Corrosion Assessment for Failed Bridge Deck Closure Pour

Corrosion of reinforcing steel in concrete is a significant problem around the world. In the United States, there are approximately 600,000 bridges. From those bridges 24% are considered structurally deficient or functionally obsolete based on the latest, December 2010, statistic from the Federal Highway Administration (FHWA). Mainly, this is due to chloride attack present in deicing salts which causes the reinforcing steel to corrode. Different solutions have been developed and used in practice to delay and prevent corrosion initiation.

The purpose of this research is to investigate the influence of corrosion on the failure mechanism that occurred on an Interstate 81 bridge deck. After 17 years in service, a 3ft x3ft closure pour section punched through. It was part of the left wheel path of the south bound right lane of the bridge deck. The bridge deck was replaced in 1992 as part of a bridge rehabilitation project, epoxy coated reinforcement were used as the reinforcing steel. Four slabs from the bridge deck, containing the closure, were removed and transported to the Virginia Tech Structures and Materials Research Laboratory for further evaluation. Also, three lab cast slabs were fabricated as part of the assessment program.

Corrosion evaluation and concrete shrinkage characterization were conducted in this research. The corrosion evaluation study included visual observation, clear concrete cover depth, concrete resistivity using single point resistivity, half-cell potential, and linear polarization using the 3LP device. Shrinkage characteristics were conducted on the lab cast slabs only, which consisted of monitoring shrinkage behavior of the specimens for 180 days and comparison of the data with five different shrinkage models. Based on the research results, guidance for assessment of other bridge decks with similar conditions will be constructed to avoid similar types of failures in the future.