Plasma Oxidation of Polypropylene Fibers for Concrete Reinforcement

In this project, the fibers were applied to increase the tensile strength of the concrete and produce fiber reinforced concrete (FRC). Polypropylene (PP) is employed as a fiber due to its economic benefit and richness. Based on the hydrophobic nature and lack of functional groups in polypropylene fibers, they could not bond efficiently with the concrete. Therefore, the hydrophilicity of the fibers was increased by the plasma oxidation technique for enhancing the tensile strength of the concrete. The effect of plasma oxidation time was explored on the pullout force, tensile strength, Young’s modulus, and the characteristics of six analyzed samples. The oxidation process was approved by XPS analysis, FTIR spectroscopy, and SEM techniques. Afterward, the strength of bonded fibers to concrete was measured at different degrees of oxidation by adding fibers to the concrete and pulling them out and it was confirmed by SEM images. Finally, the optimum plasma oxidation times for maximum adhesion of fibers to concrete were achieved at 3 min. The fibers which were oxidized at 3 min showed a 14.3% upgrade in stress compared to raw ones. Also, 3 min oxidized fibers embedded in concrete showed 47.8 and 97.16% improvement in tensile strength compared to raw fibers and 5 min oxidized fibers embedded in concrete, respectively. The XPS spectrum revealed 57.49% carbon and 32.47% oxygen, indicating the oxidation process on the fiber. The PP fibers have improved the transmission and control of microcracks at the microscopic level.