Sustainable activation of pumice with partially variable substitutions of metakaolin and/or fumed silica

Abstract

Sustainable alkali activation of pumice from Turkish origin was studied by a partial replacement of metakaolin and/or fumed silica additives. Following the characterization of as‐received pumice by X‐ray fluorescence spectroscopy, x‐ray diffraction, and nuclear magnetic resonance spectroscopy, a series of powder mixtures were prepared by introducing metakaolin and/or fumed silica (8, 14, and 20 M) into 1 M of the pumice. The mixtures were then dissolved in 11 M NaOH or sodium silicate solutions. The slurries were poured into polyacetal molds to obtain geopolymer samples for mechanical testing and cured in a constant 50°C temperature in a humidity oven for 48 h and then left for 1 week to undergo additional curing at ambient temperature. The microstructural, mechanical, and thermal properties of the final geopolymer samples were determined by XRD, scanning electron microscopy, Weibull analysis of 3‐point flexural and compressive tests and thermal conductivity measurements. Results showed that all the Weibull values were best for 14 M of metakaolin and/or fumed silica. The metakaolin‐added pumice yielded higher compressive strengths of (53.78 ± 33.30 MPa) than fumed silica (10.87 ± 4.04 MPa) and fumed silica plus metakaolin (41.22 ± 5.16 MPa). Thermal conductivities (0.19–0.46 Wm–1K–1) were also comparable to the thermal conductivity of metakaolin‐based geopolymers.