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

Abstract

The corrosion of steel reinforcements in concrete is of great importance in the view of safety and durability of reinforced concrete structures. This study is focused on the corrosion behavior 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 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-to-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 steels are proposed. The present study provides the realistic chloride limit for corrosion initiation of reinforced concrete structures, which can be used efficiently in the future technical specification.

Investigation on the effect of supplementary cementitious materials on the critical chloride threshold of steel in concrete

“…Limiting to the tests in concrete, which are expected to be intrinsically more realistic compared to tests in solution, methods proposed by different Authors differ regarding the way concrete is contaminated by chloride ions, corrosion initiation is detected and the chloride content at the depth of the bar is measured. Chlorides can be forced to penetrate into concrete through external sources [8, 19, 20, 22, 24, 25, 29, 31, 32, 38, 40, 45-47, 50, 52-54, 56, 57], as for instance ponding with chloride-containing solutions [32,46], or alternatively can be added to the concrete mix [2,30,32,35,39,41,47]. The way chlorides are introduced into concrete has several consequences.…”

“…corrosion potential and corrosion rate) [2,8,19,25,29,32,35,38,40,41,46,56] and, seldom, by extraction of bars and visual inspection [20] or weight loss [52,53]. As far as the measurement of the chloride content is concerned, the analysis of total chloride content is frequently applied in practice.…”

“…As far as the measurement of the chloride content is concerned, the analysis of total chloride content is frequently applied in practice. Different criteria for sampling have been proposed: directly from the bar site at the time of corrosion onset [3,19,28,31,41,50,54,57] or far from the bar considering the same bar depth [25,39,40,45,52,53] (sometimes even in reference samples exposed to the same exposure conditions, provided similar conditions for chloride penetration occur [38]. Tests can also be different for other aspects such as, for instance, the bar surface conditions, the specimen geometry, etc.…”

“…For instance, Thomas and Matthews [53], Oh et al [41] and also Song et al [49] reported a reduction in the critical chloride threshold of fly ash (FA) concrete compared to portland cement (OPC) concrete. Conversely, according to Breit and Schiessl [17] and Choi et al [21], the critical chloride threshold for FA concrete was higher than for portland cement.…”

“…Alonso et al [3] did not find significant differences in the critical chloride threshold when portland cement was partially replaced with fly ash. Controversial results were also obtained with the replacement of ground granulated blast furnace slag (GGBS): Oh et al [41] observed a negligible influence of GGBS on the critical chloride threshold, while Breit and Schiessl [17] reported a higher critical chloride threshold for GGBS concrete.…”