3027 2025 eng 24 13 17 article MDPI Basel 0 -- 2025-07-02 -- Noncorrosive concrete reinforcement, such as polymer fibers, is needed to overcome the current issues caused by corroded steel reinforcements. Fibers made of polypropylene show a low bonding behavior in concrete. Fillers can help to overcome this issue but often lead to reduced mechanical properties. Core-shell fibers, which split the mechanical properties and the bonding behavior between the core and the shell component, could be a solution. This study investigates mono-material and core-shell fibers produced with calcium carbonate and bentonite fillers and compares their behavior in tensile tests, density measurements, contact angle measurements, topography measurements, single fiber pull-out tests, reflected light microscopy, and thermogravimetric analysis. The fillers caused an increased drawability, resulting in higher mechanical properties. Further, in the core-shell fibers, the calcium carbonate increased the surface roughness, which led to a better anchoring of the fiber in concrete, which was also visible in the deformation during pull-out observed in reflected light microscopy pictures. The thermogravimetric analysis showed a delay in onset of degradation for fibers containing bentonite. Polymers 10.3390/polym17131781 Ja Ja publish false false 2 Jonas Herz Dirk Muscat Nicole Strübbe eng uncontrolled fibers eng uncontrolled extrusion eng uncontrolled coextrusion eng uncontrolled polymer drawing eng uncontrolled polypropylene eng uncontrolled calcium carbonate eng uncontrolled bentonite eng uncontrolled core-shell eng uncontrolled mono-material eng uncontrolled concrete Fakultät für Ingenieurwissenschaften Zentrum für Forschung, Entwicklung und Transfer Technische Hochschule Rosenheim