Backscattered electron imaging of the steel–concrete interface

Abstract

Backscattered electron images were obtained under low vacuum conditions on polished sections of the steel–concrete interface to examine whether the formation of any of the hydration products of cement is favoured at this location. It was observed that the hydration products at the steel are typical of those in the bulk of the cement paste. In particular, there was no general indication of preferential formation of calcium hydroxide at the steel. This provides further support for the suggestion that the early hypothesis concerning the formation of a lime layer at the steel, which inhibits corrosion initiation, should be extended to include the effects of all solids with pH dependent dissolution characteristics. These include both the inhibitive effects of other solid phases that resist a local fall in pH and the aggressive nature of ions like chloride that may be released by a local pH reduction.