The chances are that, at least up until recently, you hadn't heard of reinforced autoclaved aerated concrete (RAAC). Despite having written an entire chapter about cement and concrete in Material World, I confess I was completely unaware of this somewhat obscure type of concrete up until recent months. But when RAAC began to hit the headlines in the UK recently, my ears pricked up. It transpires that a lot of municipal buildings, notably a fair few English schools, have rather a lot of RAAC in their structures. And this RAAC has been associated with a risk of sudden collapses of…