Synergistic modification mechanism and pavement performance of waste LDPE/SBS composite modified asphalt mixture via dry process

To promote the beneficial reuse of waste plastics and overcome the poor compatibility between recycled Low-Density Polyethylene (LDPE) and bituminous binders, we engineered a combined LDPE/Styrene-Butadiene-Styrene (SBS) modifier and subsequently applied it to asphalt mixtures using a dry-incorporation approach. The modification mechanism was investigated using Dynamic Shear Rheometer (DSR) and Bending Beam Rheometer (BBR) tests, together with microstructural analyses. Thereafter, the engineering performance of dry-process AC-13 mixtures was systematically assessed with respect to rutting resistance, low-temperature cracking resistance, water-induced damage resistance, fatigue durability, and short-term aging behavior. Furthermore, a comprehensive performance assessment based on multiple evaluation indicators was employed to determine the optimum modifier composition. The results suggest that LDPE and SBS mainly interacted through physical blending, producing a more stable polymer-rich structure in the asphalt phase and improving high-temperature rheological behavior. The dry-process composite-modified mixtures showed improved overall performance compared with the base mixture. Among the investigated dry-process composite mixtures, the mixture containing 6 wt% LDPE and 6 wt% SBS (6L6S) exhibited the most balanced performance. Its dynamic stability was 49.14% higher than that of the dry-process SBS-T reference mixture. At a stress ratio of 0.6, its fatigue life was approximately 77.8% higher than that of the base mixture and reached 94.6% of that of the dry-process SBS-T mixture. Overall, the proposed LDPE/SBS composite modification shows laboratory-scale potential for dry-process asphalt mixture applications, although further field validation is still required.