CSI Section 04 22 20: Autoclaved Aerated Concrete Masonry Units

Commercial production of autoclaved aerated concrete (AAC) began in 1930 in Europe, where it has been widely used for decades. Concrete masonry units (CMUs) made from AAC are lighter than conventional CMUs, generally have no cores, and provide higher insulation levels (R-values of up to 1.25 per inch, an order of magnitude higher than standard concrete). The insulating value of AAC allows it to function simultaneously as structure and insulation system. It has about 20% of the density—though only about 10% of the compressive strength—of regular concrete. Manufacturers may increase the product’s strength by including reinforcing steel rods or mesh. Structural applications of unreinforced AAC are limited to low-rise buildings; in high-rise buildings it may be used in partition and curtain walls. AAC has very good sound-absorbing characteristics and can be worked with conventional carpenter’s tools, making site modifications relatively easy. It’s also nontoxic, fire-resistant, insect-proof , and can be produced using coal fly ash as a substitute for some of the sand in conventional AAC. But because AAC is a porous material, it must be protected from moisture with claddings or coatings. AAC is not a 1:1 substitution for conventional CMU in terms of installation; greater care must be taken in installation because the shallow mortar bed does not allow for alignment adjustments easily made with the deeper mortar beds of conventional CMUs.

(See also 03 11 19 - Insulating Concrete Forming.)

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PRODUCTS

ACCOA ACCOA Aerated Concrete Corporation of America E-Crete E-Crete SafeCrete AAC SafeCrete AAC HEBEL Autoclaved Aerated Concrete Xella Aircrete North America	E-Crete E-Crete
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