Properties of fly ash-based lightweight-geopolymer mortars containing perlite aggregates: Mechanical, microstructure, and thermal conductivity coefficient

Abstract

It is known that studies on lightweight geopolymer using fly ash need more research. Therefore, in this study, class F fly ash-based lightweight geopolymer mortar samples were produced by using river sand, raw perlite, and expanded perlite as aggregates. The study was planned in two groups. In the first group, river sand, raw perlite, and expanded perlite were used as aggregates. In the second group, raw perlite and expanded perlite were used as aggregates. Expanded perlite replacement rates in both groups were determined as 0%, 20%, 40%, 60%, 80%, and 100%. The produced geopolymer mortar samples were cured at 75 °C for 24 and 48 h. After heat curing, unit weight, ultrasonic pulse velocity, water absorption, porosity, thermal conductivity coefficient, and flexural and compressive strength tests were performed on the samples. In addition, the elevated temperature resistance of the geopolymer mortar samples was tested at 300 °C, 600 °C, and 900 °C temperatures. Moreover, the microstructures of geopolymer mortar samples before and after elevated temperature were examined using a field emission scanning electron microscope. According to the results obtained, with the use of raw and expanded perlite, unit weight, UPV, flexural and compressive strengths of geopolymer mortar samples decreased, while water absorption and porosity increased. Using raw and expanded perlite resulted in an increase in the thermal insulation performance of the geopolymer mortar samples. Furthermore, the use of expanded perlite in geopolymer mortar samples increased the strength of geopolymer mortar samples exposed to elevated temperatures of 900 °C.