Effects of Calcium Nitrite and Microsilica Admixtures on Corrosion Resistance of Steel in Concrete


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Title: Effects of Calcium Nitrite and Microsilica Admixtures on Corrosion Resistance of Steel in Concrete

Author(s): N. S. Berke and K. M Sundberg

Publication: Special Publication

Volume: 122


Appears on pages(s): 265-280

Keywords: admixtures; calcium nitrite; chlorides; concrete piles; corrosion resistance; diffusion; marine atmospheres; reinforced concrete; reinforcing steels; silica fume; Materials Research

Date: 6/1/1990

Chloride-induced corrosion is a problem common to steel reinforced concrete exposed to chloride ions. A severe case is the use of reinforced concrete in seawater. The high-chloride concentration in salt water, the geometry of concrete piles, and the moisture differential between concrete above and below the water line are all factors that complicate the problem. The corrosion resistance of steel reinforced concrete is a function of the concrete cover of the steel, concrete permeability, surface chloride concentration, and ambient temperature. In this paper, the authors present diffusion curves for chloride ingress into concrete piles. The diffusion coefficients are based on extensive laboratory and field studies. They also discuss the usefulness of this model, based on Fick's law of diffusion. By estimating the chloride ion concentration at the steel reinforcement after a given amount of time, the lifetime of the structure can be predicted. In addition to concrete quality, concrete admixtures affect the corrosion of steel in concrete. Two concrete admixtures are discussed--calcium nitrite and microsilica. As demonstrated in other publications, both of these additives delay the onset of corrosion. It has also been shown that calcium nitrite affects the rate of corrosion upon initiation. The appropriate dosage of each admixture can be determined using the chloride diffusion curves. Examples are described in the paper.