Chloride ion penetration in bridge deck concrete

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 the Texas Department of Transportation, to explore the possibility of opening the bridge decks to full traffic following construction/repair earlier than the 10 to 12 days as practised now in Texas. Seven concrete mixtures typically used in Texas bridge decks were evaluated for chloride permeability using the ponding test. 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. The results of this investigation indicated that chloride permeability decreased with increasing curing duration for the top 1 in (2.5 cm) layer of concrete. It was also 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. In addition, increasing the amount of cementitious materials such as fly ash from 20% to 30% considerably reduced the chloride permeability.