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Developments in building materialsP. J. SeredaPublished online: 15 Apr 2008.

To cite this article: P. J. Sereda (1974) Developments in building materials, Building Research and Practice, 2:6, 329-335, DOI:10.1080/09613217408550343

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Developments inbuilding materials

by P. J . Sereda UDC 691.001.5 CI/SfB a

This brief survey of some recent developments in building materials and productsrelates largely to the North American scene and is by the head of the InorganicMaterials Section of the Division of Building Research in Canada, Problems ofpollution control, energy costs and performance criteria will influence future trends,he suggests.

Consideration of the source of the raw material fromwhich a new product is to be made may well becomea greater factor than Jow cost in the future. Forexample, current and future fuel shortages for energyproduction put all materials produced from hydro-carbons in jeopardy, including most plastics andasphalt-based materials. The fact that some sourcematerials are non-renewable and even now in limitedsupply will undoubtedly place a great constraint onthe development and production of certain products.The question of pollution by gaseous and solid by-products is also now a social and political problemand will probably play an important role in decisionsregarding the development of new materials. Theproblem of fire is also of prime importance, particu-larly with the advent of high-rise buildings, which alsorequire a higher degree of sound insulation than wastraditionally required.

Wood and metals in buildingAlthough considerable development has taken placein these major classes of traditional materials, it willnot be possible to deal with them in this paper.Wood has been the chief building material in Canadafor over a century and is still very important, althoughnot necessarily in traditional form or for traditionaluse.Nature has formed wood as a composite, tailor-madeto meet the specific requirements of the stem of a tree.Man takes advantage of this property when he uses itas a structural material. To decrease the effect of thenon-isotropic nature of the material, plywood hasbeen developed as well as a variety of glued laminatesthat exploit designs for maximum strength andrigidity while minimising dimensional instability.Finally, as the supply of wood has diminished, it hasbecome increasingly important to make full use of theentire log. Waste material such as sawdust and woodchips in lumbering and lignin in papermaking have

The two articles that follow - by Dr P. J.Sereda and Professor B. Givoni - areabridged versions of papers presented atthe NBRI Building Research Congressheld in Durban, South Africa, last May.

Building Research and Practice Nov/Dec 1974

been recombined to produce chipboard, a processdeveloped in Canada by the Forest Products Labora-tory in recent years.Building products made from metal are currently alsoundergoing considerable design development in aneffort to make better use of sheet metal for structuralelements where wood was used previously. Improve-ments have been significant; for example, corrosionresistance has been improved by a variety of new alloysand surface treatments, including prepainting of rolledsheet stock.

Bright future for cement

Cements, for the purpose of this paper, include allinorganic binding materials: Portland cement, lime,gypsum, magnesium oxychloride cement, aluminacements and variations to produce special purposecements. It should be noted that concrete made fromPortland cement is used more widely than any otherman-made material, amounting to about one ton percapita (world). This fact alone makes it a mostimportant building material, but other attributes -low cost, inexhaustible raw materials, fire resistance,good sound insulation, low pollution, great versatility,and the fact that low-grade fuel (garbage) can be usedfor its production - account for active developmentand support the idea that future work must considerit as the basic material.

High early strength cementConsiderable success has been achieved in producingcements that give high early strength, largely byproducing finer ground cement and increasing theC3S content (ref 1). Various .chemical admixtureshave also improved early strength. Active research isunder way to improve the reactivity of basic cementconstituents by the addition of certain ions such aschromium at the clinkering stage. It may be possibleto make the C3S component in cement more reactiveby the addition of certain ions. It can be expectedthat considerable progress will be made in this regard.

Regulated-set cementDeveloped by Portland Cement Association (USA),this cement incorporates a compound, CnA7 CaF2,that is added to normal portland cement in amounts

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DEVELOPMENTS IN BUILDING MATERIALS/continued

of up to 50 per cent. One-hour strength can rangefrom 200 psi at 5 per cent addition to over 3000 psiat 50 per cent addition. There are various applicationswhere the added cost of this cement will be justified,especially in repair work of highway bridges, etc.Citric acid is used as an admixture to control handlingtime. Handling time of from one to 45 minutes canbe obtained without the admixture, but addition of0-5 per cent citric acid by weight of regulated-setcement can extend the time to two hours.Concrete made with regulated-set cement is verysimilar in its general behaviour to normal Portlandcement concrete. It is used in highway and bridgerepair, lightweight insulating concrete for roof decks,concrete pipe, shotcrete tunnel linings, and applica-tion as a mortar for pre-assembly of masonry panels.

Shrinking-compensating cements

A serious limitation of concrete has been its dryingshrinkage. Coupled with low tensile strength, thisresults in cracking, but it can be prevented by subject-ing the concrete to compressive stresses. A compres-sive stress in concrete can be imposed by pre-tension-ing the reinforcement which results when concretehas a potential to expand during setting. The actionof shrinkage compensating cement accomplishes thisresult if the concrete has suitable reinforcing, with atleast 0.15 per cent steel suitably placed to restrainexpansion in each direction. The level of compressivestress required in shrinkage-compensating concrete isfrom 25 to 100 psi. As the amount of prestressdeveloped increases to 500 psi the concrete becomesself-stressed.

Three types of shrinkage-compensating cements areproduced commercially. They are designated by AC1(ref 2) as types K, M, and S. The expansive productformed during hydration is 'ettringite' (3 CaO.A12O3. 3CasO4.32H2O). The source of the aluminatein type K is anhydrous calcium aluminosulphate(C4A3S); in type M cement it is calcium aluminate(CA and C12A7); and in type S it is tricalciumaluminate (C3A). The other constituents in all threetypes are normal portland cement and gypsum.Many cases have been documented where shrinkage-compensating cement has been used in construction inrecent years (ref 3). The world's largest parkingstructure at O'Hare International Airport in Chicagocalled for about 120 000 cubic yards of shrinkage-compensating concrete. This six-level structure ismore than a quarter of a mile across and is designedto accommodate 9500 vehicles. The main purpose inusing this type of concrete in such structures is toprevent cracks in the floor slabs and thus to avoidleakage of water carrying de-icing salts and other

materials leached on to parked cars. This type ofconcrete has been very successful in floors of multi-purpose arenas, tennis courts, etc.Cost of the three types of shrinkage-compensatingcement is about 50 per cent higher than that ofPortland cement. It is argued that this extra cost isoffset by savings in construction and maintenance,and improved performance of the finished product.

Use of by-productsBlastfurnace slag cement has been used for some timeand much work on this development has been done inSouth Africa. World production of iron in 1969 was630.4 million tons, and quantities of slag and ironare nearly equal. Although a small amount of slagis used to produce cements, it is believed that muchmore will be used in the future (ref 4).Fly-ash has also been used as a cementing ingredientacting as a pozzolanic material. More recently, it hasbeen recognised as a binder with lime during auto-claving for the production of brick and tile. Inter-national Brick and Tile Co. Ltd., located nearEdmonton, Alberta, has begun operations designedto produce 6.25 million units annually.Ontario Hydro also has recently commissioned a fly-ash processing plant at Mississauga, Ontario, to makepozzolana cement; and a number of cement manu-facturers are beginning to market portland cementwith fly-ash intermixed. (There are indications thatreactivity might be improved by better control of theprocess producing the fly-ash.) It is clear that muchmore fly-ash will be used in such applications, notsimply to make use of a waste material but also togain the advantages that can be realised in variouscementitious building materials by the addition of thistype of product, e.g. increased stability, chemicalresistance and improved workability.Phospho-gypsum, a by-product of phosphoric acidproduction, constitutes a substantial potential sourceof gypsum for the production of plaster products andfor manufacturing portland cement. Development inthis area should be significant in the near future(ref 5).

Sulphur has recently become a by-product of con-siderable importance because it must be removed fromnatural gas prior to pipeline transmission and, insome cases, to meet anti-pollution legislation.Additional large tonnages of sulphur come from thesmelting of sulphide ores. At present, Canada has aninventory of over 10 million long tons (ref 6). It wasbecause of this surplus that the Sulphur DevelopmentInstitute was founded in 1973 to direct funds fromgovernment and industry into research on new usesfor sulphur. One project involves use as a binder (inplace of portland cement) for production of sulphur-

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base concrete (sulphurcrete), made possible by thelow cost of sulphur (about 6 dollars a long ton f.o.b.Alberta).It is not yet certain whether this use of sulphur(available as a pure element) is justified where itmerely replaces a satisfactory building material basedon Portland cement, for which raw materials arevirtually inexhaustible, not to mention other ad-vantages of fire resistance and established technology.On the other hand, sulphur has been foamed toproduce thermal insulation in the ground, and thisappears to be a potentially useful development fornorthern climates.

New concretes and aggregatesConcrete is a composite in which fine and coarseaggregates are bonded by inorganic cements, oftenreinforced by steel. Pre-stressing is merely a sophisti-cation of the reinforcement. Whether the material iscast /"/; situ in forms or precast in suitable sections forlater assembly on site is a question of variation inexecution rather than material. It is evident that thebasic material, concrete, is undergoing significantdevelopment (ref 7) in response to demands fortailor-made materials to meet set requirements and loavoid problems with conventional materials. Thesechanges are taking place in the cements and in theaggregates, as well as in reinforcing materials.Aggregates from blastfurnace slag and expanded clayor shale are well established and represent productionof over 15 million tons annually in the USA. To thesemay be added a more recent development usingsintered, extruded,- or pelletised fly-ash. Produced inthe first instance as a solid by-product (waste) fromcoal-fired power stations, this material has shown theway concrete can be adapted to utilise to advantagea material that would otherwise be superfluous andpose a problem of solid-waste disposal.It does not follow that concrete can be a disposalreservoir for any solid waste. What should berecognised and fully exploited is the fact that con-cretes with different specific properties are requiredfor various applications, and that suitable concretescan be produced by using various types of syntheticaggregate and cement. These, in turn, can often beproduced from solid by-products (wastes). Wheresuch matching of requirements and properties can beachieved, great economic and social benefits canresult. A recent development in Canada has involvedpuffed and carbonised wheat as a lightweight aggregatein concrete. Such use is, however, in competition withfood needs, which will continue to grow as thepopulation increases. In any event, it is an expensiveway of incorporating voids in concrete, since this ismainly what it does.

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The effect of steel fibres on the fracture toughness ofconcrete.

Reinforcing materialsThere has been considerable development in theproduction of fibre-reinforced concrete incorporatingrandomly distributed, discrete, short, discontinuousfibres. These fibres may be metals, minerals ororganic materials. Mortar employing a high contentof small-diameter wire-mesh as reinforcing, calledferrocement, has received a great deal of attention inrecent years, its chief object being the production ofa low-cost concrete composite with specific propertiesfor particular applications. It has been shown thatimpact resistance can be increased 10 to 25 times by theuse of polypropylene and nylon fibres as reinforce-ment, although the strength of such concrete isactually decreased.The most important development involves the use oflow carbon steel fibres produced by shearing flatsheets. These fibres are 8 to 16 by 10 to 25 mils incross-section and half to two inches in length, havingan aspect ratio of about 30 to 150. Aspect ratio ofabout 100, length of about one inch, and volumefraction of about 2 per cent by volume are the mostcommon proportions tried in field applications. Thechief advantage of this type of reinforcement is theincrease in fracture toughness.Steel-fibre-reinforced concrete is being applied assurfacing for bridge decks and airport runways whereits advantages can be fully utilised, a developmentlargely credited to Battelle Memorial Institute. TheBritish Building Research Establishment also has hadreasonable success with the development of glass fibre.Glass has been produced with high resistance toalkali and can be used in place of asbestos for makingsheet materials from cement with glass fibre re-inforcing.

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DEVELOPMENTS IN BUILDING MATERIALS/continued

Polymer-impregnated concrete

Development of concrete with superior chemicalresistance has been stimulated by the special require-ments of water desalination plants and bridge decks,where de-icing salts can cause serious deterioration ofnormal reinforced concrete. Since 1966 the Bureauof Reclamation and Brookhaven National Laboratory(USA) have combined to develop polymer-impreg-nated concrete as a new building material. Details ofthis development are contained in four topical reports(refs 8, 9, 10, 11). In principle, dry concrete is im-pregnated by various monomers containing chemicalpromoters, resulting in polymerisation in situ. Suchmonomers - for example, methyl methacrylate,styrene, acrylonitrile, chlorostyrene, trimethylol pro-pane trimethyl-acrylate and polyester-styrene (10 to90 per cent) - have low viscosities and under vacuumreadily fill the voids in concrete.The significant virtue of the system may be thepossibility that, where deterioration has begun,normal concrete could be restored to good conditionby this means. Extensive research is under way,aimed at the restoration of concrete bridge deckswhere various stages of deterioration have occurred.Polymer-impregnated concrete has many advantagesover normal concrete, but the most important may beits increased durability under severe exposure con-ditions. It has not yet been proved conclusively thatthe advantage in durability indicated by variousaccelerated tests will be fully borne out by serviceperformance. A number of applications are currentlyunder investigation, however, including a precas'ttunnel support and lining system, concrete pipe,multi-stage flash distillation vessels for desalination ofwater, and precast bridge deck slabs.A variation of the system involves the use of so-calledpolymer-concrete (PC), in which aggregate andmonomer are mixed together and the monomer ispolymerised following placement. Recent develop-ment work with PC has shown that the material iseasily fabricated, that the processing cost should bemuch lower than that of polymer-impregnatedconcrete, and that many of the properties are com-parable.

Solid wasteSociety has at last realised that solid waste in garbage,which represents about 1500 lb per capita, must beconsidered for recovery of fuel potential and forrecycling of usable constituents. Fuel content is nowbeing recovered in a limited number of plants forcentral district heating, and attempts are being madeto use it in a cement kiln in the Kingston area The

solid residue from incinerated garbage contains about44 per cent glass. The possibility of using it as thebasis for new materials is the subject of much currentstudy in North America.Investigation of uses for solid waste began with thepassing by the US Congress of the Solid WasteDisposal Act of 1965. It provides grants for researchtotalling over 25 million dollars through the PublicHealth Service, which has established the Environ-mental Protection Agency and its Bureau of SolidWaste Management, Rockville, Maryland. In Canadaan institute has been set up at the University ofSherbrooke, Quebec, under the name, Potential Usesfor Discarded or Detrimental Industrial and NaturalGarbage (PUDDING). The chief chemical, physicaland mechanical characteristics of waste materials willbe assessed and their economic use examined.In 1969 T-A Materials Inc., Palisades Park, NewJersey, was founded and developed a 'Tech Process'for the production of bricks out of any inorganicmineral or mineral waste. Cement is used as binderand the unit is made under high pressure. RecentlyInternational Brick and Tile Co. Ltd. was founded toproduce bricks from fly-ash based on a processdeveloped by the Coal Research Bureau of theUniversity of West Virginia.Various new building materials have been developedfrom waste glass. One such material is used in theproduction of glass-clay mosaics and tiles (ref 12).Another development uses glass as a binder for solidwaste materials (ref 13). It is believed that theseprocesses for the re-use of glass hold greater promiseof success than those involving portland cement asbinder, because the problem of reaction of glass withthe alkali of cement may be difficult to solve.

Advances in brick masonryContrary to recent predictions that brick masonrywould disappear as an economic construction materialowing to high labour costs in Canada, the brickindustry is experiencing a boom. One reason for thisis the development of the through-the-wall (TTW)brick unit and the introduction of structural brickmasonry. Although the structural brick unit currentlydesignated as TTW was developed in 1952 by theStructural Clay Products Research Foundation inthe USA, its large-scale use in structural brickmasonry for buildings over 10 storeys in height beganin Canada only in 1967, encouraged in part by theacceptance of engineered masonry by the NationalBuilding Code.

TTW bricks are modular in size and designed toprovide in one unit the required thickness of a wall,

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WOOD NAILER'AT CEILING

exclusive of finishing. Length is nominally 12 inchesand width either 6 or 8 inches. Height is 2\ inches.In recent years other sizes of units have been produced,so that a range of choices is available.The main economic advantage of structural masonrywalls is the elimination of a structural frame ofreinforced concrete or steel. In structural masonry,however, crosswalls and rigid floor elements arerequired to provide the necessary rigidity to thestructure. Connections between cross-walls andperimeter walls are made by means of heavy steel tiesrather than by brick bonding units. Walls of structuralTTW brickwork generally require bricks exceeding8000 psi compressive strength, laid in strong mortarsuch as Type M or Type S, CSA Specification A179.The success of structural brickwork is attributed tothe system of building that has been developed for it.The masonry walls are constructed one storey heightat a time, and the floor as a concrete slab of reinforcedconcrete, precast or cast in situ, is placed on top andthe process repeated. The two operations are carriedout by two separate crews of labourers in a 'flip-flop'sequence, on one half of the building the walls areerected while on the other half the floor is placed.Possibly the most serious concern with this con-struction is the potential rain leakage problem. It hasbeen largely solved by parging the back face of themasonry and installing rigid cellular insulation.When this system of construction is used in earthquakezones, walls require reinforcing. This is provided inthe cores of the masonry units and bonded by mortar.

Plastics in buildingsMost developments involving the use of plastics inbuildings can be considered to be of recent origin forthe purposes of this paper. Thus, their service recordis too short to allow for total prediction of per-formance. The following is a list of items whereplastics are used in buildings (ref 14).

water pipes, DWV goods and underground drain-pipes - rigid PVC.'hard' floor coverings - plasticised PVC'soft' floor-coverings - flexible foams and syntheticfibresdecorative wall coverings - plasticised PVCexternal claddings - GRP or rigid PVCwindow frames - GRP or PVCsanitary ware - acrylics, GRPhard wall coverings and working surfaces - mela-mine/PF laminatessmall engineering items - nylon, polyacetalspecial glazing materials - acrylics, rigid PVC, andpolycarbonates

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S O U R C E : M O D E R N P L A S T I C S A N D I N D U S T R YE S T I M A T E S .

a - I n c l u d e s s i d i n g , c l a d d i n g , p a n e l s , d o o r s ,w i n d o w c o m p o n e n t s , e t c .

b - I n c l u d e s p i p i n g , w i r i n g , b a t h r o o m u n i t s ,l i g h t i n g , e t c .

c - I n c l u d e s w a l l c o v e r i n g s , f l o o r i n g ,i n s u l a t i o n , m o u l d e d t r i m a n d d e c o r a t i v ee x t r u s i o n s , l a m i n a t e s , p a n e l s , e t c .

Top, construction technique for an exterior wall usingthe modular TTW 'through-the-walls' brick, nowincreasingly popular in North America.

Above, statistics on the projected use of plastics inbuilding in the USA.

pre-formed sealing materials - neoprene and othersynthetic rubbers.mastics and sealants - polysulphides, silicones andpolyurethanesenclosure materials and general purpose sheetings -polythene and PVC sheetinsulants - polyurethane, polystyrene and urea-formaldehyde foams

Plastics amount to less than 0.5 per cent of the totalof all materials used in construction (2.2 millionmetric tons of resins) (refs 15, 16). It may be notedthat developments in plastics have in some measure

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DEVELOPMENTS IN BUILDING MATERIALS/continued

been a response to demands for tailor-made materialsfor specific uses. Where development was carried outin response to clearly stated requirements, and wherecost was not a limitation, such materials have meteven the most stringent requirements. One need onlycite the example of space technology for confirmation.Unfortunately, however, developments in plastics forconstruction have been restricted by cost, since plasticproducts must compete with other materials. Fre-quently, serious requirements such as safety from fireand smoke have been compromised. This aspectculminated in 1973 when the Federal Trade Com-mission, USA, announced that it planned to issue acomplaint against ASTM and the Society of PlasticsIndustry and 26 companies in the plastics field,claiming they knew but had failed to disclose thefiammability characteristics of polystyrene andurethane foam.

The problem of fire and plastics has become evenmore serious as more and more high-rise buildings areconstructed. Because high-rise buildings cannot beevacuated in the event of fire, smoke must be kept outof all areas likely to be occupied during a fire. Itwould be desirable to restrict from use materials thatproduce smoke and toxic gases. From this standpointplastic materials require much further development.It should be stated that production of plastics relieslargely upon raw materials from petroleum sourcesand that it will therefore be in competition withenergy needs. This may well become a seriousconsideration affecting future development of suchmaterials.

Glass-reinforced polyester (GRP)GRP is a glass-plastic composite of classic designproviding a rigid sheet material of minimum thickness.In 1969 West Europe used 83 000 tons in building andconstruction and the USA 56 000 tons (ref 17). Mostof this was translucent sheeting. In 1971 the USAused 79 000 tons in construction, but this amountwas only about 0-1 per cent of the total cement used.One of the chief drawbacks with plastics has been aninability to automate the production of GRP sheetmaterial.Recently, however, there has been a great advance inthis area, and sheet moulding compounds (SMC)have become available that can be handled by thefabricator in much the same way as metals. Sheetmoulding compounds are a complete blend containingcatalysed polyester resin, chopped glass strandreinforcement, pigments, fillers and thickeners. Theyare in sheet form, typically an eighth of an inch thickby 4 ft wide, packed in rolls between films of poly-ethylene. The fabricator can cut the pieces to thedesired size, load them into a press and mould them.

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Test results on plastics. Top, loss of light transmissionof GRP roof lights and, above, absorbence of PVC sheetexposed to fluorescent sunlamp.

The shelf life of SMC is about three months (ref 18).It seems reasonable to expect that glass-reinforcedpolyester will bring about a significant change inconstruction, since it offers the opportunity toexploit the virtues of prefabrication and factory-builthomes. A number of successful applications of sand-wich panels construction are already being introducedinto buildings for assembly in remote areas such asthe Canadian North. The most reliable appear to bebased on a design in which GRP is used as interiorand exterior membranes on a polyurethane core in aprefabricated sandwich panel mounted on a steelstructural frame. These panels incorporate windowsand doors and are designed to provide certainarchitectural features. The exterior finish can in-corporate prefinished coatings that should provideadequate durability for low maintenance cost.There is about ten years' experience of serviceperformance of GRP in both Canada and the UK.Some difficulty has been experienced with pop-outs ofglass fibres near the surface of GRP, but this failurehas been attributed to fatigue resulting from cycling

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moisture and temperature (ref 19). In addition,surface micro-cracking has been attributed to UVradiation (ref 20). These types of failure show up alsoas decreased light transmission and absorbance (ref21). Attempts are being made to overcome suchshortcomings by various coatings applied to thesurface, and there is justifiable expectation that theseproblems will be solved.Attempts have also been made to produce sandwichpanels of GRP for a complete wall of a one-storeyhouse. A similar panel has been designed to serve asa roof section. Integral joints between panels of wallsand roofs are made by field application of polyesterand glass lay-up. Such a design system still suffersfrom problems of thermal movements transferred tointerior partitions. If such movements were permittedto be taken up by each joint between panels, theproblem would be transferred to the joint material,i.e. to the sealant. To date, however, there do notseem to be fully successful systems using panels ofGRP for walls and roofs without a structural frameagainst which an assembly of panels with suitablejoints can be made.

Foamed plastic insulationThermal insulation is essential for northern climates.Recent developments of various types of foamed orcellular plastic insulation have proved to be mostuseful. Polystyrene, polyurethane, and PVC are theprincipal types available. They are commonlyprovided in sheets one to two inches thick, and areattached to the exterior of the structural part of thewall by means of adhesive. Several plastics areadaptable for foaming in situ. Polyurethanes areusually applied in this way, but because of their goodbonding properties they can be used as core materialsin sandwich-type panels as well. This application wasbriefly described in connection with GRP panels. Arecent application of foamed plastic insulation hasbeen in road construction to prevent frost heaving ofcertain types of sub-soil. It is being tested in the FarNorth where the insulation prevents melting of thepermafrost, and can be used in lieu of heavy coursesof gravel, which is often hard to find.

4 GUTT, w. 'Manufacture of cement from industrialby-products'. Chemistry and Industry. 13 Feb. 1971,pp. 189-97.

5 GUTT, vv., and SMITH, M. A. 'Utilisation of by-productcalcium sulphate'. Chemistry and Industry. 7 July 1973,pp. 610-19.

6 PEARSE, G. H. K. 'Sulphur'. Canadian Minerals Yearbook1972. Department of Energy. Mines and Resources,Mineral Resources Branch, Ottawa, Canada.

7 SHAW, s. P. 'Mineral, organic or metallic fiber re-inforced concrete'. Proceedings. Conference held atthe University of Illinois at Chicago Circle, Chicago,111., 15-17 Dec. 1972.

8 STEINBERG, M. el ul. Concrete-polymer materials: firsttopical report. BNL 50134 (T-509) and USBR GeneralReport no. 41. Dec. 1968.

9 STEINBERG, M. et al. Concrete-polymer materials secondtopical report. USBR REC-OCE-70-1 and BNL50218 (T-560), Dec. 1969.

10 DIKEOU, J. T. et al. Concrete-polymer materials: thirdtopical report. USBR REC-ERC-71-6 and BNL

50275 (T-602), Jan. 1971.11 KUKACKA, L. E. and DEPUY, G. w. (ed.). Concrete-

polymer materials four topical report. USBR REC-ERC72-10 and BNL 50328, Jan. 1972.

12 TAUBER.E., and MURRAY, M. J. 'Glass-clay mosaics andtiles'. Journal of the Australian Ceramic Society, vol. 7,no. 2, 1971, pp. 47-51.

1 3 S H U T T , T . C , CAMPBELL, I I . , a n d ABRAHAMS, J R . , J. I I .'New building materials containing waste glass.'Ceramic Bulletin, vol. 51, no. 9,1972, pp. 670-1.

14 BRIMLEY, K. J. 'Durability related to product develop-ment.' Proceedings. Conference on Durability of Plasticsin Building, Ministry of Public Building and Works,London, April 1969.

15 Modern Plastics, vol. 50, no. 1, Jan. 1973, p. 61.16 Modern Plastics, vol. 50, no. 10. Oct. 1973, p. 84.17 British Plastics, vol. 45, Mar. 1972, p. 66-67.18 Chemical and Engineering News, 1 Feb. \91l,pp. 12-13.19 BLAGA, A., and YAMASAKI, R. S. 'Mechanism of break-

down in the interface region of glass-reinforced poly-ester by artificial weathering.' Journal of MaterialsScience, vol. 8, 1973, pp. 654-66.

20 BLAGA, A. 'Weathering study of glass-reinforcedpolyester sheets by SEM.' Polymer Engineering andScience, vol. 12, no. 1, Jan. 1972, p. 53.

21 CROWDER, J. R., and LANT, T. P. R. 'Assessment ofdurability'. Proceedings. Conference on Durability ofPlastics in Building Ministry of Public Building andWorks, London, April 1969.

References1 'New materials in concrete construction' (Ed.s.i'.siiAW)

Proceedings. Conference held at the University ofIllinois at Chicago Circle, Chicago, III., 15-17 Dec. 1972.

2 Report of ACI Committee 223. 'Expansive cementconcretes - present state of knowledge'. ACI Journal,Aug. 1970, pp. 583-610.

3 PRICE, R. E. 'Expansive cements and field problems'.Proceedings, Conference held at the University ofIllinois at Chicago Circle, Chicago, III., 15-17 Dec. 1972.

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