Engineered bicomponent polypropylene fibers: Effects of mineral particles on spinnability, surface roughness, mechanical strength, and adhesion in cementitious matrices

Polypropylene (PP) fibers are widely used in fiber-reinforced concrete (FRC) and Strain-Hardening Cement-based Composites (SHCCs), to improve crack control, reduce plastic shrinkage cracking, and enhance ductility. However, their smooth surface and low chemical reactivity limit fiber-matrix interaction. The goal of this research is to develop engineered core-shell bicomponent PP fibers and improve their interfacial adhesion with cement-based binders by gradually increasing the amount of fine ground calcium carbonate (GCC) powder in the fiber shell. The influence of stepwise increasing GCC content on fiber spinnability, surface micro-roughness, and tensile strength, was assessed to optimize the particle content for stable and continuous spinning. Differential Scanning Calorimetry (DSC) revealed that GCC hinders the dynamic crystallization and affects the melting temperature, potentially influencing melt-spinning by altering flow behavior and solidification kinetics. Single fiber pullout (SFPO) tests demonstrated that fibers with optimized GCC content exhibited higher energy absorption due to increased surface micro-roughness, promoting mechanical interlocking with the matrix, as confirmed by scanning electron microscope (SEM) observations of localized matrix deformation. The SEM observations also suggested that GCC particles promote cementitious hydration phase growth after immersion in the cement solution. A threshold particle content of 20 vol% marked the transition from pullout-dominated to partial fiber breakage, while higher contents led to premature fiber rupture. These results demonstrate that GCC-induced surface roughness can effectively enhance microscale fiber–matrix interactions and energy dissipation during pullout.