Research On Anchorage Properties For Corroded Bars In Concrete

Based on existing achievements, this thesis conducted further work concerning the bond performance between corroded rebar and concrete, in both theoretical and experimental ways.First, a theoretical model is presented to analyze the corrosion-induced cover cracking problem. This model can forecast the corrosion ratio simultaneous with cover cracking in uniformly corroded members without stirrups accurately at a certain extent, and can also calculate the corrosion-induced expansion force before cracking.Second, a friction model for calculation of bond stress of uniformly corroded smooth bar is presented, which can theoretically indicate the influence of corrosion on bond performance of smooth bar before cover cracking.Third, a micro-mechanics model is established to calculate the bond stress of uniformly corroded deformed bar. This model indicates the corrosion influence on bond performance of deformed bar before cover cracking in theoretical way.Besides, the author presented an electro-migration method for corrosion simulation based on electrochemistry theory, and thus managed to make bar corroded non-uniformly.In experimental way, pull-out tests were firstly conducted to study the bond-slip performance of non-uniformly corroded bar. Then beams with stirrups were used to study the bond-slip performance of hooped members, and mechanical performance of lapped members with different corrosion ratio was also studyed.The following conclusions can be obtained with the above work:As for the corrosion ratio and followed crack width, they have less relativity in hooped members. On the contrary, the two indexes coincide with each other well in non-hooped members, that is, the crack width increases with the corrosion ratio.When rebar being corroded, stirrups will play an important role. For members without stirrups, the bond strength will decrease on the moment of cover cracking. Then the larger the crack width is, the less the bond strength is. But for hooped members, the bond strength will not be weakened within the corrosion ratio of 5%, even the crack width up to 5mm. Thus it can be considered that the crack width has little influence on bond performance of hooped members.However, corrosion has certain influence on both bond stiffness and the slip at ultimate load in despite of stirrups or not. Along with increase of corrosion ratio, the bond stiffness increases also, simultaneously, the slip at ultimate load decreases. That is, the ductility decreases and brittleness increases when member destroyed.Corrosion has more influence on lap performance than bond peformance in the same situation. When hooped in lapped area, the lap performance will not be highly affected by corrosion-induced crack width, and the lap performance almost keeps as the same within the corrosion ratio of 2%.If designed according to existing standards normally, the bond performance of reinforced concrete members will not be evidently affected by corrosion when the crack width reaches its normal use limit state. When calculating or checking the bearing capacity of corroded members, the decrease of bond strength need not be considered, that is, rebar and concrete still work together well in this situation.