RSM optimized mechanical performance and chemical durability of nano silica, nano alumina fiber reinforced alkali activated mortar

This study investigates the mechanical performance, chemical durability, and environmental sustainability of alkali-activated mortars (AAM) reinforced with nano-silica (NS), nano-alumina (NA), and polypropylene fiber (PPF). Using a Central Composite Design (CCD) within Response Surface Methodology (RSM), 17 mixtures were prepared with fly ash (FA) and ground granulated blast-furnace slag (GGBS) as binders. The study achieved a maximum compressive strength of 82 MPa with 2% NA and a maximum flexural strength of 12 MPa with 1% NS and 0.5% PPF. ANOVA results confirmed the models' statistical significance, with R² values of 0.984 and 0.977 for compressive and flexural strength, respectively. Nano-alumina significantly improved strength compared to nano-silica, and the combination of both nanomaterials enhanced microstructure density through C-(A)-S-H and N-A-S-H gel formation. PPF improved durability by preventing microcracking and enhancing resistance to acidic and saline environments. Specimens with 2% NS and 2% NA showed over 20% higher residual strength under sulfuric acid exposure. SEM analyses revealed that nanomaterials accelerated early strength development by filling micro-voids and creating a homogeneous matrix. A CO₂ emission analysis indicated a 607.4 kg CO₂/m³ emission, representing a 26% reduction compared to conventional cement-based systems. The results demonstrate that AAM provides a strong and sustainable alternative to conventional mortars, highlighting its practical potential.