Influence of Thermal Fatigue Cycles on Concrete Cold Joints

Abstract

Mass concrete structures in northern climates experience extreme oscillations in temperature each year. These fluctuating conditions incur large thermal stresses, which are of particular concern at cold joint locations. To better understand the behaviour of cold joints subjected to these thermal fatigue cycles, an experimental program was conducted at the University of Manitoba, focusing on the performance of concrete cylinders with concrete-to-concrete interfaces. Specimens were prepared with joints oriented either horizontally to evaluate direct tensile performance or at a 35˚, 40˚, or 45˚ angle for slant shear. These cylinders were then installed in specially designed vertical translation-restricting frames and placed in an environmental chamber, where they were subjected to temperatures cycling between -25˚C and 40˚C. Static testing after 50, 150, and 250 cycles was performed to ascertain remaining bond strength. An increase in performance of approximately 20% was observed in direct tension after 50 cycles, followed by a subsequent decrease. In general, the thermal fatigue cycles did not appear to detrimentally impact bond strength after 250 cycles in both direct tension and slant shear. Additionally, interface friction demonstrated no meaningful trend between specimens that had experienced zero to 250 cycles, remaining relatively consistent with their corresponding roughness level defined in the Canadian Design of Concrete Structures code, and bond cohesion appeared to follow a similar trend to mean direct tensile bond strength results.