Internal Curing of Concrete Bridge Decks in Utah

The objectives of this research were (a) to monitor in situ bridge deck properties such as moisture and diffusivity for both conventional concrete and concrete containing prewetted lightweight fine aggregate, which is intended to provide internal curing; (b) to compare deck performance in terms of early-age cracking; and (c) to evaluate the compressive strength and chloride permeability of concrete mixtures in the laboratory using cylinders cast in the field at the time of deck construction. The research scope included four bridges—two constructed with conventional concrete and two containing prewetted lightweight fine aggregate—in northern Utah. Data from sensors embedded in the concrete decks indicated that the moisture content of the internally cured concrete was 2% to 3% higher at 28 days than the moisture content of the conventional concrete. Although the internally cured concrete had a higher moisture content, the electrical conductivity values were approximately the same for all decks after a few months; these values suggested that the two types of concrete had similar diffusivity. At 28 days, the average strength of the internally cured concrete was 1% higher than that of the conventional concrete, and the internally cured concrete passed between 2% and 30% less current during the rapid chloride permeability test than the conventional concrete. After 2 months, three to five cracks about 0.2 to 0.3 mm in width were found on each of the conventional concrete bridge decks, but no visible signs of cracking were found in the bridge decks with internal curing.