11 years performance of 18 bituminous test sections on a major freeway.

This report summarises the experience of a field trial placed on one of the heaviest trafficked roads in North America: Highway 401, carrying some 250,000 AADT in 1985. The trial consisted of 18 different test sections representing a comprehensive range of asphalt surface course mixes. Mix designs ranging from sand mix to high stone content mixes of various materials and compositions were involved. The conditions of the test sections were monitored periodically for eleven years and samples were obtained for laboratory testing and analysis. While the primary objective of this study was to establish the most effective mix designs for improving the frictional characteristics of the travelled surfaces for urban freeways, other parameters relating to the material properties and performance of the mix designs and their various relationships were also evaluated. The evaluation of these test sections had lead to formation of policies regarding the use of high quality asphalt mixes on provincial highways. All the test sections performed better than expected for single course thin overlays on concrete pavement under the heavy traffic prevailed. The open and dense mixes performed equally well. It was found that, for optimum friction characteristics for high speed roads, a surface must possess sufficient macrotexture for bulk surface water drainage and microtexture for penetrating the remaining thin water film in the contact area. In order to design mixtures with these properties, the coarse aggregate content should be set above 50% and 60% for dense and open friction course mixes respectively. Good quality polish restraint aggregate should be used for both the coarse and fine aggregates. In conclusion, the analysis confirmed that the Canadian Ministry of Transportation policies set forth previously based on the earlier results and the current practice of using Open Friction Course (OFC) and Dense Friction Course (DFC) for treatment of highways requiring friction surfacings are sound and adequate. (Author/publisher)