Autoclaved Aerated Concrete (AAC):

Rogerio Miranda (Brazil)

(From Dean Still Apr 26 2003) Rogerio wrote that he's using AAC Autoclaved Aerated Concrete in the very nice stoves he's making in Brazil. I checked with a manufacturer of AAC here in the States and his reply seems pretty positive: I'm going to try a batch myself.

Q. AAC seems like another great material for combustion chambers. Rogerio, how does AAC seem to be working for you?

A. The AAC can withstand 1800 degrees indefinitely. However, the smoke and flame will erode the AAC surface over time.

Roberto Escardo, KUTRALDUM, Efficient Wood Stoves for the Patagonian Andes, Argentina

(April 2003) Some time ago we investigated in depht AAC. Gonzalo, a young engineer of our team (now working in a gas field in Bolivia) was in contact with the Hebel support enginer here (trained in Germany). I think it will be prudent to recheck it. Roberto.

(September 2002) The HEBEL support engineer here gave as the following info:
All cement-based materials are vulnerable to the attack of atmospheric carbon dioxide In concrete due to the scarce diffusion of gas in their interior; the effect is only superficial. AAC is a lot more permeable to air and it absorbs carbon dioxide easily, then the hydrated lime, either from the cement free lime or from the Si and Al hydrates reacts with the CO2 forming calcium carbonate:

Ca(OH)2 + CO2--------CO3Ca + H2O

Carbonatization causes a decrease of volume, denominated "carbonatization contraction". If CO2 concentration is high, or the exposure time is enough long, the contraction originates fissures. In AAC during the curing Ca hydrates react with the sand Si forming highly stable tebermorite so "carbonatization contraction" tends to be small. The risk from atmospheric CO2 contamination is very low, but is not the case in a combustion chamber or chimney.

HEBEL of Germany recommends coating chimneys or smoking conduits with refractory bricks to avoid carbonisation.

Other point in combustion chambers is permanent exposure to flames. AAC resists a flame temp of 1000 ºC 240 minutes without any loss of stability. If exposure time is much longer, the combined water of moisturized cement will evaporate, degrading the material

Dean Still, Aprovecho

(April 27, 2003) From an AAC Supplier in the US:

Q. We are using AAC as insulation in a stove prototype. Can you tell me how long AAC lasts at temperatures around 1800F.?

A. The AAC can withstand 1800 degrees indefinitely. However, the smoke and flame will erode the AAC surface over time.

Yes, we can make a AAC special mix that will improve properties for you.
Your cost FOB Adel, GA will be in the range of $4.00 per cubic ft. Plus shipping.
We make the following sizes, you can easily cut to shape with bandsaw.
2x8x24 inches

Reference Links

Autoclaved Aerated Concrete: Is North America Finally Ready? Building Environmental Building News From Volume 5, No. 2 -- March/April 1996

Autoclaved Aerated Concrete: An Overview (pdf) AzPath October 2001