Impact of chloride corrosion on the pull-out resistance of recycled steel fiber in cement mortars

The study examined the pull-out behavior of crimped recycled fibers made from annealed and galvanized steel wires and compared it with commercial Dramix 4D fibers. These fibers were degraded in tap water and sodium chloride (NaCl) solutions with 3.5% and 7% concentrations. The objective was to evaluate how chloride-induced degradation affects the interfacial bond and mechanical performance of recycled steel fibers embedded in cement mortar. Unlike previous studies focused on commercial fibers, this work introduces recycled crimped fibers. It integrates pull-out, tensile, and compressive testing with SEM-EDS analysis to correlate corrosion with mechanical response. A total of 105 specimens were tested to determine maximum pull-out stress and toughness. Degradation tests were performed for 30 and 60 days, during which the compressive strength of mortars and the tensile strength of degraded fibers were also measured. Surface characterization was conducted by digital microscopy, Scanning Electron Microscopy (SEM), and Energy-Dispersive Spectroscopy (EDS). Annealed steel fibers showed the lowest corrosion resistance (8% mass loss), while galvanized fibers exhibited the highest (0.67%). After 30 days, chloride exposure caused slight mortar hardening and increased interfacial friction, raising pull-out forces for Dramix (=40%) and galvanized fibers (=7.5%). After 60 days, matrix weakening reduced adhesion and pull-out resistance, while the annealed steel fibers failed by rupture due to their high bond strength, with ductility decreasing up to 12.3%.