Experimental Studies On Durability Of Reinforced Concrete Members In Chloride Environment

Sufficient attention may be paid attention to the durability of reinforced concrete structure widespread all over the world. The concrete structures fail pre-maturity due to the lack of durability in many cases in ingress environment. Under marine conditions and de-icing environment, reinforced concrete structures, in which concrete subjected to freeze-thaw cycles and chloride ingress, resulting in corrosion of reinforcing bars, induced early deterioration and loss their durability. This is a main problem in engineering practice. Based on the project of Science and Technology Fundation of Liaoning Province (No.001077), this thesis carried out following aspects:1. A series of concrete specimens was exposed in a flexural loaded state in a container filled with 3.5% sodium chloride solutions for long-terms, and the effect of sustained flexural loading was estimated from chloride ingress level. The results show there is a relationship between diffusion coefficient and the loading level. The diffusion speed of chloride in concrete was accelerated and the chloride concentration increases under high-level loading. A diffusion coefficient with sustained load and a time-dependent diffusion coefficient are calculated based on the second Fick's law.2. Concrete specimens subjected to the action of freezing-thawing cycles were exposed to 3.5%NaCl solutions for long-terms. The effects of freezing-thawing cycles on the chloride concentration profiles in concrete were investigated and its mechanism was analyzed. The microcracking and deficiency of concrete interior was further developed under the action of freezing-thawing cycles. Therefore, the diffusion speed was accelerated significantly due to degradation of concrete resulted by the freeze-thaw action. The chloride concentration and diffusion coefficients increase with numbers of freezing-thawing cycles. A diffusion coefficient with freezing-thawing cycles and a time-dependent diffusion coefficient are calculated based on the second Fick's law.3. The degradation of concrete due to the action of freezing-thawing cycles and corrosion of reinforcing bar due to chloride ingress always occurs in the de-icing environment. Beam specimens that experienced different freezing and thawing cycles and degree of corrosion are tested and compared with experimental studies of identical beam specimens that did not experience freezing and thawing cycles and corrosion of reinforcing bar. The effects of the individual action and combined action of freezing-thawing cycles and corrosion of reinforcing bar on the bond behavior between steel reinforcement and concrete are reported. The results show that the maximum bond resistance and bond stiffness decreases as the numbers of freezing cycles increases while the bond mechanism was modified. The ultimate bond strength increases in theprecracking stage and decreases with an increase in the degree of corrosion when reinforcement corrosion is in the cracking and post-cracking stage. The slip at the ultimate bond strength decreases significantly with an increase in the degree of corrosion. Also the bond characteristic would further deteriorated with the combined action of freezing-thawing cycles and corrosion of reinforcing bar.4. For real structures, corrosion of reinforcing bar takes place while they begin to carry load, a simulated experiments are carried out. Based on the accelerated corrosion experiments of two series of reinforced concrete beams, one subjected to reinforcement corrosion while maintaining a sustained load, the other subjected to previous loading and then unloaded for corrosion tests, the effects of mechanical loading on corrosion of reinforcing steel, as well as their combined effect on serviceability limit state and limit state of reinforced concrete beams were studied. The results indicate that loading has significant effects on corrosion. Under simultaneous load and accelerated corrosion conditions, the time-dependent deflection of the beams increases with progressive corrosion of the reinforc...