It is an economical, sustainable, solid block that provides thermal and acoustic insulation as well as fire and termite resistance. AAC is available in a variety of forms, ranging from wall and roof panels to blocks and lintels. Although it has been a popular building material in Europe for over 50 years, AAC has only been introduced to the U.S. in the past two decades.
To manufacture AAC, Portland cement is mixed with lime, silica sand, or recycled fly ash (a byproduct from coal-burning power plants), water, and aluminum powder or paste and poured into a mold. The reaction between aluminum and concrete causes microscopic hydrogen bubbles to form, expanding the concrete to about five times its original volume. After evaporation of the hydrogen, the now highly closed-cell, aerated concrete is cut to size and formed by steam-curing in a pressurized chamber (an autoclave). The result is a non-organic, non-toxic, airtight material that can be used for wall, floor, and roof panels, blocks, and lintels which according to the manufacturers, generate no pollutants or hazardous waste during the manufacturing process
AAC units are available in numerous shapes and sizes. Panels are available in thicknesses of between 8 inches to 12 inches, 24-inches in width, and lengths up to 20 feet. Blocks come 24”, 32”, and 48” inches long, between four to 16 inches thick, and eight inches high.
AAC features include structural capacity, thermal, fire, and acoustical resistance properties. With an R-value of approximately 1.25 per inch, dependent on density, AAC significantly outperforms conventional concrete block or poured concrete. Consistency in quality and color may be difficult to obtain in AAC made with fly ash. Unfinished exterior walls should be covered with an exterior cladding or parged with mortar when exposed to physical damage, dirt, and water, because atmospheric debris can collect in the open cells. If installed in high humidity environments, interior finishes with low vapor permeability, and exterior finishes with a high permeability are recommended.
Because of the thermal mass of AAC and its ability to store and release energy over time, AAC may be beneficial in climates where outdoor temperature fluctuates over a 24-hour period from above to below the indoor temperature conditioned air set point.