Test And Analysis On Durability Degradation Process Of Slag - Cement - Based Materials Under Calcium Dissolution

The concrete structures which are in the water environment for a long time will happen durability degradation phenomenon for the erosion media in the water. It is mainly because that the calcium element in hydration products of cement base material instability exists and gradually spread to the water environment in the form of calcium ions. So that the durability of concrete structure will be damaged due to calcium leaching. Therefore, representing the calcium leaching process and its porosity changing law is of great significant to research the durability degradation law and carry out the durability design of the concrete structure. In order to study this problem, experimental design, immersing the specimens, porosity tests, corrosion dept tests, microscopic tests and numerical modeling on calcium leaching were used to express the calcium leaching process of cement-based material in soft water. The main contents and conclusions are as follows:(1) Testing the porosity regularly of pure cement slurry and slag-cement composite cement paste which were leached in the accelerated corrosion liquor of ammonium chloride and choosing different leaching time points to observe the change rule of micro structure before and after leaching and the influence of different slag dosage and different curing age on the pore structure before and after leaching by scanning electron microscope(SEM). The resaults show that the cement past which is mixed with amount of slag has better compactness and lower porosity which can significantly reduce the degree of calcium dissolution of cement-based material and improve the service life of cement-based material.(2) According to Fick’s law and Gerard solid-liquid equilibrium equation, calcium dissolving model of cement-based material cylindrical specimens was established under soft environment, and considering the mineral admixtures-Influence of slag on cement-based materials calcium dissolution of the model parameters, thereby improving the slag-calcium dissolving model cement composite binder. Then compiling related computer program to solve iterative matrix equation by Matlab language. Making the numerical simulation of the calcium dissolution process of pure cement slurry and the calcium dissolution process of pure cement slurry and the slag-composite cement paste under the condition of ammonium chloride accelerates dissolution by using Matlab computer language. Analying the process simulation results and the experiment of the specimens porosity under different corrosion time measured. The results show that the model calculated value tallies with the experiment test values. The model can be used for the analysis of the calcium dissolution regularity of cement-based material under the soft water environment.(3) Using the calcium leaching model which has been verified correct to simulate the calcium leaching process of cement-based materials during the long leaching time and analyzing these parameters which are porosity, calcium ion diffusion coefficient, calcium hydroxide content and CSH content in the process of corrosion. The results show that the corrosion resistance of hardened cement past which is added proper amount of slag is higher than that cement past without slag, and the optimum content of slag is 30 percent to 40 percent.