Experimental Study And Life Prediction Of Reinforced Concrete In Western China’s Saline Soil Area

Saline soil of western China with high concentration of corrosive ions,such as sulfate,chloride and magnesium salts and the dry and windy climate with strong sand storms as well as ultraviolet rays,caused serious corrosion,cracking and other diseases of the local reinforced concrete structures,which seriously reduced its service life.Although scholars at home and abroad had carried out some research on the corrosion damage of reinforced concrete under environmental action,there were still some deficiencies in the indoor accelerated test of reinforced concrete,the research of the corrosion damage of reinforced concrete was lack of pertinence,and the corrosion mechanism was not clear.Further research on the corrosion process and mechanism of concrete corrosion was needed for the actual service environment of reinforced concrete.In view of this,according to the characteristics of the corrosive environment in the saline soil area of western China,a new test method for accelerated corrosion of reinforced concrete by constant current and salt spray dry-wet cycles was designed,and the applicability of the constant current accelerated corrosion test method for reinforced concrete was studied.The natural exposed corrosion test in the western saline soil area and the constant current accelerated corrosion test of the saline soil environment and the accelerated corrosion test with salt spray dry-wet cycles were carried out.Taking corrosion current density,polarization resistance of reinforcement,weight loss rate of concrete and damage degree of concrete as durability degradation indexes,a comprehensive evaluation system for durability deterioration law of reinforced concrete under corrosive environment in saline soil area of western China was established.Combined with the macroscopic,microscopic and microstructural damage evolution process of reinfored concrete,the corrosion deterioration law of reinforced concrete under different corrosion effects was analyzed,and the corrosion failure mechanism was revealed.Based on the Weibull distribution function,the durability degradation model of reinforced concrete under different corrosive environments in western saline soil was established and the residual life prediction was carried out.Based on the equivalent reliability condition,combined with the concept of equivalent weight,the equivalent relation between indoor accelerated corrosion tests and natural exposed corrosion test in saline soil area was established by a comprehensive consideration of the competition failure between concrete covers and steel bars in the process of reinforced concrete durability degradation.The results of these experiments provided a reliable basis for research on reinforced concrete’s durability in saline soil of western China.The primary results and conclusions of this paper are as follows:（1）Through the degradation process of reinforced concrete,the current efficiency and the composition of corrosion products on the surface of steel bars,the applicability of the constant current accelerated corrosion test of reinforced concrete in wet salt sand environment was studied.The results show that the deterioration process in the constant current accelerated corrosion of reinforced concrete in a wet salt sand environment is similar to that in the natural environment,the current efficiency can be as high as 44.0%～63.9%,the corrosion products on the surface of the steel bars are consistent with those under natural corrosion,mainly Fe₂O₃primarily.On the whole,the constant current accelerated corrosion test method of reinforced concrete in a wet salt sand environment has better applicability and can effectively simulate the corrosion of reinforced concrete in the natural environment.（2）In the process of constant current accelerated corrosion in the saline soil environment,the corrosion degradation rate of the reinforced concrete is slow when the corrosion of steel bars is caused by the action of external current alone in the early period of electrification.In the later stage period of electrification,the corrosion degradation rate of the reinforced concrete grow rapidly when the corrosion of the steel bars is caused by current and chloride ions.Under the influence of the p H value of the concrete pore solution,the corrosion deterioration rates of the steel bars in the groups PF,PS and PFS are higher than that in the group P under the constant current accelerated corrosion in the saline soil environment.（3）During the process of the accelerated corrosion with salt spray wet-dry cycles,the ability of reinforced concrete to resist corrosion increases firstly and then decreases gradually due to the salt spray’s combined strengthening effect and degrading effect with the increase of dry-wet cycles.In the early period of the wet-dry cycles,the strengthening effect is greater than the degradation effect,while in the middle and later periods,the degradation effect is greater than the strengthening effect.Fly ash and mineral powder can effectively improve the ability of concrete covers and internal steel bars to resist corrosion under the accelerated corrosion with salt spray dry-wet cycles and the effect of mineral powder is better than fly ash.（4）In the process of natural exposure corrosion in saline soil area of western China,in the early period of exposure corrosion,due to the corrosive environment’s combined strengthening effect and degrading effect,the ability of reinforced concrete to resist corrosion fluctuates repeatedly with the prolongation of exposure time.In the later period of exposure corrosion,the ability of reinforced concrete to resist corrosion gradually decreases with the prolongation of exposed time,and the degree of damage deterioration gradually increases.The addition of active mineral admixture can effectively improve the ability of reinforced concrete to resist corrosion during the exposure corrosion in saline soil of western China.（5）The damage degree deterioration and corrosion current density index are suitable for evaluating the deterioration trend in reinforced concrete’s durability in the process of constant current accelerated corrosion in the saline soil environment,accelerated corrosion with salt spray wet-dry cycles and natural exposure corrosion in saline soil area of western China,in which the deterioration law with the corrosion time conforms to the Weibull distribution function.The durability damage degradation model of reinforced concrete based on the Weibull distribution function can effectively describe the durability degradation law of reinforced concrete under different corrosive environments.（6）The constant current accelerated corrosion test in the saline soil environment,accelerated corrosion test with salt spray wet-dry cycles and natural exposure corrosion test in saline soil area of western China are comparable,and the equivalent relation can be studied.Based on the equivalent reliability conditions of the Weibull distribution function,and the concept of equivalent weight,taking into consideration the competitive failure of concrete covers and internal steel bars in the process of reinforced concrete’s corrosion degradation,the calculation method for the equivalent relation between two indoor accelerated corrosion tests and the natural exposed corrosion test in saline soil areas of western China are established.