Comprehensive study of GFRP bar-concrete bond behavior using pull-out and three-point bending tests

The GFRP bar-concrete bond behavior is known to be influenced by factors such as bar surface
treatment, bar diameter, and concrete strength. This study aims to provide a comprehensive
understanding of the bond behavior of GFRP bars embedded in concrete. Pull-out specimens are
cast from two concrete batches with different compressive strengths. Two surface coating conditions
are considered, i.e., one with a lacquer finish and one without. Specimens with three
bonded lengths are used to determine the role of the bonded length in the bond mechanism (i.e.,
5db, 10db, and 20db, where db = nominal bar diameter). Two free end conditions of the pull-out
specimens are examined: one with the bar protruding at the free end and another with the bar cut
at the free end (i.e., the bar is cut flush with the concrete surface). The pull-out test responses are
analyzed in terms of applied load versus loaded end slip and free end slip. Three-point bending
(TPB) tests are conducted on concrete notched beams with two different widths (75 mm and 150
mm). Beams are either reinforced with a single GFRP bar or they are not reinforced and used as
benchmark. Notched beams are only cast from one of the concrete batches used for the pull-out
test specimens. This study shows how the protrusion of the bar can affect the bond strength in
pull-out tests. In addition, the different bond behavior of the GFRP bars observed in pull-out tests
and TPB tests of notched beams is discussed considering the length of the stress transfer zone for
bars with different surface conditions.