Modification of asphalt using polyurethanes synthesized with different isocyanates

To study the effect of isocyanates on the properties of polyurethane (PU) modified asphalt, three kinds of polyurethane with different hard segments were synthesized, by the reaction of polyethylene adipate (PEA) with diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI) and polyaryl polymethylene isocyanate (PAPI), respectively. These three kinds of polyurethane were used to modify the asphalt and study the effects of isocyanate on the performance of polyurethane modified asphalt by experiments. The Fourier transform infrared spectrometer (FTIR), and the gel permeation chromatography (GPC) were used to analyse PU samples. The dynamic shear rheology (DSR), bending beam rheology (BBR), multiple stress creep test (MSCR), Fourier transform infrared spectroscopy (FTIR), atomic force microscope (AFM), and differential scanning calorimetry (DSC) were used to research rheological properties, modification mechanism and microstructure of the asphalts, respectively. The results show that isocyanates influence the structure of polyurethane molecules, the distribution of soft and hard segments and the content of hard segments, and affect the distribution of asphaltenes in asphalt, resulting in different modification effects on asphalt. Of the three isocyanates, the PU synthesized by TDI provides the best improvement to the asphalt in terms of resistance against permanent deformations, low-temperature property and storage stability. Improvement effects of PU synthesized by PAPI on resistance against the permanent deformations and storage stability are better than that of MDI, but the effects on low-temperature property are worse with that of MDI.