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Asphalt evidence on slippery ground


I found the headline 'Asphalt is slippery on dry and wet roads says TRL report' (News 31 January) unhelpful and misleading.

Is this problem limited to stone mastic asphalts (SMA) only? Or are we to assume this covers hot rolled asphalt, bituminous Macadams and anything that is termed a 'thin surface' as this will include both positive and negative textured materials?

To make such a charge without knowing the details of the material is irresponsible.

What type of material is it, and does it have a BBA/HAPAS certificate? And what is the viscosity of the bitumen as this will make a big difference when the surface is subjected to heat and shear stresses generated by a locked wheel? What are the sources of all the aggregates in the mix?

The polished stone value (PSV) of the aggregate may well seem negated when the surfacing is freshly laid because the larger aggregate will be coated with bitumen. However, approximately 25% of the aggregate in the mix will be material passing the 2.36 micron sieve/screen and this fine material will be part of the larger aggregate binder coating.

It only requires a minimum amount of vehicle wear for this finer aggregate to be exposed to tyre wear and increase the skid resistance value (SRV).

Steve Brown, 120 Leicester Road, Groby, Leicestershire

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