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Can We Recycle WMA with Wax?
Since warm mix asphalt (WMA) was introduced in early 2000, many of these pavements were built more than 10 years ago. Therefore, the WMA recycling research is important and necessary. However, the recycling issue of WMA has lagged behind other researches such as moisture sensitivity and long-term performance of WMA. If the aged WMA is incorporated into the asphalt mixes, the mixing and compaction temperatures of the mixtures are expected to decrease by the warm additives. The effect of warm additive after in-service period needs to be evaluated to see if the aged WMA can be used in asphalt pavements.
The main objective of this study was to evaluate the properties of recycled asphalt binders containing long-term aged (LTA) WMA binders through Superpave asphalt binder tests. The WMA binders were manufactured with two wax additives, LEADCAP and Sasobit, and artificially aged using rolling thin film oven (RTFO) and pressure aging vessel (PAV) procedures. The aged WMA binders were recycled at 15% and 30%. The viscosity properties for the binders in the original state, the rutting properties in the original state and after RTFO aging, the fatigue cracking properties at intermediate temperature after RTFO+PAV aging methods, and the low temperature cracking properties after RTFO+PAV procedures were evaluated.
The following conclusions were drawn for the materials used in this study:
(1) Although the addition of LTA into virgin binder increased the binder’s viscosity, the binders containing wax additives had significantly lower viscosities compared with the unmodified binders at all recycling content (0, 15, and 30%).
(2) Even though the binder with wax experienced the aging processes, the wax additive within recycled binder was effective to decrease the binder viscosity at almost the same degree, provided with the actual amount of wax in recycled binders.
(3) The binders containing wax additive had higher G*/sin δvalues than control binders at each recycling content. It means that the wax additive still plays an important role in increasing rutting resistance, even though the additive was aged within asphalt binder.
(4) From the DSR test at intermediate temperature, it appears that the higher recycling content seemed to have negative effects on resistance to fatigue cracking, regardless of the wax additive.
(5) The recycled WMA binders at 30% recycling content were observed to have significantly lower resistance on low temperature cracking (measured by the BBR test). It is recommended that the WMA be recycled in a lower contents in cold regions.
