The Study Of Bond Strength And Crack Shape In Corrosion Induced Cracking Concrete Under Load And Environment

The chloride attack is always regarded as the main reason that will cause the service performance deterioration of reinforced concrete structure. The coupling effect of environment and loads on the corrosion cracking of reinforced concrete has significant meaning for the accurate prediction of service life of reinforced concrete structure. Following this rule, this research focuses on the corrosion cracking process of concrete cover. The main research works include:(1)The electrifying corrosion method can quickly simulate the corrosion process of reinforcement in concrete, while conclusions vary tremendously under different electrifying corrosion methods. In this research, four electrifying corrosion methods were applied to simulate the corrosion process of reinforcement in concrete under loads, and the surface characteristics of corroded reinforcement were analyzed together with the microstructure and elemental composition of corrosion products.(2)According to the non-uniform corrosion characteristic of steel bars, the bond properties between corroded deformed steel bars and surrounding concrete were studied. The research was conducted based on a microscopic model of bond strength between un-corroded deformed steel bars in micro level and a model of bond strength between uniformly corroded deformed steel bars and concrete. In considering the non-uniform corrosion of steel bars in actual environment, the prediction model of bond strength between corroded deformed steel bars and concrete was established using elastic mechanics. The ultimate bond strength between corroded deformed steel bars and concrete was proposed and an analysis on the ultimate bond strength between corroded deformed steel bars of no lateral constraints was performed. Based on the model, the critical attack penetration depth of steel bar corresponding to the cracking of concrete cover was predicted.(3)To enhance the service performance of concrete structures, the cracking process of concrete cover due to corrosion of reinforcement was studied. Through the analysis on the corrosion cracks in a reinforced concrete beam containing chlorides inside which was loaded and corroded for18months, and taking the stress state of reinforced concrete and the relative position between cracks and aggregates into consideration, the cracking pattern of corrosion cracks and rust distribution were studied. Furthermore, the cracking pattern of concrete cover is also analyzed, and a design method on the corroded reinforced concrete beams was put forward. This is very important for the estimation on the service performance of reinforced concrete structures and their repairing.The research was financially supported by High Technology Research and Development Program of China (863Program,2012AA050903), National Natural Science Foundation of China (Grant No.51178413.51008272and50838008) and National Basic Research Program of China (973Program, Grant No.2009CB623200).