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

This study aims to optimize the mechanical performance, durability, and environmental sustainability of alkali-activated mortars (AAM) incorporating nano-silica (NS), nano-alumina (NA), and polypropylene fiber (PPF). A three-factor, three-level Central Composite Design (CCD) within the Response Surface Methodology (RSM) framework was employed, generating 17 experimental mixtures prepared using fly ash (FA) and ground granulated blast-furnace slag (GGBS) as binder materials. The maximum compressive strength of 82 MPa was achieved in the mixture containing 2% NA, while the maximum flexural strength (12 MPa) was recorded in the mixture containing 1% NS and 0.5% PPF. ANOVA results confirmed the statistical significance of the developed models, with R² = 0.984 and R² = 0.977 for compressive and flexural strength, respectively. Nano-alumina produced a greater increase in strength than NS, and the combination of both nanomaterials enhanced the density of the microstructure through the formation of C-(A)-S-H and N-A-S-H gels. The incorporation of PPF improved durability by preventing microcrack formation and enhancing resistance to acidic and saline environments. For example, specimens containing 2% NS and 2% NA demonstrated more than 20% higher residual strength under sulfuric acid exposure compared with reference specimens. Scanning Electron Microscopy (SEM) analyses showed that the nanomaterials accelerated early strength development by filling micro-voids and creating a more homogeneous matrix structure. A CO₂ emission analysis indicated that the optimized AAM mixture emits approximately 607.4 kg CO₂/m³, representing a reduction of about 26%. The results demonstrate that alkali-activated mortars provide a strong and environmentally sustainable alternative to conventional cement-based systems, highlighting the efficiency and practical potential of this approach.