UHPC Shear Keys in Concrete Bridge Superstructures

Shear keys are used between bridge superstructure elements to provide load transfer from one girder to an adjacent girder. Transferring load to adjacent girders increases the load carrying capacity of the bridge by increasing shear and moment distribution factors. In service, shear keys often deteriorate in a manner that starts with loss of bond between the grout and the superstructure elements. Once bond is lost, water can seep into the previously bonded area and cause degradation through freezing and thawing, leaching, or other mechanisms. Repair of deteriorated shear keys requires chipping open portions of the shear key and removal of the original grouting material. New grout should be introduced in a manner that successfully re-seals the joint by establishing a strong bond with the girders. While new construction and rehabilitation projects generally utilize non-shrink grout mixtures, this research project will investigate the use of ultra-high performance concrete (UHPC) produced with local materials to fill shear keys between girders. UHPC has been shown to have exceptional durability and strength properties that have the potential to greatly extend the service lives of shear keys in bridge superstructures. This project will develop technology and/or procedures that will allow ultra-high performance concrete (UHPC) produced with local materials to be used in shear keys between precast concrete girders in bridge superstructures.