| Rubber powder modified asphalt has a good improvement effect on high temperature deformation,low temperature cracking resistance and fatigue performance of pavement,but it still faces the problem of water damage to a large extent.The interface bonding of asphalt material and aggregate is very important to ensure the engineering performance of asphalt pavement,and the interface performance directly determines the stability of asphalt mixture and its service life.However,the action of water in the environment leads to the gradual peeling of asphalt from the surface of the aggregate,which deteriorates the interface between asphalt and aggregate,resulting in the instability of asphalt pavement structure.The existing studies do not have a comprehensive understanding of the microscopic behavior of water at the interface of rubber powder modified asphalt and aggregate,and do not have a deep understanding of how water affects the adhesion mechanism of its interface.Therefore,based on the theory of molecular dynamics,this paper establishes the interface models of different bitumen/glue powder modified-aggregates and bitumen/glue powder modified bitumen-water-aggregates through Materials Studio software,and explores the interaction mechanism of bitumen/glue powder modified bitumen-water-aggregate interface from the molecular scale.By analyzing the interaction between asphalt/glue powder modified bitumen and aggregates under the action of water and the movement characteristics of water and asphalt components on the surface of aggregates,the influence of moisture action form,rubber powder type and aggregate mineral type on the interface adhesion was revealed,so as to explain the mechanism of action between rubber powder modified bitumen and aggregates under the action of moisture.Firstly,in this study,an asphalt/glue powder modified bitumen(-water)-aggregate interface model was established.In this paper,the twelve-molecule model of asphalt is selected,and the proportion and number of each component are calculated from the measured fourcomponent content.Rubber powder considers two components: natural rubber(Nature RubberNR)and cis-butadiene rubber(Butadiene Rubber-BR);The aggregate is made of three representative minerals: calcite,quartz and dolomite.At the same time,based on the mechanism of water damage,two positions of water molecules in the model were determined,inside asphalt and at the asphalt-aggregate interface,in which the number of water molecules at the interface was of four orders of magnitude.Based on the magnitude of the above three types of asphalt,three mineral aggregates and four types of water molecules at the interface,3×3×4 sets of models were constructed and the rationality of asphalt molecules was verified by density,and the molecular dynamics simulation and data analysis were carried out to explore the interaction between molecules at the interface under the action of water.Secondly,the mean square shift and diffusion coefficient are used to evaluate the diffusion effect of different aggregate surface moisture and asphalt components.In terms of water diffusion,the diffusion coefficient showed a nonlinear increase trend with the increase of the number of water molecules at the interface.As far as the diffusion of asphalt components is concerned,in most cases,the diffusion coefficient of each component of asphalt increases with the increase of the number of water molecules,and the diffusion coefficient of saturated components is the largest,and the addition of rubber powder may affect the diffusion of components,but the overall motion law is still that the diffusion coefficient of light components is greater than that of heavy components.Thirdly,the interface energy in the simulation results was used to calculate the adhesion work,shedding work and energy ratio(Energy Ratio-ER)to evaluate the adhesion performance of the rubber powder modified bitumen and the aggregate interface under different moisture effects.The work of adhesion can be used to measure the energy required for an object to decompose a single surface into two separate surfaces in a vacuum environment,and the greater the work of adhesion,the better the adhesion performance.The results show that the adhesion work at the interface between asphalt/rubber powder modification and calcite is the largest,and the selection of aggregate type with high calcite content is conducive to increasing the interface adhesion.With the increase of moisture at the interface,the adhesion work decreases significantly,indicating that the moisture reduces the degree of interface adhesion.The adhesion work of the interface between the modified bitumen and the aggregate is greater than that of the matrix asphalt,indicating that the modified bitumen can effectively improve the adhesion performance of the interface with the aggregate.The shedding work is defined as the energy used by water to displace the rubber bitumen from the aggregate interface,and the greater the shedding work,the more likely it is to cause water damage.The results showed that the interfacial shedding work was the largest when dolomite was selected,indicating that its anti-spalling ability was the worst.With the increase of the number of water molecules at the interface,the shedding work tends to increase,and it is more inclined to peel.ER represents the ratio of adhesion work in dry conditions to shedding work in wet conditions.The results showed that the ER value was the largest when the aggregate was calcite,indicating that calcite water sensitivity was low.The addition of glue powder reduced the exfoliation power of the interface and significantly increased the ER value,indicating that the addition of glue powder was conducive to improving its ability to resist water intrusion at the interface with the aggregate.Secondly,the mean square shift MSD and diffusion coefficient were used to evaluate the diffusion effect of different aggregate surface moisture and asphalt components.In terms of water diffusion,the diffusion coefficient showed a nonlinear increase trend with the increase of the number of water molecules at the interface.As far as the diffusion of asphalt components is concerned,in most cases,the diffusion coefficient of asphalt components increases with the increase of the number of water molecules,and the diffusion coefficient of saturated components is the largest,and the addition of rubber powder may affect the diffusion of components,but the overall motion law is still that the diffusion coefficient of light components is greater than that of heavy components.Thirdly,the interface energy in the simulation results was used to calculate the adhesion work,shedding work and energy ratio Energy Ratio(ER)to evaluate the adhesion performance of the rubber powder modified bitumen and aggregate interface under different moisture.The work of adhesion can be used to measure the energy required for an object to decompose a single surface into two separate surfaces in a vacuum environment,and the greater the work of adhesion,the better the adhesion performance.The results show that the adhesion work at the interface between asphalt/rubber powder modification and calcite is the largest,and the selection of aggregate type with high calcite content is conducive to increasing the interface adhesion.With the increase of moisture at the interface,the adhesion work is significantly reduced,indicating that the moisture reduces the degree of interface adhesion.The adhesion work of the interface between the modified bitumen and the aggregate is greater than that of the matrix asphalt,indicating that the modified bitumen can effectively improve the adhesion performance of the interface with the aggregate.The shedding work is defined as the energy used by water to displace the rubber bitumen from the aggregate interface,and the greater the shedding work,the more likely it is to cause water damage.The results showed that the interfacial shedding work was the largest when dolomite was selected,indicating that its antispalling ability was the worst.With the increase of the number of water molecules at the interface,the peeling work tends to increase,and it is more inclined to occur peeling.ER is the energy ratio,and its value is the ratio of the adhesion work under dry conditions to the shedding work under wet conditions.The results showed that the ER value was the largest when the aggregate was calcite,indicating that calcite water sensitivity was low.The addition of glue powder reduced the exfoliation power of the interface and significantly increased the ER value,indicating that the addition of glue powder was conducive to improving its ability to resist water intrusion at the interface with the aggregate.Finally,the pulling strength is obtained by carrying out the macroscopic drawing test after water bathing to characterize the adhesion between asphalt and aggregate under the action of water.Four water bath times are used to correspond to four orders of magnitude of the number of water molecules at the interface.The results show that the intrusion of water greatly reduces the adhesion of the asphalt-aggregate interface,and the longer the water bath time,the smaller the drawing strength and the higher the pulling loss rate.Compared with matrix asphalt,the loss rate of drawing strength of rubber powder modified bitumen is small,which indicates that the use of rubber powder modified bitumen improves the adhesion between bitumen and aggregate minerals to a certain extent. |
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