Inhibitory effect and mechanism of zinc stearate on the sulfidation gases from crumb rubber modified asphalt

The utilization of crumb rubber modified asphalt (CR MA) releases odor sulfidation gases due to the desulfurization and degradation of crumb rubber, posing risks to the environment and construction workers. By inhibiting the desulfurization and degradation of rubber powder in asphalt may provide a new direction for achieving sulfidation gases emission reductions. Zinc stearate (ZS), a crumb rubber vulcanization accelerator, demonstrates the ability to improve the degree of vulcanization. In this paper, the inhibitory effect of rubber vulcanization active agent ZS on the release of H2S, CH4S, COS, and CS2 were investigated. Toluene insoluble and potentiometric titration were used to reveal the effect of ZS on the desulfurization and degradation of crumb rubber in asphalt. Zinc stearate has the ability to react with polysulfide hydroxyl groups, additionally, the reaction mechanism of ZS with sulfidation gases was also studied. The results indicate that ZS can effectively reduce the concentration of H2S, CH4S, COS, and CS2 released by CR MA. Specifically, with a ZS content of 1.50 %, the concentrations of these gases were reduced by 39.69%, 36.60%, 29.48%, and 23.93%, respectively. Furthermore, the addition of ZS also reduced the release of CH2O, NH3, CH4, H2, CO, and volatile organic compounds. ZS inhibited the desulfurization and degradation of crumb rubber, consequently reducing the concentration of sulfidation gases. Moreover, the reaction of ZS with H2S and CH4S led to the formation of ZnS. After incorporating ZS, the high-temperature stability of CR MA was enhanced, while its low-temperature crack resistance continued to satisfy the standards.