Influence of shearing process on the property and microstructure of bitumen modified by polyethylene and ethylene-vinyl acetate copolymer

As an important regulation parameter, shearing process during bitumen modification can be easily adjusted. However, the effect of shearing time on the properties of modified bitumen and its original reason is still unclear. To explore this concern, bitumen/polyethylene (PE)/ethylene-vinyl acetate copolymer (EVA) blend (PMB) with fixed weight ratio of 100/5/5 was studied by imposing different shear time within 1-4 h under 180 degrees C. It was found longer shearing time could improve rutting resistance but deteriorate the ductility at low temperature. Due to the crystalline nature of PE/EVA and the immiscibility between these polymers and bitumen, the possible reason was firstly explored on terms of crystallinity and phase structure of PMBs. A shearing-heating system connected with optical microscopy was innovatively employed for in-situ phase structure observation. After excluding both effects of crystallization and phase separation on the different properties of PMBs, the relationship between thermal ageing and shearing was subsequently explored. An in-situ quiescent TGA measurement under 180 degrees C for 3 h revealed a continuous weight loss of PMBs. FTIR results suggested the thermal-oxidation behavior of EVA. Combined these two results, the thermal-oxidation process and hardening effect were the main reasons for different properties of PMBs with different shearing time.