Anyone in the building trade know what's the score with this dodgy concrete? Did they only use it to build schools? Why are no buildings in other uses getting closed? Is there a time when this concrete started to be used and has it stopped being used. It's all very strange. And of course you can't rely on the media to ask the right questions.
I have no idea if this is the correct answer, but it's just popped up on a news feed. RAAC is a lightweight, precast, cellular concrete building material made from quartz sand, calcined gypsum, lime, portland cement, water and aluminum powder. It started being used predominantly in public sector roof construction in the UK and parts of Europe in the 50s and continued to be used until the 90s, but the material has been found to have structural issues that means it begins to deteriorate after 40 or 50 years. That means much of the RAAC that remains in British buildings is now at risk of causing a collapse. Professor Chris Goodier, an expert in construction engineering and materials who led a major national research project on RAAC for the University of Loughborough, explains: “Like many countries, the UK has an old building stock, which needs to be adequately repaired and maintained. In the post-war period the country built numerous new buildings with a variety of different methods, many of which are now feeling their age. “One innovative construction material and process was RAAC, which is an aerated lightweight cementitious material with no coarse aggregate; the material properties and structural behaviour therefore differs significantly from ‘traditional’ reinforced concrete. “Tens of thousands of these structural panels exist across a broad cross-section of buildings, many constructed in the 60s and 70s, and many are showing signs of wear and tear and deterioration. The vast majority form the roof of the structure, usually flat, and hence are difficult to access, survey, maintain and replace.” A report published in May 2019 highlighted the significant risk of failure of these planks and in September last year the Government sent a notice to relevant property owners stating that “RAAC is now life-expired and liable to collapse”. Professor Goodier said it is RAAC “from the 50s, 60s and 70s that is of main concern, especially if it has not been adequately maintained”. “RAAC examples have been found with bearings (supports) which aren’t big enough, and RAAC with the steel reinforcement in the wrong place, both of which can have structural implications. Prolonged water ingress (not uncommon on old flat roofs) can also lead to deterioration,” he said. However, not all RAAC is dangerous by nature. It is s still manufactured and installed all over the world and can be an appropriate construction material if properly designed, manufactured, installed, and maintained. What is RAAC? Why aerated concrete school buildings must close in England and the safety fears explained (msn.com)
