Two kinds of coal ashes were investigated about their reactivities. One was fly ash discharged from a pulverized coal combustion boiler and the other was FCB ash discharged from a fluidized-bed combustion boiler. Both of these ashes have similar chemical compositions because their origins are inorganic substances such as clay minerals, quartz and feldspars contained in coal. However, these ashes have considerably different structures and characteristics depending on the combustion temperature of the boilers.
The results of the investigations for practical utilizaton of these ashes are as follows.
(1) The formation of C2AS from FCB ash and limestone, as well as the decomposition of C2AS to C2S and C3A occured rapidly up to 1250°C. But the production rate of C3S from both of the ashes at higher temperatures didn't differ from that from clay generally used in cement production.
(2) Higher strength was obtained when FCB ash was used as a pozzolan in steam curing. But fly ash was superior in strength to FCB ash as a pozzolan in autoclave curing.
(3) The rate determining step of the pozzolanic reaction of fly ash was the ionic diffusion through the inner hydrate layer.
(4) FCB ash showed higher reactivity in low temperature synthesis of molecular shieve, Na-A type zeolite. Fly ash gave only a small amount of Na-P type zeolite rather than Na-A type zeolite under the same conditon.
