Effect of Calcium Hydroxide addition on mechanical and thermal performance of fly ash geopolymers

Abstract

In this research, the effect of calcium hydroxide addition on mechanical and thermal performance of fly ash geopolymer is being investigated. Ca(OH)₂ was added in fly ash geopolymer with 0%, 2% and 4% with the various thermal exposure temperature at 200°C, 400°C, 600°C, 800°C and 1000°C. Compressive test show that fly ash based geopolymer with the addition of 2% of Ca(OH)₂ and thermal exposure of 200°C resulted in the formation of a high strength (40.421 Mpa) geopolymer. Visual examination shows that increasing the elevated temperatures from 600°C up to 1000°C will cause the thermal cracks distribution and width appearing on the specimen whereas bulk density shows density of the of the fly ash geopolymer cube decreasing from 0.001784 to 0.00146 g/cm³ as the mass percentage of Ca(OH)₂ and the temperature exposure increase. From the infrared spectra of the functional group analysis (FTIR), the major functional group that can be observed in the geopolymer are stretching vibration of Si-O-T(T=Al, Si), stretching vibration of O-C-O, strong and broad stretching vibrations of O-H and H- bonded and O-H bending. Fly ash geopolymer with the addition of 2% Ca(OH)₂ at 200°C indicates the highest intensity of Si-O-T (T=Al, Si) bonding. For the conclusion, the addition of 2% Ca(OH)₂ at 200°C thermal exposure is the most suitable in order to increase the strength of fly ash geopolymer.