This new concrete, from Lafarge Tarmac, could potentially be a very
useful tool in combating urban flash flooding from sudden, heavy storms.
In its promotional materials, the company uses the example of the 2007 floods that devastated England, costing the economy some £3.2bn. Of the 57,000 homes affected by the floods, two-thirds were damaged not by rivers that overflowed but by storm-water run-off.
There are some caveats to the technology, which works the way it does
because there are empty spaces between particles that allow water to
flow through. Topmix concrete, which is applied over a base layer of
gravel that further filters water, is less able to handle heavy vehicle
loads and intense traffic than conventional paving materials.
Also its ability to absorb water can be compromised by dirt and other
particulate waste, such as sawdust or silt. Damage from freezing water
is a potential concern with permeable pavement, although Lafarge Tarmac
says its product has “excellent freeze-thaw resistance.”