Multiscale experimental investigation and molecular dynamics simulation of the performance enhancement of sisal fiber-reinforced concrete by sodium lignosulfonate

Sisal fiber-reinforced concrete (SiFRC) exhibits improved crack resistance and toughness; however, fiber agglomeration and weak fiber – matrix bonding limit its reinforcing efficiency. This study investigates sodium lignosulfonate (SL) as a multifunctional modifier for SiFRC by establishing the multiscale relationship among interfacial characteristics, microstructural evolution, and mechanical performance. The results showed that 0.4% SL achieved the optimum enhancement, increasing compressive and flexural strengths by 8% and 29%, respectively, compared with unmodified SiFRC, and by 16% and 82% compared with plain concrete. SEM observations revealed fewer visible interfacial defects and improved local fiber – matrix contact after SL modification. XRD and FTIR analyses indicated variations in hydration-related phase characteristics and chemical environments, suggesting the regulatory effect of SL on the cementitious matrix. Molecular dynamics simulations further demonstrated that SL improved C–S–H/SiF interfacial interactions by increasing adhesion energy, enhancing hydrogen bonding and ionic association, and reducing atomic mobility. These findings indicate that SL improves SiFRC performance through local microstructural optimization and enhanced atomistic interfacial interactions. The potential effect of SL on bulk fiber dispersion requires further three-dimensional verification. This study establishes a cross-scale mechanism linking SL-induced interface regulation with the mechanical enhancement of plant fiber-reinforced cement composites.