An Innovative Experimental Procedure to Study Local Rebar-Concrete Bond by Direct Observations and Measurements

This paper describes an innovative experimental procedure that aims at gaining a better understanding of the mechanisms that govern rebar-concrete bond at the local level. The proposed experimental set-up enables direct continuous observation and measurements of the concrete displacements and thereby strains in the vicinity of the rebar rib throughout the pull-out process of a deformed rebar. The set-up is based on a standard pull-out test of a cylindrical specimen in which a 90° “window” sector is left open during its casting. Measurements of the concrete displacements are performed by a sequence of timed high resolution digital photographs that are later analyzed. The proposed technique has been verified by comparison of its global, load–displacement response with that of a matching control specimen that did not include a “window”. The experimental results as well as a corresponding numerical analysis show that when the height of the “window” is limited, its effect on the global response is minor whereas the gained new information is invaluable. Hence, the proposed experimental procedure provides an opportunity to examine the evolving displacements and strains in the concrete near the ribs, during the pull-out of the rebar. Such experimental observations were not available till now and the exact interaction mechanics between the rebar and the concrete is still obscure.