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

Under the coupled effects of climate and traffic loading, resistance to moisture damage is an important controlling factor affecting the in-service performance of recycled asphalt mixtures. This study examines plant-mixed hot recycled asphalt mixtures (RHAM) and seeks to reduce moisture susceptibility 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), and used range analysis to quantify and rank factor effects. The Fourier Transform Infrared Spectroscopy (FTIR) characterized binder blending at 60 s, 120 s, and 180 s, with multiscale support from Gel Permeation Chromatography (GPC), Atomic Force Microscopy (AFM), and Dynamic Shear Rheometer (DSR). Extending mixing duration, increasing mixing and RAP preheating temperatures, increasing binder content, and decreasing RAP content reduced moisture susceptibility. The range analysis shows that mixing duration has the most significant impact on moisture susceptibility, followed by RAP content. 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 reduces moisture susceptibility primarily by increasing blending between virgin and aged binders, providing a basis for parameter selection and mixture design.