Phenolic compounds to amplify the effect of sulfur on Bitumen's thermomechanical properties

This paper evaluates effects of phenolic compounds on the role of sulfur in a bituminous matrix. This is especially important because the concentration of sulfur in bitumen has been increasing mainly after a strict restriction was placed on sulfur content of marine fuel, which led refineries to divert sulfur from fuel to bitumen. There are documented challenges associated with the use of high-sulfur bitumen, such as sulfur's oxidation to hazardous hydrogen sulfide during bitumen application as well as increased moisture susceptibility in bitumen. This paper specifically examines how specific bitumen constituents can promote sulfur reactions that in turn amplify the effect of sulfur on bitumen's thermo-mechanical properties. To do so, we use density functional theory (DFT) and rheometry to examine and compare the effects of sulfur on bitumens that contain different concentrations of polar aromatics and phenolic compounds. Our DFT results highlight the role of polar groups and heteroatoms in the addition reactions of sulfur radicals to C[dbnd]C bonds, which mostly improve the formation of organo-sulfur compounds. Our results show that presence of phenolic compounds can work as an activator for sulfur interactions within bitumen. This in turn indicates that the effect of sulfur can be more noticeable in a bituminous matrix having a high content of phenolic compounds. Our DFT results are further supported by experiments showing that among studied asphalts, those modified with wood-based bio-oil containing 76% polar compounds including nearly 41.8% phenolic structures (among molecules recognized by chromatography) had the highest change in their thermomechanical properties when sulfur was introduced. In contrast, asphalts modified with waste vegetable oil containing 12% polar compounds and nearly no phenolic structures showed the least change due to the addition of sulfur. This in turn shows effects of sulfur on bitumen's property can be tuned by introducing specific compounds. The outcomes of the study provide insights about variational role of sulfur in bitumen containing various bio-modifiers to allow more informed use of sulfur to promote sustainability of construction.