Preparation Process and Performance of Polyurethane-Modified Bitumen for Ultrathin Asphalt Layers

Abstract

To adapt to the high temperatures in the summer and resist the shrinkage effect caused by high-temperature differences, this study developed an asphalt material with excellent high-temperature stability and applied it to ultrathin asphalt layer technology to extend the service life of asphalt pavement. The base bitumen was modified using a polyurethane (PU) polymer, which had a significant influence on the high-temperature performance of the bitumen. To achieve the best modification effect, four response indicators (softening point, rutting factor, 135°C rotational viscosity, and dispersion coefficient) were used to evaluate the high-temperature stability, compatibility, and hot-storage stability of the PU-modified bitumen (PMB). Using grey relational analysis and principal component analysis, the four response indicators were transformed into a single-objective parameter (grey correlation degree) to optimize the best combination of parameters for the PMB preparation process. The test results showed that the comprehensive effects of the PMB on the preparation process parameters, from greatest to lowest, followed the order of PU content, shearing time, shearing temperature, and shearing speed, and the optimal process parameters were a PU content of 20%, shearing time of 60 min, shearing temperature of 155°C, and shearing speed of 2,500 rpm. The performance was as follows: a softening point of 90.2°C, rutting factor of 21.21 kPa, rotational viscosity of 2.24 Pa·s, and dispersion coefficient of 0.924. The PMB had good high-temperature stability and hot-storage stability, which allowed it to be effectively applied to ultrathin asphalt layer technology. The preparation process of the PMB provides a technical reference for the development of novel modified bitumen suitable for ultrathin asphalt layers.