Bond Characterization and Interfacial Coefficients at Precast UHPC and Cast-in-Place UHPC Interface

Abstract

Ultrahigh performance concrete (UHPC) is an advanced composite material that exhibits superior compressive and tensile strengths as well as negligible permeability. Although the mechanical properties of UHPC are extensively investigated, the bond strength between UHPCs cast at different times due to the construction process or its application is not fully understood and needs to be quantified. The interface between precast UHPC (PC-UHPC) and cast-in-place UHPC (CIP-UHPC) cold joints is subjected to various stress conditions ranging from tension, shear, compression-shear, and tension-shear. To date, no comprehensive study has been conducted to consider all possible stress conditions at the interface. The objective of this study is to quantify the effect of roughness on bond strength at the UHPC-UHPC cold joint under tension, shear, and a combination of compression and shear stresses. Roughness on the interface of the precast UHPC was achieved using commercially available formliners with five mean texture depths ranging between 1.32 and 4.28 mm. The interfacial parameters, such as cohesion and shear friction, which have not been identified for cold UHPC joints, were determined. Specimens prepared with a mean texture depth of 4.28 mm experienced the highest bond strength under the most tested stress conditions. The results indicate that the interface, which was ultimately without fibers, experienced cohesion values that were lower than the reported values from some design codes. The friction coefficients were higher than the maximum reported value from the design codes.