Advancing durable and sustainable asphalt binder: Hybrid binders with recycled low-density polyethylene and crumb rubber

Recycling end-of-life plastics and tyres into asphalt binders offers a sustainable pathway to reduce waste while enhancing pavement performance. This paper presents a unified evaluation framework for emerging hybrid crumb rubber–recycled polyethylene binders, integrating formulation and mixing-protocol effects with two major ageing pathways through complementary linear and non-linear rheological characterisation and extracted-network morphology assessment. Hybrid binders incorporating recycled low-density polyethylene (RLDPE) and crumb rubber (CR), compatibilised with polyethylene-graft-maleic anhydride (PE-g-MA) and sulphur, were produced using two shear-mixing protocols and assessed under both pressure ageing vessel (PAV) and ultraviolet (UV) ageing for viscosity and storage stability, linear viscoelasticity (frequency sweeps and black diagrams), rutting resistance (multiple stress creep recovery), fatigue resistance (linear amplitude sweep interpreted within the simplified VECD framework) including repeated sweeps with controlled rest intervals, and low-temperature cracking tolerance (stress ratio). High-shear mixing improved storage stability (top–bottom softening-point difference of approximately 3.1 °C) while lowering viscosity (approximately 0.74 Pa·s), supporting workability. Black diagrams and MSCR results indicated promising high-temperature performance in the hybrid binders, with UV ageing generally further reducing non-recoverable creep compliance and increasing percent recovery. Fatigue performance improved substantially, with hybrids extending fatigue life relative to the neat binder by up to 763 % at 1 % strain, and higher CR and RLDPE contents providing further benefits. Low-temperature performance remained the main trade-off: hybrids showed limited stress relaxation compared with the styrene–butadiene–styrene benchmark, although some formulations exhibited modest improvement relative to the neat binder. Overall, compatibilised CR/RLDPE hybrids delivered a practical balance of workability, rutting resistance, and fatigue performance under hot-climate ageing conditions, while highlighting the need to manage low-temperature cracking risk. • SEM: 6 % RLDPE crosses percolation to co-continuous films; high shear homogenises • LAS-VECD: 35 % G *·sin δ can under-rate hybrid fatigue; PSPSE/DE gives fair ranking • High shear delivers storage stability and low viscosity • Black diagrams: at 7.5 % CR/RLDPE softens; at 15 % CR it stiffens; high shear weakens