Laboratory testing and field application of devulcanized rubber/SBS composite modified asphalt

Styrene-butadiene-styrene copolymer (SBS) and recycled tire rubber are the typical polymers for asphalt modification. The dispersion of crumb tire rubber (CTR) dominates the composite effect of rubberized asphalt. And the multiscale of CTR in mixtures always challenges the design and construction of asphalt mixtures. The multiscale dispersion of CTR can be controlled by pre-devulcanization. In this study, lightly devulcanized rubber (LDR) with various dispersive scales in asphalt from microns to dozens of microns, and deeply devulcanized rubber (DDR) with micro-nano scales were prepared and analyzed, respectively. The devulcanized rubber (DR) was further compounded with SBS to prepare composite modified asphalt. The influences of rubber content on the structure and properties of modified asphalt and mixtures were investigated, and the dispersive structure model of asphalt mixture was also established. Furthermore, a high viscoelastic rubberized asphalt was prepared with 4% SBS and 20% DDR in the field plant and paved in a field project, a new first-grade national highway. The results showed that the devulcanization of CTR can help the dispersion of CTR in asphalt by improving the compatibility among CTR, SBS, and asphalt. And the dispersive scale and the content of DR can affect the binder content, high and low temperature performance of asphalt mixtures. The field project showed that the high viscoelastic rubberized asphalt exhibited similar mix design and construction process but better high and low temperature performance compared to SBS modified asphalt.