Indeed, it's light enough in some formulations to float in water. So in the decades after, AAC became a very popular type of building block used in many roofs and also, since it is fireproof and an excellent thermal insulator, for some walls.In particular, a lot of flat roofs were made using RAAC, but then in the 1990s structural engineers discovered that many of the RAAC planks used in Britain were losing their strength - especially when they came into contact with standing water.
One of the reasons why concrete has become such an important building material is that we now have centuries of experience in using it and, just as important, century-old buildings we can point to to reassure ourselves that this material can stand the test of time.'Most parents should not be worried'
This is what brings us back to that thesis about fixing climate change. There are many exciting formulations for new low carbon concretes being tested. Some involve fiddling with the formulation of cement, some entail a change to the way that concrete is prepared and some involve entirely new recipes. There are promising trials under way, many of them in laboratories.
Traditional concrete - for all its shortcomings - is at least a known, tested building material. New recipes are viewed with understandable caution.