Impact of FRP rebar and fiber on concrete cracking

This research explores two key strategies to reduce durability issues. The first part of the study investigates the impact of the shape and texture of Fiber Reinforced Polymer (FRP) rebars to resist cracking in concrete. FRP rebars were tested using the split beam test and crack widths at different loads were compared for seven different types of FRP rebars and one steel rebar with a diameter of 10 mm and 13 mm. The performance of the FRP bars varied based on the shape and texture of the rebar. FRP rebars with deformations that are wider, with a greater height, and more surface roughness performed the best. One FRP rebar reduced crack widths at service loads by 30% compared to a steel rebar because of improvements in the shape of the FRP bar despite the FRP bar having an elastic modulus three times lower than the steel rebar. Other FRP with less desirable shape exhibited crack widths that are 70% larger than a steel rebar. This shows that the bonding created by rebar with improved shape and texture is more important than the rebar stiffness to reduce cracking in concrete. Next, the second part of the study quantifies the cracking and finishability of fiber reinforced concrete with the split beam test and the float test. Nine different macro synthetic fibers were tested at dosages of 0.25%, 0.5% and 0.75% by volume and three different steel fibers were tested at dosages of 0.25%, 0.33% and 0.5% by volume. The investigation shows that the fibers can reduce the crack width by up to 80% compared to the control sample that only has rebar. The findings also indicate that the crack reduction depends on the fiber dosage, material type, fiber length and surface texture. Polypropylene fibers and steel fibers with a smooth surface and sufficient fiber length showed superior performance. The study also highlights that high fiber dosage may reduce cracking but can compromise the finishability of the concrete. This suggests that a lower fiber dosage of 0.25% and 0.5% provides improved cracking and satisfactory finishability. Together, these studies provide valuable insights to optimize the fiber and FRP selection for concrete and help engineers to improve the durability and constructability of concrete structures.