Materials firm Aardvark is selling concrete that allows rainwater to pass directly through it to improve flood drainage in urban areas.
The porous material, already widely used in the US, lets water seep through to the surrounding ground at a rate of 8-12 gallons per minute per square foot.
Where Keller made its money
Keller’s first-half turnover split
UK £44.8m (2007: £35.4m)
US £245.5m (£232.7m)
Europe, Middle East and Asia £204.4m (136.2m)
Australia £74m (£39.6m)