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Hotbox Test R-value Database

Hebel Wall Systems



Description Of Wall

During the period of September 1998 to December 1998, the Hebel wall was built and tested in the guarded hot-box under steady-state conditions. The Hebel units were made of autoclaved aerated concrete (AAC).

AAC is made with cement, lime, water and sand. The sand is ground to a fine powder. A small amount of aluminum paste is added to the mixture. This reacts with the alkaline elements in the cement and lime causing the mixture to aerate, filling with millions of tiny finely dispersed bubbles. When the concrete is partially cured, it is stripped from the mold, cut into blocks or panels and steam cured in an autoclave under high pressure and temperature. The result is a concrete that’s only about one fifth of the weight of conventional concrete. Autoclaved aerated concrete was invented in Sweden in the 1920’s and Josef Hebel began commercial production in Germany in 1940.

The tested Hebel AAC (autoclaved aerated concrete) wall system was based on solid blocks (7-13/16 x 23-5/8 x 7 13/16-in.). The density of aerated concrete was about 31.9 lb/ft3. The Hebel blocks were joined using 1/16-in. thick mortar. Normally, the Hebel wall is covered by light weight stucco on the outside and plaster on the inside. An unfinished wall was used for the hot-box tests at Oak Ridge National Laboratory’s Buildings Technology Center.



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