Synergistic effects of rice husk ash and extracted microsilica on the performance of high-strength concrete

The construction industry's urgent need for sustainable alternatives to ordinary Portland cement (OPC) has spurred significant interest in supplementary cementitious materials (SCMs). Therefore, this study investigates the synergistic effects of rice husk ash (RHA) and extracted microsilica (EMS) as partial replacements for cement in high-strength concrete (HSC). RHA was produced by controlled combustion of rice husk (RH) at 600-700 °C, while EMS was obtained through an optimized extraction process. Along with control mix (CM), three ternary mixes incorporating 15-35% RHA and 5-15% EMS were investigated to evaluate their effects on the mechanical and durability properties, as well as microstructural characteristics. Experimental results demonstrated that samples containing 20% (5% EMS + 15% RHA) and 35% (10% EMS + 25% RHA) as cement replacement exhibited enhanced performance, increasing the 28-day compressive strength by 11.56% and 5.98%, respectively, as compared to conventional concrete. Durability assessments of the optimal mixes revealed a significant reduction in water absorption (WA) and permeability. Physiochemical characterization confirmed the increased formation of dense calcium silicate hydrate (CSH) gels and a reduction in portlandite content, indicating high pozzolanic reactivity. However, the 50% replacement mix (15% EMS + 35% RHA) showed inferior performance due to the particle agglomeration and higher porosity. This study shows that the strategically formulated combinations of EMS and RHA blends (up to 35%) can produce sustainable HSC with improved mechanical properties and durability while mitigating environmental impacts. These findings provide valuable insights for advancing eco-friendly construction materials, supporting global sustainability initiatives in infrastructure development.