Temperature Dependence of thermal Conductivity of Different Geopolymer Materials for Green Building Applications

Three types of geopolymer were produced by using flying ash, sodium hydroxide and sodium silicate for recycling the waste of coal-fired power plants. The goal was to prepare an alternative inorganic insulation material that can be used even in wet conditions and provide a substitute material for cement-based products. Thermal conductivity was investigated in different mean temperatures, ranging from −5 to 40 °C which are the most common operational temperatures in a temperate climate zone. Beside the components of the three samples, the geometrical size and distribution of voids were investigated to determine their effect to the values of thermal conductivity. Results showed that the size, the bulk density and numbers of voids greatly affected the thermal conductance. Specifically, the foam with the lowest density and smallest voids provides the best thermal insulation, with thermal conductivity values up to 18% lower across the temperature range. In contrast, foams with larger and interconnected voids showed increased thermal conductivity due to enhanced internal convection mechanisms, particularly near 4 °C. The findings highlight that controlling void size (≤ 1 mm), and preventing inter-void connectivity are critical for optimizing low-density geopolymers as insulation materials. This research contributes practical insights for designing durable, low-carbon, and moisture-resilient thermal insulation suitable for green buildings.