Investigation of synergistic modification mechanisms of cotton stalk fiber/nano-calcium carbonate composite modified asphalt

In recent years, frequent extreme heat events have imposed higher demands on the service performance and durability of asphalt pavements. To synergistically enhance asphalt performance, this study modified matrix asphalt with cotton stalk fibers and nano-calcium carbonate as composite admixtures, producing cotton stalk fiber/nano-calcium carbonate composite modified asphalt. Through aging tests, DSR and BBR tests, the anti-aging performance and high-temperature/low-temperature rheological properties of the composite modified asphalt were systematically evaluated. SEM, AFM, and infrared spectroscopy were employed to analyze its microstructural characteristics and modification mechanism. Results indicate that compared to single-component nano-calcium carbonate modified asphalt, the composite modified asphalt exhibits superior aging resistance and significantly enhanced high-temperature rutting resistance, demonstrating the distinct advantages of the composite modification system under high-temperature service conditions. Microscopic analysis revealed uniform dispersion of cotton stalk fibers/nano-calcium carbonate within the asphalt matrix. These components exhibited excellent oil absorption and thermal stability, forming a stable three-dimensional network structure that provided effective bridging and support functions. Compared to single-modified asphalt, the composite modified asphalt exhibits a 94.4% reduction in root-mean-square roughness (Rq) and a 96.4% decrease in arithmetic mean roughness (Ra), indicating that the composite admixture substantially regulates the asphalt microstructure. FTIR analysis revealed no significant chemical reactions during composite modification, with the mechanism primarily involving physical dispersion and interfacial compatibility. The synergistic effect of Cotton stalk fibers and nano-calcium carbonate effectively enhances asphalt's high-temperature and anti-aging properties, offering a novel technical pathway for agricultural waste resource utilization and green modification of high-performance asphalt materials. • An optimal preparation method for Cotton stalk fiber/nano-calcium carbonate composite–modified asphalt was developed, resulting in enhanced asphalt performance. • The synergistic mechanism by which Cotton stalk fiber and nano-calcium carbonate optimize the microstructure of asphalt was elucidated. • The underlying mechanisms through which Cotton stalk fiber/nano-calcium carbonate improve the high- and low-temperature rheological properties of asphalt and reduce asphalt aging were clarified.