Self-healing Characteristics Of High Ductility Cementitious Composites And Its Influence On Chloride Ion Transportation And Corrosion Charateristic Of Steel Bar

Cement concrete is brittle and easy to crack under the effect of confined shrinkage and tensile load,and the cracks tend to expand rapidly,which will affect the durability of concrete structure.This problem is especially serious under deicing salt environment,marine environment and salt lake environment:the cracked reinforced concrete structure will rust rapidly under the effect of chloride ions,leading to structural failure.High Ductility Cementitious Composites?HDCC?has the characteristics of strain hardening and multiple cracking.The excellent crack control ability of HDCC brings the material good durability.Application of HDCC to repairing of the constructions in deicing salt environment,marine environment and salt lake environment is expected to solve the durability problem of concrete,which caused by crack propagation.However,it is not clear how the micro-cracks?uder 100?m?affect the structural durability yet,restrict the application of HDCC under deicing salt environment,marine environment and salt lake environment.In this paper,ultrasound nondestructive testing,comprehensive thermal analysis,electrochemical methods and X-ray tomography were employed to study the effect of crack width on the chloride ion transportation of HDCC and the corrosion characteristics of steel bars,the self-healing properties of micro-cracks on HDCC was studied at the same time.Firstly,this work investigated self-healing characteristic of HDCC.During the wet-dry cycles,the amount and the average width of micro-cracks on the HDCC specimens decreased gradually,the dynamic elastic modulus and the flexural toughness recovered gradually.The self-healing performance of HDCC was achieved through the hydration of unhydrated cement particles,the pozzolanic reaction of fly ash particles and the crystalline-deposition of CaCO₃,at the same time,the filling effect of chloride reaction products also played a role in self-healing process.Secondly,the parameter of chloride ion transport depth increment??d?was defined to characterize the effect of crack width on chloride ion transport.Chloride ion content and?d at the tip of the crack increased gradually,as the crack width increases.When the crack width reaches 120?m,the increase trend of?d is no longer obvious.The crack sidewall has a certain hindrance to chloride ion transport,the smaller the crack width is,the more obvious the self-healing effect of the crack is,and the greater the hindrance to chloride ion transport is.Finally,corrosion Characteristics of embedded reinforcement bars in HDCC was studied.Compared with the normal concrete?NC?,the corrosion of internal reinforcement in HDCC is less likely to occur.When the surface of HDCC specimen has a pre-crack extending to the steel bar,the chloride ions will transport to the surface of the steel bar through the crack and cause corrosion quickly,but just a small area of steel bar around the crack pits slightly.The corrosion current density decreased gradually because of the filling effect of corrosion products and self-healing products.At the same time,the prediction model of cracking time was modified based on the corrosion depth model,which can reflect the influence of W/B on cracking time.