Surface modification of fly ash by waste engine oil under mechanical activation enhanced the sustainable service life of asphalt

Oxidative aging of asphalt leads to changes in its molecular structure and chemical composition, deteriorating the properties. Therefore, extending the service life of asphalt materials is essential for environmental protection and sustainable development. In this study, waste engine oil (WEO) with similar components and chemical composition to asphalt was used to modify the fly ash (FA) surface by a high-energy ball grinding process to produce a well-compatible compound fly ash modifier (CFAM). This process achieved ultra-refinement and surface modification in one step, enhancing the chemical bonding and anchoring force between FA and asphalt, thereby effecting the ageing resistance of the asphalt. Dynamic light scattering tests showed that the oil grinding process enhanced the stability of CFAM, whose median particle size (654 nm) increased by only 103 nm after four months of storage. Thermogravimetric (TG), BET tests showed that the FA surface was grafted with a large amount of WEO, and the CFAM after de-oiling and rinsing had a WEO content of 1.39 wt%, which gave it excellent compatibility with asphalt. The nano-indentation and Fourier transform infrared spectroscopy (FTIR) experiments showed that CFAM reduced the changes in micro hardness, modulus of elasticity, carbonyl content and sulfoxide group content of asphalt before and after ageing and provided an excellent anti-ageing effect. The oil grinding process activated the reactivity of the FA that could chemically bond with the carboxylic acids in the asphalt, stabilizing the chemical components of the asphalt and delaying the ageing of the asphalt, thus achieving sustainable service of the asphalt.