Flexural Performance of Concrete Slabs Reinforced with GFRP Bars and Long Polypropylene Fibers

This paper presents the results of experimental studies describing the response of concrete slabs reinforced with GFRP composite bars to bending forces. The experimental program consisted of five slabs reinforced with GFRP bars, divided into two groups differing by the dosage of long polypropylene fibers (LPPF) and concrete specification. The mixture for the GFRP-LPPF group was prepared using a basalt aggregate base to achieve high-strength concrete. The load bearing capacity was determined experimentally to compare the results of LPPF-enhanced slabs with a control group of GFRP slabs without fiber addition. As part of the experiments, deflections and specific crack kinematics were observed using Digital Image Correlation (DIC) technology, providing a detailed investigation of slab behavior supported by high-resolution camera records. Subsequently, the experimental data were compared with ACI standard predictions to define the theoretical-to-experimental capacity ratio. The study provides new data concerning the behavior of GFRP slabs strengthened with LPPF, highlighting key observations such as the percentage increase in load capacity, deflection at failure, crack width reduction, and energy absorption. Furthermore, the results demonstrate that the hybrid reinforcement system significantly enhances the post-cracking ductility of the elements, mitigating the typical brittleness of GFRP-reinforced sections. These findings suggest that integrating LPPF into high-strength basalt concrete offers a viable strategy for improving the serviceability and structural integrity of composite-reinforced infrastructure.