Preparation, properties and modification mechanism of polyurethane modified emulsified asphalt

To prepare new polyurethane (PU) modified emulsified asphalt (EA), and further understand modification mechanism of PU to EA, effects of PU on basic engineering performances, chemical composition compatibility, morphology and element compositions, thermal properties, phase microstructures of EA were discussed. The results indicate that basic properties of PU modified EA firstly meet relevant requirements of technical specifications. Improvement effects of PU with a suitable content on penetration and ductility is better than that of styrene butadiene styrene (SBS), but their softening points are similar. Secondly, PU modified EA process includes physical and chemical modifications. PU is dispersed uniformly in evaporation residues of EA when PU content is less than 6%, and meta-stable two-phase interface transition layers are formed between PU and asphalt binder, forming a uniform dispersion system and interpenetrating network structures in modified EA. The compatibility between PU and EA is satisfactory, forming a stable multiphase structure in modified EA. This is conductive to improve high-temperature stability and low-temperature ductility of modified EA. Thirdly, the contents of such main chemical elements as carbon (C), oxygen (O) and sulfur (S) in evaporation residues of EA show no obvious changes before and after modified by PU, indicating that physical modification is main method during the preparation of PU modified EA. Fourthly, PU is difficult to form a continuous crystalline phase in EA. However, the molecular chain spacing and microcrystalline size of PU modified EA are decreased at a suitable PU content, generating more compact interpenetrating network of molecular chains. Motions of asphalt molecules are limited, improving thermal stability and mechanical properties of EA. Finally, a suitable PU content of 6% is proposed to prepare modified EA.