Field Evaluation of Staged Concrete Bridge Deck Pours Adjacent to Live Traffic

Staged construction is the practice in which traffic is maintained on a bridge while it is constructed in phases. When cast-in-place concrete decks are used with staged construction, the concrete deck must cure while subjected to loads and displacements caused by the adjacent traffic using the same structure. Traffic-induced displacements and vibrations may damage the freshly placed concrete, its bond with the embedded reinforcement, or the integrity of the concrete joint. To determine the effects, if any, of staged construction practices on long-term bridge performance, this research examined bridge decks in Wisconsin that were constructed or widened using staged construction through visual inspection, field monitoring, and finite-element modeling. Some minor defects were observed in the field inspections of slab-on-girder bridges, such as underconsolidated concrete in the construction joint region and leakage through the joint itself. The inspected haunched-slab bridges showed severe deterioration at the construction joints. Field-measured differential displacements were small, with a maximum of 1.1 mm (0.043 in.), both during construction and several weeks after. Finite-element modeling confirmed these observations. Modeling results indicated that as long as nominal stiffness was provided by the deck or even the formwork between girders adjacent to the longitudinal joint, these deflections were unlikely to cause deterioration. Longer-span bridges may experience larger differential displacements across the joint, but these may be controlled by preventing larger vehicles from using the lane adjacent to the fresh concrete for approximately one day.