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SBS (styrene-butadiene-styrene block copolymer) is a thermoplastic elastomer with properties most similar to rubber. SBS asphalt modifier is mainly composed of a styrene-butadiene-styrene block copolymer with a certain amount of additives and stabilizers. SBS-modified asphalt binder has always been the most commonly used pavement material both domestically and internationally. However, conventional wet-process SBS-modified asphalt binder requires manufacturers to produce it in advance and transport it to a mixing plant for blending. This has provided an opportunity for unscrupulous businesses to reduce the amount of SBS by adding other substances, allowing inferior asphalt binder to pass inspections undetected. At the same time, conventional wet-process SBS-modified asphalt tends to undergo phase separation and experience a decline in performance as the storage time increases. However, dry-process SBS-modified asphalt can be directly added at the mixing plant, effectively addressing the issues associated with conventional wet-process SBS-modified asphalt. It also helps to reduce environmental pollution to a certain extent. This study investigates the extraction process of dry-process SBS-modified asphalt binder. It clarifies the performance and modification mechanisms of two types of dry-process SBS-modified asphalt binder at different dosages through various testing methods, including basic indicators, rheological properties, infrared spectroscopy, and fluorescence microscopy. The results indicate that due to the incorporation of oil, crosslinker, solubilizer, and other substances into dry-process SBS modifier, there is a small amount of chemical reaction with asphalt in the melting process. The high- and low-temperature properties and fatigue properties of the two dry-process SBS-modified asphalt binders at a 7% dosage are close to wet SBS-modified asphalt binder at a 5% dosage. [ABSTRACT FROM AUTHOR]

Currently, the utilization rate of fine reclaimed asphalt pavement (FRAP) in hot recycled asphalt mixtures is low. Therefore, this study focuses on the development and performance optimization of recycled gussasphalt (RGA) with a FRAP content of 38.5%. The total content of reclaimed asphalt pavement (RAP) is 50%. The impact of various factors on the pavement performance of RGA, including modifier dosage, asphalt content, type of asphalt, rejuvenating agent, mixing time, and RAP preheating temperature was analyzed. The results show that RGA has good workability and fatigue resistance. Its high- and low-temperature performance meets the requirements of the Chinese specification for gussasphalt, but it is still slightly inferior to gussasphalt made from virgin materials. Increasing the preheating temperature of RAP and extending the mixing time of RGA can enhance the performance of RGA. But excessive increases will cause asphalt aging, which negatively affects RGA's low-temperature performance and fluidity. More attention should be given to improving the low-temperature performance of RGA, which can be improved by selecting asphalt with better resistance to aging or by incorporating a rejuvenating agent. RGA offers significant economic benefits, with a cost reduction of approximately 27% compared to GA. • Recycled gussasphalt (RGA) containing 50% RAP was developed. • This RGA exhibits satisfactory workability, fatigue resistance, and economic benefits. • Choosing suitable asphalt or reinforcing modifiers is important for improving the high-temperature performance of RGA. • The impact of mixing time and preheating temperature of RAP on the performance of RGA was investigated. • Adding rejuvenating agents is the optimal strategy to improve the low-temperature performance of RGA. [ABSTRACT FROM AUTHOR]

This study focused on developing a high-toughness composite-modified asphalt (CMA), to enhance the performance of rich bottom layer mixes and its crack resistance. The content of crumb rubber (CR), epoxy resin (ER), and polyaryl polymethylene isocyanate (PMDI) were chosen as design parameters. Response surface methodology (RSM) was employed to develop models for creep strength (S), fatigue performance parameter (N f), yield energy (YE), and Brookfield viscosity (BV) of CMA. Then, these models were used to optimize the content of modifiers. Additionally, rich bottom layer mixes were designed using SBS-modified asphalt (SMA) and the newly developed CMA as binders, and their performances were evaluated. The results demonstrated the accuracy and predictive ability of the RSM models. The composite-modified asphalt mixes (CMAM) showed superior road performance and crack resistance compared to SBS-modified asphalt mixes (SMAM). Importantly, CMAM aligned effectively with the functional requirements of the rich bottom layer. This research contributes novel materials and methods for enhancing pavement crack resistance, providing valuable insights for improving the durability and longevity of pavements. • The content of modifiers in the composite-modified asphalt was optimized based on response surface methodology. • Rich bottom layers mixes were designed and evaluated for performance. • The crack resistance of both rich bottom layers mixes is explored. [ABSTRACT FROM AUTHOR]