Are concrete-concrete bond tests comparable?

The effectiveness and durability of a concrete repair or retrofit is mostly affected by its bond and compatibility to the existing substrate. Although our understanding of concrete-concrete bond has advanced greatly, there remains a major uncertainty in the adoption of a proper methodology to assess the quality of bond, comprising the accuracy of reproducing the stresses that the interface undergoes in a structural application, the problem of disturbed stress paths, size & rate effects, drilling-induced damage, and the possibility of conversions between shear and tensile bond. A discussion on comparability of bond tests in tension and shear is presented. The study is based on a roundrobin-like test program in two independent labs in Canada and Austria (UBC, CUAS) and encompasses normal strength, high strength, and fiber reinforced concretes. The raw data comparison is complemented with an investigation of semi-empirical methods and predictive models, conversions between shear and tension coefficients, and suitability/limitations of various methodologies for assessing the effects of fiber reinforcement on bond.