Aerated autoclaved concrete
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Aerated autoclaved concrete (AAC) was first developed by a Swedish engineer between the years 1920 and 1932. It has since been refined into a high thermally insulating concrete-based material used for construction both internally and externally. Besides insulating capability, one of AAC's advantages in construction is its quick and easy installation since the material can be routed, sanded and cut to size on site using standard band saws, hand saws and drills.
Even though regular cement mortar can be used, 98% of the buildings erected with AAC materials uses thin bed motar, which comes to deployment in a thickness of 1/8 inch. This varies on national building codes and creates solid and compact building members. AAC material can be coated with a stucco compound ore plaster against the elements. Siding materials such as brick or vinyl siding can also be used to cover the outside of AAC materials.
Raw materials
Quartz sand, lime and/or cement as binding agent. Aluminum powder in 5%–8% by volume (depending on the pre-specified density) and Water. Mixed and cast in forms, several chemical reactions take place of which one is of great importance: Aluminium powder reacts with calcium hydroxide and water to evolve hydrogen, this creates gas bubbles up to 1/8 inch in diameter and this stimulates the raw product to foam up and double its volume. At the end of the foaming process, the hydrogen escapes to the atmosphere where it reacts with air to form water. The hydrogen which was contained in the bubbles is replaced by air.
After the forms are opened, the material carries a certain structural stability. It is cut into blocks and panels by wire. However, to reach full structural integrity and strength, now the material needs to be autoclaved. Only under the specific conditions of autoclaving further chemical reactions for hardening of the material can take place. During the steam pressure hardening process, when the temperature reaches 374 °Fahrenheit and the pressure reaches 12 bars, quartz sand reacts with calcium hydroxide and evolves to calcium silica hydrate which account for the material's physical strength properties.
After the production process of autoclaving has ended the material is ready for use. Depending on its density, up to 80% of the volume of the mass is air. Density also accounts for the variable structural compression strength of AAC material, which can carry loads up to 1,200 PSI.
Since 1980, there has been a worldwide increase in the use of AAC materials and new production plants are being built in the United States, Eastern Europe, Israel, China, Bahrain, India and Australia. AAC is increasingly used by developers, architects and home builders.
External links
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