Rheological properties and micro-characteristics of polyurethane composite modified asphalt

•A newly-developed composite modified asphalt was prepared with polyurethane (PU) and rock asphalt (RA).•Performance and its influencing factors of PU composite modified asphalt were revealed.•PU can improve the low temperature performance of base asphalt.•The chemical reaction mechanism in PU composite modified asphalt was studied through the FTIR test.•The optimum additive amount of the PU and RA were put forward.