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PROCEEDINGS OF THE 3RD RILEM INTERNAnONAL SYMPOSIUM ON AUTOCLA VEDAERATED CONCRETE/Z~CH/SWITZERLAND /14-16 OCTOBER 1992

Advances in AutoclavedAerated ConcreteEdited byFOLKER H. WITfMANNSwiss Federal Institute ofTechnolog.\~ Zurich

A.A. BALKEMA / ROTTERDAM / BROOKFIELD /1992

AUTOCLA VED CELLULAR CONCRETE:

THE BUILDING MATERIAL

FOR THE 21ST CENTURY

by:

Edward C. Pytlik, ProfessorDepartment of Technology Education

West Virginia University

Jeeta Saxena, Research AssociateDepartment of Technology Education

West Virginia University

Sponsored by:

"

[j Energy and Water Research CenterL. West Virginia University.:, Morgantown, WV 26506: "t:

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Table of Contents

Introduction 1

History of ACC 2

Raw Materials and the Manufacturing Process 3The Superior Properties ofACC 6

Applications 8

Uses for ACC 10

Fly Ash Utilization in ACC 10

Cost Comparisons 13

Status of Autoclaved Cellular Concrete in North America 16

Conclusions 17

Bibliography 17

List of Figures

1. Flow Sheet for the Manufacture of ACC

2. Energy Consumption in the Manufacture of A CC

List of Tables~~

1. U.S. Per Capital Income and the Average Cost of a Home (1977 -1987)

2. Average Annual Pay vs. Average Cost of Homes

3. The Major Manufacturers of ACC

4. Dimensions of Aerated Concrete Units5. Suggested Ranges for the Chemical Composition of Fly Ash in ACC

6. Chemical and Physical Requirements of Fly Ash

7. Cost of a Traditional Wall in a Single/Multi Family House

8. Cost ofa Siporex Wall in a Single/MultiFamily House

9. Cost comparisons and Propenies of Steel, Precast Concrete and Siporex

Building Envelopes

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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 average cost of a

home in the United States has 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 average cost of building a home was 8.5 times the per capita income, $104,500 vs.

$12,287 (See Table 1). From 1977-1987 our per capita income increased by 13%,

whereas in the same period the average cost of a home has increased by 114%.

Table I

U.S. Per Cal2ita Income and the Avera~e Cost of a Home (1977-1987)

Year Per Capita A verage CostIncome of Home

1977 10,850 48,8001978 11,245 55,7001979 11,223 62,9001980 10,740 64,6001981 10,592 68,9001982 10,573 69,3001983 10,892 75,3001984 11,301 79,9001985 11,635 84,3001986 12,096 92,000I 1987 12,287 104,500

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

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 increase of 9%. The average cost of building a home during that same period

has increased from $84,300 to $104,500 a 24% increase (See Table 2).

This disproportionate increase in the cost of building a home compared to the per capita

income has made it more difficult for the average American family to purchase their own

home. This has promoted research in designing or finding suitable alternatives that can

make home ownership more economically viable for the average American family, while

maintaining a high level of quality and functionality. The cost considerations in building

economics include not only the cost of the building material, but other influential direct and

2

Table 2AYera~e Annual Pa~ vs. A vera~e Cost of Ho~

Year A verage Cost of Home A verage Annual Pay

1985 84,300 19,1841986 92,000 19,9961987 104,500 20,855

Source: u.s. Bureau ofCen...us (1988}

indirect variables such as transport, assembly, fmishing cost and the energy efficiency, fIre

protection, maintenance, durability, and environmental implications of the materials beingused.

Amazingly, a building material favorable to many of these considerations has been

manufactured and used successfully in Europe and around the world for over 60 years, butis virtually unknown in this country. This product, Autoclaved Cellular Concrete or

Autoclaved Aerated Concrete, is being manufactured in over 35 countries worldwide.

In 1987, the worldwide use of ACC was estimated to be 23 million cubic meters (Mathey,

1988). Twenty three million cubic meters would make a wall 3.3 feet high, 3.3 feet wideand 13,800 miles long, that would circle more than half the Earth's circumference at the

equator (which is 24,000 miles). Despite the fact that ACC is more cost-effective and

provides a greater degree of energy efficiency than traditional U.S. construction materials,

it is currently not being manufactured in the United States or Canada.

HISTORY OF ACC

The current processes for the manufacture of ACC are based on a number of patents that

have been granted since the early 1900's. The earliest U.S. patent for the use of powdered

aluminium and calcium hydroxide as gas forming agents in a cementitious mixture was

granted to Aylsworth and Dyer in 1914. In 1929, U.S. patents were granted to Adolf andPohl for the use of hydrogen peroxide and sodium or calcium hypochlorite as gas forming

agents.

The fIrst patent for the manufacture of ACC was granted in 1923 to a Swedish architect,

Johann Erikkson. His patents included the use of aluminium powder in moist cured and

3

autoclaved concretes. It was Erikkson's patent which eventually led to the fonnation of thefirst, and still one of the largest ACC manufacturers -- YTONG of Gennany. YTONG

presently licenses and owns more than 25 plants in 17 different countries.

Other important patents include: Bayer's patent in 1923 for the use of foaming processes in

the preparation of cellular concretes, where autoclaving was recommended; Lindman's

patent in 1931 for the use of fly ash as a raw material in ACC; and Sahlberg's patent in

1937 for the use of finely divided silica in aerated concretes (Valore, 1954).

Factory production of ACC began in Sweden in 1924 and expanded to other parts of

Western Europe soon after. Over the years, as the merits of the product were realized by

others, the manufacturers began providing licensing technology and know-how to other

countries.

In addition to YTONG, several other manufacturers were among the pioneers in the

international use of ACC. Siporex was established in Sweden in 1939 and presently

licenses and owns plants in 35 locations around the world. H + H, began production in

Denmark in 1937 and presently has 6 plants in Denmark and has a subsidiary in the United

Kingdom which operates 4 additional plants. Hebel began manufacturing ACC in

Gennany in 1942. The company presently owns and licenses 35 plants in various

countries. Thennalite was fonned in the United Kingdom in 1951. They presently operate

7 plants in the U.K. Durox, based in the Netherlands, owns and operates 10 plants around

the world. SILBET, a State-owned research institute in Estonia, operates 29 plants in the

USSR and many of the fonDer communist block nations. These companies annual

production capacity and product ranges are listed in Table 3.

RAW MATERIALS AND THE MANUFACTURING PROCESS

Autoclaved Cellular Concrete is a lightweight building material, unique from lightweight

aggregate concrete and other types of concrete in that it is composed of millions of

microscopic cells generated during the manufacturing process. Also unlike most other

concrete products, it is steam cured in a high pressure autoclave. The raw materials and the

manufacturing process are also unique, resulting in a building material superior in

characteristics to most of the building materials presently available in the United States.

Although all the manufacturers have slightly different fonnulas for the manufacturing

_I "...

4

Table 3

The Major Manufacturers of ACC

Manufacturer No. of Annual Product ran2e(country, yr.est.) Plants Production

million m3(year)

Celcon 4 1.3 Range of blocks.(United Kingdom) (1988)

Durox 10* not known blocks, and block elements;(Netherlands, 1953) roof, wall and floor panels,

partition panels and shellpanels.

H+H(Denmark, 1937) 6* not known range of blocks, panels,

roof/floor slabs, lintels.(Conlite Subsidiaryof H + H) 4 as above

Hebel 35* 7.1 blocks, wall elements, wall(Germany, 1942) (1983) panels, roof slabs, ceiling

lintels.

Sll...BIT 29 6 wall panels, roof and floorUSSR,) 1961) (1988) slabs, (insulating panels,

blocks, partition panels.

Siporex 35* 3 blocks, wall panels, roof(Sweden, 1936) (1988) slabs in loadbearing and

non-ioadbearing varietieswith/withoutreinforcements.

Thern1alite 7 1.5 range of blocks(U.K., 1951) (1988)

YTONG 31 * 5 precision blocks,panels,

(Sweden, 1928) (1987) reinforced units, monarjoint blocks.

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

process, the basic raw materials are common -- portland cement, limestone, aluminium

powder, powdered silica sand, water and in some manufacturers' formula, fly-ash. The

,.

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aluminium powder reacts with calcium hydroxide and water to produce hydrogen gas

which aerates the mixture producing millions of microscopic non-connecting cells.

Another less commonly used method for the formation of gas according to the Comite

Euro-lntemational du Beton (CEB), is the adding of foam or whipping the mixture until the

desired consistency is achieved (1978). This mixture is then poured into oiled moulds

(commonly 20 x 4 x 2 ft.) and allowed to rise and set for approximately four hours

(Mathey, 1988). For loadbearing panels or slabs, steel reinforcement mats, coated with a

compound of portland cement, latex and finely ground sand or a bituminous compound,

are placed in the moulds before the mixture is poured (See Figure 1). The chemical

reaction that occurs is:2Al + 3Ca(OH)2 + 6H20 --> 3CaO.AI203.6H20 + 3H2

Aluminum powder + hydrated lime becomes Tricalcium Hydrate + hydrogen.

(Dunn, 1971)

Fi~ure 1

Flow Sheet for the Manufacture of ACC

FLay SHEET FOR THE t1ANUF ACTURE OF ACC. 1 I I I ~ :~ $~d \?$h c.m.nt 1Vn. / ~~~:=:~~ '

$ or.V. tr¥1$portv\v. dlnq T

,~ ~ 9~ f.,tsh~ & p.ck.V~

~~;~;:~; ~:~~j~~:~~::=:~,: VI for: t n q ~o $ Y19:i;f . u t c c 1.. vtlV --~ :_-_c '-'--- mtxVlV

J. J. polrw,9

Or"'~' ,~_~"'~ -J ~ &

After the mixture has set, it is removed from the moulds and sliced, trimmed and profiled to

prescribed lengths using a precision cutting machine. The cutting process yields a productwith high dimensional accuracy. Mter cutting, the material is steam-cured in an autoclave

at approximately 356°F at 10-12 atmospheres from eight to 14 hours, depending on the

product formula. The chemical reaction that takes place in the presence of steam in the

autoclave is:

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Ca(OH)2 + SiO2 + xH20 --> CaO.SiO2.xH20

Lime in binder + Silica + Water becomes Monocalium 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 ofbuildings -- homes, commercial buildings, high rise structures -- can be consn-ucted using

ACC.

High pressure autoclaving might give the impression that the manufacturing process is

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 dense concrete

uses less energy than ACC (See Figure 2).

Figure 2

Energ~ Consum~tion in the Manufacture of ACC

. Dense Concretec.8 B ACC- ..c II Clay bricks

~ ~ Mineral wool

0

~: Adapted from Bave (1983)

THE SUPERIOR PROPERTIES OF ACC

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, reduces construction time

and results in savings on transportation costs.

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ACC has hieh coml1ressive streneth in relation to its weight. The density and strength of

ACC can be adjusted to meet specific structural requirements. The average value of

compressive strength for a dry density of 25 pounds per cubic foot is about 290 pounds per

square inch. For a dry density of 44 pounds per cubic foot the compressive strength is

about 870 pounds per square inch. (Mathey, 1988). According to another report, the

t compressive strength of ACC blocks having a density of 40 to 44 pounds per cubic footranged between 800 - 1000 pounds per square inch (Valore, 1954).

Thermal insulation ACC has high thermal capacity or the ability to absorb and retain

relatively large amounts of heat energy. This quality of ACC is similar to the widely

recognized benefit of adobe brick construction. ACC, like adobe, will absorb large

quantities of radiant energy and not transmit it through the structure very rapidly. ACC

also provides a high degree of thermal insulation. In its most common density of 31

pounds per cubic foot, ACC provides an approximate R value of 1 per inch or about 8 for

an eight inch thick block (R. Valore, personal communication, January 1989). According

to a report issued in 1989 by the Council of American Building Officials (BOCA) regarding

the German ACC manufacturer, YTONG, the R-value per inch of aerated concrete

manufactured by YTONG is 1.66 per inch or 13.28 for an eight inch thick block (BOCA,

1989). In comparison, an eight inch thick traditional concrete block has an R value of

1.20. In a typical wood frame construction, a wall constructed of 2" X 6" studs, 5/8"

sheathing, felt paper, shingles, 1/2" gypsum board and R -13 fiberglass insulation has an

R-value of approximately 15.23 (Albright, Gay, Stiles, Worman & Zak, 1980). As noted

above, a typical eight inch thick ACC wall without added insulation can provide an R-value

of 13.28 with the added benefit of the ability to retain air-conditioning/heating for longer

periods of time.

Fire resistance ACC provides approximately twice the fIre resistance of dense concrete.

Data from tests conducted in 1968 at the Fire Research Station at Boreham Wood in the

United Kingdom indicated that a four inch non-loadbearing wall of ACC without surface

I finishes has a fire resistance of four hours. In comparison, a four inch thick non-

loadbearing dense concrete block wall has a fIre resistance of two hours. ACC loadbearing

walls of four inches and six inches have been tested to have a fire resistance of two andI three hours respectively, again about twice the fIre resistance of dense concrete blocks

(Malhotra, 1968).

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Water Resistance In areas prone to high-moisture weather conditions, ACC combined with

certain construction methods, greatly reduces dampness and condensation as compared to. u-aditional concrete. For example, in the U.K., ACC is used in combination with cavity

wall construction, leaving conduits to prevent the interior of the home from becoming

damp. A resin based moisture protective coating can also be applied as a moisture

repellant.

W orkabili~ One of the more unique features of ACC is that it can be easily sawn, cut,

drilled, chased or nailed with ordinary woodworking tools. This makes the installation of

plumbing, electrical wiring, and fmishing both the internal and external walls convenient

and simple.

Cost Com~etitive The cost considerations in building economics must include not only the

cost of the material, but other influential direct and indirect variables. Costs of

transportation, assembly, and fmishing, as well as the energy efficiency, fire protection,

maintenance, durability, and environmental implications of the materials being used must

also be considered. For example, typical construction of an average sized home in the

U.S. is six weeks to two months. Skilled or semi-skilled laborers are needed to 'custom'

fit and install the building material. When building a typical home with ACC the exterior

shell and interior partition walls can be constructed in as little as three days, by three

persons using a small crane. The time and hence the cost is greatly reduced by using ACC.

I This is in addition to the benefit of lower transportation costs (because ACC is

lightweight), lower energy bills and lower maintenance costs.

Finally, since ACC is inorganic, it is 100% termite resistant. In addition, it is not affected

by rotting or mold.

APPLICATIONS

Construction using ACC is efficient, given the precast, standardized nature of the material.Each of the products -- blocks, wall panels, roof/floor slabs and lintels -- are manufactured

in a range of sizes depending on the specific application (See Table 4). For example, the

range for wall units varies from unreinforced blocks to large reinforced panels. Anillusu-ation of a building in Sweden shows wall panels five feet in width and twenty feet in .

height used to construct a curtain wall (CEB, 1978).

81

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Table 4

Dimensions of Aerated Concrete Units

Type of Units Range of dimensionsLength Width Thickness

inches inches

Roof and floor units up to 20 ft 5 in 18-24 3-12Wall units (load-bearing 7 ft 6 in to 20 ft 5 in 18-24 3-12Partitions (non-load-bearing) 7 ft 6 in to 20 ft 5 in 18-24 3-4

~: Central Electricitv Generatinl! Board, 1967, p.12

Depending on the design of the structure and the construction system, wall panels are

joined vertically or horizontally using mortar or glue as specified by the manufacturer.

Loadbearing and non-ioadbearing panels can be manufactured with or without

reinforcement in thickness ranging from three to twelve inches and a maximum length of

twenty feet. The width of these panels is commonly two feet, but panels are made in

broader widths.

ACC blocks, available in a broad range of sizes, can also be used for the construction of

walls. Because of their lightweight, ACC blocks are larger than regular blocks and are

precision manufactured. They range in thickness from 2 to 14.2 inches and in surface area

from 8.6 to 17.6 inches long by 2.6 to 11.6 inches wide. They can be used in loadbearing

and non-load bearing walls as specified by the manufacturer.

Floor slabs too, are available in a wide range. Some manufacturers produce a range of

reinforced and unreinforced slabs between 4 to 12 inches thick and up to two feet wide, in

lengths up to 20 feet. They can be bun jointed or tongue and grooved.

Roof slabs for flat or sloping roofs can be manufactured for specific applications. Thewidth of these units is up to two feet and the thickness ranges from 3 - 12 inches. The

maximum length of these slabs is 20 fl Ceiling slabs for solid mounted ceilings for

industrial and housing construction are also manufactured. In addition, loadbearing and

non-loadbearing lintels are also manufactured by most of the ACC manufacturers.

USES FOR ACC

The versatility of ACC allows it to be used in different climatic zones in a wide range of

.1 0

applications, which cater to the building traditions of many countries. For example, in the

United Kingdom, ACC blocks are primarily used in cavity wall construction.

In Germany, large ACC wall panels and roof/floor slabs are used for modular-type

construction. Throughout the world, ACC is used in the construction of single- and multi-

family residences, apartment blocks, high rise structures, and commercial and industrialconstruction.

In a unique use the Consolidation Coal Company recently used fly ash based ACC block in

the construction of walls in one of their West Virginia coal mines. Gary Dadisman,

Manager of Construction, Consolidation Coal, stated that the lightweight blocks "made

transponation and handling of the unit significantly easier, resulting in improved efficiency

and safety characteristics." It was further reponed by Dadisman that, given the uneven

surfaces in the mines, the ability to cut and shape ACC blocks with ordinary carpentry tools

enhanced the construction process. (Proceedings of the Conference on ACC, 1989).

Although the major use of ACC blocks is in housing and commercial building construction,

it's potential for use in underground mines in the U.S. and elsewhere is considerable. In

Virginia, West Virginia and Pennsylvania, the Consolidation Coal Company alone annually

consumes 5 million cement blocks. (Proceedings of the Conference on ACC, 1989).

FL Y ASH UTILIZATION IN ACC

Earlier patents for the manufacture of ACC included sand as a raw material. It was

Lindmans' (1931) and Sahlbergs' (1937) patents that described the use of fly ash as a

siliceous raw material that could totally or partly replace sand in ACC. Technically, fly ash

use is related to the percentage replacement of quartz sand and cement as a raw material in

ACC.

Not all of the manufacturers of ACC use fly ash in ACC. But those that do have clearly

established that the use of fly ash does not negatively affect the properties of the final

product. In fact, the American Concrete Institute, (ACI 212) recognizes that the use of fly

ash and other finely divided materials improves the workability, strength and sulfate

resistance of concrete (Tennessee Valley Authority, 1979).

iI

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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 Standards C

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 Dusquene Light power

plant operating in Southwest Pennsylvania, 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 used in ACC research conducted by the

Weyerhauser Corporation in Tacoma, Washington.

The major issues related to the use of fly ash depend on the type of collection system,

source and type of coal, plant operating conditions and the temperature of combustion. The

variability of the physical and chemical properties of fly ash can be compensated for

through comprehensive testing. Tests performed generally include specific gravity,

fineness, loss on ignition and pozzolanic activity with lime and cement and a chemical

analysis (Tennessee Valley Authority, 1979). Both YTONG and SILBET have published

acceptable ranges for the mineral composition of fly ash that are suitable for use in ACC.

(See Table 5)

The fineness of fly ash panicles is another variable to be considered for use in ACC.

Fineness affects the pozzolanic activity of the material. The recommended method for

testing the fineness of fly ash is ASTM Method C430. Fly ash with a high volume of

cenospheres is not suitable for use in concrete. These cenospheres are lighter than water

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1 2

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

surface of the finished product.

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

Organization Si02 F~O3 Al203 CaO MgO SO3 K30+Na20 Loss on C

ignition

YTONG 45 - 0 - 10 10 - 30 0 - 5 0 - 2 0 - 5 0 - 5 0 - 10 0 - 10

SILBET 26 - 34 4 - 7 6 - 10 16 - 24 7.5 - 4 3 - 6 2.5 - 3.5 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 6Chemical and Ph~sical ReQuirements of Fl~ Ash

ASTM (C-618)Chemical R~uirements PercentagesSilicon dioxide (SiOV plus

aluminum oxide (Al203) plusiron oxide (Fe203), (min) 70.0

Magnesium oxide (mgO), (max) 5.0Sulphur trioxide (SO3), (max) 5.0Loss on ignition, (inax) 2.0Moisture content, (max) 3.0Available alkalies as Na20, (max) 1.5

Source: Tennessee Valley Authority. (1979). Pro~rties and Use of R~ Ash in Portland CementConcrete. (Technical Report (R- 79-2). Knoxville, TN: Author

"--"'--' ~'-""'.";j,

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COST COMPARISONS

Cost benefits from ACC during and after constt1lction include lower transportation costs,

reduced constt1lction time, lower energy bills, and lower maintenance costs. Another of

the major considerations is the relative cost of ACC when compared to traditional

construction materials.

In 1984, Siporex, a Swedish finn manufacturing ACC, conducted two comparative

building costs studies in Florida. The fIrst study compared the cost of residential, office

warehouse and commercial buildings constt1lcted with Siporex and similar buildings built

with commonly used constt1lction materials. The second study compared

Precast/Prestressed concrete and steel frame with Siporex material. One study indicated

that, based on the cost per square foot of a wall surface, the cost of a traditional wall in a

single-family/multi-family house would be about $3.92. (See Table 7). This wall was

calculated to have an R value of 5.5, and a fIfe resistance of two hours.

Table 7

Cost of a Traditional Wall in a Sin~le/Multi Famil~ House

Traditional Wall

8tt Concrete block masonry $ 1.34

Tie beams and columns. $ 1.77

Furring $ .18

Drywall, 1/2 inch $ .46

Insulation (R=3 spray) L.J1

Cost per square foot $ 3.92

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

In comparison, the cost per square foot for an eight inch thick Siporex panel was $3.48

(See Table 8) and it had an R value of9.1, without any added insulation, and a fire

resistance of four hours. The costs include the contractor's direct costs and direct

equipment costs. Finishes, roofing and fenestration have not been included. For light

industrial and commercial buildings the cost of traditional walls ranged from $3.92 per

square foot (concrete blocks) to $4.81 per square foot (tilt up wall panels).

".. ,,",:'.1~-';.:~;;---

14

Table 8

Cost of a Si~orex WaIl in a Sin~le/Multi Famil~ House

Si~orex WaIl

8" Siporex wall panel $ 2.60

Transportation 30 miles $ .10

Assembly $ .18

Crane $ .55

Supervision ~Cost per square foot $ 3.48

Source: Com12arative Building Cos~, Siporex (1984)

The cost of walls built with vertical or horizontal panels ranged from $3.20 to $3.87 per

square foot 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 resistance of all walls was four

hours, with the exception of the concrete block wall which had a fIre resistance of two

hours. For cost comparisons of roofs, traditional insulated steel roof on bar joists was

estimated at $2.16 per square foot 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 resistance of two hours.

The second study determined the total cost of the envelope of a light industrial building,

including columns and beams and the enclosing shell. Equal spans of 70 feet were

assumed between primary beams in the three alternatives selected -- steel, precast concrete

and Siporex. The cost comparisons are listed in Table 9.

The insulation value provided by each of the systems was similar, but the Siporex system

provided higher fire resistance and savings on insurance costs. The study also indicated

that where sprinkler systems are 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

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Table 9

Cost Comcarisons and Procerties of Steel. Precast Concrete and Si~rex Building

Enveloces

Estimated costT~~e of Material Used cer sg.ft. (dollars)

Steel-framed SU11cture 7.06

Precast Concrete Structure 8.58

Siporex SU11cture 7.70

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

YTONG in 1988 for a West Virginia plant, the selling price had increased to an estimated

$4.44 per cubic foot for reinforced ACC products and $2.48 per cubic foot for block

material.

STATUS OF AUTOCLAVED CELLULAR CONCRETE IN NORTH

AMERICA

Although the worldwide production of ACC exceeds 24 million cubic meters, ACC is not

currently manufactured in the United States. The only plant in North America is located in

Mexico.

In the United States there are more than two dozen buildings made from imported or

domestically produced ACC. In Rhode Island for example, Brown and Sharp Inc. owns

and operates a 750,000 square foot building made with imported Siporex cellular concrete.

It was consU11cted in 1964, of reinforced 2 inch by 6 inch by 25 foot panels. A 40,000

square foot building was consU11cted in Orlando, Florida in 1986 of Siporex material, by

the AB SANI company. According to a Siporex publication, the wall and roof units were

manufactured in Dalby, Sweden and imported to the United States in 55 containers

(Siporex Pulse, 1987).

In the past, European fmns have proposed or have actually had operating plants in North

America for short periods of time, in locations such as Calgary and suburban Montreal,

Canada; Denver, Colorado; St. Louis, Missouri; and, Minneapolis, Minnesota.

Investigations into the reasons why these plants were not successful have revealed that, for

16

the most part the plants were undercapitalized. The one exception, a Siporex licensed plant

operated by Domtar, Ltd. near Montreal, closed after five years of operation main! y

because of labor problems.

Presently, Thermalite and Celcon from the United Kingdom, Hebel and YTONG of

Germany, and Siporex of Sweden are exploring the potential market for ACC building

products in the United States. Celcon, YTONG, Durox and Hebel have representatives in

the U.S. YTONG and Siporex have both obtained HUD and BOCA approvals for their

products. (Council for American Builders and Architects, 1989; Housing and Urban

Development, 1988). Since 1988, representatives from Thermalite, Ltd. have visited the

West Virginia region several times to research the potential of establishing plants in the

area. They have also been in contact with power companies in the region to explore

potential fly ash sources.

Between 1987 and 1989, the U.S. fInn Weyerhaueser, a worldwide leader in the wood

products industry, investigated ACC as a potential new building product industry for the

U.S. Favorably impressed with its potential, Weyerhaueser pursued this endeavor until, in

mid-1989, they abandoned virtually all activities not directly related to their core business,

wood and wood products. The Hoppmann Corporation of Chantilly, V A, initially a joint

investigator with Weyerhauser, is still pursuing ACC related activities. They are currently

conducting research related to testing, process design and marketing of ACC. Their

research is sponsored by EPRI and the New England Power Company. Other U.S.

interests are also in various stages of initiating ACC plants.

CONCLUSIONS

ACC has been successfull~ used around the world for over 60 years. The product has

defmite potential for use in the United States, especially in present times with a growing

concern for energy efficiency in buildings and the rising cost of housing. Advantages

include a replacement for high priced wood, reduced construction time, high thermal

capacity, increased fIfe resistance and lower maintenance costs in the use of a highly

functional, quality building material with a time-tested reputation. Once an ACC

manufacturing plant is initiated in this country, these benefits will help promote its wide-

scale adoption. The construction industry of the 21st century may very well be dominated

by Autoclaved Cellular Concrete.

i!~~~

17

BIBLIOGRAPHY

Albright, R., Gay, L., Stiles, J., Worman, E., Worman, N., and Zak, D. (1980). ~com12lete book of insulation. Brattleboro, VT: The Stephen Green Press.

Bave, G., Bright, N.J., Leitch, F., Rottau, W., Svanholm, G., Trambovetsky V.P. andWeber, J.W. (Eds.) (1978). Autoclaved aerated concrete -- Comite Euro-

International du Beton.(.CEm. Lancaster: The Construction Press.

Central Electricity Generating Board. (1967). Aerated concrete. England: Author.

Chusid, M. (1990). The future of Autoclaved Cellular Concrete. Pro~essive

Architecture, May, 1990.

Coal Ash Market Report. (Sept. 1990). ACC at WVU. Vol.4, No. 18. McLean, VA:

Author.

CorDite Euro-International du Beton (CEB). (1978). Autoclaved aerated concrete.

Lancaster: The Construction Press.

Council for American Builders and Architects (BOCA) (1989) (Report No. NER-192).

illinois: Author.

Council for American Builders and Architects (BOCA) (1989) (Report No. NER-297).

illinois: Author.

Department of Technology Education, West Virginia University (1987). Autoclaved

Cellular Concrete Buildin~ Products Utilizin~ Pulverized Fuel Ash, Morgantown,

WV: Author.

Department of Technology Education, West Virginia University. (1990). Diffusion and

i n f A I v II 1 B il in Pr u in W ir 'ni PhaI, June 1988 - July 1989.

Department of Technology Education, West Virginia University. (1990). Diffusion and

Ado12tion of Autoclaved Cellular Concrete Buildin~ Products in West Vir~nia PhaseII, June 1989 - July 1990.

De Vore, P. & Monkurai, T. (1987). The Utilization of Fuel Ash in the Manufacture of

Autoclaved Cellular Concrete Building Materials. Proceedin~s of the Ei~ht

International Coal Ash S~m12Qsium. Palo Alto, CA: EPRI.

Dunn, R. H. (1971). Precast low density concrete units. Li~htwei~ht Concrete.

Publication SP29. Detroit: American Concrete Institute.

EPR! quarterly Report, (August, 1990). EPRI S12onsors Cellular Concrete Investi~ation.

Vol. 7, No.3. Palo Alto, CA: Author.

, I.I~.-. ,""' ,.,-~

_~r -=' -

1 8

EPRI quarterly Report, (February, 1990). An old technolo~~ to brin~ new use for coal ash

in the United States. Vol. 7, No.1. Palo Alto, CA: Author.

Fronsdorff, G. and Clifton, J. R. (1981, March). FI~ Ashes in Cements and Concretes:

Technical Needs and Oaoortunities. NBSIR 81-2239. Washington, D.C.: National

Bureau of Standards.Hebel International GmbH. Hebel Presents the Id~a. Munchen, West Gennany: Author.

Hickock, F. (1977). Home imarovements for conservation and solar ener~. St.

Petersburg, FL: Hour House Publishers.

Housing and Urban Development (HUD) (1988) (Materials release No. 10906).

Washington, DC: Author.

Internationella Siporex (1987). Siaorex Pulse. Malmo, Sweden.Internationella Siporex. Siaorex - The flexible s~stem. Malmo, Sweden.

Malhotra, H. L. (1968). The fIfe resistance of Autoclaved Aerated Concrete. Proceedings

of the fIrst international con~ess on li~htwei~ht concrete (pp. 129-131). London:

Cement and Concrete Association.

Mathey, R.G. (1988). A review of autoclaved aerated concrete 12roducts (Report No.

NBSIR 87-3670). Gaithersburg, MD: U.S. Department of Commerce.

Pytlik, E.C. & Saxena, J. (1990). Autoclaved Cellular Concrete: A Useful Shelter

Technology for developing countries. Paper presented at the Global Shelter

Conference. East Carolina University, Greenville, NC.(October 1990)

Pytlik, E.C. & Saxena, J. (1990). Fly ash based Autoclaved Cellular Concrete: The

building material of the 21st Century. Paper to be presented at the ~International Coal Ash Association S~ml2Qsium. Orlando FL. (January 1991)

Pytlik, E.C. (Ed.).(1989). Proceedin~s of the conference on Autoclaved Cellular

Concrete. Morgantown: Department of Technology Education/Energy and Water

Research Center, West Virginia University (1990)..Pytlik, E.C., Hester J.E. & Saxena, J. (April, 1990). Autoclaved Cellular Concrete: The

buildin ~ material of the 21 st Cent~. Paper presented at the International

Technology Education Association Annual Conference in Indianapolis, IN.

SILBET. (1989). Personal correspondence.Tennessee Valley Authority. (1979). Pro£2erties and Use ofFl~ Ash in Portland Cement

Concrete. (Technical Report CR-79-2). Knoxville, TN: Author.

Thermalite Ltd. The Product Ran~e. London, U.K: Author..

Thermalite Ltd. Thermalite Handbook. London, U.K: Author..

Valore, R. C. (1989). Personal communication.