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New porous asphalt protects windscreens from flying stones

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SHATTERED WINDSCREENS caused by flying stones dislodged from roadside filter drains could become much less common after the launch this week of a new form of porous asphalt.

Dubbed Drainfalt, the product was developed by Hanson in conjunction with bitumastic binder supplier BP. Its first trial was along the A4232, near Cardiff, where its success prompted the Welsh Office to approve a second trial in the central reservation of the M4 close to Port Talbot.

'When large vehicles veer off the road, they can spread 20mm aggregate from the drains over the carriageway, which can then be flicked up and hit windscreens or worse, ' explained Hanson product technology head Chris Curtis.

'Drainfalt, however, acts as a highly porous capping layer which can sustain heavy loads and keeps the stones in place.'

Described as a very open texture mix of 28mm and 40mm aggregate with very few fines and a polymer modified binder, Drainfalt is laid around 150mm thick and finished flush with the road surface.

Tests on cores taken from the A4232 trial showed that water flowed through the new material 15 times faster than through conventional porous asphalt, Hanson claimed.

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