Effects of warm mix asphalt additives on aging characteristics of bituminous mixtures

Since the utilization of Warm Mix Asphalt (WMA) technology is increasing rapidly around the world, it?s commonly believed that there are some unknown characteristics of this technology which should be investigated more sensibly. As most of the field practices of this technology have been applied recently, there is nearly no chance to evaluate long-term characteristics of existing WMA pavements practically.Within the scope of this study, short- and long-term aging conditions were applied to mixtures prepared with various contents of four different WMA additives as well as to control specimens with no additive content. WMA additives, which were distinctly assessed in this study, are Sasobit and Rediset WMX as non-foaming granular additives; moreover Advera and Natural Zeolite both in powder form as foaming additives, respectively. To estimate the proportion of hardening of WMA mixtures containing different types of additives, Indirect Tensile Strength (ITS) of both short- and long-term aged specimens were determined as well as of un-aged specimens. Based on relative aging indices (as the ratio of ITS results of aged specimens to ITS results of un-aged specimens), comparisons were made between four WMA additives to assess their effect on aging characteristics of mixtures. The defined Aging Index (AI) for each WMA additive can give us an evaluation capability to predict how a WMA pavement would be subjected to damages during service life of a pavement in comparison to a Hot Mix Asphalt (HMA) pavement.The results showed that aging indices for WMA technologies are rather less than the index for HMA mixture. The defined aging index is a relative parameter; the less aging index of a mixture is the better that mixture is in terms of aging characteristics. Rediset® WMX represented the least aging index. Sasobit performed nearly similar to Rediset WMX. Foaming additives including Advera and natural zeolite represented relatively weak aging strengths.