Biomass Waste to Produce Phenolic Compounds as Antiaging Additives for Asphalt

This paper evaluates the antiaging characteristics of phenol-rich bio-oils and includes two distinct parts. The goal of the first part is to produce phenol-rich bio-oils from different types of biomasses using a two-stage pyrolysis process consisting of auger and fluidized bed reactors. The goal of the second part is to evaluate these bio-oils as antiaging bio-modifiers for the asphalt binder. In the first part of the study, two-stage pyrolysis was conducted with biomasses from four sources: softwood, hardwood, wood bark, and agricultural residue. These were the six biomasses selected: fir, birch, pine bark, peanut shells, walnut shells, and coconut husks. In pyrolysis, the total bio-oil yield ranged from 43 to 66 wt %, with the highest yield from birch. Phenol-rich bio-oils were produced from the fluidized bed reactor (500 °C) of the two-stage pyrolysis process. The concentration of phenolic compounds in the bio-oils from the fluidized bed reactor ranged from 9 to 53 wt % with the highest concentration from pine bark. In the second part of this study, each bio-oil was incorporated separately into the asphalt binder at 10 wt % as an antiaging additive. The performance of each bio-modified sample of asphalt binder was evaluated after exposure to accelerated laboratory aging that made the sample resemble the asphalt binder at the end of its service life. Study results showed that the bio-oils from birch and pine bark were the most effective against aging. Our molecular modeling showed that the observed effectiveness of a bio-oil is due to its phenolic compounds, which can interact with the free radicals generated during oxidative aging. The phenolic compounds can neutralize free radicals by hydrogen donation, resulting in phenoxyl radicals that act as free-radical scavengers. The study provides insights into the relationship between a bio-oil's molecular composition and the bio-oil's efficacy as an antiaging bio-modifier for the asphalt binder. This use of biomass promotes a circular economy and a biomass value chain while enhancing sustainability in agriculture, forestry, and construction.