The Transport Scotland Pavement Forum (TSPF) was set up in 2007 to improve communication across the road industry and to share and implement best practice quickly. As part of this remit, the TSPF introduced an annual monitoring procedure in 2008 to assess the performance of asphalt surface courses laid on the trunk road network. The annual survey is undertaken by the Scottish Inspection Panel (SIP), which comprises a cross-industry membership with individuals representing Transport Scotland, the Performance Audit Group (PAG plus), the Mineral Products Association (MPA) Scotland and TRL. The visual condition of the surface course, or surface treatment, is assessed by the SIP team to record its condition at the time of inspection. The results are gauged against previous surveys of materials of a similar age. The survey team also record any features that are likely to influence the long-term performance of the surface course and to establish initial causes and typical modes of failure. Transport Scotland’s pavement management system, IRIS, was used to provide information on materials laid during the 2013/14 surfacing season. In total, 47 two-year-old schemes were selected for inspection, representing around 37% of the road schemes completed in 2013/14. Schemes were chosen to represent a range of sites in terms of climate, terrain, geographical location, traffic loading and surfacing type. The surface courses comprised Thin Stone Mastic Asphalt (TSMA), Thin Asphaltic concrete (TAC) and TS2010. The 2015 SIP survey assessed 85% of the two-year-old surfacing sites to be defect free and performing very well. A comparison with the SIP 2008-2014 surveys showed the surface courses examined in 2015 received the highest ever percentage of Excellent and Good markings. Only three sites (6% of total) were recorded to exhibit aggregate loss which is historically the most common defect. This noteworthy reduction in aggregate loss is very encouraging, particularly in terms of optimizing long-term durability. Only one of the 2015 sites was noted to exhibit some type of joint defect, this compares to four sites in 2014 and seven sites in 2013. Ninety-three percent (13 out of 14 sites) surfaced with TS2010 were assessed as either Excellent or Good by all the panel members. An examination of data based on site stress showed that there is a trend towards specifying smaller stone aggregate sizes on highly stressed sites and in general the mixtures containing smaller stone sizes are performing well. Poor maintenance and defective drainage was witnessed at two sites. Based on the observations and results of the 2015 SIP survey, several recommendations are made, including reviewing maintenance strategies, investigating preservation treatments and continuing visual inspections to ensure positive changes are being implemented and maintained. Future visual inspections are also proposed to provide information for asset management purposes, life-cycle planning and demonstrating value for money. (Author/publisher)
Abstract