Long-Term Effectiveness of Antistripping Additives

Abstract

Hydrated lime and liquid antistripping agents are often used as additives in asphalt mixes to improve their resistance to moisture damage. Most laboratory studies have evaluated the effectiveness of these additives on the basis of a short-period intensive moisture conditioning procedure, usually a freeze–thaw cycle. Whether this short-term conditioning sufficiently simulates the actual field conditions is unknown. Questions have arisen about the performance of asphalt mixes exposed to moisture for a long period and the effectiveness of antistripping additives after long-term conditioning. This research was conducted in the laboratory to answer these questions to some extent by two test methods: the indirect tensile strength ratio test and the flexural beam fatigue test. A moisture-sensitive mix was treated with the hydrated lime and liquid antistripping agents, saturated by vacuum, and conditioned in a humid environment for a period of up to 1 year. Mix properties were measured and analyzed every 4 months. It was found that most of the detrimental effects of moisture occurred in the first 4 months, and the reduction of strength or stiffness in the late stages became small. Both tests revealed that the antistripping additives were effective even after 1 year of moisture conditioning. Equivalency between the short-term intensive conditioning and the long-term mild conditioning was also found in this study.