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Effect of Supplementary Cementitious Materials on Chloride Threshold and Corrosion Rate of Reinforcement
O'Reilly, Matthew Farshadfar, Omid Darwin, David
O'Reilly, Matthew
Farshadfar, Omid
Darwin, David
Citations
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Abstract
Supplementary cementitious materials (SCMs) are commonly used
as a means of reducing cost, reducing environmental impact, or
reducing permeability of concrete, but the current field of research
has found mixed results in terms of the resulting time to corrosion
initiation and corrosion rate of concrete containing SCMs. This
paper examines the time to corrosion initiation, the water-soluble
critical chloride corrosion threshold, and the corrosion rate after
initiation for uncracked concrete specimens containing cementitious
material consisting of 100% portland cement, mixtures with
volume replacements of cement by 20% and 40% Class C fly ash,
20% and 40% Grade 100 slag cement, and 5% and 10% silica
fume. Specimens had 1 in. (25 mm) concrete cover and a watercementitious
materials ratio (w/cm) of 0.45.
Test results show that many specimens containing SCMs exhibited
repassivation of the reinforcement after a “first” corrosion
initiation. This “first” initiation occurred at chloride thresholds
comparable to or lower than the chloride threshold for reinforcement
in 100% portland-cement concrete. The reinforcement
remained passive for varying lengths of time (from 3 to 50 weeks)
before reinitiating. At reinitiation (“final” initiation), specimens
with concrete containing SCMs exhibited times to corrosion initiation
two to seven times that observed in specimens containing
100% portland cement and corrosion rates after initiation approximately
an order of magnitude lower than that observed in specimens
containing 100% portland cement. Increasing the amount of
SCM generally lowered the corrosion rate after initiation. Chloride
thresholds at final initiation for specimens containing fly ash
or slag were 66 to 200% higher than that observed for specimens
containing 100% portland cement. Chloride thresholds at final
initiation for specimens containing silica fume were 40 to 60%
higher those observed for specimens containing 100% portland
cement.
Description
Date
2019-01-01
Journal Title
Journal ISSN
Volume Title
Publisher
American Concrete Institute
Research Projects
Organizational Units
Journal Issue
Keywords
Chlorides, Corrosion, Fly ash, Silica fume, Slag cement, Supplementary cementitious materials
Citation
O’Reilly, M., Farshadfar, O, and Darwin, D., “Effect of Supplementary Cementitious Materials on Chloride Threshold and Corrosion Rate of Reinforcement,” ACI Materials Journal, Vol. 116, No. 1, Jan. 2019, pp. 125-133.