Which Shear Test for Bonded Concrete?

While hundreds of standards exist for testing the physical properties of many materials, there is no industry standard for testing shear strength in concrete. Ascertaining the actual shear strength across a bonded concrete interface, such as at repairs or construction joints, is particularly problematic. In investigating planar strength, the shear strength between concrete surfaces is of primary importance. Studies from the late 19th century to the present day have not resulted in a universally accepted standard test to determine the bonded concrete shear strength. Although there is no ASTM standard for a direct shear test at the bonded concrete interface, several methods used in various locations throughout the United States include the Brookhaven National Laboratory Guillotine Shear Test and the Iowa Shear test. Other shear test methods available include the Asymmetric Four-Point Bending, Bond Test (also called the Tensile Bond Test or Pull-Off Test), CTL Thompson Method, Iosipescu-65 Method, Jacking Shear Test (also called Push-Off Test), Slant Shear Test, Torsional Shear Test, and US Bureau of Reclamation Shear Tests. Also, this paper summarizes historical and recent research results at the University of Colorado Denver where different devices test direct shear in bonded concrete specimens. The research objective is to determine each shear test method’s pros and cons, and recommend one method as a universal standard regardless of the bonding agent or method.