| The current extensive cement production pattern has exerted serious damage on local resource consumption and the environment.Several industrial by-products can be used as supplementary cementitious materials,replace cement clinker,control the particle gradation of cement clinker and improve the performance of cement-based materials.With the increase in the components and amounts of the cement-based cementitious system in actual projects,existing research results on the single-or double-admixture composite system cannot be directly used in the multi-system,leading to the limited development of multi-system performance.Existing theoretical and experimental research have failed to keep up with the actual engineering application of fine admixtures.Given this research background,this thesis adopts the multi-element composite cementitious material system as the research object,and statistical optimisation design methods,laboratory tests and computer simulations are used to develop the internal correlation between multi-system performance and the hydration mechanism.The main research content and innovation results are as follows:(1)The statistical optimisation method is used to evaluate the performance development law of three kinds of fine admixtures with large differences in activity and particle size when mixed with a benchmark cement.The focus is on the nonlinear relationship between the multi-component performance relationship and the interaction effects between the components.The results show that the response surface function fitted by the regression model of fluidity,rheological parameters,hydration heat,compressive strength and drying shrinkage performance is fully significant,and the model is stable.(2)The hydration exotherm characteristic value of the multi-grain composite cementitious system is tested using the isothermal calorimetry method,and the hydration kinetics process of the composite system is studied with the method of chemical reaction kinetics.The results show that the overall hydration heat release rate of the quaternary system is significantly lower than that of the control group,and the second heat release peak is significantly delayed.The early heat release rate curve of the fine group blended with silica fume overlaps with that of the reference group,and the hydration rate gradually increases compared with the rate for the reference group after hydration for four hours.The hydration half-life time of the multi-component system is between 11 and 13 h,and the difference between the total heat release obtained by fitting and the cumulative heat release at 72 h is within 10%.The Krstulovic–Dabic model is used to simulate the compound high reliability of system hydration kinetics.(3)Five statistical methods are utilised to study the relationship between the early hydration heat release characteristics and the compressive strength of the multi-system.The results show that the correlation coefficient fitted by the Spearman method is the highest overall,followed by the linear correlation coefficient fitted by the Pearson method and that fitted by the Kendall method(the smallest overall).The correlation coefficient between 28 d compressive strength and the characteristic value of early hydration heat release is generally higher than that of 3d compressive strength.However,under multiple correlation conditions,the correlation between hydration heat release characteristics and mechanical properties undergoes a fundamental change.In particular,under the four-fold correlation conditions,the correlation coefficient between the 3 d compressive strength and the characteristic value of the early hydration heat release is higher than the 28 d compressive strength.(4)The HYMOSTRUC3D model is used to simulate the hydration process of the multi-system and the law of microstructure development.The results show that the system hydration degree increases as the water–cement ratio increases.The larger the water–cement ratio is,the smaller the hydration degree increment is for the same hydration time.Before the system is hydrated for about 100 h,the hydration degree increases rapidly and reaches a high level at 150 h;then,it gradually stabilises.The elastic modulus of the different systems presents an increasing trend with the increase in hydration degree.As the degree of hydration increases,the porosity of the different systems decreases.Through the above research,the performance development law of the multi-grain cement-based composite cementing system was revealed,and the multiple statistical relationship between the early hydration characteristics and the mechanical properties of the multi-grain composite system was obtained.The research results can provide a reasonable use plan for some industrial by-products with low activity,further improve the comprehensive utilization rate of industrial by-products,and minimize the amount of cement clinker.It has important theoretical,economic and environmental significance. |
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