Effect of Aging on Healing Capacity of Bituminous Composites Containing Polyphosphoric Acid

This study examines how aging affects the healing capacity of bituminous composites containing polyphosphoric acid (PPA). PPA is commonly used in bituminous composites to enhance its elasticity, however, PPA effectiveness highly depends on other constituents on the matrix and the environmental (internal and external) factors. In terms of internal factors, the interplay between PPA and various bitumen modifiers have been extensively studied. Here, we study how external factors such as exposure to ultraviolet radiation affect PPA's efficacy, measured in terms of change in bitumen's healing index. The study results showed that the introduction of PPA to bituminous composites significantly increases the bitumen healing index, however, the change in the healing index becomes less pronounced as aging progresses. The presence of additives such as taconite were found to affect the effect of PPA on bitumen's healing index. For instance, bitumens containing 30% taconite showed the highest increase in their healing index in the presence of PPA among studied scenarios. Overall, bitumen containing PPA had a higher healing index than those without PPA regardless of the extent of aging and dosage of modifiers. This, in turn, indicates that PPA is highly effective for enhancing bitumen healing. This can be attributed to the role of PPA in promoting intermolecular interactions within the bitumen matrix.