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.
Dheyaaldin et al. (Sun,) studied this question.