Investigation of Premature Failure of Dense Friction Course Asphalt Highways in Ontario

Dense friction course asphalt (DFC) has been used since the late 1980s as the premium surface course on the Ontario Ministry of Transportationʹs (MTO) major highways. It was designed for a 12–15 year service life with minimum maintenance, primarily to resist excessive rutting problems associated with heavy commercial vehicles. However, in many cases, major rehabilitation of DFC highways was necessary within 4–7 years of paving. Failures occurred through abundant loss of fine aggregate, potholing, raveling, and occasionally delamination. MTO attempted to solve the problem by increasing the asphalt cement content of DFC, a procedure that proved costly and inefficient. This study used a 32 factorial experimental plan to assess the effects of the asphalt cement content and the addition of either a liquid chemical or powdered antistripping agent on the durability of DFC mixtures. In addition, a field investigation on Highway 401 was conducted. It was found that stripping of aggregates due to the action of water is the major cause of DFC failures, and that the addition of an appropriate antistripping agent was effective in inhibiting the problem. Construction related problems, such as lift thickness variations, lack of compaction, and mix segregation, were also identified as additional causes of DFC failures. Although initial research on antistripping agents dates back around 40 years, the industry needs a fresh look at this issue.