Recycling waste engine oil as a viscosity reducer for asphalt rubber: an insight from molecular dynamics simulations...

Traditional asphalt rubber (AR) has a high viscosity and poor fluidity, which makes its construction very difficult. Reducing viscosity has been identified as one of the effective way of solving these problems. Meanwhile, the mass production and improper discharge of waste engine oil (WEO) have a serious impact on the ecological environment, and its rational reuse needs to be addressed. In this paper, molecular models of AR and WEO-modified asphalt rubber (WEOMAR) was established by molecular dynamics (MD) simulations. The influence of WEO on asphalt component's behavior was studied by radial distribution function (RDF) and diffusion coefficient (D). Then, the microscopic mechanism of viscosity reduction was evaluated. Furthermore, the viscosity reduction behavior of WEO in AR was analyzed and verified by basic properties and low field nuclear magnetic resonance (LF-NMR) laboratory tests. The results showed that the RDF peak value of rubber molecules in WEOMAR is 14.07 higher than that of AR, at r = 2.16 Å. The D of saturated and aromatic components in WEOMAR obviously increased by 140% and 67.9%, respectively. The light component molecules increased after adding WEO into AR. The rubber molecule reduces the contact with asphaltene and resin, and the viscosity of AR is significantly reduced, which is confirmed by the macro tests.