190 / 2022-04-30 22:41:27

Effect of uniform and non-uniform corrosion on cracking propagation and bonding performance of mortar and ECC specimens

Uniform corrosion; Non-uniform corrosion; Engineered Cementitious Composite (ECC); Cracking pattern; Bond strength

Engineered Cementitious Composite (ECC), which has a strain-hardening behavior under tension, has been widely used for repairing and retrofitting the reinforced concrete structures. In such applications, the performance of the bonding between the ECC and corroded rebar is critical for the service life prediction of the repaired structures.



In this work, a new experimental method was firstly proposed to rapidly induce non-uniform distribution of rust layers around steel bars. The proposed method is based on the impressed current method with short testing duration, but capable of inducing morphologies of rust distribution closer to those observed in natural corrosion environments than other existing methods. X-ray microtomography with image analysis techniques was implemented to quantify the rust formation and propagation in the proposed setups. A finite element model to systematically and semi-quantitatively investigate several experimental parameters (e.g., the distance between anode and cathode, the anodeto-cathode area ratio) was established and verified by a series of independent experimental programs. The corrosion current density distributions of uniform and non-uniform corrosion simulation are presented in Fig. 1. It can be seen that in non-uniform corrosion simulation, the corrosion current was mostly concentrated around the steel rebar on the side near the cathode (i.e., steel wire), while on the side facing away from the cathode, the corrosion current density was low. The corrosion current density was uniformly distributed in uniform corrosion simulation model.



The uniform corrosion induced cracks evenly distributed around the steel rebar while the non-uniform corrosion induced cracks concentrated in a line perpendicular to the rebar -steel wire line which can be attributed to the rust accumulation.Pull-out induced cracks developed along with the corrosion induced cracks. The pull-out cracks of uniform corroded specimens uniformly distributed around the specimen surface while the non-uniform corrosion specimens showed concentrated pull-out cracks on one side with more rust, which can be attributed to the corrosion pits which increased the friction and mechanical forces on the side close to the steel wire.



The bond strength of ECC and mortar specimens is independent with corrosion method. Both ECC and mortar specimens showed a trend of increasing first and then decreasing with the development of corrosion rate. The threshold corrosion rate for mortar specimen is 0.125% while the ECC specimen has the threshold corrosion rate value of 0.922%.