Improving the bond between polypropylene fiber and cement matrix by nano calcium carbonate modification

• Polypropylene (PP) fiber is modified with nano calcium carbonate. • Fiber surface roughness and adjacent hydration product are both enhanced. • Improved fiber/cement matrix bond is observed via single fiber pullout test. • Chemical bond is confirmed after fiber modification via the same test. • Flexural properties of concrete with modified fibers are also improved. Polypropylene (PP) fibers are commonly used for reinforcing cementitious composites due to their reasonable strength, good chemical stability and relatively low cost. However, chemically inert surface causes relatively inferior bond with cement matrix. Therefore, this study applies nano calcium carbonate to modify the surface of polypropylene fibers. After modification, the surface roughness increased and dense hydration product with high hydration degree can be generated around the fiber surface. Single-fiber pullout tests confirmed chemical bonding and bond strength of fiber/cement matrix interface were enhanced by modification. Although frictional bond between modified fibers and cement matrix decreased slightly, more energy can be absorbed than normal PP/cement matrix interface during fiber slippage. Flexural properties including peak resistance and energy absorption were improved when modified PP fibers were incorporated into cementitious composites. In summary, surface coating treatment by nano calcium carbonate is a promising approach to modifying surface properties of polypropylene fibers to enhance bond performance with cement matrix, which may facilitate the application of PP fibers in fiber-reinforced cementitious composites (FRCC) for enhanced strength and ductility.