Analysis of factors influencing bond behaviour between reinforcing steel bars and FRC under monotonic loading

Bond phenomenon allows the variation of the bar tensile action to be transferred to the surrounding concrete by means of shear stresses developing along the lateral surface of the bar. This mechanism entails the formation of radial transversal pressure as a result of the wedge action of the crashed concrete between the ribs. The latter may cause the onset of longitudinally splitting cracks when the tensile strength is reached in the cover. This phenomenon depends mainly on the post-peak behavior of concrete, which can be significantly enhanced with the addition of fibers. Based on the available results from the literature, in the first part of the paper an analysis on the bond behavior between steel rebars and FRC is presented. The influence of several parameters, such as concrete strength, fibers content, aspect ratio and concrete cover is evaluated. Finally, the preliminary results of pull-out tests on short anchorages will be also presented under monotonic loading, embedded in plain concrete and fiber reinforced concrete. The test set up was able to simulate the influence zone of one stirrup. A volume content of steel hooked fibers equal to 0.38% has been investigated. The test results shows the addition of steel hooked steel fibers increases bond strength and reduces splitting crack opening in conventional FRC.