Bond strength development between concretes of different ages

The bond between substrate and overlay is often the main factor concerning the serviceability of a composite member consisting of concretes of different ages. In the current paper, existing bond strength test methods are discussed and fundamental influences on bond strength development and bond serviceability and durability are investigated. Two new experimental methods for the evaluation of interface shear strength are introduced, which have proved to be practical and indicative of fundamental bond mechanisms and factors influencing bond durability. Shear bond strength between substrate and overlay was found to be governed largely by mechanical and physical material properties of the overlay close to the interface. Bond strength development could be linked to the development of the compressive strength of the overlay. Interface texture was found to have a significant influence on the durability of bond strength. 'Interface bond failure' could, in most instances, be identified visually to have occurred in the overlay close to the interface. The term 'interface failure' commonly used for the discussion of bond characteristics therefore appears to be ambiguous.