Turning two waste streams into one solution for enhancing sustainability of the built environment

This study reveals a synergy between an industrial waste (sulfur) and an urban waste (waste cooking oil). It further explores how sulfur binds to hydrocarbon derivatives in the presence of waste cooking oil to create a solution for enhancing sustainability of the built environment. Here, we chose a high-sulfur bitumen (hydrocarbons of high molecular weight) modified with a waste cooking oil rich in alkenes. Changes in the physicochemical and rheological properties of bitumen were used to track the extent of sulfur's binding to hydrocarbon derivatives. The study results show that sulfur radicals attack the double bonds of bio-oil molecules leading to an addition reaction. Our analysis via Density Functional Theory (DFT) showed the latter reaction involves a two-step process: first, the sulfur radical attacks alkene groups of bio-oils; and second, the reaction stabilizes the resulting molecule. It was also showed that the second step releases four times the free energy of the first radical attack. The latter addition reaction leads to strong intermolecular interactions and formation of sulfur-carbon bonds within the bitumen matrix, enhancing bitumen's rheological properties and subsequently its performance properties. Our computational modeling was supported by spectroscopic and rheometric analysis showing an increase in sulfur-carbon bonds as well as a significant increase in bitumen's complex shear modulus. Study results provide comprehensive insights into the stabilization of sulfur elements within bitumen modified with waste cooking oil. Considering that sulfur is a major indusial waste and waste cooking oil is a major urban waste, their synergistic application in bituminous composites mostly used in outdoor construction promotes resource conservation and sustainability of the built environment.