Application of Plastic Waste as a Sustainable Bitumen Mixture—A Review

Plastic waste is growing rapidly, while asphalt binders remain heavily reliant on petroleum bitumen. Incorporating recycled plastics into bitumen can divert waste and enhance pavement performance. This review compiles 251 experimental records from 56 studies to evaluate how plastic type, dosage, and processing conditions affect softening point, penetration, and viscosity. Across studies, plastics (PET, LDPE/HDPE/LLDPE, PP, and hybrids) consistently stiffen binders, reducing penetration and increasing softening point and viscosity, thereby improving rutting resistance while potentially raising mixing/compaction demands. Using grouped cross-validated machine-learning models (median baseline, ridge, random forest, XGBoost), we quantify the predictability of binder properties and show that nonlinear methods outperform linear baselines for softening point. Prediction of penetration and viscosity shows larger scatter, reflecting study-to-study variability and incomplete reporting of key processing variables. We identify research needs in standardized testing, compatibility/dispersion characterization, and life-cycle assessment. The curated dataset and modeling workflow provide a data-driven foundation for designing durable, higher-performance plastic-modified binders.