Influence of fine aggregate type on geopolymer mortar performance in an elevated temperature environment

This paper focuses on developing a sustainable, high-temperature-resistant geopolymer mortar by selecting the most optimal fine aggregate type for high-temperature conditions. The developed building material has superior properties to conventional concrete and could possibly be significant in the context of fire-safety building materials. Ceramic brick waste (CBW) from open landfills and metakaolin waste (MKW) from an expanded glass production company (Lithuania) were used as precursor materials in a geopolymer system. The precursors were systematically substituted from 0 to 100% weight in five distinct compositions (F1-F5). The alkaline activator was a blend of 8 M sodium hydroxide and sodium silicate (Na₂SiO₃/NaOH = 1.5). Five types of fine aggregates were examined: ordinary river sand (OSA), granite (GRA), basalt (BAS), ceramic waste (CBW), and corundum (COR), with a fraction size from 0 to 3 mm and the constant fine aggregate to precursor (FA/P) ratio of 1.5. Geopolymer mortar specimens were prepared to assess their compressive strength and density before and after exposure to high temperatures ranging from 200 to 800 °C. A two-way analysis of variance (ANOVA) was conducted to evaluate the reliability of the residual compressive strength outcomes. The study showed that properly selected fine aggregates in an appropriate binder system improves high-temperature resistance. After 800 °C exposure, mortars with 75% CBW and 25% MKW precursors containing CBW and COR aggregates exhibited minimal microcracking and residual strengths of 34.7 MPa (78.7%) and 53.0 MPa (108.6%), respectively. This performance is attributed to partial reactivity, low thermal expansion, and inherent thermal stability.