Experimental study on moisture susceptibility of plant-mixed hot-recycled asphalt mixtures

Under coupled climatic variability and traffic loading, resistance to moisture damage governs the durability of recycled asphalt mixtures. This study examines plant-mixed hot recycled asphalt mixtures (RHAM) and seeks to enhance water stability by optimizing mixing parameters and material proportions. We evaluated the effects of mixing duration, mixing temperature, and reclaimed asphalt pavement (RAP) preheating temperature, together with binder content and RAP content, using freeze–thaw splitting and Moisture-induced stress tester (MIST) tests, and used range analysis to quantify and rank factor effects. FTIR characterized binder blending at 60 s, 120 s, and 180 s, with multiscale support from GPC, AFM, and DSR. Extending mixing duration, increasing mixing and RAP preheating temperatures, increasing binder content, and decreasing RAP content improved water stability. The relative influence followed the order mixing duration > RAP content > binder content > mixing temperature > RAP preheating temperature. FTIR showed blending increased from 30.5% at 60 s to 81.6% at 120 s, and reached 83.6% at 180 s, indicating diminishing returns. Together, these observations indicate that adjusting process and material variables enhances water stability primarily by increasing blending between virgin and aged binders, providing a basis for parameter selection and mixture design.