Numerical Simulation Of Microcapsule Concrete Transmission Performance

In recent years, a new idea and technology of self-healing concrete has been proposed for obtaining good durability of concrete. Self-healing concrete can be achieved based on intelligent sensors, operation of the trigger of the self healing system during deterioration due to aggressive environment. It should be of great significance to increase the service life of concrete. The thesis mainly focuses on the ion transportation of the self-healing concrete with microcapsules. The thesis investigated a large number of experimental data in the literature on diffusion of chloride ion.Then simulated the relevant results by using the COMSOL Multi-physics software. A one-dimensional model was used in Nernst-Planck equation simulation, which is generally used to model the motion of charged particles in a fluid medium. The results show that, with appropriate initial experimental data, the computed results based on the chloride ions diffusion model was very close to the experimental data. Microcapsule composed mainly capsule shell and core, and the capsule shell has a chemical trigger type, as well as it has a physical damage type. Before the numerical simulation, the thesis firstly study the characteristic and demand of the microcapsule shell, and then chose the appropriate shell material of the capsule. Finally, the chemical trigger type shell was chose to be simulated,which used chloride ion as the trigger agent. In order to better simulate the trigger mechanism of the self-healing concrete with microcapsules, this thesis is not only considered Nernst-Planck equation, but also consider the effect of chemical reaction on the concentration of ions.The chemical capsule shell used in the thesis are PbSO₄ and silver alginate. Silver alginate is a Polymer compound which has a complex chemical reaction mechanism, and therefore it’s a subject investigated just as a theoretical Polymer compound. In this thesis, microcapsules are assumed that dispersed evenly distributed in a one-dimensional model of concrete, and the pore solution of concrete model is assumed as water saturated state. By using the COMSOL software, the Nernst-Planck equation was solved coupling with chemical reaction, it calculated the variation of concentration of chloride ion which has a reaction with the capsule shell. In contrast to pure diffusion model, there’s a certain degree of consumption of chloride ion in the process of the trigger breakage of microcapsules. The changes in the concentration of shell material show that shell material are consumed and reacted when the chloride ion diffused in concrete gradually. Considering the effect of the capsule core in the above model, microcapsules core of the thesis is divided into two types: physical and chemical repair capsule type. The mostly physical core in this thesis is epoxy resin,and the self-healing efficiency of the capsule core in the ion transport is mainly embodied by filling the pore and agglutinating the cracks, thereby reducing the diffusion rate of chloride ion and delaying the penetration of chloride ions in concrete. The chemical core chose in this thesis is the inhibitor of Calcium nitrite.The healing efficiency of calcium nitrite is to prevent the corrosion of the reinforcing bar. By computing the change curve of OHconcentration, p H value of the solution can be calculated.By the calculation of the ratio of Cl-/OH-, the inhibition effect of the capsule core of reinforcing bar in concrete can be reflected. According to the calculation and comparison of the above model, the thesis analyzed the various factors which influence the healing efficiency, and obtained the optimal composition of capsule shell and core. The numerical results of the thesis based on the theoretical calculation model, which play a guiding role in the design of self-healing microcapsules. The actual healing efficiency of the microcapsules also need further experiments.