Enhancement of geopolymerization reactivity and thermal resistance using mixed types of fly ash

Geopolymer prepared with class C-fly ash (FA) often suffers from the flash geopolymerisation rate, making it difficult for working. Class F-FA, however, may have a low reactivity so admixture must be added to solve this problem. This research highlighted the use of mixed class C - and class F-FA as a precursor for geopolymer preparation to alleviate the above problems. Optimization of the precursor recipe and the solid to liquid ratio (S/L) was assessed. The highest compressive strength (30.54 MPa) and the suitable initial (136 min) and final (240 min) setting times were obtained with S/L = 2.00, and 50:50 of class C to class F-FA. The fire resistance test on a 10 mm-thick geopolymer panel at 1000°C for 180 min showed a maximum temperature of ∼570-580 °C on the reversed side without catastrophic failure, suggesting the ability to use in a fire retardation application.