Feasibility of preparing the stable high-content rubber modified asphalt with low mooney viscosity crumb rubber powder: formulation design and modification mechanism

• Stable high-content asphalt prepared with low-Mooney crumb rubber. • 40% rubber content balances viscosity, rutting, and crack resistance. • Microstructure and MD confirm dense rubber networks and strong interaction. • Sustainable recycling of waste tires into durable, eco-friendly road asphalt. High-content rubber-modified asphalt (HC-RMA), incorporating over 25 % waste tire rubber powder, delivers environmental sustainability alongside enhanced pavement performance. However, a rubber content exceeding 30 % typically induces excessive viscosity and phase separation. To address these issues, HC-RMA samples were prepared using rubber powder with Mooney viscosities ranging from 40 to 120 MU. Among these, the binder containing 40 % rubber powder with 40 MU viscosity (CR40D) showed a practical viscosity of 1.34 Pa s at 180 °C and demonstrated superior performance, including enhanced high-temperature rutting resistance and improved low-temperature crack resistance. Microscopic analyses (CLSM and AFM) combined with Delaunay triangulation confirmed that the CR40D formulation promoted the formation of a uniform, dense rubber particle network with increased crosslinking density. Molecular dynamics (MD) simulations identified a critical rubber content of 40 % by mass, at which optimal binder compatibility and the strongest intermolecular interactions (van der Waals forces up to 5.4 kJ/mol) were observed. Further increases in rubber content led to a notable decline in these interactions. In conclusion, incorporating 40 % low-Mooney-viscosity (40 MU) rubber powder optimizes the performance of HC-RMA. The resulting material is a high-performance, cost-effective, and eco-friendly paving binder with strong potential for sustainable road construction.