Bond of gfrp bars in reinforced concrete through splice in beams submitted to bending

Abstract

Fiberglass reinforced polymer bars, GFRP bars, have high tensile strength, superior to conventional passive reinforcement steel, and are not susceptible to corrosion. The use of these materials in structures subjected to high environmental aggressiveness, such as marine or coastal regions, can reduce the overall cost of construction throughout its useful life, reducing the costs associated with repairs caused by corrosion of metallic reinforcements. However, these materials have, in addition to anisotropic behavior, low adhesion to concrete. That factor is determinant in the design of this material for use as structural reinforcement. In this study, four beams were molded, two of those beams using self-compacting concrete and polyolefin fibers and two without the last one.  Two different splice lengths were used, twenty-five and forty diameters, and two beams with polyolefin fibers. These beams were reinforced with GFRP bars of a national manufacturer. The test methodology was the splice of longitudinal reinforcement in GFRP in the middle third of the beams, constant moment region, in order to evaluate the bond stress at the interface between bars in GFRP and concrete. Most of the works for adhesion evaluation use pull-out tests, which do not correspond to the actual tensile state around the bars in elements submitted to bending. Therefore, in this work, in addition to the evaluation of bond strength in GFRP Brazilian bars, using a test methodology never published in Brazil, one was able to verify the contribution of polyolefin fibers to bond in self-compacting concrete for the use of bars in GFRP. This solution of bars in GFRP and reinforced concrete with polyolefin fibers represents a breakthrough in terms of durability, since none of the materials is subjected to metallic corrosion, unlike traditional metal reinforcements. It was found that longer splice lengths of reduced bond tension, as reported in several studies, increasing the ultimate load of the beams, the use of polyolefin fibers increased the maximum bond tension by up to 57% and the ultimate load by up to 12.87%. The contribution of polyolefin fibers is more relevant for shorter splice lengths. The rupture pattern is compatible with splice rupture.