23rd November 2023

Do you Have RAAC?

Introduction

You have no doubt seen the headlines this year with large-scale closures of schools and public buildings due to risks of Reinforced Autoclaved Aerated Concrete (RAAC). This blog aims to provide an overview of the risks and what action should be taken to mitigate the risks of RAAC should you have it within your premises.

What is RAAC?

RAAC has been widely used in the construction industry in the UK. It was primarily used from the 1960s up until the early 1990s. RAAC offered several advantages, which contributed to its popularity during that time. Chemicals were added to the concrete aggregate mix which formed gas bubbles making it lightweight in nature, and easier to handle and transport. It also has excellent thermal insulation properties, providing energy efficiency to buildings. Additionally, RAAC offers good fire resistance and sound insulation, for these reasons it was predominantly used to make roofs, floors and walls in such buildings as schools, hospitals and other similar developments.

However, the use of RAAC declined over the years due to some drawbacks. One significant issue was the presence of steel reinforcement within the panels, which caused corrosion problems. This led to structural instability and potential safety concerns. As a result, the production and use of RAAC was discontinued.

How can you Identify RAAC?

Identifying RAAC in a building can be challenging as it may not always be visually apparent. RAAC is a lightweight material and therefore looks visually lighter in appearance than regular concrete. The panels typically have a cellular structure visible on the surface. The cells are formed during the manufacturing process and create a honeycomb-like pattern. Look also for steel reinforcement bars or mesh embedded within the panels.

One way to spot compromised or failing RAAC is if appears damp. Signs of dampness in RAAC are the very first indication that the concrete might have a problem. That’s because many of the problems inherent in RAAC stem from the presence of moisture. If you notice that the exterior of any RAAC in a property you own or manage is damp, then it could be a sign that further problems have developed.

What’s the Problem?

RAAC is permeable meaning that the concrete is open to water damage causing it to degrade. There is a risk that the permeating water can cause the supporting steel bars to corrode leaving the brittle and the RAAC without any internal support.

Consequently, as the concrete itself crumbles, and is likely to fail. In some instances, this failure can be sudden and completely catastrophic.

Problems with RAAC were highlighted in August 2023, when a ceiling panel that had previously been classed as non-critical by inspectors, collapsed at a school.

In response, the Department for Education issued an urgent alert. More than 156 schools were identified as being at risk.

Recent evidence shows that the behaviour of these panels can no longer be predicted reliably due to uncertainties in the material and the mechanical properties of the panels, which are highly impacted by deterioration. This is simply because the panels have been used so far beyond their intended design-life and in many cases without proper maintenance.

If you suspect that a property you own or manage does feature RAAC, then it’s important to act sooner rather than later. Arrange for an assessment by a structural engineer with RAAC experience. They will be able to assess the building and provide an evaluation of the risk with advice on any remediation works that may be required.