Understanding chemistry at play in RAAC explains weakening of concrete

Managers of schools, hospitals, courts and theatres are urgently reviewing their buildings as the crisis concerning Reinforced Autoclaved Aerated Concrete (RAAC) continues. Shortly before the start of the school term, the government advised education settings to vacate all spaces known to contain RAAC, unless they had mitigations in place to make the building safe. The move caused significant disruption and highlighted the importance of maintaining the structural integrity of buildings over time.

RAAC is a lightweight material typically used in precast panels in buildings erected between the mid-1950s and mid-1990s. ‘We have known about issues with RAAC since about 1992,’ says Phil Purnell, professor of materials and structures at the University of Leeds. ‘The Building Research Establishment produced a report in 1996 that effectively killed any further use in the UK. [However] this was a common building material outside the UK and still is.’