This research investigated the use of locally produced ultra-high performance concrete (UHPC) as a grouting material to repair deteriorated shear keys. Shear keys are used in adjacent girder superstructures to produce monolithic behavior and load transfer across the structure. Shear key durability is a concern since shear key degradation can jeopardize the integrity of the structure. Transportation agencies have reported that 75% of distress in adjacent girder bridges is due to cracking and de-bonding along shear keys. Previous research has shown that locally produced UHPC has excellent mechanical and durability properties. UHPC has also been shown to have good bonding characteristics that are desirable in a potential grouting material. Several tests were conducted to evaluate the potential of UHPC as a shear key grout material. Bond strength between UHPC grout and substrate concrete was evaluated using slant-shear and direct tension tests. Results showed that adequate bond was achieved at seven days. However, 28-day strengths were less than recommended bond strengths. The low strengths were attributed to the low strength of the substrate concrete. Shrinkage of UHPC grout was also investigated. Total shrinkage was approximately 2000 μstrain with approximately half occurring in the plastic state. Full-scale testing was used to evaluate load-deflection behavior of channel girder assemblages with grouted shear keys. The results showed that UHPC grout and non-shrink grout had similar mechanical performance. Excellent bond was achieved with all grouts, even with minimal surface preparation. In fact, the shear keys remained bonded to the girders even when service load deflections were exceeded and no lateral restraint, such as post-tensioning, was provided. A non-shrink grout slightly outperformed the UHPC grout. While this outperformance of the non-shrink grout may not be significant, it does indicate that UHPC grout does not provide a mechanical benefit over the non-shrink grout.
Newtson, C., Weldon, B., Flores, E., Varbel, J., & Toledo, W. (2019). UHPC Shear Keys in Concrete Bridge Superstructures. Retrieved from https://digitalcommons.lsu.edu/transet_pubs/36