Investigation of Polyurethane Modified Cold Bitumen for Fast Cold In-Place Recycling

Cold in-place recycling is gaining more attention worldwide because of its lower energy consumption, while the normally used asphalt emulsion and foamed asphalt cannot meet this requirement of short traffic disturbance and road performance of the surface layer. In this research, a polyurethane-modified cold binder (PMCB) was designed and investigated for the fast and high-quality cold in-place recycling of reclaimed asphalt. For the first step, functional group analysis and fluorescent microscopy were used to reveal the curing process and the modification mechanism of the PMCB. Then a series of rheological tests were used to comprehensively evaluate the viscoelastic properties of the PMCB at different curing stages. Finally, the mechanical performance of the PMCB mortar sample was evaluated with the monotonic tensile test and tensile fatigue test. The results indicated that the polymerization reaction in the PMCB consisted of three reactions, and the urethane/urea linkage led to the formation of the polymeric network. The polyurethane polymeric network led to a significant increase in the complex modulus and a decrease of the phase angle. The PMCB also exhibits suitable viscosity at environmental temperatures, good relaxation properties at low temperatures, and less temperature sensitivity. Compared to the base asphalt and styrene butadiene styrene polymer modified bitumen mortar samples, the PMCB mortar samples showed significant advantages in tensile strength, dissipation energy, and tensile fatigue properties. Furthermore, the polyurethane-modified cold asphalt mixture (PMCM) showed better indirect tensile strength than the porous asphalt mixture with fresh aggregate and fresh asphalt binder when the curing time of the PMCM reached 6 h.