![]() ![]() ![]() The results showed that chloride accumulation first increased and then decreased as the drying time increased. The proportion of drying time in a wetting-drying cycle increased with increasing altitude. Field tests for a concrete harbor deck in the tidal zone were carried out at different altitudes by Zhang and Jin. Cyclic wetting and drying conditions can significantly accelerate chloride penetration in concrete. ![]() During drying periods, chloride diffuses from the exposed surface to the deeper areas that have a lower chloride concentration. During wetting periods, chloride ions are brought into concrete along with seawater absorption. In a tidal zone, concrete is subject to periodic drying and wetting processes during the ebb and rise of the tide. The free chloride is responsible for destroying the passive layer of steel and initiating steel corrosion. During the chloride transport process, some chloride is dissolved in pore water and the rest is bound by cement hydrates, i.e., free chloride and bound chloride, respectively. Diffusion is caused by differences in chloride ion concentrations in pore water while convection is due to water transport carrying chloride ions. Ĭhloride ions move into concrete by the mechanisms of diffusion and convection. Furthermore, the mechanical properties of steel bars were greatly impacted by the increase in corrosion degree. Expansion of corrosion products may cause cracking and spalling of the cover concrete, which will then no longer protect the reinforcing steel effectively. When the chloride content at the steel surface reaches a critical level, the passive layer of the steel is destroyed and steel corrosion occurs. Costa and Appleton studied concrete structures exposed to a marine environment in Portugal and found extensive deterioration due to chloride-induced corrosion of the reinforcement. Among these factors, chloride penetration is the most concerning for the durability of concrete structures. The degradation of reinforced concrete (RC) structures in a marine environment is related to physical and chemical processes including chloride penetration, sulfate attack, and carbonation. The results of this study would provide information concerning the chloride-induced steel corrosion under a marine environment in order to predict long-term behaviors of a reinforced concrete structure. The major phases of steel rust in the atmospheric zone were lepidocrocite and goethite, while they were lepidocrocite and maghemite in the tidal zone. Rust phases including lepidocrocite, goethite, akaganeite, magnetite, and maghemite were detected using Raman spectroscopy and X-ray diffraction. The coefficients of variability of chloride diffusivity of concrete for the bridge deck and the pier column were significantly different. The concrete in a pier column facing upstream had greater porosity due to the water impact and calcium leaching. It was found that the convection depth for chloride transport in cracked concrete was significantly larger than that in uncracked concrete. The rust phases of the steel were detected by X-ray diffraction and Raman analysis. The chloride content was measured by a potentiometric titration method and the microstructure of concrete was obtained by scanning electron microscopy and mercury intrusion porosimetry. Concrete and steel samples were obtained from a 30-year-old reinforced concrete bridge. Chloride-induced steel corrosion is the most concerning issue for the durability of concrete structures. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |