Investigation, Assessment, and Repair of Cracks in Precast Bridge Slabs

A bridge construction firm manufactured precast concrete slabs for the deck replacement of a major East Coast bridge. The slab segments were removed from the casting bed, transported to the lay-down site, and supported on dunnage. Cracks started to appear soon after. The authors were retained to determine the cause of cracking, feasibility of repair, and potential repair methods. Based on our analysis, cracking was due to excessive tensile stresses caused by the configuration and differential settlement of temporary supports at the laydown site. Assessment of concrete quality, crack type and size, and expected service level stresses identified that a gravity-fed methacrylate or epoxy repair, combined with crack injection, would restore intended serviceability of the slabs. This case study illustrates the importance of carefully considering temporary construction loads on structural members, including the significance of structural assumptions such as perfectly rigid support conditions. The study also identified sensitivity of the bridge slabs to fit-up tolerances in the likely to be encountered during permanent installation of the slabs.