The school Concrete Crisis: RAAC and the value of using the right materials
Between the 1950s and 1990’s, hundreds of schools in the UK were constructed using Reinforced autoclaved aerated concrete (RAAC) instead of traditional concrete. At the time, RAAC was believed to be a cheaper alternative to standard concrete, but it is now known that this alternative lacks the durability and strength of its counterpart and is susceptible to failure. As a result, the schools with RAAC structures pose a significant threat to health and safety and need to be refurbished. Amid the typical back-to-school chaos, schools are now scrambling to find out if their buildings are safe to use. This ‘concrete crisis’ is leading some schools to start the term off remotely out of fear for the wellbeing of their students.
Why has this only just been noticed?
At the end of last week, the Department for Education (DfE) sent out an urgent alert about the risks of RAAC in schools and initially identified 156 schools that may be affected. This figure has now exceeded 1,500 and schools are not the only public buildings they’re concerned about, with some courts, prisons and hospitals being identified too.
The truth is this hasn’t just been noticed. Concerns over the safety of RAAC in public buildings were raised over 20 years ago and the DfE previously sounded an alert over schools in 2018 after a classroom ceiling in Kent collapsed (thankfully, no one was injured).
The problem has been exacerbated following government cuts to school refurbishment funds over the last 10 years. Now, schools all over the country are frantically trying to find out if they’re affected and many are asking why this wasn’t dealt with sooner.
What is RAAC?
Reinforced autoclaved aerated concrete or RAAC was a concrete alternative first developed in the 1920’s in Sweden. It has a bubbly aerated texture that is acheived by adding an expansion agent such as aluminium powder to the fluid mixture. As the expansion agent reacts with other compounds in the mixture it generates air bubbles creating the aerated texture. RAAC was preferred over traditional concrete as it was cheaper, faster to produce and sometimes easier to install.
The material was also initially valued as it has good fire resistance properties and doesn’t require any additional plastering to achieve this. RAAC does not cause spalling either, which refers to the fragmentation of material during surface failure adding an extra perceived safety advantage.
Unfortunately, this material is not as safe for long-term use and is unreliable. The air pockets in the material allow moisture to enter, making it susceptible to failure. The material also has a markedly shorter life span than conventional concrete, sometimes only durable for 30 years.
The Standing Committee on Structural Safety (SCOSS) has stated: “Although called ‘concrete’, RAAC is very different from traditional concrete and, because of the way in which it was made, much weaker.”
RAAC is intended to be reinforced using steel rebar. However, it has often been installed in UK public buildings without this structural reinforcement. Even when it has been used, the rebar is prone to failure when moisture permeates the concrete. The steel rods are prone to rusting when in contact with moisture and become weak.
Part of what makes RAAC structures in public buildings so dangerous is that they can fail without clear signs of deterioration or wear, making failures hard to pre-empt and sudden.
The major concern surrounding this issue is, of course, Public safety. Many roofing sections have been constructed out of RAAC in Public buildings, particularly schools which presents a high risk to safety in the case of failure. Many of these structures are over 50 years old at this point and are susceptible to failure at any moment, potentially falling on an individual and causing serious injury. Some failures have already happened, such as in the case of the classroom in Kent, which collapsed in 2018. If all these buildings continued to be used without due consideration for safety and refurbishment, it would only be a matter of time before a serious incident occurred.
In response to this safety risk, a huge refurbishment and risk assessment initiative has been launched with the DfE sending teams of engineers around the country to examine RAAC structures in schools.
A list has been published by the Department of Education naming all the schools that have been affected of which there are 147. 24 of these schools have introduced partial remote learning as they are unable to cater for all their students with reduced classroom space after sectioning off some teaching areas. 4 schools have even adapted to full remote learning as a precautionary measure.
The financial cost relating to the remedial construction works needed, disruption of education practices and investigation/risk assessments is as of yet undetermined and will be very challenging to estimate accurately. It is certain that the total costs and disruption of this crisis are well beyond any extra costs and effort that using an appropriate material in the first place would have incurred. Of course, making the decision to use an appropriate material is not straightforward and part of what led to RAAC’s prolific use was due to a belief that it was superior for its intended use to alternative materials.
truly understanding the properties of a material is complex and selecting the correct one for specific applications requires a lot of research and understanding.
How does this relate to sustainability?
Sustainability principles focus on making future-proof decisions, especially when it comes to the built environment. The choice of material in a construction project is central to maintaining not only safety standards but also minimising costs and environmental impact in the long run.
Structures should be designed to last and be functional for as long as possible. By increasing the longevity of a building, the associated carbon and financial costs of development throughout its lifecycle are far reduced, diminishing the accumulated environmental impact. The choice of materials used in construction should, therefore, reflect this objective.
The concrete crisis is a clear example of how many issues can arise from incorrect material choices. Many of these public buildings have a significantly reduced lifecycle resulting from a failure to select the right construction material. This has ultimately risked the safety of the public, incurred large and avoidable financial costs and caused significant disruption.
The services provided by Firstplanit are designed to aid in making future-proof decisions. We offer a detailed evaluation of construction materials that can aid in selecting materials fit to last for their intended purpose as well as many other factors, including embodied carbon, cost and even an environmental health risk analysis of your project location using GIS.
We assess materials over 18 different metrics using vast amounts of data and compare them to up-to-date environmental targets and industry standards to provide a comprehensive assessment so that you can make the most informed decision for your build.
If you’d like to look at a more detailed investigation into the characteristics of RAAC you can look at this report by the Institute of Structural Engineers.