Mechanism And Evaluation Method Of Salt Crystallization Attack On Concrete

Salt solution attack on concrete is one of the main reasons for concrete deterioration, which has been focused along by researchers over the world. Based on the theoretical analysis by physical chemistry, thermodynamics and crystallization science and the macro/microscope testing the physical crystallization attack of ambient salt solution on concrete was studied systematically in present paper, involving the investigation of transportation process and crystallization process of salt solution in concrete as well as the corresponding mechanisms of salt crystallization attack on concrete. Furthermore, a new experimental method was developed to evaluate the resistance of concrete to crystallization attack.The main achievements and contribution obtained in the thesis are as follows:1. According to the investigation of representative environment in practice and experimental results, the deterioration characteristics of concrete served in different salt solution environment conditions were summarized. It was founded that the capillary siphon effect, windward-side effect and dry-wet-circle effect were the three main reasons resulted in crystallization attack of concrete under salt solution.2. Based on the laboratory simulation experiment by dry-wet cycles and partial-immersion method, evolution of mechanical properties and the microstructure of concrete were obtained, and the corresponding mechanism was expounded.3. Transportation process of salt solution in concrete driven by capillary siphon effect and diffusion effect was analyzed. And thus the transportation model of salt solution based upon capillary effect in concrete was proposed, as well as the transportation kinetics equation of salt solution was established.4. On the basis of analysis of salt solution crystallization process in concrete pore, it is founded that the crystal growth of in concrete pore was influenced greatly by two factors such as the evaporation rate of solution in concrete pores and ingress velocity of salt solution into concrete. And thus the crystallization kinetics equation of salt solution in concrete was established.5. Deterioration characteristics caused by physical crystallization attacks of sodium sulfate and sodium chloride on concrete, respectively, were compared. The crystal conversion of two crystals of mirabilite and thenardite of sodium sulfate is the main reason resulted in the physical crystallization attack on concrete under relative humidity change condition. The physical crystallization attack of sodium chloride on concrete is relative weak, which may be the reasons that it is hard to reach super-saturation for sodium chloride solution in room temperature.6. Based on the above theoretical analysis and experimental investigations, a new experimental method was developed to assess the resistance of concrete to crystallization attack, and the corresponding evaluating parameters were also put forward. In addition, some experiments were carried out to examine the feasibility and validity of the method.