Optimal Correlation between Thermal Insulation Properties of Fly Ash-Based Porous Geopolymer and its Strength Level

The work was focused on the qualitative improvement of porous fly ash-based geopolymer properties, by reaching a better correlation between the thermal insulation and mechanical strength properties of this product intended for application in construction. The starting mixture for preparing the geopolymer included type F-coal fly ash as an alumina-silicate precursor, silica fume as a nanomaterial, olive oil as a surfactant as well as an alkaline activator solution composed of potassium hydroxide and sodium silicate. After hardening the geopolymer paste at 70 ℃ for 24 hours, the curing process was carried out at room temperature for 7 and 28 days, respectively. Results showed excellent heat insulation properties (apparent density between 475-518 kg·m-3 and heat conductivity between 0.107-0.129 W·m-1·K-1) as well as high compression strength between 6.89-7.42 MPa (after 28 days) and in the range of 4.71-5.18 MPa (after 7 days).