Synthesis of fly ash-calcined clay geopolymers: Reactivity, mechanical strength, structural and microstructural characteristics

The roles of addition of calcined clay (CC) to fly ash and fly ash to CC, on the reactivity, compressive strength, structural and microstructural properties of geopolymers were investigated. Fly ash-CC-based geopolymers containing 0, 25, 50 and 75% fly ash were synthesised using Na2SiO3/NaOH as an activator. X-ray Florescence, XRD, FTIR, ICC and SEM/EDX were applied to characterise source materials, study geopolymerisation processes and geopolymer properties. Calcined clay accelerated dissolution/hydrolysis of fly ash, while fly ash controlled the exothermic reaction that accompanied alkaline dissolution/hydrolysis of CC. The combined roles led to the production of geopolymer with improved properties and compressive strength of 36.7 MPa at 28 days.