Concrete Catastrophe what is RAAC and why are schools closing?
Just as the summer holidays come to an end, parents across the UK are left wondering about whether it is safe for their children to return to school.
What is RAAC?
Reinforced Autoclaved Aerated Concrete (RAAC) is a construction material which was mainly used in public sector buildings in the UK between the 1950’s and the 1990’s.
RAAC is a considerably lighter weight material when compared with ordinary reinforced concrete and is made using fine aggregates with additives which react to form carbon dioxide gas resulting in a bubble like texture, think an Aero chocolate bar.
The material properties of RAAC mean that compared with conventional reinforced concrete it is weaker and has less structural capacity.
RAAC was principally pre-fabricated into panels for use in roofs, floors and walls as well as other structural elements.
If you need help identifying possible RAAC contact Desmonde Associates for a free consultation.
School Closures due to RAAC
Across the UK more than 100 schools and other education institutions have been instructed by the Department of Education (DfE) to close buildings over concerns regarding the ongoing safety of RAAC.
This has meant that some students have had a return to home schooling with the Education Secretary stating:
“in the minority of cases where home learning has been required, it has been for days not weeks.”
The government had previously requested local authorities and academy trusts to identify the possibility of RAAC being present in their respective institutions, with the Education Secretary saying:
“Where schools tell us RAAC is suspected, we send out an engineer to confirm it.
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For some schools, the engineering surveys were deemed critical so immediate action was taken. Other schools, deemed non-critical, were allowed to stay in place, although mitigating and monitoring it was still advised.”
Why use RAAC?
Following the post war building boom of the 1950’s, 60’s and 70’s RAAC was seen as a revolutionary material. It was much cheaper to produce than conventional concrete and weighs about three quarters less meaning it was also easier to transport and build with.
RAAC was ideal for pouring into molds for facilitating the rapid flat-pack-style construction of much needed institutional buildings. It was used extensively to produce flat roof panels which given the nature of the material is a vital reason why there is such a large safety concern.
The aerated nature of the material enables pollutants and water to seep into the concrete which works it’s way through the material and will corrode the steel reinforcement buried within, weakening the material until it fails suddenly and catastrophically.
How long have the risks been known?
It was known as far back as the 1960’s that RAAC had the potential to be less durable than conventional concrete. The use of the material stopped in the 1990’s when it was found that the structural durability of RAAC did not stand the test of time.
The safe lifespan of RAAC is about 30 years meaning that the buildings built in the 1950’s came to the end of their safe working life in the 1980’s. By the 1990’s several roof collapses meant that the material was no longer felt suitable for use.
The UK Government conducted research in the 1990’s with the Education Secretary stating:
“RAAC was already known as a risk, with research conducted by the Government in the 1990s, but the experts had been clear that where it was rated “non-critical”, spaces could be occupied with ongoing monitoring.”
It is important to note that given the nature of RAAC it may not always be possible to identify corroded steel reinforcement a February 2022 paper produced by the Institution for Structural Engineers: Reinforced Autoclaved Aerated Concrete (RAAC) Panels Investigation and Assessment states:
“Not all defects are visible e.g. corrosion of the reinforcement. Panels which appear to be in a good condition may conceal hidden defects which could present a risk to the integrity of the panels.”
Over the summer time a previously identified RAAC beam within a school which had previously been recorded as being “low risk” suddenly collapsed which lead to a review of the RAAC issue across the Education portfolio with all schools known to contain RAAC being marked as potentially dangerous.
Desmonde Associates are a family run firm of Construction Professionals based in St Agnes Cornwall. We have decades of experience working across private and public sector projects. For more information on how we can help please get in contact.