Road performance and mechanism of Hot in-place recycling asphalt mixture modified by direct-to-plant SBS

This study aims to supplement the degraded SBS components and improve the road-related properties of Hot in-place recycling (HIR) asphalt mixtures. Under the direct-to-plant process, a composite rejuvenating agent (SBS-CRA) composed of instant SBS, regenerant, and coupling agent is used to regenerate the HIR asphalt/asphalt mixture. Explore the effects of SBS-CRA on the properties and chemical composition of extracted asphalt using rheological and Fourier transform infrared spectroscopy tests. Evaluate the road-related properties and microstructure of SBS-CRA modified HIR asphalt mixtures under the direct-to-plant process through high and low temperature, water stability, fatigue, and scanning electron microscopy tests. And conduct performance verification by paving the test road. The research results indicate that the SBS-CRA can promote extracted asphalt's low-temperature behavior and viscosity while maintaining excellent high-temperature behavior. Under the direct-to-plant process, the SBS-CRA modified HIR asphalt mixture's high and low-temperature behavior and water stability comply with the specified requirements. After SBS-CRA regeneration, the asphalt on the surface of RAP material is smooth. Considering the road-related properties of SBS-CRA modified HIR asphalt mixture, the optimal recommended dosage of SBS-CRA is 5%, and the optimal mixing time of SBS-CRA and RAP material is recommended to be 120 s. At a 5% SBS-CRA content, the fatigue life of the HIR asphalt mixture is 407.9 times higher than that of the neat asphalt mixture. The on-site test results show that the freeze-thaw splitting strength ratio of the HIR asphalt mixture is 88.76%, which meets the specification requirements. The laboratory and on-site test results have proven that applying SBS-CRA in HIR technology is feasible. •Revealed the behavior and mechanism of SBS-CRA recycled asphalt.•Explored the effects of SBS-CRA dosage and mixing time on HIR asphalt mixture under a direct-to-plant process.•Evaluate road performance through laboratory and on-site testing.