Resistência ao cisalhamento de vigas de concreto autoadensável reforçado com fibras de aço e macrofibras sintéticas

Abstract

Due to its fresh state properties, self-compacting concrete has constructive advantages, such as reduced construction time and labor costs, in addition to eliminating noise pollution due to the use of vibrators. However, since self-compacting concrete presents low tension performance, fibers can be added to the concrete mixture to enhance its mechanical properties, creating a post-cracking behavior. It is known that steel fibers improve the shear strength of concrete beams and studies include shear strength prediction methods. Synthetic fibers can improve concrete mixture by minimizing the cracking behavior. Thus, the hybridization of the previous fibers makes it possible to take advantage of its individual characteristics, combining its mechanical properties. This work aims to analyze the influence of adding steel fibers, synthetic polyethylene macrofibers and its hybridization in self-compacting concrete beams without stirrups, in addition to verify the applicability and precision of shear strength prediction methods for concrete reinforced with steel fibers. Although hardened state concrete properties have reduced with fiber addition, fibers influence was more significant in post-cracking behavior. The use of steel and hybrid fibers guaranteed higher shear strength then reference concrete, in addition to resisting greater loads before the beginning of crack formation. Fibers were also responsible for larger crack widths, and among the mixtures, the use of hybrid fibers guaranteed the smallest width, 4,02 mm. Results show that adding fibers in concrete provided an improved matrix strength, with a post-cracking hardening behavior. Furthermore, synthetic macrofibers provided results with great variability, due to the difficulty of incorporating on the concrete mixture, seeing that they agglutinate easily than steel fibers. The predicted values of ultimate shear strength were closer to the obtained experimentally for concrete reinforced with steel fibers, as expected. The highest estimated strengths referred to concrete reinforced with synthetic fibers due to its higher fiber factor. In general, the predictions were close to the experimental.