Studies of hydrothermal reactions of UK pulverized fuel ashes. Part 1: reactions between pulverized fuel ash and calcium hydroxide

Pulverized fuel ash/calcium hydroxide pastes (C/S ratio approximately 0·8) were autoclaved at 184°C for periods up to 12 h. The pastes were analysed for loss of calcium hydroxide and ash, release of silicon, aluminium and alkalis, and by X ray diffraction. Calcium hydroxide is consumed within 6 h, which coincides with the most rapid period of ash reaction. A semicrystalline CSH phase appears initially, which converts to crystalline tobermorite at longer times. Hydrogarnet forms readily and is stable under the conditions investigated. Differences in the behaviour of the ash samples are evident that seem to be related to the particle size distribution, rather than to the amount of glassy phase present or to other measures of reactivity.