Phenolic Compounds to Hinder Sulfur Crystallization in Sulfur-Extended Bitumen

This study examines the efficacy of phenolic compounds derived from plant-based sources on hindering the progress of sulfur crystallization in the bulk of bitumen. This in turn helps retain bitumen's thermo-mechanical properties over time. A mechanism that causes gradual time-dependent changes in bitumen's thermo-mechanical properties is a progressive structuring of the amorphous sulfur to form dendritic structures giving rise to sulfur crystallization. Sulfur crystallization in bituminous composites is implicated in premature crack initiation under thermal and mechanical loads, reducing the service life of bituminous composites used in roads, airports, bridge decks, and roofs. Therefore, there is a need to control sulfur crystallization in bitumen bulk. This is even more urgent since due to the recent strict limit on the allowable sulfur content of marine fuels, refineries are shifting the sulfur from fuel to bitumen leading to production of high sulfur bitumen. Here, we hypothesize that phenolic compounds can hinder sulfur crystallization, which occurs over time and alters bitumen's thermo-mechanical properties. Our laboratory characterization showed that high-sulfur bitumen modified with bio-oil derived from wood pellet had the least property change during a period of 60 days observation. Our study of molecular level interactions showed that the predominant phenolic compounds in wood pellet oil have the capability to neutralize polysulfide radicals due to their excellent capability for hydrogen donation and electron delocalization within their phenoxyl radicals. Moreover, the radical scavenging of polysulfide by the produced phenoxyl radicals is energetically favorable. Therefore, the high efficacy of wood pellet can be attributed to its high concentration of phenolic compounds hindering the formation of sulfur dendritic structures and crystallization. Accordingly, the study outcomes show the feasibility of controlling the thermo-mechanical properties of high-sulfur bitumen by hindering sulfur crystallization using phenolic compounds. A proper design and engineering of sulfur-extended bitumen informed by chemistry of bitumen's constituents contributes to resource conservation and sustainability in construction. For Table of Contents Only: Incorporation of phenol-rich bio-oils derived from wood-based biomass in the hindering sulfur self-assembly in sulfur-extended bitumen by neutralizing polysulfide radicals.