Masonry Magazine June 2008 Page. 36
AUTOCLAVED AERATED CONCRETE
How AAC is made
To make AAC, sand is ground to the required fineness in a ball mill, if necessary, and is stored along with other raw materials. The raw materials are then batched by weight and delivered to the mixer. Measured amounts of water and expansive agent are added to the mixer, and the cementitious slurry is mixed.
Steel molds are prepared to receive the fresh AAC. If reinforced AAC panels are to be produced, steel reinforcing cages are secured within the molds. After mixing, the slurry is poured into the molds. The expansive agent creates small, finely dispersed voids in the fresh mixture, which increases the volume by about 50 percent in the molds within three hours.
Within a few hours after casting, the initial hydration of cementitious compounds in the AAC gives it sufficient strength to hold its shape and support its own weight.
After cutting, the aerated concrete product is transported to a large autoclave, where the curing process is completed. Autoclaving is required to achieve the desired structural properties and dimensional stability. The process takes about eight to 12 hours under a pressure of about 174 psi (12 Bars) and a temperature of about 360°F (180°C), depending on the grade of material produced. During autoclaving, the wire-cut units remain in their original positions in the AAC block. After autoclaving, they are separated for packaging.
AAC units are normally placed on pallets for shipping. Unreinforced units are typically shrink-wrapped, while reinforced elements are banded only, using corner guards to minimize potential localized damage that might be caused by the banding.
AAC strength classes
AAC is produced in different densities and corresponding compressive strengths, in accordance with ASTM C1386. Densities and corresponding strengths are described in terms of "strength classes" (See Table 1).
Typical dimensions of masonry-type AAC units
Typical dimensions for masonry-type AAC units (masonry-type units) are shown in Table 2 below.
Typical AAC masonry applications
AAC MASONRY CAN BE USED in a wide variety of structural and non-structural applications. For example, in applications used in projects in Arizona and Las Palmas, Mexico, the thermal and acoustical efficiency of the AAC makes it an attractive choice for a building envelope.
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