Critical Chloride Ion Concentration Of Reinforcement Corrosion And Residual Life Prediction Of Concrete

Service life prediction of concrete has been a hot topic in recent years. Based on Fick's second law, most of the researchers studied chloride ion distribution in concrete and predicted service life of concrete structures. But the boundary conditions of Fick's second law were not coincident with the field conditions. In addition, the predicted service life of concrete structures was not accurate because of the influence of concrete compositions and chemical binding effect.In this thesis, the service life of concrete structure was predicted through accelerated chlorid ion penetration test under various voltages. According to change rule of chloride ion content in concrete under various voltages, the relationship between critical concentration time and voltage was obtained. Based on the obtained results, the service life of concrete structures in natural marine environment was predicted.In this study, the critical chloride ion concentration leading to steel corrosion was considered as boundary condition of service life prediction. That meaned service life of concrete structures terminated when chloride ion concentation reached critical value. With steel bar and reference electrode casted in concrete specimens, the rapid steel corrosion test was done under 20V, 12V, 6V and 3V voltage. Through the analysis of the experimental results, the critical chloride ion concentrations of C30 control specimen, C30 specimen with mineral admixture and air-inducing agent, C60 control specimen and C60 specimen with mineral admixture and air-inducing agent were obtained.For the concrete specimens mentioned above, the accelerated chloride ion penetation test was done under 20V, 12V, 6V and 3V voltage. The research results indicated that chloride ion content increased linearly with time after 3 days. Through the establishment of relationship between critical concentration time and voltage, the service life prediction equation was obtained. Based on the obtained results, the service life of concrete structures in natural marine environment was predicted.For the breakwater concrete structure with service time of 14 years in Qingdao, the specimens were distrilled and the residual life was predicted through chloride ion penetration test under various voltages. The predicted result was 18.72 years. For the new concrete specimens with the same mixing proportions, the predicted service life was 35.01 years. The difference between the two predicted results mentioned above was 16.29 years, which was 2.29 years shorter than the actual service life. So through the rapid chloride ion penetration test, the residual service life of concrete structures could be prediced precisely.For C30 control specimen, C30 specimen with mineral admixture and air-inducing agent, C60 control specimen and C60 specimen with mineral admixture and air-inducing agent, salt frost test were done with 100 and 150 freezing and thawing cycles. The results showed that C30 control specimen can not resist the 100-cycle salt frost damage and was fully destroyed. After salt forst test, the residual service life of C30 specimen with mineral admixture and air-inducing agent, C60 control specimen and C60 specimen with mineral admixture and air-inducing agent were predicted. For C30 specimen with mineral admixture and air-inducing agent, the predicted residual life were 29.62 years and 24.9 years afer 100 and 150 cycles. For C60 control specimen, the predicted residual life were 35.51 years and 32.17 years afer 100 and 150 cycles. For C60 specimen with mineral admixture and air-inducing agent, the predicted residual life were 50.85 years and 45.66 years afer 100 and 150 cycles. Through the introduction of salt frost damage coefficient k_yd, the relationship between k_yd and freezing-thawing cycles was obtained and service life prediction model before and after salt frost test were established.Compressive pressure with value of 20% and 40% ultimate load was applied to concrete specimens. After 200-cycle repeated-load test, the residual service life of specimens mentioned above was predicted. The experimental results showed that the predicted results were 21.61 and 16.66 years after repeated-load test with pressure of 20% and 40% ultimate load for C30 control specimen. For C30 specimen with mineral admixture and air-inducing agent, the predicted results were 33.3 and 32.97 years after repeated-load test with pressure of 20% and 40% ultimate load. For C60 control specimen, the predicted results were 38.24 and 34.82 years after repeated-load test with pressure of 20% and 40% ultimate load. For C60 specimen with mineral admixture and air-inducing agent, the predicted results were 49.8 and 44.84 years after repeated-load test with pressure of 20% and 40% ultimate load. Through the introduction of repeated-load damage coefficient k_yl, the relationship between k_yl and peak load value was obtained and service life prediction model before and after repeated-load test were established.