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| Wall made by aerated concrete blocks |
Aerated blocks are made from cement, lime, sand, pulverised
fuel ash (from power stations) and water. First the PFA sand and water are
mixed to form slurry. This is then heated and mixed with cement and lime and
finally a small amount of aluminium powder is evenly dispersed through the
mixture before it is poured into moulds. The aluminium powder reacts with the
mix to form millions of tiny pockets of hydrogen. These subsequently diffuse
from the material to be replaced by air (see photo). When the mixture has
partially set the long strips of aerated concrete are wire cut into blocks of
the right size and the cut blocks are transferred to an autoclave for high
pressure steam-curing. During this process calcium silicates are formed which
bind all the ingredients together.
Aerated blocks can be used for
lightweight partitions and loadbearing internal walls. They have been available
for about 40 years or so and have replaced earlier lightweight blocks made from
a variety of lightweight aggregates. Aerated concrete blocks can be used in the
external leaves of cavity walls (they are usually rendered). It's even possible
to built solid (non cavity walls) in aerated blocks as long as an external
cladding is fixed to the wall for reasons of appearance and weather protection.
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| Aerated Concrete Block |
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