Molecular Dynamics Simulation On Adhesion Of Emulsified Asphalt-Aggregate Interface

Emulsified cold recycling mixture is one of the most commonly used cold recycling methods for asphalt pavement.It has the advantages of low cost,fast construction speed,energy saving,emission reduction and environmental protection,and a good engineering economy.The obvious problems with emulsified cold recycled mixture are early strength and curing time,and the interface properties are an important factor in determining the strength.Molecular simulation technology has the advantages of physical and chemical analysis,which can explain various phenomena and properties of asphalt system from the perspective of molecular motion.Based on this,this paper studies the diffusion and adsorption behavior of emulsified asphalt-aggregate interface and the internal interface strength characteristics of emulsified asphalt cold recycled mixture from the molecular point of view,providing a basis for the analysis of the strength formation mechanism of cold recycled pavement.This paper firstly established the molecular model of emulsified asphalt,aggregates,reclaimed asphalt pavement,and cement hydration products in emulsified asphalt cold recycled mixture.Then the models are compared and verified in terms of density,solubility parameters,cohesive energy density,glass transition temperature,viscosity parameters.The diffusion behavior of emulsified asphalt on the aggregate surface was simulated and analyzed.In the cold regeneration mixture,water molecules were the power source for the adsorption of emulsified asphalt to the aggregate surface.The emulsifier drove the asphalt molecules to adsorb to the aggregate surface finally.The emulsifier acts as a bridge between aggregates and asphalt to achieve the purpose of interfacial strength formation.The interrelationship among water,aggregate,and asphalt was further analyzed by wetting simulation:the hydroxylatedα-quartz surface was more hydrophilic than asphalt.Wetting simulations show that the cationic emulsifier CTAC has better adsorption to aggregates than the anionic emulsifier SDBS.Furthermore,the adhesion state and effect analysis of the inner interface of the emulsified asphalt cold recycled mixture is carried out.The adhesion energy range of emulsified asphalt and aggregate is-215m J/m~2～-288m J/m~2,which is in line with the test data range.The results showed that when the emulsifier content increases,the adhesion between CTAC emulsified asphalt and aggregate is more potent than SDBS emulsified asphalt.The effect of temperature on the adhesion energy of each emulsified asphalt-aggregate interface was inconsistent.When the emulsifier content is 3%,the water damage resistance of anionic emulsified asphalt is better than cationic emulsified asphalt.The cohesion of emulsified asphalt and matrix asphalt at average temperature is dominant,resulting in destruction at the interface between asphalt and aggregate.The pull-out mechanical simulation analysis showed that whether it is adhesion or cohesion,CTAC emulsified asphalt is better than matrix and SDBS emulsified asphalt,which is consistent with the adhesion energy result.At room temperature,interface adhesion failure is more likely to occur.The cohesion force is significantly more substantial than the adhesion force,consistent with the results obtained from the energy theory calculation.The binding energy between emulsified asphalt and RAP was significantly weaker than that between emulsified asphalt and silica,showing weak or non-bonded bonding.The water damage resistance of the RAP model was smaller than that between silica.The cement hydration products can effectively improve the adhesion between emulsified asphalt and aggregates.The bonding strength of emulsified asphalt mortar and silica will increase with C-S-H gel content in the cement hydration product.The cement-emulsified asphalt mortar-aggregate interface model is more prone to adhesion failure from energy and mechanical analysis.To enhance the strength of the cold recycled mixture,it is very important to enhance the adhesion between the interfaces from the aspects of the type and amount of emulsifier,the type and content of cement hydration products,and the improvement of RAP performance.