Investigation Of The Interaction Between Cement And Asphalt Emulsion And Its Mechanism

As a kind of key engineering material used in the system of ballastless track in High-Speed Railway?HSR?,cement-asphalt?CA?mortar is mainly grouted in the long and narrow structure between the concrete base and the track slab,which could ensure the high speed train running safety and smooth at the speed of more than250km/h by adsorbing damping.As a kind of grouted material,the workability of CA mortar is closely related to the rheological property during the early period,however,the workability loss of CA mortar was often occurred in the engineering practice,which could apply the adversely effect on the process of construction significantly.The CA paste is composed of cement,asphalt emulsion,superplasticizer and water,which is an important part of CA mortar and also would exert significant influence on the rheological property of CA mortar directly.The thesis investigated the interactions between different compositions of CA paste,and the main influencing factors of the rheological loss of CA paste was proved,the rheological modeling of CA paste based on the evolution of microstructure was established,and also the technical measures for controlling the rheological loss of CA paste during early period was put forward.The main achievements of the thesis can be listed as follows.1.Asphalt emulsion delayed the process of cement hydrationIn the CA paste,the process of cement hydration would be affected by anionic asphalt emulsion,and the retardation effect of anionic asphalt emulsion on cement hydration was validated by the following experimental results of setting time,hydration heat,electrical resistivity,in-site XRD,MIP,X-CT and SEM.The retardation mechanism of anionic asphalt emulsion on cement hydration could be disclosed as below:?1?The surface of cement particles was adsorbed by anionic asphalt emulsion via anionic emulsifier,which resulted in the ion dissolution being hindered due to the“activity sites”of cement particles were occupied by anionic asphalt emulsion,and thus delayed the cement hydration process.?2?The Ca²⁺generated from cement hydration entered into the double electrode layers of anionic asphalt emulsion,which resulted in the demulsification of anionic asphalt emulsion and caused the formation of asphalt membrane.Therefore,the ion dissolution and hydration process were hindered due to the coverage of asphalt membrane onto the surface of cement particles.?3?Much more hydrogen bonds formed between different water molecules around anionic asphalt emulsion,which decreased the chemical reactivity of water molecules with cement particles,and thus hindered the cement hydration process.2.Cement hydration promoted the demulsification of anionic asphalt emulsionAdded the CaCl₂ electrolyte solution into the anionic asphalt emulsion,the results indicated that:the average particle size of the anionic asphalt emulsion became larger obviously,the anionic asphalt emulsion demulsified and resulted in the aggregation of asphalt particles observed by the optical microscope;in addition,the zeta potential of anionic asphalt emulsion decreased,which implied that the electric double layers was compressed.Under the action of cement slurry filtrate,the average particle size of the anionic asphalt emulsion became larger gradually over time,and the variation trend of which was similar to the action of the CaCl₂ electrolyte solution.That is to say,the cement hydration would cause the demulsification of anionic asphalt emulsion.The main reason for the demulsification of anionic asphalt emulsion caused by cement hydration,which can be attributed to the following:?1?Partial negatively charged of the surface of anionic asphalt emulsion was shielded by the Ca²⁺generated from cement hydration,which compressed the electric double layers,and thus decreased the repulsion between asphalt emulsion particles;?2?With the formation of hydration products and the consumption of water,the anionic asphalt emulsion being adsorbed on the surface of cement particles would aggregate with each other,and finally formed a coverage of continuous asphalt membrane onto the surface of cement particles.3.The competitive adsorption relationship between superplasticizer and anionic asphalt emulsion on cement particlesWhile incorporating the superplasticizer into the CA paste,the amount of the asphalt emulsion which has been adsorbed onto the surface of cement particles decreased gradually with the diffusion of superplasticizer into the CA paste,indicating that the desorption of asphalt emulsion from the surface of cement particles caused by the addition of superplasticizer.In other words,the competitive adsorption relationship between anionic asphalt emulsion and superplasticizer on the surface of cement particles was further confirmed by the aforementioned results.The competitive adsorption mechanism of superplasticizer and anionic asphalt emulsion on the surface of cement particles can be proposed as below:?1?In comparison to anionic asphalt emulsion,the migration speed of superplasticizer was much quicker due to the smaller particle size,which resulted in the priority adsorption of superplasticizer on the surface of cement particles.?2?The charge density of superplasticizer was higher than that of the anionic asphalt emulsion,which caused the adsorption driving force between superplasticizer and the surface of cement particles much stronger.4.The early period rheological,modeling and controlling measures of CA pasteAnionic asphalt emulsion delayed the process of cement hydration and hindered the formation of hydration products,which implied that cement hydration was not the main reason for the early rheological loss of CA paste.Adding CaCl₂ solution into anionic asphalt emulsion would cause the demulsification of anionic asphalt emulsion,which would also result in the obvious increase of the yield stress and the viscosity of CA paste,namely the workability loss of CA paste.However,the rheological property of pure cement paste was hardly affected by adding CaCl₂ solution,which could deduce that the rheological loss of CA paste was mainly caused by the demulsification of anionic asphalt emulsion.In addition,much more hydrogen bonds would be formed between water molecules around the anionic asphalt emulsion,which resulted in the increase of the viscosity of water in CA paste,and this also may be considered as one of the reasons for the rheological loss of CA paste.The early period rheological modeling was established according to the evolution of the microstructure of CA paste in the thesis;Superplasticizer could be utilized to control the cement hydration process and rheological behavior of CA paste during early period.