Improved methodology for selecting polishing resistant aggregates for chipseals

In 1997, based on earlier work in the United Kingdom (UK), the New Zealand (NZ) State Highway agency introduced a procedure for identifying sites where treatment is required to improve skid resistance. Subsequent versions of the T/10 specification (1998, 1999 and 2002) gradually modified the procedure. However, all of the revised versions still relied on the Polished Stone Value (PSV) test to select aggregates that provided adequate skid resistance performance in-service on New Zealand's state highways. In response to the perceived inadequacies of the 2002 methodology, the New Zealand Transport Agency (NZTA) included the concept of assessing the actual in-service performance of an aggregate's resistance to polishing in the updated T /10:2012 Specification for State Highway Skid Resistance Management. The concept of assessing aggregate polishing performance described in T/10:2012 is a significant step in the right direction. However the authors believe that the methodology described is too generic, and does not ensure that an aggregate selected for a specific site will provide adequate in-service skid resistance performance. This paper proposes a simple methodology to compare the polishing performance of different aggregates on sites with similar characteristics. The proposed methodology processes the data using simple filters that reduce the data set to sites with similar characteristics. Much of the data and characteristics are available within data sources currently available to the industry. This paper identifies the key characteristics and discusses improvements to the aggregate polishing assessment methodology that will ensure that the most appropriate aggregate will be selected for each resurfacing site.