Physicochemical and thermal analyses of polyurethane modified bitumen incorporated with Cecabase and Rediset: Optimization using response surface methodology

This paper presents physical, thermal, and chemical analyses of polyurethane (PU) modified bitumen added with two types of warm mix asphalt (WMA) additives namely; Cecabase and Rediset. The response surface method (RSM) was used to determine the optimal amount of PU modifier in the bitumen, via central composite design (CCD). Numerical optimization showed that the optimal amount of PU in the modification of bitumen was at 3 wt%. Modified bitumen comprising of 3 wt% PU (B-PU) was then mixed with 0.5 wt% Cecabase and 0.6 wt% Rediset. These new materials were then evaluated using the penetration, softening point, ductility, viscosity and storage stability tests; thermogravimetry (TGA), Raman spectroscopy, and Fourier transform infrared (FTIR) spectroscopy analysis. Testings of the asphalt mixture include resilient modulus at different temperature and loading, and dynamic creep test was conducted to investigate the performance of modified mixtures. Results showed that PU increased the stiffness of bitumen either with or without the addition of Cecabase and Rediset. Inclusion of PU modifier into bitumen increased its viscosity, which consequently improved rutting resistance. However, adding both Cecabase and Rediset to B-PU reduced its viscosity, and this resulted in decreasing the mixing and compacting temperatures while simultaneously increasing the fatigue resistance of the mixtures. All modified bitumen were storage stable blends at high-temperatures. TGA analysis showed that the addition of PU, Cecabase and Rediset has limited effect on the thermal stability of the bitumen. Raman spectra analysis revealed that modified bitumen did not change the order structures and bee-structures of the pristine bitumen. This is consistent with result from the FTIR spectroscopy analysis, which showed the absence of chemical interaction in the modified bitumen. The addition of PU can improve resistance to fatigue and rutting at both intermediate and higher temperatures. Therefore, the addition of 3 wt% of PU showed great potential as a bitumen modifier.