Synergistic Effects of Fiber Hybridization on the Mechanical Performance of Seawater Sea-Sand Concrete

This study investigated the effect of hybrid fibers and their synergic interactions on the mechanical properties of seawater sea-sand (SWSS) concrete. These properties include compressive strength, elastic modulus, splitting tensile strength, compressive stress-strain behavior, and ductility, as well as slump and air content. Two hybridizations were incorporated: hybrid micro-fibers (hybridization of the type of fibers) and hybrid micro- and macro-fibers (hybridization of the length of fibers). The hybrid fibers comprised three micro-fibers—polypropylene (PPS), polyvinyl alcohol (PVA), basalt (BF)—and two macro-fibers—polypropylene (PPL), and twisted polypropylene (TPPL)—with a total volume fraction of 0.25%. The findings revealed that if designed properly hybrid micro-fibers can outperform mono-fibers in mechanical properties and ductility, bridging micro-cracks. This study revealed that incorporating PVA/PPS and BF/PPS hybrid micro-fibers enhanced both interlocking, facilitated by the chemical bonding of PVA and BF, and elongation, enabled by PPS. This synergistic effect led to a significant 33–35% increase in compressive elastic modulus compared to mono PPS fibers. At the same total dosage of fibers, PVA/BF hybridization significantly improved SWSS concrete total energy absorption and residual strength under compression by 44% and 181% over mono BF incorporation. Increasing BF in hybrid fibers significantly reduced ductility and increased brittleness. In PVA/PPL hybridization, PVA fiber improved PPL bonding strength and tensile capacity through chemical bonding with concrete, enhancing ductility and residual strength under compression by 59% and 65% over mono PPL fiber. Overall, hybrid fibers improved the mechanical properties and ductility of SWSS over mono-fibers. This was due to positive synergy and inter-fiber performance due to mechanical and chemical bonding, overcoming individual fiber type limitations (e.g., poor bonding, tensile strength, or ductility). This effect was more pronounced with micro- and macro-fiber hybridization. The findings of this study can be used to provide an improved performance for SWSS concrete by adding hybrid fibers to the mix considering the synergic interactions of fibers.