The Polished Stone Value of Aggregates and In-service Skidding Resistance

For many years, aggregates for use in new surfacings have been selected according to their ability to resist polishing, as measured by their Polished Stone value (PSV). However, decisions are now having to be made for more heavily-trafficked roads than were included in the original research, and experience has suggested that expected performance is not always achieved in practice. A database of skidding resistance, aggregate properties and traffic levels was used to review aggregate performance in service. From an analysis of these data, new models for predicting skidding resistance from PSV and traffic data were derived. A series of laboratory studies of polishing was also carried out to investigate some of the phenomena observed. The study found that the current specification for PSV does not adequately reflect in-service performance for skidding resistance under present-day conditions. A Table to replace that in the Design Manual for Roads and Bridges, has been proposed as an interim specification. This is based on the new relationships but targeted at selecting aggregates which will meet the investigatory level requirements of the Skidding Standards. The work has shown a need for further research to provide a more rigorous assessment of materials. (A)