Early and mid life skid resistance

Safety applies to all stages of highway or airfield construction i.e. from initial design, selection of materials to use of the surface by the user. In the UK, criteria such as noise, negative texture, spray generation, layer thickness, availability and cost of limited sources of higher PSV aggregate have resulted in a shift towards thinner, smoother and quieter surfacings. These materials typically use a modified bitumen or have thicker coatings of bitumen to hold the aggregate particles together. The authors recognised that the early life safety of these materials needed consideration given that bitumen has poor wet skid resistance. This paper considers the development of skid resistance for an SMA surface using high PSV greywacke aggregate and polymer-modified bitumen. This surface has been periodically measured using a GripTester to determine how skid resistance has developed from early life through to mid life. The findings show how this is different from a conventional chip seal or positive textured asphalt surface. A new theory is proposed that explains how skid resistance develops for these types of surfacing.