Corrosion Assessment for the Failed Bridge Deck Closure Pour at Mile Marker 43 on I-81

About the report:

Corrosion of reinforcing steel in concrete is a significant problem around the world. In the United States, there are approximately 600,000 bridges. Of those bridges, 24% are considered structurally deficient or functionally obsolete based on the December 2010 statistics from the Federal Highway Administration. The primary cause is chloride attack from deicing salts, which corrodes the reinforcing steel. Different solutions have been developed and used in practice to delay and prevent corrosion initiation.

The purpose of this research was to investigate the influence of corrosion and shrinkage on the failure mechanism that occurred on an I-81 bridge deck. After 17 years in service, a 3 ft by 3 ft closure pour section punched through. The closure was positioned under the left wheel path of the southbound right lane of the bridge deck. The bridge deck had been replaced in 1992 as part of a bridge rehabilitation project, and the reinforcement was epoxy coated. Four 4.5 ft by 10 ft slab sections, containing the closure, were saw cut from the deck, removed, and transported to the Virginia Tech Structures and Materials Research Laboratory for further evaluation. Also, for comparison, three new slabs were fabricated as part of the assessment program.

Corrosion evaluation and concrete shrinkage characterization were conducted in this study. 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 was characterized on the lab cast slabs only. This consisted of monitoring shrinkage behavior of the specimens for 180 days and comparing of the data with five different shrinkage models. The joints of the lab cast specimens were monitored for cracking and leaking.

Based on the research results, it is recommended that similar joints be inspected for leaking and evidence of reinforcement corrosion every two years and all similar joints should be sealed to prevent leaking. In addition, it is recommended that construction joints in future decks built with staged construction use corrosion resistant reinforcement.

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