Rheological Properties and Modification Mechanism of Crumb Rubber–Epoxidized Soybean Oil Composite-Modified Asphalt Crack Sealants

Abstract Cracks are one of the most common asphalt pavement distresses in cold regions, particularly in Northeast China, where large temperature fluctuations accelerate low-temperature cracking. To address this issue, a crumb rubber/epoxidized soybean oil (CR/ESO) composite modified asphalt crack sealant was developed using base asphalt, CR, ESO, and a compatibilizer. The preparation process was optimized through an orthogonal design, and performance was evaluated by cone penetration, softening point, ductility, flow, and elastic recovery tests. High- and low-temperature rheological properties were further characterized using a dynamic shear rheometer and bending beam rheometer. Fourier transform infrared spectroscopy results indicated that the interactions of CR and ESO with asphalt were mainly physical, preserving the original chemical structure. Thermogravimetric analysis showed that CR improved high-temperature stability, while ESO reduced it; the combined CR/ESO system exhibited delayed decomposition and higher residual mass. Differential scanning calorimetry revealed that ESO decreased the glass transition temperature ( T g ), enhancing low-temperature flexibility, whereas CR increased T g ; their combined use provided the best balance of thermal resistance and crack resistance. In addition, a carbon emission analysis based on the heating process of 1 t of sealant demonstrated that the self-prepared CR/ESO composite consumed less natural gas and reduced emissions by 4.92 × 10 8 mg compared with commercial sealants. The optimal formulation (33% CR, 18% ESO, and 0.1% compatibilizer) thus achieved improved mechanical and thermal performance while delivering significant environmental benefits in line with dual-carbon goals.