Sustainable fibercement reinforced composites: flexural enhancement and microstructural evolution with rice husk-derived silica micro and nanoparticles

Fibercement is a lightweight and highly resistant material composed of cement, additives, and fibers and is mainly used in lightweight construction systems. This study investigates the effect of incorporating micro and nanosilica particles derived from rice husk into fibercement composites, aiming to enhance their mechanical performance and sustainability. Fibercement samples were prepared with varying silica concentrations (0, 1, 3, 5, and 7 wt.%) and cured for 28 days under ambient conditions. The composites were characterized in terms of density, water absorption, flexural strength, thermal stability, morphology, and phase composition. X-ray diffraction showed the formation of hydration products such as tobermorite, and with silica addition reducing portlandite content, indicating a pozzolanic reaction. Scanning electron microscopy confirmed improved fiber-matrix entanglement and densification of the microstructure. Thermogravimetric analysis corroborated the reduction in portlandite and carbonate phases with silica addition. The flexural strength improved with silica addition: samples with 5 wt.% micro and nano silica exhibited increases of 48.1% and 71.6%, respectively, compared to the control sample. Although higher silica contents slightly increased water absorption and reduced density, all samples met the NTC 4694 standards for fibercement products. These results demonstrate that rice husk-derived silica, especially in nanoparticle size, enhances the mechanical and structural performance of fibercement composites, offering a sustainable alternative for the construction industry.