| With the economy and technological development,the assembled building has become an important development trend of the future construction industry,whose main components are prefabricated in factories.Therefore,the development of a crystal-type early strength agent that can shorten the setting time of cement,improve early strength,and thus accelerate the turnover rate of formwork,improve production efficiency,and facilitate large-scale use in assembled buildings is of great significance to the development of assembled buildings.In this thesis,the crystal seeds were prepared by mechanical grinding,and the variation laws of different types,particle sizes,and admixtures of crystalline seeds on the setting time,flow rate,and compressive strength of cement net slurry were investigated.The influence laws and mechanisms of crystalline seed types on the hydration kinetic process of cement were analyzed by measuring the heat of hydration,and finally,the specimens were analyzed and characterized by SEM,XRD,and TG-DSC techniques to reveal the influence mechanisms of crystalline seed types on the workability of cement net slurry and to elucidate the influence mechanisms of crystalline seed types on the strength of cementite.Crystal seed species significantly affect the setting time of net cement slurry,by investigating the type of crystal seed,particle size,and dosing amount,the following rules were found: mixing with calcium oxide,slag powder,kaolin,silica powder can significantly shorten the setting time of net cement slurry,and the smaller the particle size or the larger the dosing amount,the more obvious the shortening,mixing with fly ash because of the water-reducing effect of fly ash will make the setting time of net cement slurry longer.Crystal seed significantly affects the flow of net cement paste,through the investigation of the type of crystal species,particle size,e,and dosing,found the following laws: mixed with calcium oxide due to the reaction of calcium oxide and water to produce calcium hydroxide to reduce its flow,mixed with slag powder,fly ash can significantly improve its flow,mixed with silica powder because it will adsorb a lot of free water will reduce the flow,and the greater the dosing or the smaller the particle size the smaller the flow.Crystal seed can improve the early compressive strength of cement stone,by investigating the type of crystal seed,particle size,and admixture,the following rules were found: the admixture of calcium oxide at the age of 1d can improve the compressive strength more than other crystal seed because it reacts with water to produce calcium hydroxide and releases a large amount of heat to increase the system temperature,which accelerates the rate of hydration.The incorporation of slag powder,fly ash,and kaolin significantly improves the early compressive strength of cement stone and increases with the amount of incorporation,but in decreasing order;the incorporation of silica powder significantly improves the 1d and 3d compressive strength of cement stone due to its crystalline nucleation effect,but has almost no improvement on the 7d compressive strength as it is an inert crystal seed.The crystal seed can significantly increase the hydration rate and the total exothermic heat of hydration of the cement paste.The following patterns were found through the investigation of the crystal seed: the hydration kinetics of pure cement paste and cement paste mixed with slag,fly ash,metakaolin,and silica powder follow the NG(nucleation and growth)-I(interaction at phase boundaries)-D(diffusion)process,while the hydration kinetics of cement paste mixed with calcium oxide is the I-D process,without crystalline nucleation and crystal growth reaction processes.The crystal seed has different effects on the N,I,and D processes,which in turn affect the setting time and flow of the net cement paste.The crystal seed significantly improves the microstructure of the hydration products and the crystal seed have different effects on the microstructure of the cement paste,which in turn affects the compressive strength of the cement stone The crystal seed significantly influences the cement hydration process and the crystal seed have different effects on the hydration products of the cement,which in turn affects the compressive strength of the cement stone and the setting time and flow of the net cement paste. |
