Characteristics of Silica Fume Nano Alumina Ternary Blended Mortar

This study investigates the contribution of nano-alumina (nA: 1-3 wt.% binder) to the performance of silica fume (SF-10%) and ordinary Portland cement (OPC) binary blended mortar. Microstructural analysis and qualitative characterizations examined the fresh (workability, setting time) and hardened (compressive strength and thermal resistance; 300 degrees C for 1 h) properties. Nano alumina (nA) contributed positively to the consistency of SF blended mortar but negatively to that of OPC mortar. The presence of nA retarded the reactivity of calcium and the fluid absorption capacity of SF in the fresh mortar. The initial (180 min) and final (220 min) setting times in SF blended mortar were reduced by 18.4 and 21.8%, respectively, upon adding up to 3% nA. The optimum nA was 2% in the SF-nA ternary blended mortar with 3-d and 28-d compressive strengths of 28 and 43.2 MPa, respectively. These values were reduced by 14.3% and 29.4% in SF-OPC (binary) and 25.2% and 16.7% in OPC mortar, respectively. The nepheline and tobermorite in the SF-nA ternary blended binder provided a denser microstructural density than in SF-OPC and OPC mortars. Finally, SF-nA ternary mortar was more susceptible to carbonation due to the presence of aluminum and calcium carbonates, despite its superior performance in thermal resistance and strength compared to SF blended and OPC mortars.