Performance of Cold Recycled Micro-Surfacing with WER Asphalt and Ultrasonic–Mechanical Pre-Regenerated RAP

Recycled micro-surfacing is a sustainable pavement maintenance technique, yet using fine Reclaimed Asphalt Pavement (RAP) is challenging due to aged asphalt and particle agglomeration. This study aimed to develop cold recycled micro-surfacing with waste edible oil (WEO) and Waterborne Epoxy Resin (WER)-modified emulsified asphalt and proposed a novel pre-regeneration method using ultrasonic–mechanical mixing for fine RAP with WEO before preparing mixtures. Molecular dynamics (MD) simulation and Dynamic Shear Rheometer (DSR) tests were conducted to assess rejuvenator diffusion and rheological recovery. In addition, mixtures with 0–25% WER were tested for wear, rutting, low-temperature splitting, and water resistance to optimize the WEO content, mixing time, and WER dosage. The results of MD simulation showed that WEO diffused faster than aged asphalt molecules and mutually interacted. DSR results indicated that 4% WEO (by mass of aged asphalt) gradually restored the complex modulus and phase angle to the levels of matrix asphalt. The recycled mixtures with 4 min ultrasonic–mechanical mixing had a minimum WTAT of 136.86 g/m2, which was a 9.6% decrease compared to the mixture without ultrasonic–mechanical mixing. The 1 h WTAT, PVD, PLD, 6d WTAT, and tensile strength of recycled mixtures with 20% WER were improved by 72.6%, 68.9%, 68.8%, 75.0%, and 88.7% compared with those of the matrix asphalt mixtures. Although WER weakened the low-temperature performance of the mixtures, the tensile strain was smaller than the maximum specification requirement of 2500 με when the WER content was less than 20%. In summary, pre-regeneration with 0.4% WEO (by mass of mixtures) and 4 min ultrasonic–mechanical mixing effectively activated the fine RAP. Considering the balance of properties of fine RAP micro-surfacing mixtures, the optimum dosage of 20% WER was recommended to provide sustainable high-performance cold recycled micro-surfacing.