Short-term and creep pull-out behavior of polypropylene macrofibers at varying embedded lengths and angles from a concrete matrix

Abstract This paper reports on the short-term and creep pull-out behavior of different polypropylene fibers from a concrete matrix. 85 displacement controlled tests are carried out for two types of fibers with different embedded lengths and angles. Additionally, 15 creep tests are performed in a climate controlled room at different load ratios to study long-term loading effects. The pull-out tests show that an increase in the embedded length of the fiber increases the maximum pull-out force. More inclined fibers with respect to the load application direction initially increase the pull-out force as well, but the fibers tend to rupture more at the concrete surface, leading to a brittle failure mode. Furthermore, an oscillating post-peak behavior is observed during pull-out which is related to the embossed surface profile of the fibers. The profile is gradually abraded during the test which in turn leads to a pure-friction controlled pull-out behavior at large relative displacements. The pull-out creep tests show that the behavior strongly depends on the load ratio, with higher loads decreasing the failure time. A novel positive feedback loop mechanism is proposed to qualitatively explain the pull-out creep behavior in which the fiber creep deformations are the driving force behind pull-out creep.