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10Feb94 UK: BLACKTOP-WHITETOP DEBATE TO RAGE ON.

Future developments in materials technology will be influenced by whole life costing - and will probably ensure that the choice between concrete and asphalt does not become a foregone conclusion as a result of new procurement criteria, writes David Taylor.The Department of Transport has made it clear that it expects local considerations to influence the choice of paving material every bit as much as life-time costs.And one of the most emotive of these local concerns is tyre noise. Both concrete and asphalt engineers have come up with formulations which have been designed to minimise surface noise. Both have their advantages and disadvantages.Porous asphalt has been used extensively on mainland Europe - particularly in Austria, the Netherlands and France.The effects of its 'spongey' texture are two-fold: first, it absorbs more tyre noise than traditional, dense blacktop; second, it allows surface water to drain away quickly, improving visibility and safety.The asphalt lobby in Britain has been trying for more than 10 years to persuade the DoT to produce a specification for porous asphalt, but with little success.If anything, the whole life cost considerations could work against this material. Its maintenance requirements are high, regular attention being necessary to ensure the open texture does not get clogged, and its lifespan is even shorter than traditional blacktop.Meanwhile, another continental development - known in this country as whisper concrete - has been put forward by the concrete lobby as its own answer to noise pollution.This material is now being assessed on a trial stretch of the M18 motorway in Yorkshire.Mowlem won the contract to lay the material (which employs a multi-directional surface texture to reduce noise) last summer.Even so, neither porous asphalt nor whisper concrete got a look-in when bids were invited for the Brockworth bypass job.The alternatives laid down by the DoT ruled both of them out. CONSTRUCTION NEWS