Grant: Collaborative Research and Development Grants

Our research objective is to develop an improved chemical aging protocol to better predict the relative field performance of straight and modified asphalt cements. The current rolling thin film oven (RTFO) and pressure aging vessel (PAV) methods fail to create laboratory-aged samples that perform similarly to materials recovered from the field. The problem is best illustrated with a set of materials used in a 2003 trial on Highway 655 north of Timmins, Ontario. All materials in this trial are graded according to current standards in a narrow range between -34.6¯C and -37¯C. Hence, they were designed to survive and perform similarly with respect to thermal cracking during a cold spell of -34¯C after 7-10 years of service. This has not happened: only two sections survived largely unscathed and the remaining five sections showed serious damage after a cold spell of -34¯C in January 2004. Preliminary investigations of recovered asphalt cements from this trial have shown errors in the RTFO/PAV aging methods ranging from -2.8¯C to +12¯C. Such significant errors can help explain the observed variations in distress, with section 4 performing worst and section 1 performing best. A more realistic aging method will be developed using very thin films hardened through oxidation, volatilization and exudation in moderate temperature and pressure conditions. Accompanying nanoindentation tests, applied directly to the aged films at low and ambient temperatures, will be developed for specification grading to more accurately reflect true performance in service. Canada will benefit from this research because our roads continue to suffer from premature thermal and fatigue cracking distress. The application of these research products by user agencies will allow them to save the taxpayers hundreds of millions of dollars.