Corrosion Damage Of RC Structures Ingressed By Chloride

Corrosion damage of RC structures is of great global concern because of its huge economic costs. Although there are numerous investgatons on RC corrosion damage durability, a lot of questions still need to be studied in view of some reason, such as the discrete property of concrete, the complexity of RC corrosion damage and the error of experimental method and so on. In this paper, service life of RC corrosion damage induced by chloride has been studied. And as a main line, the service life was defined as the following three stages: reiforcement corrosion beginning sercice life, concrete cover cracking service life, and corrosive crack width propagating service life. So the following work were carried out1. Study on the rule of chloride concentration distribution in circular section concrete elementThe analytical solution of chloride diffusion equation in circular section concrete element was deduced based on the Bessel function. And the applicability of one-dimensional diffusion equation based on the Fick's second law to predict the chloride concentration distribution in circular section concrete element was studied through the example analysis. Furthermore, the rule of chloride concentration distribution in this kind of section concrete element was studied based on the analytical solution.2. A numerical simulation method for predicting the chloride concentration distribution in concreteThe presence of reinforcement alters the pathway of chloride transporting and consequently causes the chloride concentration to build up faster in the region adjacent to the reinforcement closet the exposed surface. The impact of reinforcement on chloride transmission in concrete was studied by experiment. A conservation of chloride mass matrix equation of the non-stable diffusion based on the Fick's second law was derived by defining content coefficient and transferring coefficient. Hereby, numerical simulation of the chloride concentration distributing in concrete was realized based on ANSYS by reasonable equivalent of parameters. The presented method can be applied flexibly to any other sections with complicated shape of RC member with single or multi-boundary attacked by chloride considering the presence of reinforcement simultaneously as long as a reasonable modeling. The validity of the numerical simulation method was verified by the comparison with the analytical results and the experimental results of this paper.3. Study on the service life of cover cracking induced by the corrosion products expansion The approximate analytical solution of the stress intensity factor at the crack tip was deduced considering the characteristics of existing exiguous flaws and initial cracks in concrete before load acting on RC structures, and assuming that there are one crack and two symmetrical radial initial cracks in concrete on the surface of reinforcement respectively combining with concrete cover cracking and spalling in actual enginerring. And new theoretical predicting models for the critical corrosion-induced expansive force were derived. Furthermore, the prodiction method for service life of cover corrosive cracking was presented based on fracture theory and the validity was verified.The existing study results about cover corrosive cracking were all based on round reinforcement. In this paper, a new predicting model for the critical corrosion-induced expansive force was derived based on the two hypotheses: two initial radial cracks and the bond between reinforcement and concrete is a linear combination of perfectly smooth and perfectly bonded during the process of determining the stress intensity factor at the crack tip. The the validity of the predicting model was verified preliminarily by experimental results.4. The entire process simulation for RC structures corrosive cracking based on the fictitious crack modelThe concrete cover cracking process has been analyzed through numerical simulation based on the fictitious crack model. The change of corrosion-induced expansive force during the process of concrete cover corrosive cracking has been studied and a method of estimating cover time-to-crack was presented. The impact rules of parameters such as the initial crack length, cover thickness and diameter of reinforcement on the completely cracking time were analyzed.5. Study on RC corrosive crack width propagatingCrack width is a parameter of the most practical significance for the design and service life assessment of RC structures. An accelerated reinforcement corrosion test was performed systematically to investigate the rules of time-to-crack and crack width propagating of RC affected by corrosion. The experimental variables included diameter of steel bar, concrete strength, corrosion current density, thickness of concrete cover, position and types of steel bars, etc. The mechanism of various factors affecting on time-to-crack and crack width propagating were analyzed. Based on the research results reported, a theoretical predicting method for corrosive crack width was presented. And the validity of the presented method was verified by experimental results.