Aircrete as a building material has been industrially produced since the beginning of 20th century. In the section below you read about the relatively short history of this long-lasting building material. The extended version of the AAC history can be found in an expert article published in our download section.

Early days

First developments in autoclaved aerated concrete history are based on a series of process patents. In 1880 a German researcher Michaelis was granted a patent on his steam curing processes. Czech Hoffman successfully tested and patented in 1889 the method of “aerating” the concrete by carbon dioxide. Americans Aylsworth and Dyer used aluminium powder and calcium hydroxide to attain porous cementitious mixture for which they also received a patent in 1914. Swede Axel Eriksson made a serious next step towards developing modern AAC when in 1920 he patented the methods of making aerated mix of limestone and ground slate (a so-called “lime formula”).

Chemistry of Autoclaved Aerated Concrete

All in all, the combination of cement, lime, gypsum (anhydrite), finely ground sand and most importantly aluminium powder causes the mixture to expand considerably. From the beginning to the end the simplified chemical reactions are as follows:

This is the final Tobermorite or Hydrated Calcium Silicate C₅S₆H₅.

The breakthrough in AAC production

The real breakthrough in the masonry industry came in 1923 when same architect Axel Eriksson discovered that this moist foamed mass can easily handle pressurized steam curing process, also known as autoclaving. While applying for a patent two crucial conclusions were drawn: 1. the material hardened fast thanks to the autoclaving process and 2. shrinkage was almost absent after steam curing compared to the normal air curing. Additionally, later it was also discovered that alternative materials, such as pulverized ash, could be used instead of lime/cement, allowing to economize on expensive raw material binder.

Start of Commercial Manufacturing

Eriksson’s success immediately attracted a much-needed commercial interest and in 1929 the first large scale manufacturing facility of these artificially-made crystalized stone blocks was launched in a factory “Yxhults Stenhuggeri Aktibolag“, Sweden under the name Yxhult. In 1940 the “Yxhult” name was changed to YTONG as this name was easier to pronounce. In 1932 the factory Carlsro Kalkbruk Skovde started with AAC block production and the product acquired the brand name Durox.

Important competitor arose in 1934 which started to manufacture AAC blocks under the brand name Siporit (as of 1937 a well-known Siporex). Siporex was also the first to introduce AAC reinforced elements in 1935, namely roof/floor panels and lintels. Good structural properties of the newly created AAC material soon spread all over Western Europe, with more than 6 plants in Sweden alone.

Different AAC Technologies (Ytong, Hebel, Siporex) – International Success

AAC manufacturing went international in 1937 with introduction of technology licensing and know-how transfer. After WWII, there existed only few leading AAC technology suppliers: Siporex and Ytong (both belonging to the Swedes), Durox (bought by the Dutch) and newcomer Hebel (German). Throughout the rest of the 20th century all of them successfully sold AAC technology licenses around the world while at the same time annual conventions contributed to further developments in AAC production, product quality and its applications.

Given different manufacturing technologies, production of AAC blocks became associated with Ytong (tilt-cake system) while production of both AAC blocks and reinforced elements was led by Durox, Siporex and later Hebel (flat-cake systems).

Today, mass production of non-reinforced blocks is popular in Central and Eastern Europe, China and India while Japanese, South Korean, Australian and Western European markets are focusing on more technologically advanced production of AAC panels (load bearing for floors, walls, roofs and non-load bearing for partition panels and cladding) as well as dimensionally highly accurate blocks.

AAC Panels and AAC Reinforced Elements

Flat-cake technologies Durox and Hebel are leaders in supplying the reinforced AAC elements due to their more suitable and favourable cutting and curing technique. Aircrete SUPER SMOOTH Flat Cake system has been developed using and perfecting past experiences of the Dutch Durox technology. Today, AAC panels are getting more and more attention due to available number of advantages over the block masonry. In Eastern and Western Europe many AAC plants supply both autoclaved aerated concrete blocks and autoclaved aerated concrete panels.

Japan and Australia, until today, remain a 100% reinforced elements market. Since 2002 reinforced element production was further perfected by the Dutch and nowadays Aircrete Europe’s technology allows manufacturing complete prefab AAC housing solutions. Taking into consideration fast, economic and structural building with AAC panels, many countries today are looking for ways to introduce complete AAC housing solutions in their local construction markets.

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