Thermal properties of novel binary geopolymers based on metakaolin and alternative silica sources

•Novel binary and ternary geopolymers were prepared using alternative soluble silica.•The alternative silica making the production of geopolymer environmentally friendly•The thermal properties are associated with the cumulative pore volume.•The G-RHA shows the lowest thermal conductivity (0.17 J/m·K) and 35% open porosity.•The materials developed show potential thermal insulation applications for building.

The objective of this study was to evaluate the thermal properties of geopolymers based on metakaolin (MK) and alternative silica-based activators. These activators were produced by mixing rice husk ash (RHA) and silica fume (SF) with potassium hydroxide (KOH). In addition, boiler slag (BS) was used as partial substitute for the MK aluminosilicates precursor. The thermo-physical properties of the geopolymers prepared with alternative activators were compared to geopolymers activated with commercial potassium silicate (KS). In general, thermal conductivity, diffusivity and specific heat are related to porosity of the geopolymer. The values of thermal conductivity were between 0.170–0.353 W/m·K. The coefficient of thermal expansion varies between 1.06 and 1.13 × 10− 4 K− 1 and the thermal diffusivity was 0.16–0.27 mm2/s. The geopolymer with RHA (G-RHA) showed low bulk density (1338 kg/m3) and high porosity (35%). Additionally this material has the lowest thermal conductivity (0.17 W/m·K) and thermal diffusivity (0.16 mm2/s). The results obtained show that geopolymers here developed can be considered potentially useful for applications such as thermal insulation. In addition, they constitute a better ecological choice because of the type of source of alkaline activator making their production environmentally friendly.