Performance of foam concrete containing low-temperature calcined clay as a partial replacement of Portland cement

This study investigates the use of low-temperature calcined clay (metakaolin) as a partial replacement for ordinary Portland cement (OPC) in foam concrete. This study aims to enhance sustainability by reducing carbon emissions and promoting the use of alternative binders. Foam concrete mixtures were prepared using the pre-foamed method with target densities of 600, 800, and 1000 kg/m³, and water-to-binder (W/B) ratios of 0.5, 0.6, and 0.7. For W/B of 0.6 and 0.7, OPC was partially replaced with metakaolin (calcined at 650 °C for 2 h) at levels of 10 % and 20 %. Properties evaluated included fresh and dry density, workability, porosity, compressive and flexural strengths at 7, 14, and 28 days, ultrasonic pulse velocity (UPV), water absorption, thermal conductivity, and microstructure. Workability improved with increasing W/B ratio and density but decreased with higher MK content. Although thermal conductivity was largely unaffected by MK content and W/B ratio, both parameters significantly influenced strength, UPV, and water absorption. Thermal conductivity increased linearly with dry density, which also correlated with a significant increase in mechanical strength. Enhanced MK content and W/B ratios resulted in more uniform pore distribution and reduced connectivity, improving overall material performance. For dry densities ranging from 411 to 879 kg/m³, the foam concretes achieved compressive strengths of 0.60–6.45 MPa, flexural strengths of 0.27–2.11 MPa, UPV values of 1120–2268 m/s, and thermal conductivity in the range of 0.176–0.389 W/(m·K). Mineralogical analysis confirmed a decrease in calcium hydroxide and increases in calcium-silicate-hydrate (C–S–H), calcium-aluminate-(silicate)-hydrate (C–A–(S)–H), and calcium carbonate (CaCO₃) with MK incorporation, indicating enhanced pozzolanic activity. These results demonstrate that MK-modified foam concrete offers improved mechanical and physical properties suitable for insulating, non-load-bearing applications.