Intrinsic temperature and moisture sensitive adhesion characters of asphalt-aggregate interface based on molecular dynamics simulations

Abstract

Aiming to evaluate the effects of temperature and water on the adhesion characters of asphalt-aggregate interface, the molecular dynamics MD) simulations was adopted in this study to investigate the interactions between asphalts and aggregate with the presence of the water under different temperature. Based on improved Brown-Ladner (B-L) methods, the structure parameters of three asphalt binders were obtained firstly by combining elemental analyzer, gel permeation chromatography (GPC) and proton nuclear magnetic resonance (1H NMR). Three asphalt average molecular structure models were further constructed to build the asphalt-aggregate interface and asphalt-water-aggregate interface systems to simulate the asphalt-aggregate adhesion at different temperature. The high-low temperature cyclic tests were used to studying the effect of temperature changes and moisture on adhesion characters of the interface. Atomic force microscopy (AFM) adhesive force test of asphalt before and after water immersion was also performed to investigate the moisture susceptibility of three asphalt binders. According to the simulation results, when the temperature was below the softening point, the work of adhesion was ranked PEN90 > PEN70 > PEN50 at both dry and wet conditions, which were used to quantify the adhesion properties between asphalt and aggregate. The degradation of adhesion induced by moisture was more distinct at the temperature above the softening point of asphalt. For the asphalt binders from the same crude oils source, stiffer asphalt exhibited higher moisture susceptibility, while the effect of asphalt on moisture susceptibility was negligible at the relatively high temperature. Especially, when the asphalt-quartz interfaces were subjected to multi-cycling temperature changes, the interface adhesion decreased so that the moisture damage and crack were easier to occur according to the high-low temperature cyclic tests. Further, the simulation results of MD were consistent with the measurement results from AFM tests, which indicated the average molecular structure models were reasonable for simulating the interface adhesion and moisture damages. This work lays a foundation for understanding the intrinsic temperature and moisture sensitive adhesion characters of asphalt-aggregate interface at the atomistic scale.