Analysis of foaming mechanism and adhesion of foam rubberised asphalt from the perspective of molecular scale

Rubberized asphalt (RA) is characterized by its high viscosity, which necessitates elevated construction temperatures.During the mixing, paving, and compaction processes of the mixture, it consumes a significant amount of energy and releases gases harmful to both the environment and human health, thereby impeding the sustainable development of society.Foaming technology can effectively ameliorate this issue.However, RA exhibits a low foaming expansion rate, and the foaming temperature and water content have a considerable impact on the foaming efficacy.Current research on the foaming effect of RA is predominantly based on the macroscopic performance of test indicators, and the understanding of the microscopic foaming mechanism remains to be further elucidated.Additionally, some experiments have shown that foaming water can alter the microstructure of asphalt, adversely affecting the fatigue resistance and bonding strength of the asphalt binder.It is imperative to investigate the influence of water molecules on the interaction between foamed rubberized asphalt and aggregates.Therefore, it is essential to explore the foaming mechanism of rubberized asphalt by means of molecular dynamics and to evaluate the interaction characteristics between foamed rubberized asphalt and aggregates.In this study, Foamed rubberized asphalt (FRA) models were constructed by incorporating water molecules and rubber chains into the asphalt model.The foaming process was comprehended by calculating and analyzing the density and energy changes of the model.The variation patterns of the foaming expansion rate and half-life of FRA were discussed through model parameters, and the Fourier transform infrared spectroscopy of RA before and after foaming was tested.The distribution of water molecules and the aggregation characteristics between molecules in the model were further explored through model conformation and radial distribution function.The mechanism of the influence of water molecules on the viscosity of the model was elucidated.Moreover, mineral models of granite and limestone were developed using SiO2 and CaO supercells, respectively, and were combined with the FRA model to create interface models.The migration patterns of asphalt components and rubber molecules on the mineral surface were studied, and the effect of water molecules on interface adhesion was investigated through adhesion work.The study reveals that an increase in temperature and the number of water molecules can reduce the density of the model.Furthermore, the time required for the model to reach a steady state is strongly influenced by the number of water molecules, indicating that water molecules interfere with the movement of other molecules within the model.Figure 1a elucidates the aforementioned conclusion from an energy perspective.It can be observed that an increase in temperature facilitates a rise in the total energy of the model, while an increase in the number of water molecules primarily contributes to the kinetic energy of the molecules within the model.The instability of the model makes volume compression difficult, which can explain the expansion mechanism of FRA.In other words, the more challenging the volume compression, the easier the expansion process, corresponding to an increase in the expansion rate.During the NPT process, the model compresses from a low-density steady state to a highdensity steady state, which can reflect the decay process of FRA (Figure 1d).The energy difference between the two steady states is calculated in Figure 1b.It can be observed that the energy difference increases with water content at different temperatures.This suggests that the FRA model releases more energy when transitioning from a low-density state to a high-density state.This can explain the decay mechanism of FRA.In the actual foaming process, an increase