Raac in Schools and Homes: What is it?

Crumbling concrete has led to the closure of buildings at more than 100 schools in the UK. The Raac scandal sparked nationwide anxiety about the presence of this construction in other publicly owned buildings and infrastructure. This blog explains everything you need to know about Raac, its implications, and what to do if you are affected.

The Background

Reinforced autoclaved aerated concrete (Raac) has been used in the construction of UK schools from the 1950s to the mid-1990s. Unfortunately, it has recently become clear that Raac can become “crumbly” over time and prone to collapse. This has led to a national scandal, with experts calling for tens of thousands of government and privately-owned buildings to be safety checked.

Indeed, almost every type of publicly-owned building in Britain has been impacted by fears over Raac. The Local Government Association (LGA) is advising its members to check as a matter of urgency whether any buildings in their estates have roofs, floors, cladding or walls made of Raac.

What is Raac material?

With so much controversy around this popular construction material, it is crucial to understand why Raac has been used widely in UK construction. So, let’s start by breaking down the essence of Raac.

This material comprises various components that lend it its lightweight and durable nature. Primarily, it consists of sand, cement, water, and lime. These are mixed and then aerated to form a cellular structure. This aeration is achieved by introducing aluminium powder to the mixture, which reacts to produce hydrogen gas, forming thousands of tiny air pockets.

Why is Raac a potential risk?

In December 2018, the Department for Education (DfE) and the LGA warned building owners of a building component failure in a property constructed using Raac. In May 2019, the Standing Committee on Structural Safety (SCOSS) raised an alert to emphasise the potential risks from such construction, highlighting the failure of a Raac panel roof construction within an operational school. This sudden collapse came without warning. The DfE has since been made aware of further sudden collapses of RAAC panels in roofs that appeared to be in good condition.

Applications of Raac concrete

Due to its lightweight, insulating properties and ease of use, Raac concrete is commonly used to construct walls, roofs, and floors in residential and commercial buildings. Its excellent insulation properties make it an energy-efficient choice, helping reduce heating and cooling costs. It is resistant to fire and pests, further amplifying its appeal in construction.

Raac Plank

A Raac plank is a precast, reinforced version of Raac specifically designed for its structural strength. The reinforcement is typically made from steel mesh or similar materials. These planks have found wide application in the construction industry due to their unique blend of strength and lightweight nature.

Disadvantages of RAAC

However, while Raac offers numerous advantages, its drawbacks are now under the media spotlight. The material can be susceptible to moisture absorption, leading to potential mould growth if not properly sealed. Moreover, compared to traditional concrete, RAAC might not provide the same level of sound insulation.

Identifying Raac concrete

Raac has a distinct porous structure due to its aeration process, so it’s relatively easy to identify. On close inspection, you would notice the myriad of tiny air pockets throughout the material. Additionally, its lightweight nature is another distinguishing factor.

Production of Raac concrete

The production process of Raac involves several stages. The primary ingredients – sand, cement, water, and lime – are mixed to form a slurry. The aluminium powder is then introduced, causing the mixture to expand due to the chemical reactions resulting in hydrogen gas.

Once the desired expansion is achieved, the mix is poured into moulds and left to rise. Next, the hardened material is cut into blocks or panels and subjected to high-pressure steam curing in autoclaves, strengthening the material and giving it its final structure.

Raac in Schools

The energy efficiency it offers had made Raac an appealing choice for educational institutions. However, already mentioned, over recent weeks, about 150 schools have seen buildings close or measures implemented due to concerns over its safety. 

The Department of Education has been closely monitoring all confirmed cases of Raac. Recent cases have led the department to be concerned about education settings, including schools, colleges and maintained nursery schools, and the ability to carefully manage the presence of Raac in their buildings.

The government has been helping schools and responsible bodies, such as local authorities and multi-academy trusts, to manage the potential risks of RAAC since 2018 by providing guidance and funding. However, recent cases have raised concerns about education settings’ ability to carefully manage the presence of RAAC in their buildings.

Raac Around the World

Raac’s popularity has spread across various countries. European nations, in particular, have embraced this material due to its energy efficiency and sustainable properties. Countries like the UK, Germany, and Sweden have incorporated Raac in numerous construction projects.

Conclusion

If you have identified that a building may contain RAAC or need clarification, seek assistance from an appropriately qualified building surveyor or structural engineer with experience of RAAC. They can confirm if RAAC is present in any of your buildings.

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