Experimental investigation of the threshold chloride concentration for corrosion initiation in reinforced concrete structures

The corrosion of steel reinforcements in concrete is of great importance when considering the safety and durability of reinforced concrete structures. This study focuses on the corrosion behaviour of steel bars induced by internal chlorides in concrete. The main objective of this study is to determine the threshold chloride concentration causing depassivation and active corrosion of steel reinforcement in concrete. To examine the threshold concentration of the chloride ion, the half-cell potential, the chemical composition of extracted pore solutions of concrete and the extent of corroded area of the specimens were measured. Major test variables include the added amount of chlorides in concrete, type of binder, and water/binder ratios. From the present comprehensive test results, the factors influencing threshold chloride concentration are investigated, and the rational ranges of threshold chloride concentration causing active corrosion of steel are proposed. The present study will enable the specification of a realistic chloride limit in reinforced concrete structures, which can be used effectively in future technical specifications.