Condition of Concrete Overlays on Route 60 over Lynnhaven Inlet after 10 Years

About the report:

In 1996, 16 high performance concrete overlays were placed on two 28-span bridges on Route 60 over the Lynnhaven Inlet in Virginia Beach, Virginia. Thirteen concrete mixtures included a variety of combinations of silica fume (SF), fly ash, slag, latex, corrosion-inhibiting admixtures, a shrinkage-reducing admixture, and fibers; one overlay was constructed with a thickness of only 0.75 in (19 mm), and spans were overlaid with and without topical treatments of two corrosion inhibitors. With the exception of one of the overlay systems, the overlays were required to have a minimum thickness of 1.25 in (32 mm). Another overlay system had a variable thickness ranging from 1.25 to 0.75 in (32 to 19 mm) to provide good ride quality. The demonstration was designed to show that many different combinations of materials can be used for overlays. The overlays were last evaluated in the fall of 1999 after 3 years in service. The objective of this research was to determine the condition of the overlays at 10 years of age. The results indicated that all overlays have performed well with the exception of most of the areas adjacent to joints. Many of these areas were replaced by the original contractor and replaced again by the City of Virginia Beach. The overlays were ranked with respect to permeability, chloride content, and cost. The 7% SF overlay on the eastbound lane had the lowest permeability, and the 7% SF overlay on the westbound lane had the highest permeability. The overall best performing overlay was the latex-modified concrete (LMC) overlay, which had the second lowest permeability and chloride diffusion constant and the lowest chloride ion content. Overlays containing fibers and the LMC overlay were estimated to have the highest cost, and the 40% slag overlay was estimated to have the lowest cost. Although the overlays performed differently with respect to permeability to chloride ion and chloride intrusion, all of the overlays can provide good skid resistance and protection against intrusion by chloride ions and can be an economical technique for extending the life of hydraulic cement concrete decks. The Virginia Department of Transportation should continue to extend the life of bridge decks using LMC and should consider using overlays containing combinations of SF, fly ash, and slag as evaluated in this study when justified based on the cost-benefit analysis for a project.

Authors