Investigation on Moisture Damage Resistance of Plastic-Modified Asphalt Binder using Surface Free Energy Technique

Moisture damage of asphalt pavement has always been one of the major concerns for researchers in the pavement engineering field. Mitigating this moisture-induced damage is essential for improving pavement performance, extending service life, and reducing lifecycle costs. Several studies have reported that waste plastic can potentially increase the cohesion between asphalt and plastic molecules and enhance the adhesion between asphalt and aggregate, improving the moisture damage resistance of asphalt pavements. The present study aims to understand the effect of incorporating different waste plastics as modifiers on a binder’s fundamental properties, such as cohesive bond energies. To achieve this goal, three different waste plastics—high-density polyethylene (HDPE), polypropylene (PP), and polyethylene terephthalate (PET) in 2%, 4%, 6%, and 8% by weight of the total binder—were used to modify the conventional asphalt binder (PG 58-28). The surface free energy (SFE) was determined by depositing one polar and one non-polar liquid on the solid samples by using the liquid needle drop deposition technique while adopting three different theories. Finally, the cohesive bond energies of the modified asphalt binders were calculated. The results showed that waste plastics significantly increased the total SFE and cohesive bond energy of the asphalt binder up to 4% plastic addition and then dropped. Besides, the comparative analysis revealed that PP modification was most effective for improving moisture damage resistance among the three plastics. Therefore, the use of plastic waste for asphalt binder modification was found to be a promising approach for enhancing moisture damage resistance.