MODELING PROCESS OF DESTRUCTION OF PARTICLES OF CEMENT AT INITIAL STAGE OF HYDRATION
IZVESTIYA VYSSHIKH UCHEBNYKH ZAVEDENIY KHIMIYA KHIMICHESKAYA TEKHNOLOGIYA
The substantiation the existence of the destruction period of cement particles during the hydration of concrete into fragments, in size significantly larger than the average size of molecules is presented. An idealized structure of the cell representation for the cement grain and the water surrounding it in the form of nested spheres is adopted. The outer sphere does not change its coordinates, and the inner sphere imitating the cement grain decreases in the course of the process due to the
... sfer of the formed fragments into the inter-spherical space filled with water. The assumption is made that the concentration field is uniform and varies along the radius. The crushing process is described using a physical model of "pseudo-dissolution" and is based on the formulation of Fick's law. By introducing the rate of destruction associated with the movement of the interfacial boundary, a mathematical model is formulated in the form of an initial boundary value problem for the diffusion-type equation in a spherical coordinate system. By introducing a special coordinate system, the formulated initial-boundary value problem is transformed into a problem with fixed boundaries. Integration of the obtained system is performed numerically using an explicit finite-difference scheme. The computational experiment confirmed the efficiency of the proposed algorithm, which allowed to conduct a qualitative analysis of the model, which showed the correctness of the assumptions made in the formulation of the mathematical model. It is found that in a spherical cell containing an average cement grain, the fragments are localized near the interfacial surface due to the weak influence of the diffusion transfer mechanism. The estimation of the average size of the fragments, which are significantly larger than the average molecular size, further confirmed the hypothesis of the existence of the period of destruction of cement grains in the initial stage of concrete hydration.