Effects of Warm Mix Additives and Dispersants on Rheological, Aging and Failure Properties of Asphalt Cements
Paul Samy, Senthil Kumar
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Existing specifications for asphalt cement employ insufficient aging and conditioning times prior to testing and low strains during the actual test which are insufficient to predict asphalt performance, especially if the materials are modified with additives such as those used for warm mix technology. However, slightly modified protocols, like increasing the conditioning time in the bending beam rheometer (BBR) test and increasing the aging duration in the pressure aging vessel (PAV), predict asphalt performance better than the current Superpave™ specification. These improved protocols are published as new test standards through the collaborative effort between the Ontario Ministry of Transportation and Queen’s University. In this study, the effects of warm mix and other additives on rheological, aging and failure properties are investigated. The properties are measured by regular tests and by modified protocols. The latter include the extended BBR test (LS-308) and the double-edge-notched tension (DENT) test (LS-299). Changes in ductile strain tolerance within base asphalts due to the various additives as measured with the DENT test were found to be very significant. The DENT results like essential work of fracture, we, plastic work of fracture term, βwp, and critical crack tip opening displacement, CTOD, are usually helped to correlate with the cracking distress survey results of the pavement in service. The addition of amide and polyethylene waxes risks increasing the cracking susceptibility in the pavement. They show a negative effect on strain tolerance in the ductile state, which is likely to show up as premature and/or excessive cracking in service which is similar to their physical hardening behavior from low temperature grading and extended BBR testing.