Strength behavior of laterite blocks enhanced with kaolin, metakaolin and sisal fiber at different fiber aspect ratios

Laterite blocks offer a low-carbon alternative to conventional masonry units, but their wider application is constrained by low mechanical strength and brittle behavior. Pozzolanic stabilization using kaolin and metakaolin, combined with natural fiber reinforcement, presents a promising approach to enhancing strength performance; however, the combined influence of binder type, binder content, and fiber aspect ratio on laterite block strength remains insufficiently understood. This study investigated the compressive and tensile strength behavior of laterite blocks stabilized with kaolin and metakaolin at binder contents ranging from 0% to 15%, with and without sisal fiber reinforcement at varying fiber contents and aspect ratios. Compressive and tensile strength tests were conducted on replicated specimens. Statistical analysis comprised descriptive statistics, HC3 robust two-way ANOVA, Welch ANOVA, Games-Howell post hoc tests, and effect size estimation using partial eta-squared. The binder type and content had statistically significant effects on both compressive and tensile strength, with strong interaction effects observed. Metakaolin-stabilized blocks consistently outperformed kaolin-stabilized blocks, achieving higher strength values across all binder contents. Optimal compressive strength occurred at approximately 9% binder for kaolin and 12% binder for metakaolin. Sisal fiber reinforcement significantly enhanced strength up to an optimum fiber content, beyond which strength declined. Optimal fiber contents were identified as approximately 0.75% for kaolin-stabilized blocks and 0.38% for metakaolin-stabilized blocks. Tensile strength exhibited greater sensitivity to fiber reinforcement than compressive strength. The results demonstrate a strong synergistic effect between metakaolin stabilization and sisal fiber reinforcement when the fiber content and aspect ratio are optimized. Carefully designed metakaolin-sisal systems substantially improve the mechanical viability of laterite blocks, supporting their use as sustainable, low-carbon masonry materials.