Aerated concrete block, also referred to as autoclaved aerated concrete or AAC, is an innovative type of concrete containing around 80 percent air. These special concrete blocks have a number of advantages: They're strong, light and provide better sound and thermal insulation than conventional blocks. However, like any other building material, aerated concrete block also has its problems.

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Conventional concrete can withstand stress more effectively than AAC.

Cost

Buildings close to AAC production facilities benefit from short transportation and minimal shipping costs, especially since this concrete's lighter weight makes it easier to transport than regular concrete. However, AAC itself has an initial cost per unit higher than ordinary concrete. In addition, the small number of manufacturing facilities in the US could make using AAC very expensive for projects where the material must travel long distances from a manufacturer.

Strength Limitations

AAC is strong enough to use for structural parts of a building, but isn't as strong as conventional concrete. According to the Portland Cement Association, autoclaved aerated concrete has an allowable shear stress of 8 to 22 psi, and a compressive strength of 300 to 900 psi. Conventional concrete has an shear stress closer to 40 psi, with a compressive strength of 1500 psi.

Unfamiliarity

While AAC blocks are commonly used in Scandinavian buildings, according to the National Association of Home Builders, they aren't as common in the U.S. Existing building codes compiled with regular concrete block in mind may not be compatible with AAC blocks. Homeowners who wish to build with AAC may need to get special permission. Many contractors are also unfamiliar with AAC, and are unused to the special thin-set mortar required to lay it.

Environmental

AAC blocks use less material than conventional concrete block, making them more environmentally friendly. However, AAC may not be the greenest material for a given project. The autoclaving process requires significant amounts of energy. AAC is lighter and uses less resources to transport than ordinary concrete block, but is still heavier than many other materials. Depending on the project location, AAC could increase its carbon footprint over one built with locally available supplies.

Availability

Since North America has so few AAC manufacturers, this material can be hard to obtain. Homeowners who wish to use AAC may need to contact the manufacturer directly, or pay a premium to acquire this building material.