Study On Hydration Properties Of Cement-ceramic Powder Composite Cementitious Materials

During the production,transportation and use of ceramics,a large number of waste ceramics are usually generated.The recycling rate of these waste ceramics is extremely low,resulting in a huge waste of resources.The application of ceramic powder in concrete can reduce the amount of cement and solve the environmental problems caused by the landfill of waste ceramics,which has great economic and environmental benefits.The physical activity（morphological effect,micro-aggregate effect）and chemical activity（pozzolanic reaction）of ceramic powder have different effects on the properties of cement-ceramic powder composite cementitious materials.Therefore,research on its physical and chemical effects is of great significance for using ceramic powder as an admixture in concrete.Therefore,in this paper,the pure cement system,the composite cementitious material system mixed with fly ash or ceramic powder were studied at different dosages and different curing temperatures.Therefore,in this paper,the pure cement system,the composite cementitious material system mixed with fly ash or ceramic powder were studied at different dosages and different curing temperatures.Through experimental research on the hydration characteristics of ceramic powder during the hydration process of composite cementitious materials,the microstructure of cement-ceramic powder composite hardened paste,and the chemical shrinkage changes,the hydration characteristics of cement-ceramic powder composite cementitious materials were discussed.The research contents and main results are as follows:The hydration process of the composite cementitious material is the result of the interaction of each component of the cementitious material and the superposition of each other.For cement hydration reaction,different admixtures have different promotion or restriction effects,which makes the hydration reaction of composite cementitious materials complicated.The hydration process of the composite cementitious material is the result of the interaction of each component of the cementitious material and the superposition of each other.For cement hydration reaction,different admixtures have different promotion or restriction effects,which makes the hydration reaction of composite cementitious materials very complicated.The hydration heat release rate and hydration heat release rate of pure cement and composite cement materials mixed with ceramic powder or fly ash at 20℃were tested.It is found that the incorporation of ceramic powder and fly ash will reduce the heat release rate and total hydration heat release of composite cement-based systems.The incorporation of ceramic powder leads to the occurrence of exothermic peaks in the accelerated period of hydration of composite cement materials earlier than that of pure cement,and the incorporation of fly ash causes the delayed occurrence of exothermic peaks in the period of accelerated hydration.In the early stage of hydration,the volcanic ash activity of ceramic powder is not much different from that of fly ash when the content is small.When the content is more than 10%,the activity of ceramic powder and the promotion of cement hydration are stronger than fly ash.The secondary hydration reaction between the admixture and the hydration product-Ca（OH）₂ will reduce the alkalinity of the pore solution.The volcanic ash activity of ceramic powder is higher than that of fly ash,so the pore solution alkalinity of cement-ceramic powder composite hardened slurry is lower than that of hardened slurry mixed with fly ash under the same conditions.But the admixture does not affect the stability of the pore solution alkalinity in long-term age.The cement-ceramic powder composite hardened slurry has a higher amount of chemically bound water than hardened slurry with fly ash added under the same conditions.The chemical shrinkage of cement paste with ceramic powder is higher than that of composite cement paste with fly ash.As ceramic powder participates in the secondary hydration reaction,its pozzolanic activity is obviously shown in the middle and long term of hydration,so the addition of ceramic powder in the later stage of hydration will lead to the densification of the microstructure of cement-ceramic powder composite hardened paste and the optimization of pore distribution,and the improvement of the hydration degree of water mud in the system.In the cementitious material system,the mid-to-long-term hydration performance of the ceramic powder-cement composite cementitious material is inferior to that of the pure cement material,but it is superior to the system containing fly ash.The curing temperature has a significant effect on the activity of ceramic powder in composite cementitious materials.Under the condition of high temperature curing,the chemically bound water in the early hydration system was significantly improved,the degree of cement hydration was significantly improved,the chemical shrinkage of the composite cement slurry was increased,and the microstructure of the early slurry was more dense.This is because high-temperature curing has a positive effect on the pozzolanic activity of ceramic powder,and also has a significant promotion effect on the hydration reaction of cement.However,from the perspective of long-term age,the chemically bound water and chemical shrinkage of the slurry under high temperature curing will eventually be lower than the samples at normal temperature,indicating that high temperature curing is not conducive to the ultimate hydration of the composite cementitious material.