Changes in compressive strength, microstructure and magnetic properties of a high-calcium fly ash geopolymer subjected to high temperatures

In this paper, changes in the compressive strength, microstructure and magnetic properties of a highcalcium fly ash geopolymer subjected to elevated temperatures were studied. Geopolymer paste specimens were exposed to temperatures of 60, 200, 400, 600, 800, 1000 and 1200 degrees C with an increase rate of 5 degrees C/min, followed by a 60 min calcination period and natural convection cooling to ambient temperature for each cycle. The compressive strength of the geopolymer paste after being subjected to the temperature of 200 degrees C was increased due to further geopolymerization reaction. It was reduced at higher temperatures due to several factors such as dehydration, crack and disintegration of the geopolymer gel. The structural analysis indicated new phases formation especially at 800 degrees C. The magnetic properties of the high calcium geopolymer paste remained relatively unchanged up to 600 degrees C. After that, they decreased significantly with increasing temperature and switched from ferromagnetic to paramagnetic. (C) 2020 Elsevier Ltd. All rights reserved.