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Thursday, March 20, 2008 - 9:55 AM
Convention Center, Second Level, R01 (Ernest N. Morial Convention Center)
08322
Effect of Cement Alkalinity and Concrete Microstructure Upon Chloride Threshold for Corrosion Initiation of Reinforcing Steel in Concrete
A series of reinforced G109 type concrete specimens with cement of equivalent alkalinity (EqA) either 1.08 or 0.32 was cyclically ponded with a 15 w/o NaCl solution and time-to-corrosion initiation, Ti, determined. The specimens were subsequently dissected, the steel-concrete interface examined and characterized, and concrete along the top of the upper rebar sampled and analyzed for Cl-. The results revealed greater Ti and Cl- threshold for corrosion initiation, [Cl-]th, for the higher EqA specimens. In many instances, corrosion initiated preferentially at entrapped air voids at the rebar-concrete interface provided diameter of these was ≥ 2.5 mm. An explanation is proposed for the site specificity of corrosion initiation and [Cl-]th variability for seemingly identical specimens that considers both entrapped air voids and the spatial distribution of coarse aggregates within the Cl- ingress path.