materials when he mixed straw in-to his sun-baked clay bricks and, more recently, whenhe mixed horsehair into plaster.

S t rengthening cement by adding fibers dates back to1908, when asbestos-cement entered the market. Thisf i b e r-cement composite soon became a major buildingp roduct because it overcame the main weakness of ce-ment products—brittleness. Reinforced concrete de-pends upon the addition of continuous re i n f o rc e m e n tsuch as steel rebars or welded wire fabric, to give itn e c e s s a ry tensile strength. Asbestos-cement, however,obtains strength from dispersed tiny fibers, so thatmaking thin board products, shingles, siding, pipe anda number of other products is possible.

The nature of asbestos-cement manufacture favorsmass factory production of standard shapes. The de-sire for a more versatile product, one that could evenbe field mixed and applied, as well as the recentstress on hazards of asbestos fibers have helpedstimulate accelerated research on other syntheticfibers for cement product reinforcement.

There were earlier effor ts, but serious syntheticfiber research really started in the late fifties and earlysixties, and commercial products and applicationshave only begun to appear in the last five or six years.

Researchers have evaluated a number of fibers, in-cluding carbon steel, stainless steel, carbon, variousplastics, rock wool and glass. The success of glassfiber reinforcement for plastics had made glass fibermixed into cement and concrete look like a winner. Re-searchers struck out when they first tried this, howev-er. Test samples were initially strong but the strengthdropped off as the samples aged because the highlyalkaline environment provided by portland cement at-tacked sur faces of the glass fibers.

In 1971, scientists at Pilkington and the BuildingResearch Establishment, also in England, announcedjoint development of an alkali-resistant glass fiber. Inthe U.S., Owens-Corning had developed an alkali-resis-tant fiber concurrently. The two firms subsequentlyworked out a technology exchange and both are doingcontinuing research on the fibers. Pilkington received“The Concrete Society Innovation Award” for 1974 forits work on the material.

* Wallace Neal is a professional freelance writer, consultant and researcherwith 24 years of construction industry background. His articles appear in anumber of construction and general business publications. He has been formany years an active member of the Minneapolis-St. Paul chapter of theConstruction Specification Institute.

† Numbers in parentheses refer to metric equivalents listed with this article.

‡ The proprietary initials “GRC” for “glass fiber reinforced cement” and thegeneric initials “FRC” for “fiber glass reinforced cement” have been widelyused for products made of fiber glass and cement, even when they containaggregate and are really concrete. In this article the initials “GFRC” will beused throughout to denote “glass fiber reinforced concrete,” although insome cases the products described may not actually contain any aggregate.

e ventual use for major load-bearing elements appearsimminent, if test results continue to be good.

Physical properties of GFRC

With the alkalinity problem apparently licked (seeb ox), re s e a rch has advanced on physical pro p e rties andapplications of glass fiber cement and concrete compos-i t e s. Pro p e rties va ry of course, depending on fiber con-tent, fiber size, fiber orientation, water-cement ra t i o,type of cement, use of aggre g a t e s, use of admixture s, andtechniques of mixing and application. In general, as acomposite GFRC has chara c t e ristics intermediate be-t ween the rigidity and compre s s i ve strength of cementand the high tensile strength of glass fiber. Typical phys-ical pro p e rties are shown in Table I.

Un d e r s t a n d a b l y, physical pro p e rties are stated con-s e rva t i vely and caution is used in recommending appli-c a t i o n s. Test results to date are ve ry good, both acceler-ated and real time. Unlike cement and concre t ep ro d u c t s, the strength of GFRC falls off after initial cur-ing, but the rate of loss decreases with time.

Ne ve rt h e l e s s, GFRC scores high enough in strength tosuggest many uses where its pro p e rties can be used toa d va n t a g e, even allowing ample safety factors. Its impactresistance is 20 times that of asbestos-cement. Gl a s sfiber re i n f o rced concrete offers two to three times thef l e x u ral strength of unre i n f o rced concre t e. Mo re ove r, them a t e rial under increasing load doesn’t fail abruptly butyields gra d u a l l y.

T h e o rists in the mechanics of cement and concre t esuggest tensile failure begins with micro c racks and mi-c roscopic separa t i o n s. These combine into a cohesivec rack, a weakness which quickly tra vels in brittle cement

and causes a break. The presence of glass fibers prov i d e sc rack arre s t e r s. When the first crack occurs in the matri x ,the strong fibers pick up the load. That support iss t ronger than the matrix itself, so the next crack must oc-cur elsewhere. Mo re loading adds only new cra c k s, im-mediately arrested, rather than causing first cracks top ro p a g a t e. Fa i l u re develops as a gradual, plastic-likeyielding. Fractus when fibers pull out or bre a k .

Composition of GFRC

Ge n e ra l l y, higher cement contents are used in ce-ment-sand mixtures and concretes that contain glassfiber re i n f o rcement than in those that do not, part i c u-larly when more than minimal amounts of fiber areadded. A lower content and smaller size of coarse aggre-gate in GFRC concrete is also typical. The GFRC mix iss t i f f e r, with less slump. Wo rkability thus decre a s e s. Si n c eaddition of excess water should be avoided because itp roduces weaker concre t e, water- reducing admixture sa re frequently used to ease placing and finishing. No r-mally Type I portland cement is used. Vi b ration is need-ed to consolidate the placed materi a l .

Fibers are normally supplied in either continuous orchopped stra n d s. GFRC producers who buy continuouss t rands use a ro t a ry-blade device to chop them into themix. A strand is usually a bundle of 204 individual fila-m e n t s, each of which is 0.0005 inch( 5 ) in diameter. Du eto the addition of sizing on the surfaces of the filamentsthey remain bound into a strand in the cement matri x .Ex p e riments with binders which permit filaments to beindividually dispersed have produced concrete withl ower physical pro p e rties and less work a b i l i t y.

Commonly used fiber lengths are 0.5, 1, 1.5, and 2i n c h e s.(6) Because batch mixing re q u i res use of short e rfibers to obtain more uniform fiber distribution, the 1-i n c h( 7 ) length is commonly used. Sp ra y-head mixing per-mits use of longer fibers, often the 1.5-inch( 8 ) length. On ep roducer has developed a spra y-head system which per-mits use of 4-inch( 9 ) f i b e r s.

Fl e x u ral strength of GFRC increases up to a fiber con-tent of about 7 percent by vo l u m e. As fiber content in-c re a s e s, density decreases because it is more difficult tocompact and dewater the mix. For most spra y- h e a d -mixed products glass fiber content is generally 4 to 5 per-cent. For batch-mixed products fiber content tends to bel e s s. Putting more fibers in a mixer makes it more diffi-cult to achieve completely unifo the fiber surf a c e s. Fo rbatch-mixed product applications, howe ve r, high fibercontent is often not critical. Often a desired pro p e rt ysuch as crack resistance is achieved with as little as 0.25p e rcent fiber content.

Production methods

T h ree practical methods are being used to pro d u c eG F RC .

Pre m i x i n g

Premix is simply batch-mixed GFRC, using conve n-

Property U.S. customary units SI metric units

Modulus of rupture 3000 to 4600 21 to 32

(ultimate flexural psi megapascals

strength)

Limit of

proportionality 1000 to 1600 7 to 11

(ultimate tensile psi megapascals

strength)

Compressive 7200 to 11,400 50 to 79

strength psi megapascals

57 to 143

Impact strength inch pounds 10,000 to 25,000

per square inch newtons per meter

Young’s modulus 1.5 to 3.0 x 106 10,500 to 20,500

(elasticity) psi megapascals

1.70 to 2.10

Density 105 to 130 pounds megagrams

per cubic foot per cubic meter

TABLE I. Typical ranges of physical properties at 28 days of GFRCapplied by direct spray

Source: Cem-Fil Corporation

tional concrete mixing equipment. It is the simplestp rocess and re q u i res minimal capital outlay. St re n g t hl e vels achieved are more modest than those with thes p ray pro c e s s e s, because high fiber concentration is dif-ficult and because the fibers become randomly ori e n t e din three dimensions. The premixed material is usuallyplaced into a mold and vibrated but it can altern a t i ve l ybe applied by trowel or spra y.

T h e re is experimental evidence that when coarse ag-g regate is used mixing and compaction may cause dam-age to fibers, decreasing the GFRC strength. To minimizethis possibility, the glass is added near the end of themixing cyc l e.

Automatic spray-suction pro c e s s

The second method is a spra y-head mixing pro c e s swhich can be adapted to continuous-line factory pro-duction. This automatic spra y-suction process consistsof spraying a fairly wet cement slurry and simultane-ously chopping fiber strands onto a perf o rated pan cov-e red with filter media. Suction re m oves excess water andhelps compact the material. The method produces two-dimensional fiber orientation, allows more fibers to be

used with good distribution, and permits use of longerf i b e r s. The result is a stronger composite. Sheet materi a lcan be made. The sheets are initially plastic but cohesiveenough to be lifted soon after making and shaped to amold. Profile suction molds can also be used.

Di re c t - s p ray mixing

The third method is a spra y-head mixing techniquesimilar to that used for re i n f o rced plastics. Not limited byv i b ra t o r-mounted casting molds or by suction machin-e ry, the dire c t - s p ray method is versatile and produces ap roduct with the strength advantages of automatics p ra y-suction process pro d u c t s. It is sophisticated buthas a broad range of applications, including large panelswith thin cross sections and complex pro f i l e s.

The dire c t - s p ray method warrants a more detailed de-s c ription because the end products can be va ried andcomplex. He re are the production steps used by one firmspecializing in the pro c e s s :

A glass-fiber- re i n f o rced plastic mold is made to the re-q u i red pattern and coated with a release agent. GFRC isapplied from a spray head that combines a cement-sands l u r ry gun and a glass fiber chopper. Typically the ap-plied thickness ave rages 3⁄8 to 3⁄4 i n c h .( 1 0 )

The mix is then compacted with a disc roller to re-m ove air bubbles and ensure that the material conform sto the mold. Anchors, inserts or re i n f o rcing steel areplaced, and over them additional material is spra ye dand rolled. An altern a t i ve technique is to spray up a flatsheet at the same time the mold is spra yed. The sheet isc o h e s i ve enough to be picked up and laid over the an-chors and re i n f o rcement. The sheet is formed to enve l o pthe re i n f o rcement and lap onto the original coat, and is

This 30-inch(33) GFRC sewer pipe has a straight exteriorand thin walls, yet meets strength requirements. Fieldtested, it is now marketed commercially in England.

Crews place a curtain wall panel of GFRC concrete 10 feetby 21 feet 6 inches(11) averaging 3⁄4 inch(4) in thickness andweighing 2000 pounds(32) on the Lutheran Social Servicesbuilding, Minneapolis. The panel has a deep shadow boxprofile with integral window frames in the recesses. Part ofthe tan colored surface is fluted and part is smooth.

Photo courtesy of Cem-Fil Corporation Photo courtesy of Glas-Con Inc.

then rolled to bond the two layers together.The completed section is cured in the mold for about

16 hours, then stripped and moist cured in polye t h y l-ene wrapping for 7 days.

Applications

The cost of GFRC by the cubic yard is not low becauseadding glass fiber to a cubic yard of concrete canq u a d ruple its raw material cost. Producing GFRC is atleast as labor intensive as producing regular concre t ep ro d u c t s. A typical thin-wall GFRC product may cost$4.00 to $8.00 per square foot.( 1 1 )

Sh a p e, aesthetics, surface chara c t e ristics and we i g h tsavings are what make GFRC an ideal product for somekinds of applications. For these, despite its bulk cost,G F RC can offer savings in cost.

Adding glass fiber to cement creates a compositewhich can be molded in fine detail. Co rners and thinsections have high impacchipping, making fine detailingp ractical. The molded surface of GFRC is smooth, aes-thetically pleasing, easy to maintain and resistant to wa-ter penetra t i o n .

G F RC ’s high flexural strength makes possible deep-p rofile concrete shapes made with thin-wall sections, sothat hollowed-out units can be made. This adva n t a g e

can be utilized, for example, in the sculptured facadecladding of a building to eliminate the mass otherw i s eneeded for deep relief in ord i n a ry concre t e.

In the Lu t h e ran Social Se rvices building mentionedin the beginning of this art i c l e, GFRC panels we i g h e do n e - s e venth what arc h i t e c t u ral precast concrete sec-tions would have. Those panels, typically 10 feet by 21feet 6 inches( 1 2 ) we re re m oved from molds and handled inthe shop with an ord i n a ry fork lift truck. The plasticmolds themselves we re re l a t i vely light. Ma s s i ve form swould have been needed for regular deep-section pre-cast panels which would have had to be about 6 inches( 1 3 )

thick. The 7-ton( 1 4 ) cast sections would have re q u i re dh e a v y-duty cast-in attachments for lifting, and could noth a ve been handled by a light-duty cra n e.

G F RC offers the architect freedom to design complexshapes in larg e, light sections with the option of usingcolor and texture and achieving fine detail. Molds aresufficiently inexpensive to justify reusing them the limit-ed number of times re q u i red by a small project. Sa n d-wich panels with foam insulation are easily made.

The tendency tow a rd shrinkage cracking is greatly re-duced in GFRC. For this reason it has been used for sep-tic tanks, burial va u l t s, picnic tables and tra n s f o rm e rp a d s. Co n c rete industrial floors up to 100 feet( 1 5 ) in length

The worker is securing a 115-pound(34) GFRC curtain wall panel to the building frame by welding. An unerected panel is inforeground. Structure is an office-retail shops building in Dayton, Ohio.

Photo courtesy of Owens-Corning Fiberglas Corporation

h a ve been successfully placed without contra c t i o nj o i n t s.

Specific examples of some of the other va ried appli-cations for GFRC are given in Table II. Some have beenp roduced pri m a rily for field testing. Others have beenp roduced commerc i a l l y.

Future uses of GFRC

The GFRC industry is enthusiastic but cautious inspeaking of future applications of this composite. Thei n d u s t ry is not just waiting for time-related data; furt h e rtesting under stress conditions and other re s e a rch has tobe conducted, and it is anticipated that it may be thre eor four years at least before the industry can commit it-self to promoting purely stru c t u ral uses, depending onwhat happens in testing. Va rious firms are now buildings t ru c t u ral prototypes for testing and evaluating, includ-ing a shell roof stru c t u re in Ge rm a n y.

If no snags occur in the continuing development ofG F RC, we may see some interesting products in a fewye a r s. Some of those listed in Table III are already underd e ve l o p m e n t .

Design precautions

While using engineering calculations based on pub-lished physical pro p e rties and applying suitable safetyfactors may be adequate for established materi a l s, de-velopment of GFRC applications which are at all cri t i c a lor dependent on stru c t u ral behavior should pro c e e dm o re conserva t i ve l y. An essential first step should be toconsult with a GFRC producer because each pro d u c e rhas a close working relationship with the re s e a rch labs ofa fiber manufacture r. Products which will be exposed towind loads and other stre s s e s, such as building panels,should be load tested.

Drying shrinkage and moisture-induced expansion is

g reater in GFRC than in ord i n a ry concre t e. Mo i s t u re - vo l-ume change will tend to dictate maximum dimensions.Jointing and anchoring must allow for such move m e n t .

The wall thickness of dire c t - s p ra yed GFRC should bekept to a minimum, for economy in weight and materi-al. A practical ave rage thickness may be 3⁄8 to 3⁄4 i n c h(10) d e-pending on application, allowing for minimums due tos u rface va riations of from 1⁄4 to 1⁄2 i n c h .( 1 6 ) Stiffness is thenp rov i d e d n s, contours or attached studs.

Because GFRC panels are thin in contrast to pre c a s tc o n c rete sections they can warp more readily if designedi m p ro p e r l y. For example, applying an impervious coat-

This hollow GFRC base being lowered into an excavationwill support pad-mounted electrical gear at approximatelyground level. Such units will support up to 7500 pounds(25) ofequipment.

TABLE II. SOME VARIEDAPPLICATIONS OF GFRC

Sewer pipe: No steel; thin walls; in-wall joint, not belljoint

Retaining walls: Made of hollow hexagonal GFRC unitslinked by steel bars

Coffer units: Integral forms for wide-span structuralconcrete floor

Corrugated sheets: Integral forms for bridge deck

Sewer liner: Thin, grooved curved sheets assembledwith bolts to make jointed tube liner for deterioratedsewer. Grout pumped through holes in liner to fill be-tween it and existing sewer

Ventilation ducts: For underground parking structure.Wall thickness varied from 1⁄2 to 1 inch.(18) Ducts de-signed to withstand impact of car at 5 miles per hour(19)

Precast trench lids: 3⁄4 by 20 by 32 inches,(20) weighing50 pounds,(21) compared with 125 pounds(22) for con-crete lids

Equipment bases: For electrical industr y. Up to 30inches by 6 feet by 6 feet(23) with 5⁄8-inch(24) walls, to sup-port equipment weighing up to 7500 pounds(25)

Pavement overlays: Test slabs for highways and run-ways. 6-inch-thick(26) GFRC slab equivalent in perfor-mance (in test slabs in Texas and Ohio) to 8-inch-thick(27) steel-reinforced concrete

Fire-resistant coverings: 3⁄8-inch-thick(28) GFRC integralform used to cast 8-inch-square(29) reinforced concretecolumn. In Building Research Establishment (England)fire test, the column sustained its load 100 minutescompared with 40 minutes for a column cast in woodforms. Improved fire resistance attributed to preven-tion of spalling over rebars at corners

Artificial rock: For zoos, marine aquariums, and simi-lar exhibits. Actual rock formations utilized to createthe molds used

Simulated wood shake roofing shingles: 5⁄8- by 15- by36-inch(30) panels made by replica molding

Marine uses: Schooner, workboats, pontoons, buoys

Miscellaneous: Acoustic foam-lined trough for air con-ditioner, infant caskets and vaults, planters, litter bins,picnic tables, street signs, junction boxes, wheels fortraffic striping, watering troughs for livestock

ing to one side may create an imbalance in moisture - i n-duced movement. Thermal expansion and contra c t i o nof GFRC is similar to that of ord i n a ry concre t e. It is pos-s i b l e, howe ve r, that a ve ry large sandwich panel with in-sulation core could bow due to tempera t u re extre m e sb e t ween inner and outer surf a c e s, intensified by the in-s u l a t i o n .

One fiber producer cautions against the embedmentof large or long sections of rebar or other steel intoG F RC, saying it may cause distortion or cracking due tothe shrinkage of the concre t e. They recommend castingin attachment sockets and keeping the large metal sec-tions external to the panel.

Bridging of fibers has been a potential problem whens p raying into sharp angles, fine pro j e c t i o n s, gro oves ors l o t s, or spraying around inserts such as sockets. Fi b e r sb ridge across narrowly spaced points and don’t re c e i vean adequate cover of cement matrix. Weakness results insuch are a s. This may be dealt with to some extent by carein spraying and rolling. Recent re s e a rch to create a soft-er fiber may lead to reduced bridging pro b l e m s.

Specifying GFRC

A perf o rmance approach to specifying GFRC buildingcomponents is appro p ri a t e. Specifiers should tolera t ep re f e rences in production, stru c t u ral design, anchora g eand erection techniques. This may be done by statings t ru c t u ral and aesthetic results to be achieved and byre q u i ring complete details in shop dra w i n g s. Re q u i re dsubmittals should also include ra n g e - b racketing sam-ples for color and texture. Load tests on each typicalpanel or similar GFRC component should be re q u i re d .

The panel specification section should include cast-ina n c h o r s, related loose anchorage part s, cast-in lifting in-s e rts if re q u i red, and erection as responsibilities of the

panel contractor or manufacture r. Items to be specifiedin other sections include stru c t u ral support, fra m i n gand backup walls, anchors embedded in the stru c t u re,caulking and final cleaning and pro t e c t i o n .

Outlook

G F RC is on the scene. Although a new arri val, futuresuccess seems assured, enhanced by its pare n t a g e. Thep roduct is being carefully shepherded by the two sub-stantial corporations who developed and produce thea l k a l i - resistant glass fiber: Owe n s - Co rning and Pilking-ton. Both companies have conducted much re s e a rch onG F RC and are actively continuing product deve l o p m e n tand eva l u a t i o n .

A va riety of construction industry products has beenmade of GFRC with the major volume emphasis beingon building panels. Even as testing continues, cautiousc o n s i d e ration of new more demanding uses is likelyw h e re there are cost or strength advantages despite ahigh raw material pri c e. In the future, the cost FRC andc o n ventional materials may possibly narrow, openingup broader applications.

Editor’s note:This article has been reprinted by permission of the Con-struction Specifications Institute, 1150 Seventeenth Street,N.W., Washington, D.C. 20036. It originally appeared in TheConstruction Specifier, March 1977, pages 20-23, 26-28,30-32.

Metric equivalents(1) 3 meters (19) 8 kilometers per hour

(2) 910 kilograms (20) 19 by 510 by 810 millimeters

(3) 6350 kilograms (21) 22.5 kilograms

(4) 19 millimeters (22) 57 kilograms

(5) 0.013 millimeters (23) 0.760 by 1.83 by 1.83 meters

(6) 13, 25, 38 and 51 millimeters (24) 16-millimeter

(7) 25-millimeter (25) 3400 kilograms

(8) 38-millimeter (26) 150-millimeter-thick

(9) 100-millimeter (27) 200-millimeter-thick

(10) 10 to 19 millimeters (28) 9-millimeter-thick

(11) $43 to $86 per square meter (29) 200-millimeter-square

(12) 3.05 by 6.55 meters (30) 16- by 380- by 915-millimeter

(13) 150 millimeters (31) 8.5-meter-diameter

(14) 6.4-megagram (32) 910 kilograms

(15) 30 meters (33) 760-millimeter

(16) 6 to 13 millimeters (34) 52-kilogram

(17) 125 millimeters

(18) 13 to 25 millimeters

TABLE III. SOME POSSIBLEFUTURE USES OF GFRC

Large shell structures: Prototype 28-foot-diameter(31)

domes 10 feet(1) high placed on membrane that is laterinflated by air

Modular housing units: Especially for developingc o u n t r i e s

Plaster repair coats: For deteriorating concrete struc-tures. Test installations made on locks and dams

Accurate replicas: To reproduce deteriorating decora-tive features of historic buildings, such as metaldraperies, flowers and gargoyles. Plastic molds can bemade directly from existing pieces

Extruded window sills and copings: Extrusion processreorients fibers parallel to axis of extrusion and im-proves flexural strength. Some cross-sectional shapesthat cannot be cast can be extruded

Miscellaneous: Pedestrian skyway bridge enclosures,acoustical ceiling panels, roof decks, roof tiles, trans-mission towers, light standards, pools and foundations

P U B L I C AT I O N# C 7 8 0 6 4 4

Copyright © 1978, The Aberdeen Gro u p

All rights re s e r v e d