Study Of Hydration Model Of Cement With Mineral Admixtures And Its Application

The durability of construction projects requires people to have a better understanding on the hydration process of cement-based materials. This research studies the hydration process of pure cement paste and cement paste mixed with mineral admixtures, establishes the corresponding hydration model, uses the model to further study the development law of electrical resistance of cement paste, the development law of compressive strength and moisture diffusion of concrete. The main research works include:(1) In order to accurately predict the cement hydration process and analyze the time-dependence of micro-structure development of cement during hydration process, based on microstructure information and Krstulovic-Dabic hydration kinetics formulas, the concept of hydration unit was proposed to bridge the relationship between cement hydration degree and microstructure. Taking water/cement ratio, chemical compositions of cement, free water in porosity, temperature, interfacial contact area between hydration products and free water, and diameter distribution of cement particles into consideration, an improved kinetics model of cement hydration was established. In this research, the thermo-gravimetric analysis (TGA),mercury intrusion test and ESEM were employed to study the development of hydration degree^porosity and microstructure of cement paste. The experiment results agree well with the model prediction results which indicates that the model can accurately simulate the time-dependent development of cement hydration process.(2) As fly ash/slag hydration process is similar to cement, based on cement hydration model, model for fly ash/slag hydration was established. Taking the dilution effect, physical effect as well as chemical effect (pozzolanic activity)of fly ash and dilution effect, chemical effect of slag into account, a model for cement blended with fly ash/slag was established, which can simulate the hydration process of cement blended with fly ash/slag and predict the following properties:hydration degree of fly ash/slag, chemical bound water, CH content, porosity. In this research, the selective dissolution method,thermo-gravimetric analysis(TGA), mercury intrusion test and ESEM were employed to study the development of hydration degree of fly ash/slag, chemical bound water, CH content, porosity and microstructure of cement blended with fly ash/slag, the experiment results agree well with the model prediction results which indicates that the model can accurately simulate the time-dependent development of hydration process of cement blended with fly ash/slag.(3) The hydration model of cement paves the way to predict the performance of concrete, from which we can extract the specific contact area, connected solid volume fraction and outer hydration products volume fraction to study the electrical resistivity, the compressive strength and moisture diffusion of the concrete. No-contacting resistivity measurement has been used to monitor electrical resistivity of cement paste. The relationship between electrical resistivity and microstructure parameters has been studied. On the basis of Maekawa’s formula on compressive strength and the hydration model in this paper, taking water/cement ratio, chemical compositions of cement, effects of different mineral content and paste to aggregate ratio into account, we can predict the development law of compressive strength of concrete, and the accuracy of the model was verificated by experiments. Besides, Moisture diffusion coefficient formula has been revised and proved by existing experiment.The research was financially supported by High Technology Research and Development Program of China (863Program,2012AA050903), National Natural Science Foundation of China (Grant No.51320105013,51178413,51378012), National Basic Research Program of China (973Program, Grant No.2009CB623200) and Key Science and Technology Innovation Team Program of Zhejiang Province(2010R50034).