Adequate skid resistance of the reinstated running surface must be maintained by selection of the polished stone value (PSV), aggregate abrasion value (AAV) and texture depth of the aggregate exposed at the road surface. The exposed aggregate may be precoated chippings rolled into the surface (HRA), coarse aggregate within the surface course, coated material to BS 594987, or any chippings or other aggregate applied in any form of surface dressing or slurry sealing treatment.
Reinstatements in smaller openings constitute a much lower degree of skidding risk, but the measurement of skid resistance, texture depth and surface regularity become progressively more difficult as the reinstatement width reduces. However, material requirements and laying conditions remain unchanged and it is expected that the skid resistance of reinstatements in smaller openings will not be significantly different.
For the purposes of identifying reinstatement sites where the risk of skidding is potentially high (Site A, S2.6.3), sections of carriageway exceeding 10% gradient should be identified from existing steep hill warning signs or by notification from the authority. Similarly, bends of less than 100 m radius in roads where the speed limit is greater than 40 mph (65 km/h) should be identified from existing bend, double bend or chevron warning signs or by notification from the authority.
Given good site conditions, it is possible to obtain reasonably representative measurements of skid resistance and surface regularity on narrower reinstatements but amended test procedures and extra care are required. The Mini Texture Meter and Rolling Straightedge should always be fully contained within the limits of the reinstatement. The actual minimum practicable width for these instruments will depend on the trench alignment and radius of curvature. Measurements can be particularly difficult when testing on tight radius bends.
The undertaker should require the suppliers of bituminous materials to regularly supply details of the constituent materials within their bituminous mixtures and in particular, PSV/AAV test results for the coarse aggregate in surface course mixtures and the aggregate used for precoated chippings in HRA.
Past use of Table S2.7 indicates that the minimum values noted are appropriate in most cases.
The requirement for PSV only relates to the directly trafficked coarse aggregate size fraction, i.e. feedstock into the asphalt production retained on 4 mm sieve. Research for the use of 53 PSV aggregate was based on crushed hard stone. Some sources of coarse aggregate limestone can have a PSV of 53 or higher. These sources should not be used in without an evidenced in-service track record. The historic track record would be versus the 3rd Edition requirement of 55 PSV. The restriction on limestone should not be misinterpreted to prohibit its use as a fine aggregate, filler or in any other application other than the coarse aggregate in the running surface. For chipped HRA applications this requirement only relates to the chippings.