Insulating and fire-resistant behaviour of metakaolin and fly ash geopolymer mortars

Abstract

To achieve the highest thermal insulation and the lowest carbon dioxide emissions, different geopolymer mortar types with low thermal conductivity, reasonable compressive strength and high fire resistance were investigated and compared with traditional cement mortar (TCM). Two different types of aluminosilicate materials, namely metakaolin (MK) and fly ash (FA), were used as source materials. Either natural river siliceous sand or expanded perlite (EP) was used as fine aggregate. Each source material and selected fine aggregate was mixed and activated with sodium silicate. After curing, density and thermal conductivity values were measured. The compressive strengths of the mortars before and after being subjected to 600°C for 2 h was determined. The results show that it is possible to use MK-based and FA-based geopolymer mortars without adding any foaming agent as insulation and fire-resistant materials. The different geopolymer mortar types exhibited ∼33·57–73·57% lower thermal conductivity and 83·87–115% higher compressive strength than the TCM. The MK-based geopolymer mortars proved to have higher fire resistance than FA-based ones, while the FA-based geopolymer mortars proved to have higher thermal insulation than the MK-based mortars. The use of EP as fine aggregate resulted in much higher thermal insulation and better fire resistance than siliceous sand.