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Advances in Autoclaved Aerated Concrete

Edited by


Swiss Federal Institute ofTechnolog.\~Zurich



by: EdwardC. Pytlik, Professor Department Technology of Education WestVirginia University JeetaSaxena, Research Associate Department Technology of Education WestVirginia University

Sponsored by:


[j L. .:, : "t:

EnergyandWaterResearch Center WestVirginia University Morgantown,WV 26506

1t.1111Introduction History of ACC






" "..'"

Table of Contents 1 2

Raw Materials theManufacturing and Process The SuperiorProperties ofACC Applications Uses for ACC Fly Ash Utilization in ACC Cost Comparisons Status of Autoclaved Cellular Concretein North America Conclusions Bibliography


6 8 10 10 13 16 17 17

List of Figures 1. Flow Sheetfor the Manufacture ACC of 2. EnergyConsumption the Manufacture A CC in of

List of Tables ~ ~ 1. U.S.Per CapitalIncomeandthe AverageCostof a Home (1977 -1987)

2. AverageAnnual Payvs. AverageCostof Homes

3. The Major Manufacturers ACC of 4. Dimensions AeratedConcrete of Units 5. Suggested Ranges the Chemical for Composition Fly Ash in ACC of 6. ChemicalandPhysicalRequirements Fly Ash of 7. Costof a TraditionalWall in a Single/MultiFamily House 8. Costofa SiporexWall in a Single/MultiFamily House 9. Cost comparisons Propenies Steel,Precast and of Concrete Siporex and Building Envelopes

-11,.1111.-INTRODUCTION The Great American Dream, that of individual families owning their own home is rapidly becoming the Great American Nightmare. In the past few years, the averagecost of a home in the United Stateshas risen significantly. In 1977 the cost of building a home was $48,800,4.5 times as much as the U.S. per capita income which was $10,850. By 1987, the averagecost of building a home was 8.5 times the per capita income, $104,500 vs. $12,287 (See Table 1). From 1977-1987our per capita income increased by 13%, whereasin the sameperiod the averagecost of a home has increasedby 114%. Table I U.S. Per Cal2itaIncome and the Avera~e Cost of a Home (1977-1987) Year 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987

Source: U.S. Bureau of Census (1988)


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Per Capita Income 10,850 11,245 11,223 10,740 10,592 10,573 10,892 11,301 11,635 12,096 12,287

A verage Cost of Home 48,800 55,700 62,900 64,600 68,900 69,300 75,300 79,900 84,300 92,000 104,500


Using the U.S. average annual pay as another indicator of housing's runaway costs, we find that the average annual salary in the U.S. rose from $19,184 to $20,855 between 1985 and 1987, an increaseof 9%. The averagecost of building a home during that sameperiod has increased from $84,300 to $104,500 a 24% increase (See Table 2). This disproportionate increasein the cost of building a home comparedto the per capita income has made it more difficult for the averageAmerican family to purchasetheir own home. This has promoted researchin designing or finding suitable alternatives that can make home ownership more economically viable for the averageAmerican family, while maintaining a high level of quality and functionality. The cost considerationsin building economics include not only the cost of the building material, but other influential direct and

2 Table2 AYera~e AnnualPa~vs. A vera~e Costof Ho~ Year 1985 1986 1987

Source:u.s. (1988}

A verage Cost of Home 84,300 92,000 104,500

A verage Annual Pay 19,184 19,996 20,855

indirectvariablessuchas transport, assembly, fmishingcostand the energyefficiency,fIre protection, maintenance, durability,andenvironmental implicationsof thematerials being used. Amazingly,a building materialfavorableto manyof these considerations been has manufactured usedsuccessfully Europeandaroundthe world for over 60 years,but and in is virtually unknownin this country. This product, AutoclavedCellularConcrete or AutoclavedAeratedConcrete, beingmanufactured over 35 countriesworldwide. is in In 1987,the worldwide useof ACC wasestimated be 23 million cubicmeters(Mathey, to 1988). Twenty threemillion cubic meterswould makea wall 3.3 feet high, 3.3 feet wide and 13,800miles long, that would circle morethanhalf theEarth'scircumference the at equator(which is 24,000miles). Despitethefact that ACC is morecost-effective and providesa greaterdegree energyefficiencythantraditionalU.S. construction of materials, it is currentlynot beingmanufactured theUnited States Canada. in or HISTORY OF ACC The currentprocesses the manufacture ACC arebased a numberof patentsthat for of on havebeengrantedsincethe early 1900's.The earliestU.S. patentfor the useof powdered aluminiumand calciumhydroxideasgasforming agents a cementitious in mixturewas grantedto Aylsworth andDyer in 1914. In 1929,U.S. patentsweregrantedto Adolf and Pohl for the useof hydrogenperoxideandsodiumor calciumhypochloriteasgasforming agents. The fIrst patentfor the manufacture ACC wasgranted 1923to a Swedish of in architect, Johann Erikkson. His patentsincludedthe useof aluminiumpowderin moist curedand

3 autoclaved concretes.It wasErikkson'spatentwhich eventuallyled to the fonnationof the first, and still one of thelargestACC manufacturers YTONG of Gennany. YTONG -presentlylicensesandownsmorethan25 plantsin 17different countries. Otherimportantpatents include:Bayer'spatentin 1923for the useof foamingprocesses in thepreparation cellular concretes, of whereautoclaving wasrecommended; Lindman's patentin 1931for the useof fly ashasa raw materialin ACC; and Sahlberg's patentin 1937for the useof finely divided silicain aerated concretes (Valore, 1954). Factoryproductionof ACC beganin Sweden 1924andexpanded otherpartsof in to Western Europesoonafter. Over the years,asthemeritsof the productwererealizedby others,the manufacturers beganprovidinglicensingtechnologyandknow-howto other countries. In additionto YTONG, several othermanufacturers wereamongthe pioneers the in international of ACC. Siporexwasestablished Sweden 1939andpresently use in in licenses owns plantsin 35 locationsaroundthe world. H + H, beganproductionin and Denmarkin 1937andpresentlyhas6 plantsin Denmarkandhasa subsidiary theUnited in Kingdomwhich operates additionalplants. Hebelbeganmanufacturing 4 ACC in Gennanyin 1942.The companypresently ownsandlicenses35 plantsin various countries.Thennalitewasfonnedin theUnitedKingdom in 1951. They presentlyoperate 7 plantsin the U.K. Durox, basedin the Netherlands, owns andoperates plantsaround 10 theworld. SILBET, a State-owned research institutein Estonia,operates plantsin the 29 USSRandmany of the fonDercommunist block nations. Thesecompanies annual productioncapacityandproductranges listedin Table 3. are RAW MATERIALS AND THE MANUFACTURING PROCESS

Autoclaved Cellular Concrete a lightweightbuildingmaterial,uniquefrom lightweight is aggregate concrete othertypesof concrete thatit is composed millions of and in of microscopic cells generated during themanufacturing process. Also unlike mostother concrete products,it is steam curedin a high pressure autoclave.The raw materialsandthe manufacturing process alsounique,resultingin a building materialsuperiorin are characteristics mostof the buildingmaterials to presently availablein theUnited States. Althoughall the manufacturers haveslightlydifferentfonnulasfor themanufacturing



4 Table3 The Major Manufacturers ACC of Manufacturer (country, yr.est.) No. of Plants Annual Production million m3 (year) 1.3 (1988) not known Product ran2e

Celcon (UnitedKingdom) Durox (Netherlands, 1953)

4 10*

Rangeof blocks. blocks,andblock elements; roof, wall and floor panels, partitionpanelsandshell panels. rangeof blocks,panels, roof/floor slabs,lintels. asabove

H+H (Denmark, 1937)


not known

(Conlite Subsidiary of H + H) 4 Hebel (Germany,1942) Sll...BIT USSR,) 1961) Siporex (Sweden,1936) 35* 7.1 (1983) 6 (1988) 3 (1988)

blocks,wall elements, wall panels,roof slabs,ceiling lintels. wall panels,roof andfloor slabs,(insulatingpanels, blocks,partition panels. blocks,wall panels,roof slabsin loadbearing and non-ioadbearing varieties with/without reinforcements. rangeof blocks precisionblocks,panels, reinforcedunits, monar joint blocks.



Thern1alite (U.K., 1951) YTONG (Sweden,1928)

7 31*

1.5 (1988) 5 (1987)

* This reflects the total plants owned and or licensed by the manufacturer indicated.

process, basicraw materialsarecommon--portlandcement,limestone, the aluminium powder,powderedsilica sand,waterand in somemanufacturers' formula, fly-ash. The


5 aluminiumpowderreactswith calciumhydroxideandwaterto producehydrogengas which aerates mixture producingmillions of microscopic the non-connecting cells. Anotherlesscommonlyusedmethodfor theformationof gasaccordingto the Comite Euro-lntemational Beton(CEB),is the addingof foam or whipping the mixture until the du desired consistency achieved is (1978). This mixture is thenpouredinto oiled moulds (commonly20 x 4 x 2 ft.) andallowedto rise andsetfor approximately four hours (Mathey, 1988). For loadbearing panelsor slabs,steelreinforcement mats,coatedwith a compound portlandcement,latexandfinely groundsandor a bituminouscompound, of areplacedin the mouldsbeforethe mixtureis poured(SeeFigure 1). The chemical reactionthat occursis: 2Al + 3Ca(OH)2+ 6H20 --> 3CaO.AI203.6H20 + 3H2 Aluminum powder+ hydrated lime becomes TricalciumHydrate+ hydrogen. (Dunn, 1971) Fi~ure 1 Flow Sheet the Manufacture ACC for of

FLay SHEET FOR THE t1ANUF ACTURE OF ACC $~d $h c.m.nt 1Vn.


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. dlnq


~ --~:_-_c '-'--~:~~j~~:~~::=:~,:


VI for:

J. J.


~~ 9~ :i;f

mtxVlV o$ Y19



1 I I I / ~~~:=:~~~

$ or.V.






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After the mixture hasset,it is removed from the mouldsandsliced,trimmedandprofiled to prescribed lengthsusinga precision cutting machine.The cuttingprocess yields a product with high dimensional accuracy.Mter cutting,thematerialis steam-cured an autoclave in at approximately356°F at 10-12atmospheres from eight to 14 hours,depending the on productformula. The chemicalreactionthat takesplacein thepresence steam the of in autoclave is:



Ca(OH)2 + SiO2 + xH20 --> CaO.SiO2.xH20 Lime in binder + Silica + Water becomesMonocalium Silicate hydrate. (Dunn, 1971) The fmished product of blocks, panels or slabs is commonly shrink-wrapped in plastic and uansponed directly to the construction site. Floors, walls and roofs for all types of buildings -- homes, commercial buildings, high rise structures -- can be consn-uctedusing ACC. High pressure autoclaving might give the impression that the manufacturing processis highly energy-intensive. But a comparison of the energy input required for the production of ACC with other building materials shows that only the manufacture of denseconcrete usesless energy than ACC (See Figure 2). Figure 2 Energ~ Consum~tion in the Manufacture of ACC


.8 .c








ACC . Clay bricks

Mineral wool



Adapted fromBave (1983)




Lightweight ACC is currently being manufactured in densities ranging from 19 to 62 pounds per cubic foot. The low density of this material makes it weigh less than one third to one half of traditional concrete. This permits easier handling, reducesconstruction time and results in savings on transportation costs.

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ACC has hieh coml1ressive streneth relationto its weight. The densityandstrengthof in

ACC canbe adjusted meetspecificstructural to requirements. The average valueof compressive strengthfor a dry densityof 25 poundsper cubic foot is about290 poundsper square inch. For a dry densityof 44 poundsper cubic foot the compressive strength is


about870 poundsper square inch. (Mathey, 1988). Accordingto anotherreport,the compressive strengthof ACC blockshavinga densityof 40 to 44 poundsper cubic foot rangedbetween800 - 1000poundsper square inch (Valore, 1954). Thermalinsulation ACC hashigh thermalcapacityor the ability to absorb retain and relativelylargeamounts heatenergy.This quality of ACC is similarto the widely of recognized benefitof adobebrick construction.ACC, like adobe, will absorb large quantities radiantenergyandnot transmitit throughthe structure of very rapidly. ACC alsoprovidesa high degree thermalinsulation. In its mostcommondensityof 31 of poundsper cubic foot, ACC providesan approximate valueof 1 per inch or about8 for R aneight inch thick block (R. Valore,personal communication, January1989). According to a reportissuedin 1989by the Councilof AmericanBuilding Officials (BOCA) regarding theGermanACC manufacturer, YTONG, the R-valueper inch of aerated concrete manufactured YTONG is 1.66per inch or 13.28for an eight inch thick block (BOCA, by 1989). In comparison, eight inch thick traditionalconcrete an block hasan R valueof 1.20. In a typical wood frameconstruction, wall constructed 2" X 6" studs,5/8" a of sheathing, paper,shingles,1/2" gypsumboardandR-13 fiberglassinsulationhasan felt R-valueof approximately15.23(Albright, Gay, Stiles,Worman& Zak, 1980). As noted above,a typical eight inch thick ACC wall without added insulationcanprovidean R-value of 13.28with the addedbenefitof the ability to retainair-conditioning/heating longer for periodsof time. Fire resistanceACC providesapproximately twice the fIre resistance dense of concrete. Datafrom testsconducted 1968at the Fire Research in Stationat Boreham Wood in the UnitedKingdom indicatedthat a four inch non-loadbearing of ACC without surface wall



finisheshasa fire resistance four hours. In comparison, four inch thick nonof a loadbearing denseconcrete block wall hasa fIre resistance two hours. ACC loadbearing of walls of four inchesand six incheshavebeentestedto havea fire resistance two and of threehoursrespectively, againabouttwice the fIre resistance dense of concrete blocks (Malhotra, 1968).

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WaterResistance areas In proneto high-moisture weather conditions,ACC combinedwith


certainconstructionmethods, greatlyreduces dampness condensation compared and as to u-aditional concrete. For example, theU.K., ACC is usedin combinationwith cavity in wall construction, leavingconduitsto preventtheinterior of the homefrom becoming damp. A resin based moistureprotective coatingcanalsobe appliedasa moisture repellant. Workabili~ Oneof the moreuniquefeatures ACC is that it canbe easilysawn,cut, of drilled, chased nailedwith ordinarywoodworkingtools. This makesthe installationof or plumbing,electricalwiring, andfmishingboth theinternalandexternalwalls convenient and simple. CostCom~etitive The costconsiderations building economics in mustincludenot only the costof the material,but otherinfluentialdirect andindirectvariables.Costsof transportation, assembly, fmishing,aswell asthe energyefficiency, fire protection, and maintenance, durability, andenvironmental implicationsof the materialsbeingusedmust alsobe considered.For example, typical construction an average of sizedhomein the U.S. is six weeksto two months. Skilled or semi-skilledlaborersare needed 'custom' to fit andinstall the building material. Whenbuildinga typical homewith ACC the exterior shellandinterior partition walls canbe constructed aslittle asthreedays,by three in persons usinga small crane. The time andhencethe costis greatlyreducedby usingACC.


This is in additionto the benefitof lower transportation costs(because ACC is lightweight),lower energybills andlower maintenance costs. Finally, sinceACC is inorganic,it is 100%termiteresistant.In addition,it is not affected by rotting or mold. APPLICATIONS Construction usingACC is efficient,giventhe precast, standardized natureof the material.

Each of the products -- blocks, wall panels, roof/floor slabs and lintels

-- are manufactured

in a rangeof sizesdepending the specificapplication(SeeTable4). For example, on the rangefor wall units variesfrom unreinforced blocksto largereinforcedpanels. An illusu-ation a building in Sweden of showswall panels five feet in width and twentyfeet in heightusedto constructa curtainwall (CEB, 1978).




Type of Units


Table4 Dimensions Aerated of Concrete Units Length




Range of dimensions Width Thickness inches inches 18-24 18-24 18-24 3-12 3-12 3-4

Roof andfloor units Wall units(load-bearing Partitions(non-load-bearing)


up to 20 ft 5 in 7 ft 6 in to 20 ft 5 in 7 ft 6 in to 20 ft 5 in

CentralElectricitv Generatinl!Board, 1967,p.12

Depending the designof the structure theconstruction on and system, wall panelsare joined vertically or horizontallyusingmortaror glueasspecifiedby the manufacturer. Loadbearing non-ioadbearing and panels bemanufactured can with or without reinforcement thickness in rangingfrom threeto twelveinchesanda maximumlengthof twentyfeet. The width of these panels commonlytwo feet,but panelsaremadein is broaderwidths. ACC blocks,availablein a broadrangeof sizes,canalsobe usedfor the construction of walls. Because their lightweight,ACC blocksarelargerthanregularblocksandare of precisionmanufactured. They rangein thickness from 2 to 14.2inchesandin surface area from 8.6 to 17.6incheslong by 2.6 to 11.6incheswide. They canbe usedin loadbearing andnon-load bearingwalls asspecified themanufacturer. by Floor slabstoo, areavailablein a wide range. Somemanufacturers producea rangeof reinforcedand unreinforced slabsbetween to 12inchesthick andup to two feet wide, in 4 lengthsup to 20 feet. They canbe bunjointed or tongueandgrooved. Roof slabsfor flat or slopingroofs canbemanufactured specificapplications.The for width of theseunitsis up to two feet andthe thickness ranges from 3 - 12 inches. The maximumlengthof theseslabsis 20 fl Ceiling slabsfor solid mounted ceilingsfor industrialand housingconstruction alsomanufactured. addition,loadbearing are In and non-loadbearing lintels arealsomanufactured mostof the ACC manufacturers. by USES FOR ACC The versatilityof ACC allows it to beusedin differentclimatic zones a wide rangeof in


In Germany,largeACC wall panelsandroof/floor slabsareusedfor modular-type

1 0

applications, which caterto thebuilding traditionsof manycountries.For example, the in United Kingdom, ACC blocksareprimarily usedin cavity wall construction.

construction.Throughoutthe world, ACC is usedin the construction single-andmultiof family residences, apartment blocks,high rise structures, commercialandindustrial and construction. In a uniqueusethe Consolidation CoalCompany recentlyusedfly ashbased ACC block in theconstruction walls in oneof their WestVirginia coal mines. Gary Dadisman, of Manager Construction, of Consolidation Coal, stated that thelightweightblocks"made transponation handlingof the unit significantlyeasier, and resultingin improvedefficiency andsafetycharacteristics."It wasfurtherreponedby Dadisman that, given theuneven surfaces the mines,the ability to cut andshape in ACC blockswith ordinarycarpentry tools enhanced constructionprocess.(Proceedings the Conference ACC, 1989). the of on Althoughthe major useof ACC blocksis in housingandcommercialbuilding construction, it's potentialfor usein underground minesin the U.S. andelsewhere considerable. is In Virginia, WestVirginia andPennsylvania, Consolidation the Coal Companyaloneannually consumes million cementblocks. (Proceedings the Conference ACC, 1989). 5 of on FL Y ASH UTILIZATION IN ACC

Earlierpatents the manufacture ACC includedsandasa raw material. It was for of Lindmans'(1931) and Sahlbergs' (1937)patentsthat described useof fly ashasa the siliceous raw materialthat could totally or partly replacesandin ACC. Technically, ash fly useis relatedto the percentage replacement quartzsandandcementasa raw materialin of ACC. Not all of themanufacturers ACC usefly ashin ACC. But thosethat do haveclearly of established the useof fly ashdoesnot negativelyaffect theproperties the final that of product. In fact, the AmericanConcrete Institute,(ACI 212)recognizes the useof fly that ashandotherfinely divided materialsimprovesthe workability, strengthandsulfate resistance concrete(Tennessee of Valley Authority, 1979).

i I

11 The major users of fly ash as the primary siliceous component in ACC are located in the U.K. and the U.S.S.R. Thermalite, Ltd. in the U.K., substitutes sand with 30 to 100 percent fly ash in it's manufacturing operation. Thermalite uses 600,000 metric tons of fly ash annually to produce 1.5 million cubic meters ofACC block. In 1989, SILBET in the U.S.S.R. used 367,200 metric tons of coal fly ash and shale-oil fly ash in the manufacture ofACC block (SILBET, 1989). The chemical properties of fly ash for use in concrete are defmed by ASTM StandardsC 618-84 Standard Specification for Fly Ash and Raw or Calcined Natural Pozzolan for use as a Mineral Admixture in Ponland Cement Concrete. This designation classifies these materials into three classes,two of which are fly ash (Fonsdorff & Clifton, 1981): Class F: Fly ash with pozzolanic properties produced by burning anthracite or bituminous coal. Class C: Fly ash produced by burning lignite or sub-bituminous coal and can contain more than 10% lime. Generally, Class F fly ash (ASTM C-618) is considered suitable for ACC. A material safety data sheet reporting the mineral composition of fly ash from a DusqueneLight power plant operating in SouthwestPennsylvania,indicated that its mineral content falls within the minimum mineral requirements for producing ACC. Fly ash from Monongahela Power Plant in Fon Manin, West Virginia has been usedin ACC researchconducted by the Weyerhauser Corporation in Tacoma, Washington. The major issuesrelated to the use of fly ash dependon the type of collection system, sourceand type of coal, plant operating conditions and the temperatureof combustion. The variability of the physical and chemical properties of fly ash can be compensatedfor through comprehensive testing. Tests performed generally include specific gravity, fineness,loss on ignition and pozzolanic activity with lime and cement and a chemical analysis (TennesseeValley Authority, 1979). Both YTONG and SILBET have published acceptableranges for the mineral composition of fly ash that are suitable for use in ACC. (SeeTable 5) The fineness of fly ash panicles is another variable to be considered for use in ACC. Finenessaffects the pozzolanic activity of the material. The recommendedmethod for testing the fineness of fly ash is ASTM Method C430. Fly ash with a high volume of cenospheres not suitable for use in concrete. These cenospheresare lighter than water is


surface of the finished product. Organization Si02 F~O3 Al203 CaO MgO



12 and during the manufacturing process, they float to the surface to foml dark streaks on the

Table 5 Su~~ested Ran~es for the Chemical Com~osition of Fl~ Ash in ACC



Loss on ignition




45 34




10 10- 30 0 - 5 0 - 2

6 10 16 24 7.5 4

0 -5 0 - 5

3 6 2.5 3.5

0 - 10 0 - 10

The chemical requirements for ASTM STANDARD

C 618 type F and C fly ash are

provided below (See Table 6). Comparing this to the ranges provided by YTONG and Sll..BETreveal that ASTM STANDARD C 618 requirements are compatible.

Requirements for other classes of fly ash than class I shown are less restrictive. An interesting scenario for potential fly ash use in ACC has been proposed by Faber (Proceedings of the Conference on ACC, 1989). According to the National Concrete Masonry Association, 4.5 billion 8" cement blocks were sold in the U.S. in 1988. Considering each ACC block would consume 25 lbs. of fly ash, the potential for fly ash use is 56.25 million tons. But if only 1% of the cement block sales are targeted, the potential for fly ash use is 500,000 tons annually in cement block alone. Table 6 Chemical and Ph~sical ReQuirements of Fl~ Ash ASTM (C-618) Chemical R~uirements Silicon dioxide (SiOV plus aluminum oxide (Al203) plus iron oxide (Fe203), (min) Magnesium oxide (mgO), (max) Sulphur trioxide (SO3), (max) Loss on ignition, (inax) Moisture content, (max) Available alkalies as Na20, (max) Source:


70.0 5.0 5.0 2.0 3.0 1.5

Tennessee Valley Authority. (1979). Pro~rties and Useof R~ Ash in PortlandCement Concrete. (TechnicalReport (R-79-2). Knoxville, TN: Author



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COST COMPARISONS Costbenefitsfrom ACC duringandafterconstt1lction includelower transportation costs, reduced constt1lction time, lower energybills, andlower maintenance costs. Anotherof themajor considerations therelativecostof ACC whencompared traditional is to construction materials. In 1984,Siporex,a Swedish finn manufacturing ACC, conducted comparative two building costsstudiesin Florida. The fIrst studycompared costof residential, the office warehouse commercial and buildingsconstt1lcted Siporexandsimilarbuildingsbuilt with with commonlyusedconstt1lction materials.The second studycompared Precast/Prestressed concrete steelframewith Siporexmaterial. Onestudyindicated and that,based the costper square on foot of a wall surface, costof a traditionalwall in a the single-family/multi-familyhouse would be about$3.92. (SeeTable7). This wall was calculatedto havean R valueof 5.5, anda fIfe resistance two hours. of Table7 Costof a TraditionalWall in a Sin~le/MultiFamil~House TraditionalWall 8ttConcrete block masonry Tie beams columns. and Furring Drywall, 1/2inch Insulation(R=3 spray) Costper square foot

Source:Com~tive Building Costs,Siporex(1984)


$ 1.34 $ 1.77 $ .18 $ .46 L.J1 $ 3.92

In comparison, costper square the foot for an eight inch thick Siporexpanelwas$3.48 (SeeTable 8) andit had an R valueof9.1, without any addedinsulation,anda fire resistance four hours. The costsincludethe contractor's of direct costsanddirect equipment costs. Finishes, roofing andfenestration havenot beenincluded. For light industrialandcommercialbuildingsthecostof traditionalwalls rangedfrom $3.92per square foot (concrete blocks) to $4.81per square foot (tilt up wall panels).



14 Table 8 Cost of a Si~orex WaIl in a Sin~le/Multi Famil~ House Si~orex WaIl 8" Siporex wall panel Transportation 30 miles Assembly Crane Supervision $ 2.60 $ .10 $ .18 $ .55


$ 3.48

Costpersquare foot

Source:Com12arative Building Cos~, Siporex(1984)

The cost of walls built with vertical or horizontal panels ranged from $3.20 to $3.87 per squarefoot The R-value of both traditional walls was about five, whereas the R-value of the Siporex walls ranged from seven to nine. The fire resistanceof all walls was four hours, with the exception of the concrete block wall which had a fIre resistanceof two hours. For cost comparisons of roofs, traditional insulated steel roof on bar joists was estimated at $2.16 per squarefoot providing an R-value of four, and without fIreproofmg, the roof would offer no fIre resistance. The eight inch Siporex roof panels would cost $2.98 per square foot and offer an R-value of 10 and fire resistanceof two hours. The secondstudy determined the total cost of the envelope of a light industrial building, including columns and beamsand the enclosing shell. Equal spansof 70 feet were assumedbetween primary beamsin the three alternatives selected-- steel, precastconcrete and Siporex. The cost comparisons are listed in Table 9. The insulation value provided by each of the systemswas similar, but the Siporex system provided higher fire resistanceand savings on insurancecosts. The study also indicated that where sprinkler systemsare mandatory, savings can be realized in the size and type of sprinklers used. In 1986, YTONG International GmbH conducted a feasibility study for a manufacturing plant in Florida and estimated a selling price of $3.90 per cubic foot for reinforced ACC products and $2.10 per cubic foot of precision blocks. In a similar study conducted by



-T~~eof Material Used Steel-framed SU11cture Precast ConcreteStructure SiporexSU11cture ~:


.Estimated cost cer sg.ft. (dollars) 7.06 8.58 7.70


Table9 CostComcarisons Procerties Steel.Precast and of ConcreteandSi~rex Building Enveloces

Com~arative Buildin~ Cos~. Siporex (1984)

YTONG in 1988for a WestVirginia plant,the sellingprice hadincreased an estimated to $4.44per cubic foot for reinforcedACC productsand$2.48per cubic foot for block material. STATUS OF AUTOCLAVED CELLULAR CONCRETE IN NORTH AMERICA Althoughthe worldwideproductionof ACC exceeds million cubic meters, 24 ACC is not currentlymanufactured theUnited States.The only plant in North Americais locatedin in Mexico. In theUnited Statestherearemorethantwo dozenbuildingsmadefrom importedor domesticallyproducedACC. In RhodeIslandfor example,Brown and SharpInc. owns andoperates 750,000square a foot buildingmadewith importedSiporexcellularconcrete. It wasconsU11cted 1964,of reinforced2 inch by 6 inch by 25 foot panels. A 40,000 in square foot building wasconsU11ctedOrlando,Floridain 1986of Siporexmaterial,by in the AB SANI company. Accordingto a Siporexpublication,the wall androof units were manufactured Dalby, Sweden importedto theUnited States 55 containers in and in (SiporexPulse, 1987). In thepast,Europeanfmns haveproposed haveactuallyhadoperating or plantsin North Americafor short periodsof time, in locationssuchasCalgaryand suburban Montreal, Canada; Denver,Colorado;St. Louis, Missouri;and,Minneapolis,Minnesota. Investigations thereasons into why these plantswerenot successful haverevealed that,for

16 themostpart the plantswereundercapitalized. oneexception, Siporexlicensed The a plant operated Domtar,Ltd. nearMontreal,closedafterfive yearsof operation by main!y because labor problems. of Presently, ThermaliteandCelconfrom the United Kingdom,HebelandYTONG of Germany, Siporexof Sweden exploringthepotentialmarketfor ACC building and are productsin the United States.Celcon,YTONG, Durox andHebelhaverepresentatives in the U.S. YTONG and Siporexhaveboth obtainedHUD andBOCA approvals their for products. (Council for AmericanBuildersandArchitects,1989;HousingandUrban Development, 1988). Since1988,representatives Thermalite,Ltd. havevisited the from WestVirginia region several timesto research potentialof establishing the plantsin the area. They havealsobeenin contactwith powercompanies theregionto explore in potentialfly ashsources. Between1987and 1989,the U.S. fInn Weyerhaueser, worldwide leaderin the wood a productsindustry,investigated ACC asa potentialnewbuilding productindustryfor the U.S. Favorablyimpressed with its potential,Weyerhaueser pursuedthis endeavor until, in mid-1989,they abandoned virtually all activitiesnot directly relatedto their corebusiness, wood andwood products. The Hoppmann Corporation Chantilly, V A, initially a joint of investigator with Weyerhauser, still pursuingACC relatedactivities. They arecurrently is conducting research relatedto testing,process designandmarketingof ACC. Their research sponsored EPRI andthe New EnglandPowerCompany. OtherU.S. is by interests alsoin variousstages initiating ACC plants. are of CONCLUSIONS ACC hasbeensuccessfull~ usedaroundthe world for over 60 years. The producthas defmitepotentialfor usein theUnitedStates, especially present in timeswith a growing concernfor energyefficiency in buildingsandtherising costof housing. Advantages includea replacement high pricedwood,reduced for construction time, high thermal capacity, increased resistance lower maintenance fIfe and costsin the useof a highly functional,quality building materialwith a time-tested reputation.Oncean ACC manufacturing plant is initiatedin this country,thesebenefitswill help promoteits widescaleadoption. The construction industryof the 21stcenturymay very well bedominated by AutoclavedCellularConcrete.



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