Investigation of modified bitumen's rheological properties with synthesized polyurethane by MDI-PPG reactive prepolymers

The main types of distresses in asphalt mixtures are rutting, fatigue, and thermal cracking at various performance temperatures. One of the beneficial approaches for improving their strength related to these failures is modifying the characteristics of bitumen by additives. The use of polymers in modifying bitumen properties is very common now. Thermoplastic elastomers and reactive polymers are a family of polymers that have a tremendous effect on the properties of bitumen. In this study, synthesized polyurethane (PU) with polypropylene glycol (PPG) functionalized by polymeric diphenylmethane diisocyanate (MDI) as an additive in the bitumen modifier is studied. Penetration degree tests, softening point (R&B), rolling thin film oven, pressure aging vessel, dynamic shear rheometer, bending beam rheometer, and Fourier-transform infrared (FTIR) spectroscopy were carried out on the modified samples. The results of these tests showed that the PU reduced the penetration degree and increased the softening point of bitumen, in which modified bitumen had higher stiffness and viscosity with a lower thermal susceptibility. It also increased bitumen resistance to permanent deformation to provide higher performance levels. In the intermediate temperature, bitumen modified with PU had a better performance and more resistant to fatigue compared to the base bitumen. The results of FTIR revealed modified PU bonds in the modified bitumen, which confirmed the formation of bonds in bitumen and determinant of chemical structure. By calculating penetration index represented the bitumen thermal susceptibility, the control bitumen had the lowest penetration indicator and bitumen sample with 7% PU had the maximum penetration indicator -0.62 and 0.91, respectively, and yielded the lowest performance temperature which was equal to -15.04 degrees C.

Automated summary

The study focused on using synthesized polyurethane (PU) with polypropylene glycol (PPG) functionalized by polymeric diphenylmethane diisocyanate (MDI) as an additive in bitumen modifier to enhance the strength and performance of bitumen. Tests conducted showed that PU decreased the penetration degree, increased the softening point, and improved stiffness and viscosity of bitumen, leading to higher resistance to deformation and better performance at intermediate temperatures. The results of FTIR confirmed the formation of PU bonds in modified bitumen, indicating a change in chemical structure. Additionally, the penetration index calculation revealed that bitumen with 7% PU had the highest penetration index and lowest performance temperature.