Polymer degradation mechanism and chemical composition relationship of hot-poured asphaltic crack repair material during thermal aging exploiting fluorescence microscopy and gel permeation chromatography

Abstract

Prolonged heating and storage of hot-poured asphaltic crack repair material (HACRM) before construction lead to serious aging phenomenon. Considering practical condition, the thermal aging of HACRM was designed as 0–12 h heating at fixed temperature and stirring rate. In comparison with asphalt binders, the aging of HACRM is accompanied by “hardening” caused by the volatilization and conversion of light components in asphalt and “softening” due to the desulfurization and degradation of polymer modifier. Accordingly, with the prolongation of aging time, the basic properties of HACRM present a parabola trend rather than a monotone change and reach the extremum at 6–8 h. Fluorescence microscopy diagrams showed that proper storage (within 4 h) is conducive to the further swelling of the polymer modifier and improving its modification effect. However, overlong aging time (more than 6 h) results in the excessive degradation of the polymer and weakens the service performance of HACRM. Gel permeation chromatography curve demonstrated that the polymer peak disappeared after aging for more than 6 h because of the excessive degradation of the polymer. Polydispersity and large molecular size portion also proved that the aging of asphalt plays a major role in the first 6 h of aging, thereby causing HACRM to “harden” gradually. With further aging, the degradation of polymer becomes dominant, and the HACRM “softened” gradually. The fundamental reason for polymer degradation lies in the oxidization of α-H atom in double bond into hydroperoxide. Subsequently, a series of chain-breaking reactions occurs and degrades into low molecular compounds.