Moisture is a primary contributing factor in the long term durability of bridge decks. Moisture is involved in freeze-thaw problems in Portland cement concrete and in corrosion of reinforcing steel. Chloride ions, another factor contributing to corrosion, are normally transported through the concrete bridge deck to the reinforcing steel by moisture.
Moisture measurement techniques were examined and one of the methods, Peltier-type psychrometers, was used to measure bridge deck moisture. Measurements were made at depths of 0.5, 1.5, 3.0 and 4.5 - 5.5 in. Both negative and positive moment regions were instrumented. The degree of saturation at the level of the reinforcing steel was found to be about 90 percent, with little variation over the two month period that measurements were taken. Moisture content fluctuations were greater in the negative moment region than the positive moment region, probably due to a higher degree of tensile cracking in the negative moment region. Moisture fluctuations could lead to increased migration of chloride ions to the reinforcing steel. Measurement of moisture content distributions before and after wetting a bridge deck could be used as an indicator of corrosion protection provided by overlays.