Highway bridge decks are often overlaid to extend service life by reducing the rate of chloride ion ingress and the rate of corrosion of reinforcing steel in the sound chloride-contaminated concrete that is left in-place. Bridge deck overlays in Virginia are usually either latex-modified concrete or microsilica concrete, and both types of overlay are considered equivalent in terms of performance. However, the latex-modified concrete overlays are more expensive to construct than the microsilica concrete overlays. Thus, it is important to determine if these overlays do perform equivalently to ensure that short-term savings do not lead to higher long-term costs. Shrinkage is one of the overlay performance parameters. Shrinkage is a three-dimensional deformation of concrete that results in an overall reduction in volume. Total shrinkage may be measured under either restrained or unrestrained conditions. This research examines the shrinkage performances of Virginia Department of Transportation-approved latex-modified and microsilica concrete overlay mixtures and was conducted on both field-sampled and laboratory-fabricated restrained and unrestrained specimens. Based on crack and delamination surveys of sampled bridge decks and laboratory test results, a shrinkage performance-based specification for the Virginia Department of Transportation was developed. There was no significant difference between the unrestrained shrinkage values of latex-modified and microsilica concrete overlay mixtures for the specified time periods. Restrained microsilica concrete specimens generally cracked earlier and more frequently than restrained latex-modified concrete specimens. However, the bridge deck crack and delamination surveys show that construction conditions and quality and traffic type and frequency may have a greater effect on cracking than the overlay material. / Master of Science

Although the application of surface treatments on bridge decks is expected to positively impact bridge deck condition, the effectiveness of specific surface treatments on extending bridge deck life has not yet been quantified on Utah bridge decks. Therefore, the objectives of this research were to develop and analyze deterioration curves for bare concrete bridge decks and decks with specific treatments commonly used in Utah. The scope of this study was determined by the types and extent of electronically available data, including selected static inventory information; maintenance, rehabilitation, and reconstruction histories; and National Bridge Inventory (NBI) condition ratings for the bridge decks. Bridge deck selection criteria and analysis procedures were developed to enable evaluation of the effects of surface treatments on bridge decks in Utah. Characteristics of a typical bridge were defined, and a list of typical bridges was produced to minimize potentially confounding effects of atypical bridge characteristics in comparisons of deterioration curves for monolithic concrete decks, decks with a bituminous overlay, decks with an epoxy overlay, and decks with a latex-modified concrete overlay. Climatic differences were taken into account by grouping bridges not only by overlay type, but also by Utah Department of Transportation region, which was used in this research as a general surrogate for latitude. Individual bridge deck deterioration curves were then combined to generate average deterioration curves aligned by deck construction time and average deterioration curves aligned by deck treatment time. To at least partially account for the potentially different effects of different treatment times, the bridge groups involving overlays were divided into two treatment time categories, early and late, for analysis. The average deterioration curves aligned by deck construction time suggest that certain treatments applied at certain times can achieve average NBI ratings greater than those for monolithic concrete during selected years of bridge deck life. The average deterioration curves aligned by deck treatment time suggest that certain treatments applied at certain times can achieve improvements in NBI ratings that correspond to apparent increases in bridge deck service life. Primarily because the NBI rating system is based mainly on visual inspection, the full benefits of early applications of surface treatments are not apparent in the results of this research. Supplemental perspectives may be gained about the performance of specific surface treatments by evaluating bridge deck deterioration in terms of delamination, half-cell potential, and chloride concentration, for example, which are direct measures of the deterioration process typically experienced by concrete bridge decks in Utah.