Using Fundamental Material Properties to Predict the Moisture Susceptibility of the Asphalt Binder: Polarizability and a Moisture-Induced Shear-Thinning Index

Many biomodifiers have recently been introduced to the asphalt industry to improve the performance of asphalt mixtures, rejuvenate aged asphalt, and/or partially replace asphalt binder. It is critical to screen these biomodifiers for their susceptibility to moisture damage before they are used in construction. This study develops a computational approach and a laboratory technique to predict the moisture susceptibility of modifiers used in asphalt binder mixtures. The computational approach uses the "polarizability" factor, which is one of the conceptual descriptors in density functional theory. Polarizability is indicative of the formation of instantaneous dipoles that are oriented in the applied field. A lower polarizability indicates a lower propensity of the chemical species to interact with other species in their chemical environment. The laboratory method defines a moisture-induced shear-thinning index. Moisture-induced shear-thinning measures the loss of interfacial bonds between the asphalt binder and siliceous surfaces due to water exposure. Both proposed indicators are used to evaluate and compare biomodifiers from four sources: waste vegetable oil, swine manure, algae, and a co-liquefied blend of swine manure and algae. In a comparative study, waste vegetable oil with a high content of long-chain alkanes and fatty acids showed the highest polarizability and the highest moisture-induced shear-thinning index, indicating the highest susceptibility to moisture damage. In contrast, the chemical composition of the biomodifier produced from the co-liquefaction of swine manure and algae showed the lowest polarizability and the lowest moisture-induced shear-thinning index, indicating the highest resistance to moisture damage.