Chiang Mai Journal of Science

Advantages of both pure fly ash and fly ash-based granules used for the production of unfired brick were studied. Granules were prepared by using either pure fly ash or the mixture of 95% fly ash and 5 % hydrated lime (Ca(OH)₂). The pellets were left moistly for 30 days and 4 days for pure fly ash granules and for fly ash based granules, respectively, before being studied by SEM, EDS and XRD. Unfired bricks made of those granules were as well observed after hydrothermal treatment at temperature of 125-140^oC and pressure of 1.2-1.5 kg/cm². New phases grew on both types of granules mostly appearing as needle-like and fibrous-like particles depending on the amounts of water used for mixing and fly ash particle size. Investigated by XRD, the new developed phases consisted of chabazite, montmorillonite and calcium silicate hydrate. The advantage of granule production was producing a high ability to retain more available moisture for the pozzolanic reaction of fly ash. For the preparation of unfired bricks, the mixture of 90% fly ash and 10% hydrated lime was used to produce granules before forming into bricks. A mesh-like coating as a secondary phase appeared to be impregnated in the matrix observed by SEM.