Development of antioxidant treatments for asphalt binders and mixtures

Asphalt binders are used extensively in the construction of pavements. More than 95% of all pavements in service today have asphalt incorporated in them. The widespread use of asphalt binders in pavements has generated great interest over the years in their durability. The durability of asphalts is greatly influenced by the oxidation process that occurs as a result of the reaction between atmospheric oxygen and asphalt. Two types of oxidation occur: first during hot-mix production called short-term aging and, secondly during service called long-term aging. The major consequence of oxidation is the progressive hardening and increased brittleness that occur over time in a phenomenon commonly referred to as age-hardening. Previous studies have shown that durability of asphalt mixes could be enhanced by controlling oxidation through the use of antioxidants. The success of using antioxidants to reduce asphalt aging has been limited and the need for more effective antioxidant treatments still remains.; Recognizing the need for more effective antioxidants to control asphalt age-hardening, eight additives were evaluated based on their potential to reduce age-hardening in asphalts. The selected additives were used to modify a PG 64-22 asphalt binder in the laboratory. The modified binders were subjected to accelerated laboratory aging using the Rolling Thin Film Oven to simulate short-term aging and the Pressure Aging Vessel to simulate long-term aging. Rheological measurements using the Dynamic Shear Rheometer and the Bending Beam Rheometer were used to screen those antioxidants showing the most promise. Asphalt concrete mixtures containing the most promising antioxidants were fabricated and subjected to a battery of laboratory mixture tests including creep compliance, dynamic complex modulus, indirect tensile strength, fracture energy, and moisture susceptibility testing. The results of the study indicate that asphalt aging could be reduced significantly through the use of antioxidant treatments developed during the research.