The Concrete Facts

May/June 2001
This article originally appeared in the May/June 2001 issue of Home Energy Magazine.
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May 01, 2001
Q: What is autoclaved aerated concrete (AAC)? Why have I only heard about it recently, when apparently it has been around for years? When should a builder such as myself decide to use this material? A: AAC is a manufactured building product that can be made in a large variety of sizes and shapes. It is a precast masonry form, and is typically made from natural materials. It provides an easily assembled building surface that reduces material use (particularly for exotic or uncommon materials), lowers embodied energy, reduces cooling energy use, and can provide solidification of fly ash.                AAC Basics         AAC is made by mixing lime, sand (silica),water, and Portland cement with an aeration or expansion agent (typically aluminum powder). This slurry mixture is poured into a mold, and the alkali compounds in the mix react with the expansion agent for several hours until the mixture takes the form of a light-colored dried cake.For structural integrity, reinforcement in the form of steel bars or mesh can be added to the mold during the first stage of production. The aluminum-while less ...

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