Effect of naphthenic oil and viscosity reduction process on fatigue life and rheological properties of crumb rubber modified asphalt

Crumb rubber modified asphalt (CRMA) has garnered attention for its superior low-temperature crack resistance, yet its high viscosity hinders practical application. Naphthenic oil (NO), employed as a viscosity-reducing agent, effectively lowers CRMA viscosity, but its influence on CRMA's fatigue and rheological properties remains unclear. This study prepares viscosity-reduced CRMA via both non-swelling and pre-swelling processes, assessing the impact of NO and the viscosity reduction processes on CRMA's fatigue life at −12°C, 25°C, and 65°C. Fourier Transform Infrared Spectroscopy (FTIR) and Molecular Dynamics (MD) simulations analyze the mechanism of NO action from a molecular energy perspective. Results show that NO and the reduction process affect the loss of polar functional groups and molecular energy in CRMA, thereby altering its fatigue life. Specifically, at −12°C, NO enhances CRMA's fatigue life, while the pre-swelling process decreases it. At 25°C, both NO and pre-swelling improve CRMA's fatigue life, but at 65°C, they diminish it. Furthermore, the coverage of CRMA surfaces by NO molecules and the poor gradation of rubber particles reduce CRMA's high-temperature deformation resistance but enhance low-temperature crack resistance. The pre-swelling process, compared to the non-swelling one, strengthens CRMA's rheological properties at both high and low temperatures.