Effect of Sulfur on Bio-Modified Rubberized Bitumen

This paper examines how the effect of sulfur on bio-modified rubberized bitumen depends on the bio-modifier's chemical composition. The study was performed on rubberized bitumen modified with bio-derived compounds from castor oil (CO), corn stover (CS), miscanthus (MS), wood pellets (WP), and waste vegetable oil (WVO). The effect of sulfur on the evolution of the thermo-mechanical and chemical properties of rubberized bitumen was monitored for 60 days. The study results showed that the introduction of sulfur significantly reduced the elasticity of rubberized bitumen. However, as curing time progressed, the elasticity was regained to some extent. Each case had a different curing rate, with WVO having the overall fastest curing rate and WP having the slowest. The observed curing phenomenon was attributed to the progress of sulfur recrystallization and sulfur-bitumen interactions. Among all scenarios, bio-modified rubberized bitumen containing vegetable oils (CO and WVO) was more impacted by the introduction of sulfur, as evidenced by the highest change in elasticity, the greatest percent recovery, and the fastest curing rate. In addition, vegetable-oil-based scenarios showed a continued gain in elasticity even after 60 days. The latter was attributed to vegetable oils having the highest content of unsaturated compounds, giving rise to sulfur-bitumen reactions. As evidenced in our infrared spectroscopy results, carbon–sulfur bond indexes continuously increased and alkene decreased during the curing time. The latter was most evident in the cases of CO and WVO, with alkene reductions of 10.7% and 10.8%, respectively, during the 60-day curing. The study outcomes provide insights pertaining to the interplay between sulfur and bitumen modifiers such as bio-oils. This in turn helps asphalt producers take advantage of the synergy between modifiers to enhance sustainability in construction.