Research On The Durability Evaluation Method Of Concrete By Sulfate

The sulfate attack of concrete is one of the most important problems in the study of concrete durability, the damage factors of sulfate attack on concrete are the most complicated and harmful and it is one of the most serious environmental erosion. When the concrete in sulfate solution of soil and underground water, sulfate ion can seep into the concrete by diffusion and react with the hydration products of cement, expansion of damage to concrete, resulting in the performance degradation of concrete structure.Concrete structure in parts of the water level fluctuation zone, splash zone,tidal zone suffered the dry wet circulation and sulfate interaction, concrete deterioration is more serious. Therefore, the corrosion and damage law of sulfate to concrete should be studied from the two aspects of wet and dry cycles and long-term immersion.This paper belongs to the Ministry of transportation construction science and technology project?Research on technical system and equipment development of reliability test and evaluation of existing concrete beam bridge?(2013 318 223 040) on the “Durability evaluation method of component level based on reliability theory for existing concrete beam bridge" sub project. According to the special requirements of the project, the following work has been carried out:1. The effects of the concentration of sodium sulfate solution and the ratio of water to cement on the compressive strength, surface hardness,mass and dynamic elastic modulus of concrete were studied. The results show that with the increase of the concentration of Na2S04 solution, the decay rate of concrete index is larger;with the increase of water cement ratio of concrete, the damage of sulfate attack can delay,but in the end, the damage degree of concrete with higher water cement ratio is higher than that of low water cement ratio.Comparing with the change of each index, it is found that the change law of the hardness value is relatively stable,which can be used to judge the degree of damage of the concrete.2. Based on the analysis of the strength and hardness of concrete specimens under different concentration of sulfate erosion in wetting and drying cycles, the relationship between the strength of concrete and the hardness of concrete was established, and the method for evaluating the durability of sulfate attack concrete based on hardness ratio method is proposed. The evaluation method is a nondestructive testing method, which has guiding significance for the detection and durability evaluation of concrete structures subjected to sulfate attack.3. The variation of sulfate content in concrete with different water cement ratio was studied by using the method of sodium sulfate solution.The test results show that the content of sulfate ion in concrete increases with erosion time,and decreased with the increase of the depth of concrete test, decreased with water cement ratio of concrete decreases.The results show that the concrete with low water cement ratio has better sulfate corrosion resistance.4. Through theoretical analysis of concrete sulfate attack reaction product damage process for concrete, and put forward the definition of critical concentration of sulfate attack concrete cracking, the critical concentration of sulfate and calculation process are presented.According to the calculation results of the critical concentration of sulfate erosion theory,experimental study on cracking critical concentration of concrete by adding sodium sulfate in concrete is designed.According to the variation rule of two indexes of dynamic elastic modulus and compressive strength of concrete with different dosage of sodium sulfate, critical concentration of concrete cracking is inferred.The experimental results show that the critical cracking concentration of concrete subjected to sulfate attack is in good agreement with the theoretical analysis.Therefore, it is proved that the theoretical analysis is correct, and it can be proved that the method of adding sodium sulfate is feasible.