Concrete doesn’t usually tend to feature in media headlines. But it dominated the front pages of British newspapers in early September thanks to the revelation that several schools and other public buildings, including hospitals, in the UK are thought to be at risk of catastrophic collapse because of the deterioration of a form of concrete used in their construction. Specifically, the alarm is about slabs of reinforced autoclaved aerated concrete (RAAC), a relatively lightweight material widely used for construction since the middle of the last century. In 2018, the RAAC roof of a school building in Kent, England, collapsed without warning, fortunately at a weekend when it was unoccupied. It transpires that the danger to other buildings has been evident for years but has not been acted on. Only now has it come to the fore, just as British schools were set to return after the summer break.
The AAC production process was devised in the 1920s by Swedish architect Axel Eriksson, and the material’s use in roof panels and lintels began during the following decade. By the mid-century, northern Europe and Scandinavia were the hubs of the worldwide AAC market, although today there are production plants also in Asia, eastern Europe and Australia. It would be easy to get the impression from the current press reports that RAAC was a disaster waiting to happen: a false economy for fast, cheap building. But, in fact, modern formulations can supply a perfectly respectable construction material, robust as well as being a good thermal insulator and sound absorber. Although concrete production itself has a big carbon footprint, the thermal properties of RAAC commend it for ‘green’ applications in highly insulated, passively heated homes, while its acoustic properties make it ideal for buildings next to noisy roads or airports.
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