Semi-quantitative Prediction of the Corrosion Risk of Steel in Concrete Using XRD Analysis

Abstract

The present study concerns a technique for determining the chloride binding capacity, using the XRD curve containing the peaks for Friedel's salt. The influence of chloride binding on the corrosion behaviour was also evaluated. The binding capacity of chloride ions in cement paste was determined by the water extraction method. As a result, it was found that the chloride binding capacity is strongly dependent on the W/C, binder type, curing age and total chloride concentration in the paste. It is notable that chloride binding has a crucial influence on corrosion propagation: an increase in the binding capacity resulted in a decrease in the corrosion rate at a given chloride concentration in mortar specimens. However, the impact of chloride binding on the onset of corrosion was marginal, presumably due to a release of bound chlorides into free chlorides at the stage of corrosion, accompanying a pH fall in the vicinity of the steel. A strong relation between the peak intensity for Friedel's salt and the concentration of bound chloride was observed, which can be used to determine the bound chlorides and thus the risk of chloride-induced corrosion of steel in concrete.

Resistance of Alkali-Activated Slag Concrete to Chloride-Induced Corrosion

“…The role of chloride binding at steel corrosion in concrete is subjected to debate. For example, Kim et al [15] suggested that there was no clear-cut relation between chloride binding and corrosion risk on the stage of corrosion initiation, although the rate of corrosion propagation might be affected by concentration of free chlorides, in turn binding capacity of chlorides. Glass et al [16] support this hypothesis that no influence of chloride binding on the corrosion risk is given, as the bound chloride chlorides could be released to be free in the vicinity of steel due to a pH fall from the electrochemistry on the steel surface.…”