Backscattered electron imaging of the steel-concrete interface

Backscattered electron images were obtained under low vacuum conditions on polished sections of the steel-concrete interface to examine whether the fo rmation of any of the hydration products of cement is favoured at this loca tion. 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 gener al 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 corro sion initiation, should be extended to include the effects of all solids wi th pH dependent dissolution characteristics. These include both the inhibit ive effects of other solid phases that resist a local fall in pH and the ag gressive nature of ions like chloride that may be released by a local pH re duction. (C) 2001 Elsevier Science Ltd. All rights reserved.