UK materials company Tarmac Lafarge has developed a kind of concrete that can protect urban areas from flash floods by absorbing water at a rate of up to 1,000 litres per square metre per minute.
The "Topmix Permeable" concrete absorbs so much water because between 20% and 35% of its structure is void. This lets water drain through into the sub-strata and dissipate, as long as the soil is not saturated.
The company says it can protect urban areas from floods caused by overwhelmed drainage systems,Â which caused more than two-thirds of the flooding that affected homes in the UK in 2007.
Craig Burgess, Lafarge Tarmac’s product development manager, told New Civil Engineer magazine that the main difficulty lay in producing a product with predictable properties once laid.
"It’s so dry it’s difficult to mix thoroughly," he said. "With Topmix Permeable we’ve concentrated on achieving a homogeneous mix with predictable permeability."
Six years of development eventually produced a mix based on a 6mm crushed granite aggregate mixed with superplasticisers to increase the fluidity of the concrete and other additives that Burgess said were trade secrets.
Watch the "thirsty concrete" at work here.