Desmonde Associates features on BBC Radio Cornwall to discuss RAAC in UK schools
Structural Engineer Philip Desmonde was asked to give his expert input regarding the recent Reinforced Autoclaved Aerated Concrete (RAAC) issues identified in over 100 schools across the UK.
Over 100 schools across the UK have either partially or fully closed after the identification of major structural issues related to RAAC. Between the 1950’s and 1990’s RAAC was used in many public buildings throughout the UK.
The lightweight material is made using fine aggregates which combined with additives forms a bubble like material similar in texture to an Aero chocolate bar. RAAC was principally formed into pre-fabricated panels largely used to construct flat roofs, floors and walls and it is the rate of deterioration of the material which has raised concerns.
The material properties of RAAC means that in comparison with conventional concrete it is overall weaker and has less structural capacity.
If you need structural engineering services such as the identification of RAAC please contact Desmonde Associates for a free conultation
Structural Engineer Philip Desmonde - Desmonde Associates
Philip Desmonde is a structural engineer at Desmonde Associates a local family run Cornish consultancy based in St Agnes. With decades of experience across the globe Philip was the perfect guest to invite onto Julie Skentenbery’s BBC Radio Cornwall show to discuss the RAAC concerns found in schools across the UK.
Giving an expert perspective on the matter he provided a brief description of aerated concrete:
“Aerated concrete is essentially a product made from mixing cement, fine sand and some lime together to form almost like a soup and then you add aluminium powder which initiates the production of the bubbles in the soup to form something like a rising cake and then the mix is put into an autoclave and subject to high pressure and steam at about 200 degrees centigrade and what comes out is a fantastic product which I would say about 80% of all new houses have in it.”
Philip goes on to mention that aerated concrete is heavily used across the UK in the form of lightweight concrete blocks. It is important to highlight that these blocks are not the same as RAAC but they do share a similar material production process.
RAAC is a form of reinforced aerated concrete where the concrete mix is poured into planks for use in forming roofs and floors with steel reinforcement running through it. The cause of the issues identified in schools throughout the UK in the past few weeks has been described by Philip as a:
“management issue once the building has been erected, [there has been] a failure to properly maintain the weather proofing characteristics of the roof surface or its enclosure”
All construction materials have a “design life” associated with them. This is a period of time which engineers consider during the structural calculations to ensure that buildings and infrastructure is able to meet the ongoing needs of the users far into the future. With reference to the RAAC panels Philip goes on to mention:
“they are coming to the end of their natural life but that life could have been easily extended if there had been a proper program of maintenance.”
A lack of maintenance of buildings is a very common issue across the UK and this is usually especially the case when it comes to civic buildings. This lack of maintenance over several years and decades is what leads to some of the most common issues we see today as professional engineers.
“I often think to myself that a building is like a car, it should an MOT test that is carried out at least every 5 years to ensure through an appraisal, an assessment
…
if you have the same approach to an MOT of a car to an MOT of a building the likelihood of these sudden problems, and they are not sudden, they build up over time and you can pick them up very quickly but it is where we are today that failure to have in these school buildings what I call the MOT process.”
The consequence of poor maintenance has had large ramifications when it comes to the long term structural capacity of the RAAC panels. Water is able to penetrate into the concrete panels and then corrode the steel reinforcement, this weakening of the reinforcement results in deflection of the panel occurring which compounds the issue of water ingress as ponding then occurs increasing the amount of water able to enter into the panel and further corroding the steel until ultimate failure.
For the full interview you can click here to listen to the full BBC Radio Cornwall show.