Cleaner Asphalt Production by Suppressing Emissions Using Phenolic Compounds

Abstract

Asphalt-paved surfaces have been reported as an important and long-lasting potential source of emissions of a complex mixture of volatile organic compounds into the atmosphere. Accelerated aging of asphalt under high temperatures and sunlight exposure is closely related to the mass loss due to asphalt-related emissions. This paper studies the capability of biomodifiers to retain oxygenated compounds in bitumen and thereby extend bitumen’s durability. It is hypothesized that phenolic compounds of biomodifiers enhance intermolecular interactions with oxygenated compounds that would otherwise be released to the atmosphere as bitumen ages. Computational modeling based on density functional theory (DFT) confirms the capability of phenolic compounds in bio-oil from wood pellets (WPs) as a modifier for bitumen to interact with bitumen’s volatile oxygenated compounds through strong hydrogen bonding. DFT-based energy results show that the efficacy of a phenolic molecule to trap bitumen’s oxygenated compounds is influenced by its molecular structure and substituents attached to the phenolic moiety; electron donor groups such as −CH3 and −OCH3 can enhance the scavenging activity of phenolic compounds. Molecular modeling also shows that the interacting complexes formed between bitumen’s oxygenated compounds and WP’s phenolic components are more thermodynamically favored than complexes formed by these volatiles and non-phenolic molecules in waste vegetable oil (WVO). Laboratory experiments confirm the delay in UV aging of biomodified rubberized bitumen containing wood-pellet bio-oil (WP-BMR) by showing lower values for aging indexes based on rheological properties (the crossover modulus and frequency, the complex modulus, activation energy, and a rutting indicator) compared to the rubberized bitumen containing a low-phenol WVO biomodifier (WVO-BMR). Therefore, the extent of aging varies between two biomodified bitumen samples depending on the biomodifier’s source and chemical composition. This study’s outcomes show how to improve the durability of asphalt by tuning bitumen’s aging resistance using phenol-rich biomodifiers made from lignin-based biomass. This can be a key to open a doorway to resource conservation and sustainability in the construction industry while maintaining or enhancing air quality.