Interface evaluations of overlay-concrete bi-layer composites by a direct shear test method

Interface evaluations of four high-performance concrete overlays cast on top of one type of normal concrete substrate were made by a new direct shear test method. Two different surface preparations such as mechanical abrasion and chemical etching were followed to manufacture 64 overlay-substrate bi-layer specimens. This paper discusses the material properties and fabrication and evaluations of bi-layer specimens. Results show that successful interface bond characterization was possible through this direct shear apparatus. The test method seems to be suitable for screening and selection of various overlays for their compatibility with substrate concrete. However, some modification in the tool is needed for assessing the high-bond capacity interface. Effects of bonding slurry also needs further study.