Long-Term Field Aging of Warm-Mix and Hot-Mix Asphalt Binders

Limited field studies have considered the aging of warm-mix asphalt (WMA) binders, especially from the perspective of long-term aging. This paper quantifies the long-term (10 to 82 months) field aging properties of WMA binders and the control hot-mix asphalt (HMA) binders and identifies the key factors associated with long-term field aging of asphalt. Asphalt binders from 23 field projects consisting of 65 HMA and WMA pavements were recovered, and high-temperature performance grade (PG) was tested. The effects of climate, month of aging, WMA technologies, and original binder high-temperature PG on field asphalt aging were analyzed. A prediction model that included multiple parameters was developed and validated. Results indicated that Evotherm WMA binder had a lower high-temperature PG than HMA binder shortly after construction, but this difference reduced with time. No statistical difference of field aging between HMA and WMA binders was observed. The climate effect on asphalt field aging was apparent within dry areas or freeze areas, whereas the aging difference between dry and freeze areas was inconclusive and requires further research. Other conclusions were that (a) the field asphalt aging affects more of top-down longitudinal wheelpath crack than transverse crack, (b) foaming WMA binder ages slowest of all binders considered, (c) PG 64-XX and PG 70-XX binders aged more than PG 58-XX and PG 76-XX binders, and (d) the prediction model had good agreement with test results and was well validated. The identified factors that affected field asphalt aging were overlay thickness, in-place air voids, effective binder content, complex shear modulus, and solar radiation.