What is RAAC Concrete and Why is it a Risk to Schools?

RAAC or Reinforced Autoclaved Aerated Concrete is a lightweight concrete that has been used in a vast array of different construction projects and buildings. RAAC is a form of concrete, but it is very different from traditional concrete because of the way it is made – which makes it much weaker than pure concrete products. Originally, panels for flooring and roofing were manufactured out of RAAC after the Second World War and from the 1950s up until as recently as the mid-1990s, it was used extensively in schools, colleges and other buildings as it seemed to be an ideal cheap-to-produce, yet strong, material for construction with great thermal properties.

However, professional engineering concerns about the longevity of the material, and therefore the safety of the schools, colleges and other buildings that had RAAC in their structures, began to be voiced. The disaster in 2018 when a ceiling of a school collapsed in Kent has caused the issue to become ever more pressing and urgent with the Department for Education (DfE) calling for government support to sort the problem out. Fortunately, in the 2018 incident, the ceilings collapsed at a weekend, meaning nobody was hurt, but it caused the closure of the school.

Following that, this year more than 100 schools, nurseries and colleges across the country have been forced to close classrooms and other parts of their buildings that contain RAAC and are in danger of collapsing, putting impossible pressure on already oversubscribed school premises. For a fast, temporary solution, MPB offers temporary modular classrooms that can be installed and better than the old ones within weeks.

Blue and White Modular Classroom

What is RAAC concrete? And what is it made of?

RAAC is made from a mixture of cement, calcined gypsum, aluminium powder, lime and water which is poured into moulds and set at extremely high heat and pressure, which is known as autoclaving, to create a lightweight and strong, but porous, material which looks rather like an Aero chocolate bar. RAAC panels are frequently strengthened by steel bars, but the porous material, when exposed to moisture, rapidly loses strength, and even more when the steel begins to rust. It has become glaringly obvious that any buildings containing RAAC need to have them replaced completely to remain structurally sound.

Who invented RAAC concrete?

RAAC concrete was first perfected in the mid-1920s by a Swedish architect and inventor working with a professor at the Royal Institute of Technology and the process was patented in 1924. The Institution of Structural Engineers (ISE) actually pointed out the risks of using RAAC as far back as 1961 and they said in a report that “it is perhaps unfortunate that the term concrete has been retained for these aerated products” – as using ‘concrete’ in the name deceives people into believing they’re stronger than they really are. The ISE explained that the panels only had a lifespan of 20 – 30 years, depending on their exposure to moisture, even if coated in protective layers such as bitumen, and that corrosion can occur without any visual indication– meaning a high risk of collapse without any warning in any panels over that age.

What does RAAC concrete look like? How to identify RAAC concrete

RAAC concrete can be difficult to identify as it looks similar to traditional concrete and other building materials. When it is cut or broken into it shows a distinct honeycomb-like structure inside although the exterior is smooth which is why it is hard to identify – especially when covered in other materials such as suspended ceilings, plasterboard or even brickwork. All schools must inspect their buildings for the material and try to identify the risks. As of September 2023 over 150 schools and nearly 30 hospitals were found to have the material in the infrastructure, and many schools had to keep their buildings or parts of their buildings closed with the growing fears of possible collapse. To identify if a school has RAAC concrete, schools need to contact a professional to conduct an inspection.

Why was RAAC concrete used?

Simply put, RAAC concrete was cheap to produce, and one of its bigger benefits is that it has good fire-resistant properties which, even when left without plaster, won’t break down in a fire. RAAC also has good thermal properties creating attractive cost savings. RAAC is not in and of itself dangerous if it is properly manufactured, installed and maintained, but the fact that it hasn’t been properly looked after in hundreds of school buildings means that it has come to the end of its lifespan, and hasn’t yet been replaced with a stronger and safer material. RAAC should not be used in a structural capacity as it cannot bear the loads that normal concrete, or reinforced concrete can.

Which schools have RAAC concrete in England?

Too many schools to list have RAAC concrete in them, and the government is going to have to fund the rebuilding of many. As of last month at the time of writing, the list had numbered over 150 and was expected to rise with more schools becoming aware of the pressing need to inspect their buildings. Large numbers of schools had to close their buildings completely, pending refurbishments, and more than 100 have had to find emergency accommodation until classrooms are made safe.

What is the risk for schools and what’s the answer?

The risk for schools is clearly that they need to be aware of the presence of RAAC materials within their school buildings and the level of risk that they might cause. Over 250 temporary classrooms have had to be ordered to help schools with the RAAC crisis.

Whether a school needs a short-term solution before refurbishments can happen, or simply needs more space in which to operate generally, a temporary classroom is the answer. With decades of experience in the sector and having provided temporary classrooms, changing rooms, toilet and shower blocks to schools all over the country, MPB is the company you can trust to offer you exceptional quality at the most competitive prices and a speedy installation to get your school routines back to normal.

Get in touch today with a member of our team, either by calling 01889 271406 or by sending an email to admin@mpbltd.co.uk to discover how our temporary buildings can help your school through its RAAC crisis.