Mechanical and thermal performance of fly ash (FA) geopolymer

Abstract

This research is carried out to study the mechanical and thermal performance of fly ash geopolymer exposed to high temperature. Fly ash (FA) is the waste product that can be the raw material to make geopolymers. The fly ash geopolymers were formed by alkali activation of fly ash with alkali activator (mixture of sodium silicate and sodium hydroxide). The fly ash geopolymers were cured at room temperature for 1 day. One set of the fly ash geopolymers was kept under room temperature until the day of testing. Other samples were subjected to elevated temperature (200 - 800˚C) for 2 hours. The samples were then tested and characterized on their compressive strength, bulk density, microstructure, functional group and thermal properties. The fly ash geopolymers exhibited density in the range between 1.65 - 2.08 kg/m3. The compressive strength of unexposed geopolymers was the highest and its strength decreased with increasing temperature. From the microstructural analysis, the geopolymers possessed combination of geopolymer matrix and unreacted fly ash particles. Cracks and pores were formed in the geopolymers due to loss of moisture from the structure. Based on FTIR analysis, geopolymer bonding at around 1400 cm-1 and 960 cm-1 were formed. No additional functional group was found after the high temperature exposure. On the other hand, the TGA analysis showed that water loss from geopolymers occurred in the range between 80-100˚C. This study shows that fly ash can merely sustain the high temperature environment. It is suggested to add fillers to further enhance the thermal properties of fly ash geopolymers.