Effect of Cold Plasma Treatment of Polymer Fibers on the Mechanical Behavior of Fiber-Reinforced Cementitious Composites

Fiber-reinforced cementitious composites (FRCC) are a class of materials made by adding randomly distributed fibers to a cementitious matrix, providing better material toughness through the crack bridging behavior of the fibers. One of the primary concerns with FRCCs is the behavior of the fiber when a crack is formed. The fibers provide a stress-bridging mechanism, which is largely determined by the bond that exists between the concrete and the fiber’s outer surface. While many studies have determined the properties of FRCCs and potential benefits of using specific fiber types, the effects of low temperature or cold plasma treatment of polymer fibers on the mechanical behavior of the composite material are limited. Polymer fibers are notable for their low density, ductility, ease of manufacture, and cost-effectiveness. Despite these advantages, the surface properties of polymers do not enable the bonding potential given by steel or glass fibers when used in untreated FRCC, resulting in pull-out failures before the full displacement capacity of the fiber is utilized. For this reason, modification of the surface characteristics of polymer fibers can aid in higher bonding potential. Plasma treatment is a process wherein surfaces are modified through the kinetics of electrically charged and reactive species in a gaseous discharge environment. This paper is a preliminary study on the use of atmospheric pressure plasma generated at approximately room temperature. This atmospheric, cold plasma treatment is a method for improving the mechanical properties of FRCC using polymeric fibers. In this study, polypropylene and polyvinyl-alcohol fibers were cold plasma treated for 0, 30, 60, and 120 s before being used in cementitious mortar mixtures. Compression and flexure tests were performed using a displacement-based loading protocol to examine the impact of plasma treatment time on the corresponding mechanical performance of the fiber-reinforced cementitious composite. The experimental results obtained from this study indicate that there is a positive correlation between fiber treatment time and post-peak load-carrying capacity, especially for specimens subjected to flexural loading.