The Effect of a Chemical Warm Mix Additive on the Self-Healing Capability of Bitumen

Abstract

ABSTRACT Warm mix asphalt (WMA) technologies reduce the production temperature of hot mix asphalt allowing for mixing and paving at lower temperatures. As a result, the use of WMAs reduces emissions and allows for longer transport times. Because of the recent increase of chemical warm mix additives in industry, the effect of a chemical warm mix additive (cWMA) on the intrinsic self-healing ability of the bitumen was investigated. Bitumen specimens containing three concentrations of cWMA were evaluated at four aging levels (unaged, rolling thin film oven [RTFO]-163°C, RTFO-130°C, and RTFO+ pressure aging vessel [PAV] aged) using the simplified–linear amplitude sweep healing (SLASH) (linear amplitude sweep with a single rest period fatigue-healing) test. Results indicate that oxidative aging of bitumen is reduced with increasing cWMA concentration but may be more heavily influenced by the aging temperature. It was also observed that RTFO+PAV-aged bitumen samples demonstrate greater fatigue restoration ability compared to RTFO and unaged binders. Supplementary work using video-based analysis of dynamic shear rheometer samples revealed that issues may arise from the calibration of the cohesive failure damage level as described in the original LASH procedure because of significant changes in sample geometry observed during the amplitude sweeps for unaged and RTFO-aged material. These results demonstrate that LAS-based healing tests warrant further research to optimize loading and rest period parameters for a wider range of bituminous materials.