The Study on the Effect of Waterborne Epoxy Resin Content on the Performance of Styrene–Butadiene Rubber Modified Micro-Surface Mixture

Conventional micro-surfacing materials often delaminate, crack, or peel. These defects shorten pavement life. High-performance polymer-modified mixtures are essential for rapid pavement maintenance. We added waterborne epoxy resin (WER) at different dosages to styrene-butadiene rubber (SBR) to create a composite-modified micro-surfacing mixture. A series of laboratory comparative tests were conducted to investigate the effect of WER content on the overall performance of the WER-SBR micro-surfacing mixture. In addition, the microstructure of the mixtures was observed to analyze the mechanism by which the composite-modified emulsified asphalt enhances material performance, and the optimal WER dosage was determined. The results showed that higher WER content improved abrasion and rutting resistance but gains plateaued above 6% WER. Below 9% WER, mixtures showed good water stability; at 3-6% WER, they also maintained skid and low-temperature crack resistance. Notably, when the WER content was approximately 6%, the WER-SBR micro-surfacing mixture showed significantly reduced abrasion damage after exposure to freeze-thaw cycles, moisture, and salt spray conditions. SEM images confirmed that 6% WER creates a uniform asphalt film over aggregates, boosting mixture performance. Therefore, we recommend 6% WER. This study has developed a WER-SBR composite-modified emulsified asphalt micro-surfacing product with excellent overall performance. It holds significant practical value for extending pavement service life and improving road service quality.