New Views on the Study of Variables Affecting Bond of Reinforcing Bars to Steel Fiber Reinforced Concrete

Fibers have a positive effect on bond of rebars to concrete since they clearly improve bond capacity in terms of ductility although their influence on bond strength, i.e. peak bond stress, is of relatively little importance. This paper reports the results of two series of pullout tests carried out on prismatic specimens made with two different SFRCs (required compressive strengths of 25 MPa and 45 MPa respectively) and comprehensively analyses the effect of four factors (fiber geometry and content, concrete cover, and rebar diameter) upon bond performance. In order to come to conclusions that can be considered as statistically reliable, all results have been analyzed by means of statistical inference based on multiple linear regression models. Furthermore, having some specimens where concrete splitted before the rebar was pulled out, the effect of the aforementioned factors on the probability of splitting has been analyzed by means of logistic regression. It has been shown that the role fibers play in bond of rebars to concrete is of the same importance as that of concrete cover. It is especially remarkable that the mere fact of adding fibers, no matter the amount, decreases the probability of splitting and increases the ductility of bond failure considerably, this underlining the role of fibers in bond performance as passive confinement.