Road Performance of Asphalt Mixture Modified with Liquid Rubber Derived from Crumb Rubber Using Olefin Metathesis

Abstract

Liquid rubber (LR) has been proven to be a valuable asphalt modifier capable of addressing the existing deficiencies associated with crumb rubber–modified asphalt (CRMA), including poor workability and storage stability. Therefore, an accessible preparation method based on olefin metathesis was explored to produce optimal LR from crumb rubber (CR) in the laboratory. This research established the optimal laboratory preparation conditions for LR and investigated the performance of liquid rubber–modified asphalt (LRMA) mixture when used in pavement. A total of 32 LR samples were generated by olefin metathesis and physical swelling under various catalytic and swelling conditions. The physical properties, viscosity, and storage ability of LRMA were evaluated to select the optimal preparation parameters for LR. A comprehensive analysis was performed to compare the physicochemical characteristics of LR and the original CR through microscopic examinations with scanning electron microscopy (SEM), Fourier-transform infrared spectrometry (FTIR), and gel permeation chromatography (GPC). An in-depth evaluation assessed the stability at high temperatures, the properties at low temperatures, and the moisture stability of LRMA and CRMA mixtures. Experimental results showed that the optimal laboratory preparation conditions for LR were a catalyst dosage between 3‰ and 5‰, a catalytic duration of 48 h, a swelling temperature of 160°C, and a swelling time of 8 h. Moreover, LR possessed a smooth surface without rubber particles. The molecular weight and distribution of LR were considerably reduced compared with those of CR after olefin metathesis and physical swelling. The introduction of LR significantly enhanced the cracking resistance of the base asphalt mixture. However, the enhancement effect of LR on the base asphalt mixture to resist high-temperature rutting and moisture damage was inferior to that of CR.