Abstract
Bitumen/PEG (polyethylene glycol)/MDI (4,4′-diphenylmethane diisocyanate)/SiO2 (nanosilica) composites were prepared by simple mixing, during which polyurethane reaction occurs between MDI and polar groups provided by either hydrophilic SiO2, PEG or asphaltenes in bitumen. To induce different sequence of polyurethane reaction between MDI and other three matters, SiO2 nanoparticles were premixed with PEG, MDI, or base bitumen. The content of SiO2 was kept as 0.08 wt% of base bitumen, and this tiny loading of SiO2 could significantly influence the performance of modified bitumen under different premixing methods. Rutting resistance under high temperature of modified bitumen was studied by dynamic shear rheometer with oscillatory frequency sweep and multiple stress creep recovery (MSCR) tests. Crack resistance under low temperature was explored by bending beam rheometer. When SiO2 premixed with base bitumen, the modified bitumen has the worst rutting and crack resistance, even worse than bitumen/PEG/MDI system without SiO2 addition. However, the rutting resistance could be obviously improved when the SiO2 premixed with PEG or MDI. Microstructure evolution was observed for estimation of phase separation, which also could be an indication of thermal stability.
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