Polyphosphoric Acid's synergy with bio-modified bituminous composites

Abstract

Polyphosphoric acid (PPA) is among the most common modifiers used to increase bitumen's elasticity, improve bitumen's performance grade, and widen bitumen's operative temperature range. Recently, attention has been directed toward significant variations in PPA effectiveness when used in different bituminous composites. In other words, the same exact dosage of PPA affects various bitumens differently. The latter has been attributed to unexpected synergitic or antagonistic interplay between PPA and bitumen components. Considering the increasing use of bio-modifiers in asphalt industry, understanding such interplay is critical in design and engineering of bituminous composites. Here, we use the laboratory experiments and computational modeling, using density functional theory (DFT), to examine and compare the synergistic effects between PPA and each of five bio-modifiers (derived from wood pellet, miscanthus, castor oil, corn stover, or waste vegetable oil) to promote the durability and sustainability of bituminous composites while enhancing resource conservation and biowaste valorization. Based on the results, the bio-modifier made from wood pellets has the highest synergy with PPA (leading to the best dosage efficiency for PPA), followed by bio-modifiers made from miscanthus, castor oil, and corn stover. The bio-modifier made from waste vegetable oil shows the least synergy with PPA. The DFT results show the strong non-covalent interactions between PPA oligomers and the lignin units of the wood-based bio-modifier. In addition, due to the higher polarity of the wood-based bio-modifier compared to the bio-modifier from waste vegetable oil, a higher phosphorylation is expected to occur in the wood-based bio-modifier when exposed to PPA.