Corrosion Behaviour of Zinc Coated Steel in Silica Fume Concrete

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Title: Corrosion Behaviour of Zinc Coated Steel in Silica Fume Concrete

Author(s): C. L. Page, G. Sergi, and N. R. Short

Publication: Special Publication

Volume: 114

Issue:

Appears on pages(s): 887-896

Keywords: chlorides; concretes; corrosion; pH; reinforcing steels; silica fume; tests; zinc coatings; Materials Research

Date: 5/1/1989

Abstract:
Zinc coatings, applied mainly by galvanizing, have been widely used to provide supplementary corrosion protection to reinforcing steel in concrete exposed to aggressive media. Their performance, particularly in concretes contaminated with chloride salts, has been variable; this is believed to be due, at least in part, to the effects of differences in cement alkalinity on the rate of zinc dissolution. To investigate this, specimens were made in which well characterized zinc coated steel electrodes were embedded in cement pastes containing various proportions of silica fume and sodium chloride. They were exposed to moist air for several months, during which time the pore electrolyte compositions were analyzed and the corrosion rates of the embedded electrodes were monitored by linear polarization. It was found that the major influence on the corrosion rate of the zinc coatings was the pH of the pore electrolyte phase, so that quite modest levels of silica fume were capable of reducing corrosion rates by orders of magnitude when compared with those sustained in the unblended pastes. The implications regarding the effective service lives of the coatings are believed to be considerable. Analysis of the relationship between corrosion potential and corrosion rate for the embedded electrodes revealed that the rates of corrosion were generally subject to anodic control, except at very high values when oxygen diffusion became the rate-limiting process.