Atomistic-scale investigation of self-healing mechanism in Nano-silica modified asphalt through molecular dynamics simulation

As one of the most widely used nanomaterials in asphalt modification, the nano-silica (nano-SiO2) can significantly improve the self-healing behavior of asphalt eco-friendly. However, understanding of the self-healing mechanism of nano-SiO2 in asphalt is still limited. The objective of the study is to reveal the self-healing mechanism of nano-SiO2 in asphalt by using molecular dynamics (MD) simulations from the nanoscale. A 10 Å (Å) vacuum pad was added between the two same stable asphalt models to represent the micro-cracks inside the asphalt. The self-healing process of virgin asphalt, oxidation aging asphalt, and nano-SiO2 modified asphalt was studied using density evolution, relative concentration, diffusion coefficient, activation energy, and pre-exponential factor. The simulation results conclude that nano-SiO2 improves the self-healing ability of asphalt by increasing the diffusion rate of molecules with aromatic structures without alkyl side chains and molecules with structures with longer alkyl chains. The self-healing capability of asphalt may be principally determined by the diffusion of light components such as saturate, while nano-SiO2 only plays an inducing role. The research findings could provide insights to understand the self-healing mechanism of nano-SiO2 in asphalt for promoting the sustainability of bitumen pavements while increasing their durability.