Research On Hardening Mechanism And Hydration Model Of Polymer-Cement Composite Materials

The method of improving concrete performance by modifying cement-based material with polymer has been widely used in infrastructure construction in China.However,the influence of polymer on the setting and hardening of cement-based materials is still mainly described qualitatively,and there is no quantitative index system and calculation method to characterize the influence of polymers.At present,the research on hydration thermodynamics of polymer-cement composite cementitious materials is not deep enough.Due to the different polymers used,the research results are also different.Therefore,taking epoxy latexes as an example,starting from the microscopic characteristics of materials,in this thesis the kinetic and thermodynamic retarding mechanism of polymer on cement hydration was discussed through experimental research,mechanism analysis and model development.Firstly,the composite cement paste with 0%,10%and 20%epoxy latex content was prepared,and the effect of polymers on the heat generated of cement paste is discussed by isothermal calorimetry.The results show that the addition of epoxy latex leads to significant differences in heat-generation rate,duration of each reaction stage and accumulated heat.Among them,the epoxy latex reduces the initial heat-generation rate of cement paste,prolongs the induction period and acceleration period,reduces the maximum peak heat-generation rate,and inhibits the formation of"sulfate consumption peak".The higher polymer content,the more obvious the effect of influencing the heat-generation rate.The retardation effect of epoxy latex on the dissolution of cement clinker minerals and the precipitation of hydration products was studied by in-situ XRD.The results show that the processes of ettringite formation,aluminate hydration and silicate hydration were significantly delayed by delaying the dissolution of cement clinker minerals and the precipitation of hydration products.Among them,the epoxy latex could delay the formation of ettringite by reducing the initial dissolution of C₃A minerals and the initial precipitation of ettringite.By slowing down the dissolving speed of C₃A minerals,the hydration reaction of aluminate was delayed.By slowing down the dissolution of C₃S minerals and the precipitation of calcium hydroxide,the hydration reaction of silicate was delayed.At the same time,based on the above tests,time-dependent retarding effect of Epoxy Latexes was put forward,and the retarding process of ettringite formation reaction,aluminate hydration reaction and silicate hydration reaction was analyzed and discussed,which provided a theoretical basis for studying the mix design of polymer modified concrete.Based on the original multi-component hydration model,the retardation effect of polymer on cement hydration was discussed from the aspects of ettringite formation reaction,aluminate hydration reaction and silicate hydration reaction,and the polymer retarding parameter K was introduced into the original multi-component hydration model to express the retardation effect of polymer on the heating rate H_iof cement clinker minerals.In addition,by comparing the experimental results with the numerical simulation results,it is verified that the model is suitable for predicting the hydration kinetics and thermodynamics of epoxy latex modified cement paste.It took into account the evolution process of the time-dependent retardation effect of polymer,which provided more details for further studying the content evolution process of cement mineral clinker,and also had important scientific value and engineering significance for designing high-performance concrete to meet the needs of water conservancy infrastructure construction in China.