Study On The Effects Of Saltwater Erosion And Freezing-thawing On Concrete Performance

It's important to study the durability of concrete that involves resistance to corrosion, freeze-thaw, carbonation, rebar corrosion and so on. However, several deterioration mechanisms may coexist in an erosive environment actually. Therefore, it is necessary to study the properties of concrete subjected to multiple deterioration mechanisms. In the north cold regions of China, the marine concrete structures are both suffering from the frost and seawater erosion. The resistance to freezing and thawing damage is one of the most important indices in regard to the durability of concrete. At the same time, seawater erosion is the most common deterioration form of marine concrete. So, to study the deterioration of marine concrete combining the two damage forms is theoretically and practically significant.The influences of the water to binder ratio, amount of fly ash and slag powder in the concrete on its resistance to seawater erosion and frost are analyzed through the orthogonal test. Based on the experimental results, the component ratio of the cementitious materials was adjusted, and the change and development of concrete properties was studied after several cycles of freezing and thawing in seawater and freshwater. The main conclusions are as following:(1) The water to binder ratio is the most important factor affecting the resistance of concrete to seawater erosion. The resistance to seawater erosion of concrete was improved by mixing fly ash and slag powder, and the resistance is the optimum if there are 15% of fly ash and 20% of slag powder in the binders.(2) As cycles of freezing and thawing in seawater increase, the surface of the specimens was coarsened and the mass and dynamic modulus of elasticity decreased. The compressive strength and resistance to chloride ion permeability were worsened as well. In contrast to frost in freshwater, the damage of frost in seawater was more serious. And the concrete with a high water to binder ratio was more sensitive to frost in seawater. When there are both fast freeze-thaw and seawater erosion, freeze-thaw damage is the dominant deterioration factor of concrete structures.(3) The component ratio of cementitious materials had some effects on the resistance to frost in seawater of concrete with a low water-binder ratio and double mixed mineral admixtures. If there are 15% of fly ash and 20% of slag powder in the binder, the microstructure of concrete was improved effectively, and the resistance to frost in seawater achieves the optimal for the materials used in this thesis.The damage valueωwas used to evaluate the damage degree of frost in seawater by using parts of the experimental data in this thesis as samples. The Gray Model (1, 1) was used to predict the damage degree. The results showed that: the predicted values of the Model were in good agreement with experimental results. It is feasible to use the Grey Model to predict the concrete damage degree of frost in seawater, and further studies are recommended.