Experimental Study On The Concrete Cracking Behavior Due To Rebar Non-uniforin Corrosion

The failure earlier than planned of reinforced concrete structures happens a lot.The main reason of the degradation of structure durability is steel corrosion.As the corrosion develops,the concrete cracking is caused by the volume expansion of the corrosion product.The appearance of corrosion-induced cracks does tremendous damage to concrete and provides a convenience for an invasion of aggressive agents,which facilitate the further steel corrosion.It means that the process from steel corrosion to concrete cracking is the key to study the structural durability.It also has important implications for predicting the serviceability and the residual life of structures.Based on this process,the experiments were carried out on concrete beams under different corrosion conditions.Then the corrosion morphology of rebars and the cracking behavior of concrete were studied.The main work of this paper can be listed as follows:(1)An existing beam exposed to a marine environment for more than 40 years was studied and high-resolution images of rebar cross-section using scanning electron microscopy(SEM)were obtained.The distribution and the geometric feature of corrosion pits were analysed.Based on the measured pitting corrosion depth,the corrosion pit shape model was established.With the development of steel corrosion,the growth trend of the pit shape was proposed.The range of the pitting factor RP,which was the ratio between the maximum pit depth and average corrosion penetration,was determined by different pit shapes.(2)Under two kinds of load level,beams were designed to bear cyclic wetting-drying in NaCl solution or the accelerated steel corrosion.After the corrosion test,concrete was removed and corroded rebars were scanned by the 3D laser scanner.The distribution of cross-section areas of corroded rebars along the longitudinal direction was measured.The influences of corrosion methods and load levels were determined by the comparison of the corrosion distribution of different rebars.The non-uniform corrosion distribution in the longitudinal direction was still presented by Gaussian function and model parameters were improved.Based on the location and width of load-induced cracks,the relationship between the load-induced crack and the corrosion form was studied.(3)The studied beams with stirrups were cut into a series of cross-section slices.The shape and distribution of corrosion-induced cracks inside concrete were recorded by digital microscope.Then the effect of stirrups on crack propagation was determined.The width of corrosion-induced cracks along the length direction was measured and then the total crack area,the crack number and the main crack area were analysed deeply.The time of concrete surface cracking in the beam with stirrups was redefined,then the corresponding steel corrosion and the cracking degree were determined.