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Over one hundred schools, colleges, and nurseries in England have received orders to close their classrooms. They also need to close other buildings containing aerated concrete that is vulnerable to collapse. The government issued them with these orders recently. Right now, you are probably wondering what this concrete is and why it is such a risk. Allow us to explain.

What is it?

Reinforced autoclaved aerated concrete (RAAC) is a lightweight concrete variant. Builders chose it for school and college construction from the 1950s to the 1990s. Other building projects also used it according to a government website.

The concrete is a mixture of water, lime, cement, and an aeration agent. You pour the mix into moulds, and then expose it to high heat and pressure. We call this process autoclaving. The result is a porous, strong, and lightweight substance.

How many schools use RAAC?

As of August 2023, records reveal there are 156 educational centres with RAAC. Out of all these, only 56 of them had “mitigations” in place. So, engineers said these sites were not a danger. This is because areas of the structures have reinforcement from other mediums or the buildings are no longer in use.

What is the risk?

There are several dangers here. Firstly, the concrete is “bubbly” and aerated. It does not contain any coarse aggregate. It’s also less dense if you compare to classic concrete. It is roughly a third of the weight according to a building constituency. All this means it is more prone to collapse with time. During 2018, it was flagged as a safety concern after a Kent school roof collapsed.

Identifying it

RAAC possesses an open texture alongside open-sided bubbles that are frequently visible. The exterior tends to be crumbly when you touch it and simple to gouge using a screwdriver. If there is a heavy coating or paint on the concrete, it can be harder to identify.

The term reinforced autoclave aerated concrete may also be located in original drawing and design plans. This is for buildings built between 1950 and 1990.

Get help from the best architects in London

At Coffey Architects, we’re a team that likes thinking outside the box. By taking such an approach, we can come up with ideas that others wouldn’t think off. This allows us to offer clients something unique.

One thing we do is look carefully at different materials for various parts of structures. There are lots of options. However, it is vital to think about stability in the long term. That way we will avoid issues like the one with RAAC.

So, if you’re interested in working with the best architects London has, talk to us. We can support you with a variety of projects.