Potential use of limestone in metakaolin-based geopolymer activated with H3PO4 for thermal insulation

Abstract The current article aims to elaborate an insulating material synthesized from metakaolin, limestone powder and phosphoric acid. For that purpose, metakaolin was activated with phosphoric acid to produce geopolymer paste. Afterward, metakaolin was partially replaced with limestone powder at ratios fluctuated from 1% to 5% with a step of 1%, by weight. After curing, the bulk density, total porosity, compressive strength and splitting tensile strength were measured at ages of 7, 28 and 91 days. The thermal conductivity was determined for the various mixtures after 28 days of curing. The results were analyzed by using sophisticated tools such as X-ray diffraction, thermogravimetric/its derivative, scanning electron microscopy and energy dispersive analytical X-ray. The results showed a good thermal insulation of all mixtures with an accepted compressive strength. The thermal insulation increased with increasing limestone powder content accompanying with higher total porosity and lower compressive strength.