Influence of cracks on chloride induced corrosion in reinforced concrete flexural members.

摘要

The penetration of chloride ions plays a crucial role in reinforcement corrosion and affects the durability and service life of marine structures. The problem is even more acute once cracking occurs in a concrete member. The presence of cracks is shown to have a significant impact on chloride penetration into concrete. It has been recognized, for concrete cracked in flexure, the chloride diffusion coefficient in the tension zone is higher than that in the compression zone. Even a single crack in the tensile zone couldcontribute to a higher diffusion coefficient compared to that of uncracked members. In this study, the influence of flexural cracks on chloride ion penetration into reinforced concrete beams has been investigated experimentally and a two-dimensional theoreticalmodel is developed. The experimental study investigated the influence of multiple flexural cracks on the chloride diffusivity of reinforced concrete beams and on the corrosion rate of reinforcing bars. The size of the reinforced concrete beams tested is 200 x 250 x 2200 mm with 20mm concrete cover. The beams were pre-cracked using a compression testing machine and the crack widths induced were maintained between 0.1 mm to 0.2 mm. The chloride profile was determined after 1 month, 1 year and 2 years of immersion in 3.0% NaCl solution. The measured chloride profiles of the beams with multiple cracks are comparedto those obtained from the uncracked (control) beam. An observation was also made on the effect of cracks on the corrosion development of steel bar after two years of immersion in salt solution.Chloride concentration varied linearly with the depth of crack (at crack planes). A twodimensionalmodel using finite element analysis is developed to evaluate the chloride penetration into cracked concrete. This model was used to verify the chloride penetration data which is obtained from the experimental results. The prediction ofchloride ingress, using the two dimensional model agrees well with the short-term and long-term chloride profiles.