Experimental investigation of shear transfer between concrete interfaces

This experimental program was focused on the effect of surface geometry (shear keys) on the transmission of shear forces between concrete cast against a hardened concrete interface. This research was part of a larger study at The University of Texas at Austin focused on several aspects of spliced precast concrete girder technology, particularly those concerning the interface between precast girders and cast-in-place splices. 14 push-through type specimens were tested with varying surface geometries, interface reinforcement ratios, and levels of prestress normal to the interface. The surface types considered included smooth, single shear keys, multiple shear keys, saw teeth of multiple depths and a monolithic specimen for comparison. The principle findings were that surfaces with properly detailed indentations could transfer significantly higher shear forces before slip occurred than smooth surfaces, and that shear keys generally displaced better performance than saw-teeth. Forces from prestress and yielding of reinforcement crossing the interface during failure were found to contribute to the strength in effectively the same manner. In addition, the shear friction based provisions of ACI 318-11, AASTHO LRFD 2012, and Eurocode 2 were found to provide satisfactory predictions of the ultimate strength of such surfaces with reinforcement ratios less than 0.75 %.