The composition and microstructure of the concrete–steel interface influences the critical chloride content for initiation of pitting corrosion and these characteristics may differ from those of the bulk concrete. This paper describes the development of a methodology for chloride profiling along the interface by means of LA–ICP–MS. For semi–quantitative analysis, microstructure characterisation of the pitting positions and distribution and composition of the corrosion products, SEM–EDS and XRD techniques were employed. The results indicate that along the interface a range of chloride levels can be expected. These varied between 0.15–1.5 wt% of concrete with higher levels around the active corrosion sites. Good agreement has been found between the results from LA–ICP–MS and EDS techniques. Interface defects strongly influenced the pitting corrosion. Several Fe(III) oxy–hydroxides accumulated at the aggregate–paste interface and in air voids at the cement paste. XRD analysis suggested the presence of akaganeite and FeCl2(rokuhnite).
Keywords: concrete–steel interface, LA–ICP–MS, SEM–EDS, chloride threshold values, pitting corrosion, microstructure, steel, chloride profiling, aggregate–paste interface, air voids, cement paste, akaganeite, rokuhnite, concrete structures, critical chloride content