Straw Fiber-Reinforced Asphalt Mixtures for Sustainable Pavements: Performance Enhancement, Multiscale Mechanisms, and Engineering Perspectives

Agricultural straw is a renewable agricultural residue with potential for sustainable pavement applications, but research on its use as reinforcement in asphalt mixtures remains fragmented. This review systematically summarizes the characteristics, modification methods, pavement performance, and multiscale reinforcement mechanisms of straw fibers in asphalt materials. The literature indicates that appropriate straw fiber incorporation can improve high-temperature stability, low-temperature cracking resistance, moisture stability, and fatigue performance, although the magnitude of improvement depends strongly on fiber type, dosage, length, surface treatment, dispersion, and mixture characteristics. The reported reinforcement effects are mainly associated with fiber-network formation, fiber-asphalt interfacial interactions, crack bridging, asphalt-component retention, and changes in internal structural organization. However, direct evidence for aging resistance remains limited, and several proposed mechanisms still require quantitative cross-scale validation. Practical challenges, including moisture control, storage, plant-scale dispersion, mixing and feeding procedures, production consistency, and field-quality control, also restrict wider engineering application. Quantitative life-cycle evidence for straw fiber-reinforced asphalt mixtures is still insufficient. Future research should integrate advanced characterization, numerical modeling, long-term field validation, and life-cycle assessment to establish more reliable structure-performance relationships and support the sustainable engineering application of straw fiber-reinforced asphalt mixtures.