Investigation on the Bond Behavior Between GFRP Bar and Polypropylene Fiber-Reinforced Concrete with Pull-out Test

Concrete and rebars should have a good bond behavior so that there is no slip between rebars and concrete under the service loads. On the other hand, one of the major disadvantages of steel bars is their vulnerability to corrosion. Covering bars as a solution is also costly and cannot be implemented in all projects. So one of the most suitable alternative methods is the use of GFRP bars. Other ways to compensate for the weakness of the concrete tensile strength as well as its low ductility are the use of different fibers. Concrete with polypropylene fibers is highly ductiled compared to conventional concrete and is completely scattered in concrete and creates isotropetic conditions and can prevent cracks. Therefore, in this study, the effect of polypropylene fibers on concrete compressive strength and bonding strength between concrete and GFRP rebar was investigated experimentally. For this purpose, the amount of this type of fiber is selected 0.15, 0.30 and 0.45 % volume of concrete, and 15cm cubic concrete samples were made in three types of 350, 400 and 450 grade and were cured at 7- and 28-day ages. In this study, the rebar diameter of GFRP was chosen 8 mm and rebars were embedded inside the concrete in a length five times the rebar diameter, and 28-day concrete samples were tested through pull-out and compressive resistance tests. Finally, the compressive strength of the samples and the force-time curves from the pull-out test were assessed. Average compressive strength values, slump values, maximum force and other important parameters were discussed. The results showed that the bond resistance between the polypropylene fiber-reinforced concrete and GFRP rebar increased with the increase in the amount of fibers. Adding fibers also has a relatively good effect on enhancement of the compressive strength of the concrete.