Thermacrete: Aerated Autoclaved Concrete Blocks

Green Architect


Aerated Autoclaved Concrete used as flooring with radiant heat

Aerated Autoclaved Concrete was invented nearly 100-years ago, but is just now getting its eco-recognition. Aerated Autoclaved Concrete works and carves like wood, but can do even more — the material has thermal and acoustic insulating properties, is highly durable, non-organic, non-toxic and load bearing. Find out more about this amazing product after the jump!

While AAC has been a popular building material overseas, it's only recently getting its due notice in the US. Here's the history of Aerated Autoclaved Concrete (AAC), according to one of its manufacturers, Thermacrete:

In 1914, a Swedish chemist discovered a mixture of cement, lime, water and sand that expands by adding aluminum powder. The reaction between the aluminum and the lime in the Portland cement 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 form and steam cured in a pressurized chamber (autoclave) for approximately eleven hours. When analyzed under a microscope, it was discovered that AAC has virtually the same molecular structure as limestone.

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The material's composition is such that it can be manipulated as easily as wood — it can sanded and carved for custom profiles and shapes, yet it is super strong and impact resistant. The material is modular, and can be used for the entire wall construction, meaning in some cases no additional insulation is needed, and depending on the desired appearance, no exterior finish is needed. It has many other sustainable properties and benefits:

  • Durable: AAC can be installed in interior and exterior applications, will not rot, warp, rust, corrode or decompose, and should have a long life-cycle with very little maintenance.
  • Thermal & Acoustic Insulation: AAC's composition gives it inherent high thermal value. Because the material is continuous, there is no thermal bridging, which can result in cold or hot spots along a conventional wall. Depending on the thickness of block used, no additional insulation may be necessary to reach desired R-Values. Additionally, AAC can be used for sound wall systems because of its ability to dampen vibrations, echos and ambient noise.
  • Fire, Pest & Mold Resistant: AAC is naturally non-combustible, and pest and mold resistant, thus avoiding any toxic chemical treatments. When used in certain thicknesses, AAC can qualify as a fire wall when needed for certain wall assemblies.

Thermacrete is a manufacturer of many types of AAC products: panels for exterior cladding, panels that can be used as firewalls and shafts, floor panels, blocks for load-bearing walls, lintels, and blocks with cores for reinforced applications.

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(Images: Nicole Gravatt/1668Jefferson; Knol)