Comparative thermal and mechanical performance of geopolymers derived from metakaolin and fly ash

This paper presents comparative thermal and mechanical performance of geopolymers derived from metakaolin (MK), fly ash (FA), and their combinations. Bending and compression tests, thermogravimetric analysis, scanning electron microscopy and energy dispersive spectrum, mercury intrusion porosimetry, and dilatometric tests were conducted on three types of geopolymers (MK, MK-FA, and FA based) to evaluate comparative mechanical properties, thermal behavior, and microstructure. Results from these tests show that MK-based geopolymers experience significant thermal shrinkage, high mass loss, and large strength degradation after exposure to high temperatures up to 800°C. FA-based geopolymers exhibit low bending and compressive strength at ambient temperature due to incomplete reaction of fly ash particles and high retention in compressive strength at high temperature, and this is facilitated from the formation of large size pores as channels to release vapor pressure and sinter reaction of fly ash particles. However, blended MK-FA-based geopolymers exhibit higher bending and compressive strength both at ambient temperature and after exposure to high temperatures up to 800°C and this is facilitated through the utilization of specific characteristics of both MK-based and FA-based geopolymers.