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Long-Term Chloride Penetration Resistance of Silica Fume Concretes Based on Field Exposure

Presented By: Doug Hooton

Affiliation: University of Toronto

Description: Cores were obtained in 2001 and 2002 from silica fume concretes in the decks of four parking garages in Ohio, Wisconsin, and Utah as well as five bridge decks in New York State and Ohio. All had been exposed to de-icing salts for between 6 and 15 years. Some concretes also contained fly ash as well as silica fume. On one bridge, silica fume concrete had been used as a repair overlay on an existing chloride-corroded deck. The cores were tested for chloride penetration profiles using mm profiling, chloride bulk diffusion by ASTM C1556 (NT Build 443), rapid chloride penetration (ASTM C1202). The results show that all of the silica fume concrete bridge decks had high chloride penetration resistance, with all full depth repaired bridge decks having between 290 and 690 coulombs on average, while the portland cement control concrete used on one of the bridge approaches had 3900 coulombs. The predicting time-to-corrosion service life using the Life-365 program gave residual life estimates of between 40 and 71 years for the silica fume structures, while the Portland cement slab was likely subject to corrosion at the time of coring. The 12-year-old silica fume repair overlay concrete only had a predicted residual life of 17 years. The parking decks all showed low chloride penetrations and residual service lives of 54 to 100 years. In all cases, depths of carbonation were negligible. It was also found that the Life-365 predictions, when based on the original mix designs and exposures, were conservative and that predictions based on results of long-term chloride exposure were at least 10 years longer than that originally predicted.

Courtesy of American Concrete Institute