Chloride Ion Transport in Bridge Deck Concrete Under Different Curing Durations (05-1485) - MP-16
Hassan Akram Ghanem, Texas Tech University
Randal Scott Phelan, Buckland & Taylor
Sanjaya P. Senadheera, Texas Tech University
Kevin Pruski, Texas Department of Transportation

During freezing temperatures, ice accumulates on exposed concrete slabs such as bridge decks. De-icing salts such as calcium chloride are applied to control this ice formation. These salts migrate down to the reinforcing steel, and they can break down the passivation layer on steel causing it to corrode. This paper is part of a broader research study sponsored by TxDOT to explore the possibility of opening the bridge decks earlier than the 10 to 12 days as practiced now, by decreasing the number of wet-mat curing days. Seven concrete mixtures typically used in Texas bridge decks were evaluated for chloride permeability using the Ponding Test (AASHTO T259). The primary experimental variables were the curing duration, type and percentage of supplemental cementitious materials, type of coarse aggregate, duration of ponding and the surface preparation of ponded concrete specimens. Results of the investigation indicated that chloride permeability decreased with increasing curing duration for the top one inch of concrete, but very little influence of curing was observed in the interior. It was observed that curing duration may be decreased for some concrete mixtures as no apparent improvement was shown after a specific curing duration, which ranged from 2 to 8 days depending on the mix. Increasing the amount of supplemental cementitious materials such as fly ash from 20% to 30% considerably reduced the chloride permeability. Also, concrete with limestone coarse aggregate performed better than mixtures containing siliceous gravel. This may be attributed to weak interface zones in siliceous gravel mixtures.