Comprehensive experimental analysis of the effects of elevated temperatures in geopolymer concretes with variable alkali activator ratios

Abstract

By growing population and rapid urbanization, demand for concrete increases exponentially. Researches on use of fly ash material in waste product class for concrete production are important to produce concrete more environmentally friendly. However, there is a need for more research to use geopolymer concrete (GPC) in every field where ordinary Portland cement concrete (OPC) is used. Therefore, it is crucial to experimentally investigate thermal properties as well as mechanical properties of geopolymer concrete. As investigated thermal properties, the main factor affecting strength development of GPC is alkali activator ratios. In this study, GPC prism samples with nine different compositions, produced by various alkali ratios. After flexural strength tests, they were cut into cubes and exposed to 400 ◦C, 600 ◦C and 800 ◦C, then they were subjected to compressive strength tests. Results obtained from different AA/FA and SS/SH ratios were evaluated as mechanical properties at ambient temperature and physical, mechanical and microstructural properties at elevated temperature. An empirical formula, which considers the effect of activator ratios, was proposed to calculate flexural strength depending on compressive strength of samples at ambient temperature. As an increase of SS/SH and AA/FA ratios, compressive strength increased, while flexural strength decreased. The increase in AA/FA ratio decreased compressive strength of samples exposed to high temperatures, while increase in SS/SH ratio did not determine at elevated temperatures. There is an inverse change with AA/FA ratio and parallel change with SS/SH ratio between compressive strengths of samples at ambient temperature and exposed to high temperature.