Effect of nano-silica on the thermal resistance and mechanical properties of pumice-blended cement pastes

Abstract

Ordinary Portland cement (OPC) is essential in contemporary building, and the incorporation of supplemental cement materials (SCM) has emerged as a global need to mitigate carbon dioxide emissions, detrimental environmental impacts, energy usage, and resource exhaustion in cement manufacturing. Therefore, the purpose of this investigation was to evaluate the feasibility of pumice as a substitute for cement and its influence on the thermal resistance. OPC–pumice composites containing 0, 15, and 20 wt% replaced pumice were prepared and modified with nano-silica (NS) (0.5, 1, and 2 wt%) to enhance mechanical performance and thermal stability and cast into 25-mm cubes (n = 4 per condition). Hardened pastes (w/b = 0.26) were evaluated at early and later hydration ages and after exposure to elevated temperatures (250, 500, and 850 °C) under different cooling regimes, with performance assessed primarily through compressive strength. According to the findings, the inclusion of NS enhanced hydration properties, decreased free lime, and increased chemically combined water content. Thermal stability was significantly enhanced at 500 °C with negligible deterioration in compressive strength. The ideal NS addition for OPC + 15% pumice is 1% by mass. The recorded strength values for various pastes heated at 500 °C and subjected to incremental cooling show that the specimens’ residual compressive strength (RCS) increased by 2%, 7%, 10%, and 9.60% RCS for the CP1, CP1NS1, CP1NS2, and CP1NS3 pastes, respectively. XRD, TG/DTG, and SEM analyses showed the presence of poorly crystalline and nearly amorphous C-S-H, C-A-S-H, and C-A-H. Pumice-blended cement pastes’ mechanical and thermal performance are greatly improved by nano-silica. The ideal NS addition for OPC + 15% pumice is 1% by mass to improve fire resistance and develop strength.