What is RAAC Concrete?

At the moment, RAAC concrete has been the focus of major news stories, and the cause of concern across the country.

Throughout the UK, RAAC concrete is causing issues in numerous schools, forcing them to close or move classrooms due to the severity of the problem.

Although this article is not a guide – and any school that thinks that they might have an issue with RAAC Concrete should get in touch with their local authority immediately – it is designed to help readers to understand what RAAC concrete is, how it is used in construction, and the nature of the issues that it causes.

What is RAAC concrete?

RAAC concrete is the shortened name given to Reinforced Autoclaved Aerated Concrete. This is a lightweight aerated concrete, which differs considerably from conventional concrete, as it does not have any coarse aggregate.

How is RAAC concrete used in construction?

RAAC concrete was used in many construction projects after the war, particularly in public buildings, as its light weight, ease of moulding, speed of production and low cost made it a very popular building material.

For these reasons, it was used in the construction of many schools throughout the country. RAAC concrete can be seen as structural panels, which are used in a range of different building elements. These include ceilings, flat roofs, pitched roofs, floors and wall panels (including both indoor and outdoor panels).

Why is RAAC concrete unsafe in some cases?

The unique texture of RAAC concrete was precisely what made it such a popular choice for construction projects. However, this property is also the reason why it is causing such major issues today.

This aerated texture significantly compromises the durability of the concrete. But, this fact wasn’t known previously, and it is only recently that we have been seeing the structural weaknesses (and consequent short lifespan) of RAAC concrete.

RAAC concrete has a different structural behaviour to other concrete types. Most critically, the concrete can allow water to enter the concrete, which can cause its structure to fail. Furthermore, if RAAC concrete is exposed to polluted air for an extended period of time, this can also significantly reduce its strength.

In fact, this means that RAAC concrete only has a lifespan of around 30 years, and we are already seeing structures made of RAAC concrete start to deteriorate.

In most cases, RAAC concrete is reinforced by a rebar and coated with a protective material (like bitumen). However, specialists are also realising that both the rebar and the bitumen coating can also degrade, decay and weaken over time.

As a result, according to The Health and Safety Executive, since many of these RAAC concrete structures have passed their predicted lifespan, they could “collapse with little or no notice.”

How can you spot issues caused by RAAC concrete?

The Department for Education is asking that all responsible bodies check their buildings, to see whether RAAC concrete is present. Unfortunately, in many cases, these issues can occur with very little warning. But in the case of RAAC roofs, cracking, bowing and deflections are among the most common ways to identify a developing issue.

If you spot any of these signs, and you know that your roof is made from RAAC concrete, then you should get in touch with your local authority as soon as possible.

What are the best ways to rectify issues caused by RAAC concrete?

If you aren’t sure whether or not your building panels are made from RAAC concrete, or you have concerns that there might be a structural issue present, then we suggest enlisting the assistance of a building surveyor or structural engineer. We would recommend looking for a qualified, accredited company, which offers a specialist ‘RAAC survey’ service.

They will be able to inspect your building, and inform you whether or not RAAC is present.

Then, if this material is present in your building, they can provide you with detailed advice about the best course of action to take. This is the best way to ensure the safety of everyone on site, especially because RAAC concrete issues are known to develop rapidly.

Alternatively, your school could also contact your local authority, to get their advice and inform them of your concerns.

If you are looking for concrete for your project, iMix Concrete can supply a range of quality concrete across London, Kent, Essex and the surrounding areas. Contact our team for a free quote!