INCREASING DEMAND for high quality aggregates triggered by the White Paper's commitment on low-noise roads has forced the Highways Agency to relax its skid resistance requirements
on certain stretches of motorway.
The White Paper states: 'We have decided that from now on, quieter road surfaces will be specified in future contracts (for new or improved roads) as a matter of course.'
But new types of low noise surfacings, such as high performance thin layer bituminous materials and whisper concrete, use more of the scarce high polished stone value aggregates than traditional hot rolled asphalt. These surfacings use high PSV aggregates throughout, compared to HRA which has only a small amount of such aggregates rolled into the surface.
Agency pavement engineering group manager Graham Bowskill said: 'We are concerned about future supplies of high PSV aggregates because only a limited number of quarries can supply them.
'But research has shown that on long straight stretches of motorway a lower PSV aggregate performs just as well, as traffic weaving is minimal.'
Bowskill said the Agency's specification table of permitted PSV values would be re-issued, to give suppliers a 'a much wider scope for using different qualities of aggregate.'
On resurfacing existing roads, the White Paper states: 'In future, whenever a road needs to be resurfaced, we shall ensure that the most appropriate noise reducing surfaces are used for those areas where noise is a particular concern.'
But the Agency has now accepted that porous asphalt is too expensive for anything but extreme cases.
'We have solved the durability problem, but porous asphalt is still twice as expensive as other options,' said Bowskill.