Ballistic impact and mechanical strength of cement-composite mortars: The role of lignosulfonate-treated sisal and piassava fibers

ABSTRACT Natural lignocellulosic (NLF) have emerged as sustainable reinforcements for mortars and concrete, however, fiber-matrix incompatibility remains a major challenge. This study investigates the use of sodium lignosulfonate (NaLS) to treat piassava (Attalea funifera) and sisal (Agave sisalana) fibers, aiming to improve their properties in cementitious composites. Fly ash (FA) and metakaolin (MK) were incorporated as supplementary cementitious materials (SCM) to lower matrix alkalinity and prevent degradation. For the first time, the impact of NaLS on the mechanical and ballistic performance of mortars with MK and FA as SCM was evaluated. Results showed that NaLS treatment improved fiber-matrix bonding, reduced porosity at the interfacial transition zone (ITZ), and mitigated fiber mineralization, particularly in sisal composites. NaLS-treated sisal fibers significantly enhanced ballistic energy absorption (+9.3%) compared to the unreinforced matrix, with no significant modifications in compressive and split tensile strength. In contrast, NaLS-treated piassava composites exhibited decreased tensile and compressive strengths, due to higher degree of fiber mineralization, with negligible change in ballistic performance. Microstructural analysis confirmed that the treated fibers promoted a denser ITZ and better interface quality, highlighting the critical role of fiber treatment in optimizing NLF-reinforced cementitious composites.