Normal concrete is like an artificial rock: the “cement” in concrete glues together different sizes of particles – from sand to pebbles – in a chemical reaction. It’s very good under compression, but weak when put under tension (that’s why it’s reinforced with steel rebar).
But it’s also very heavy – at 2.5 tonnes per cubic meter! That makes concrete construction so heavy that heavy foundations become necessary. (And if the foundation itself is made from concrete, the problem just feeds itself!)
Aerated Concrete is made adding a chemical like magnesium that creates millions of tiny bubbles inside the concrete. As a result, it is many times lighter ánd it is quite insulating. And it’s also known as cellular concrete, or in Europe, by the brand name Ytong who pioneered it.
The curing can be increased by a process that combines heating and humidity (“autoclave”) – hence the term “AAC” for aerated autoclaved concrete.
Unfortunately, the air bubbles inside make AAC relatively brittle – and often lots of material gets damaged in transport and during building.
Some qualities can still be structural – i.e. they can hold up a house without the need for a separate steel or concrete structure – but check this carefully and use an engineer to make sure that the AAC walls do not get any point loads that may just be too much for them!
Aerated concrete is available as blocks and panels.
AAC blocks are lighter, larger and easier to install than normal bricks or concrete blocks.
AAC panels often have rebar reinforcements to compensate for their brittleness, which makes them viable products for floors and ceilings.
The smoothness of many AAC blocks makes applying “wet” finishes like plastering relatively difficult – you’ll need very experienced craftsmen to avoid cracks in the plastering.
Is AAC a smart building solution?
- it’s light and easy to work with
- it thermally insulates better than concrete or brick
What are the limitations of AAC?
- brittle, causing above average of material loss
- harder to finish with “wet” finishes like plastering
- finishes may crack
- Cost efficiency: ***
- initial cost ***
- lifetime cost ***
- thermal insulation: ****
- sound insulation: ***
- air quality: ***
- embedded energy: ***
- renewable: ***