"RAAC’s structure, often compared to the bubbly texture of an Aero chocolate bar, was once seen as an asset, but its limitations have become apparent over time"
- Steve McSorley - Perega
Reinforced Autoclaved Aerated Concrete (RAAC), once hailed for its affordability and ease of installation, has now emerged as a major structural concern across the UK. Commonly used in buildings from the 1960s through to the 1990s, RAAC was a popular choice due to its lightweight, aerated structure, making it quicker to produce and easier to install than traditional concrete. However, recent discoveries in homes, schools, and healthcare facilities have raised alarms about its long-term safety.
A recent high-profile example of the risks associated with RAAC is in Aberdeen, where hundreds of homes are now slated for demolition and reconstruction, with costs estimated to reach £150 million. As the government continues to investigate the material’s presence in public and private buildings, the scale of the issue is becoming clearer and the need for urgent action is growing.
Understanding the Dangers of RAAC
RAAC’s structure, often compared to the bubbly texture of an Aero chocolate bar, was once seen as an asset, but its limitations have become apparent over time. While RAAC was designed to be cost-effective and thermally efficient, its lifespan is much shorter than that of traditional concrete if not cared for properly, sometimes lasting only around 30 years. When properly maintained, RAAC can last longer, but it is highly susceptible to moisture, which is where the real danger lies.
Moisture ingress allows water to penetrate RAAC’s aerated structure, leading to corrosion of the steel reinforcement within. Over time, this corrosion weakens the material, compromising the building’s structural integrity. In some cases, the lack of anchorage of the steel reinforcement, at the supports, particularly in planks used for roof and floor systems, may lead to sudden shear failure and collapse.
In addition, RAAC is often hidden within the building’s structure, obscured by ceilings and other finishes, making it difficult to detect without an intrusive survey. Compounding the issue is that protective material coatings which prevent water damage, such as bitumen or roofing felt, degrade over time, increasing the risk of failure.
What’s next if dangers are present?
For homes affected by RAAC, the path to ensuring safety begins with expert evaluation. Homeowners should never attempt to address RAAC issues themselves, as even a small disturbance could potentially trigger a collapse. Engaging a professionally qualified structural engineer is crucial for assessing the condition of RAAC and determining the appropriate steps to mitigate the risk.
The first step in this process is a detailed structural survey, often requiring invasive methods to expose RAAC elements and evaluate their condition. Depending on the findings, engineers will decide on the most appropriate course of action.
In cases where RAAC remains stable and intact, regular monitoring may suffice to ensure continued safety. However, if signs of deterioration are detected or bearings are deficient, reinforcement may be required. This can involve adding additional supports or applying materials to strengthen the structure. In more severe cases, where the RAAC has deteriorated beyond repair, particularly in areas exposed to moisture or where there is significant wear, complete replacement of the affected components will likely be necessary.
Filling the cracks
The scale of RAAC’s impact on residential properties is still unfolding, but the response from the UK’s construction and engineering sectors has been swift. Engineers are developing new standards and protocols for assessing RAAC, ensuring that properties are thoroughly inspected and reinforced to meet modern safety requirements. This focus on improving safety measures addresses the immediate risks posed by RAAC but also positions the industry to prevent future issues.
The ongoing RAAC crisis also highlights a key lesson for the construction industry: the importance of reviewing and scrutinising new building materials and methods. By learning these lessons, the industry can ensure that quality and safety remain a top priority in all future construction projects, ensuring homes are secure for generations to come.
