Characteristics of the steel-concrete interface and their effect on the corrosion of steel bars in concrete

Abstract

Corrosion is the most important factor affecting the durability of reinforced concrete structures. Previous studies show that the formation and evolution of steel-concrete interface have a significant impact on the corrosion process of steel bars. The main purpose of this paper is to reveal the characteristics of steel-concrete interface and their effect on the corrosion of steel bars. Reinforced concrete specimens with vertically arranged and horizontally arranged steel bars of different heights (50 mm, 250 mm, 450 mm, 650 mm and 850 mm) were designed. The steel-concrete interface was examined by backscattered electron (BSE) imaging and nanoindentation technology. The specimens were exposed to wetting/drying cycles in chloride solution, while open circuit potential (OCP) of steel bars was conducted to monitor the corrosion state. After 80 cycles, one specimen was artificially broken to check the corrosion condition of steel bars by autopsy test.The results show that for the specimens with vertically arranged steel bars, there were few defects in the steel-concrete interface. For ones with horizontally arranged steel bars, however, many defects formed in the steel-concrete interface and the majority appeared at the bottom of steel bars. The area of these defects increased with the height of steel bars, from 0.27 mm2 to 10.83 mm2 for the steel bars at 50 mm and 850 mm respectively. In addition, the chloride penetration depth along the bottom part of the steel-concrete interface also increased significantly with the height growth. The OCP and autopsy results indicated that the corrosion of steel bars at the heights of 850 mm and 650 mm initiated after 30 cycles and 80 cycles respectively. Whereas no corrosion was found on other steel bars. Hence it was confirmed that the defects in steel-concrete interface accelerated the corrosion initiation of steel bars.