COMPACTION OF the replacement porous asphalt surfacing on the controversial Newbury bypass will be to much tighter standards than the original, the Highways Agency confirmed this week.
A new binder which is more tolerant to variations in laying temperature will be also be used 'as a precaution', although the exact cause of the rapid stone loss which made complete resurfacing necessary after only 10 months is still unknown.
Agency divisional director Steve Rowsell said investigations were continuing, but blacktop supplier Hanson would be paying the cost of relaying the 9km of dual carriageway involved.
'The tests are not conclusive but it was obvious the original surfacing wouldn't last 10 years, so it had to be replaced,' a Hanson spokesman said. 'It is our responsibility to make sure the materials we supply are fit for their purpose.'
Lack of proper compaction was one of the first possibilities considered when major stone loss was first noticed earlier this year (NCE 18 March). Agency requirements were said to be less than demanding, with no requirement for the number of roller passes needed.
Rowsell said: 'There's still no reason to believe there was anything wrong with the original specification, but we have introduced some changes to the requirements for compaction to tighten them up.'
He added that there was no relationship between this porous asphalt failure and the problems with porous asphalt on the M25 last year. 'Those were due to inadequate porosity. The only other similar case we know of is a very small area of minor stone loss on the M40, which had no effect on the life of the surfacing.'
Contraflow working has been ruled out in the interests of completing the work as fast as possible. Instead, traffic from one carriageway at a time will be diverted back on to the old A34 through Newbury.
The sudden failure of the M40 last Wednesday has baffled the motorway operator UK Highways and the Highways Agency. A three-lane, 500m stretch of the M40 had to be closed for two days between junctions two and three near Oxford to allow emergency maintenance work when holes appeared after rain.