An investigation on alkali-activated fly ash pastes modified with quartz powder subjected to elevated temperatures

In this study, the opportunity of employing quartz powder (QP) to improve the workability as well as the compressive strength of alkali-activated fly ash (AAFA) pastes before and after exposure to thermal loads has been investigated. Fly ash (FA) was partially substituted with QP at percentages ranging from 0% to 30% with an interval of 5%, by weight. After curing, specimens were exposed to different thermal loads ranging from 400 °C to 1000 °C with a step of 200 °C with a heating rate of 6.67 °C/min for 2 h. Weight and compressive strength of the investigated specimens before and after being heating were exhaustively conducted. The different decomposition phases formed upon exposure to thermal loads were detected using X-ray diffraction (XRD) and thermogravimetric (TGA) techniques. The microstructure of the formed hydration products was determined by scanning electron microscopy (SEM). The results showed that the workability as well as compressive strength before and after firing improved by increasing QP content.