Lightweight concrete

aerated concrete (AAC), also known as autoclaved cellular concrete (ACC), autoclaved lightweight concrete (ALC), autoclaved concrete, cellular concrete, porous concrete, Aircrete, Hebel Block, and Ytong is a lightweight, precast, foam concrete building material invented in the mid-1920s that simultaneously provides structure, insulation, and fire- and mold-resistance. AAC products include blocks, wall panels, floor and roof panels, cladding (facade) panels and lintels.

AAC was perfected in the mid-1920s by the Swedish architect and inventor Dr. Johan Axel Eriksson, working with Professor Henrik Kreüger at the Royal Institute of Technology. The process was patented in 1924. In 1929, production started in Sweden at the city of Yxhult. From "Yxhults Ånghärdade Gasbetong" later became the first registered building materials brand in the world: Ytong. Another brand “Siporex” was established in Sweden in 1939 and presently licenses and owns plants in 35 locations around the world. The second major international cellular concrete Hebel brand goes back to company founder and technicians Josef Hebel from Memmingen. In 1943, the first Hebel-plant was opened in Germany.

Originally Ytong autoclaved aerated concrete in Sweden was produced with alum shale, whose combustible carbon content was beneficial in the production process. Unfortunately, the slate deposits used for Ytong in Sweden also contain a very low level of natural uranium, which makes the material give off radioactive radon gas in the building. In 1972, the Swedish Radiation Safety Authority pointed out the unsuitability of a radon-emitting construction material, and the use of alum slate in the production of Ytong ceased in 1975. By using new formulations, containing only quartz sand, calcined gypsum, lime (mineral), cement, water and aluminum powder, Ytong produced a new type of aerated concrete which no longer contains alum slate and thus has eliminated the problem of radon exposure from this raw material. The production of this white autoclaved aerated concrete is now state of the art and similar formulations are used by all producers around the world.

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Wikipedia