Influence of admixtures on rheological properties and heat of hydration of alkali aluminosilicate cement

The effects of selected admixtures on the set time, rheology, rate of workability loss with time and heat of hydration of an alkali aluminosilicate cement formulated with coal fly ash were investigated. The potential of these admixtures to make these aspects of the fresh alkali aluminosilicate paste behaviour more comparable to those of Portland cement paste were evaluated. Citric acid, borax and phosphoric acid were the admixtures considered in this investigation. They exhibited various degrees of effectiveness in achieving the targeted improvements in the fresh mix characteristics of alkali aluminosilicate cement. All admixtures produced favourable effects on at least one of the properties considered in the investigation. As far as rheology, set time and retention of fresh mix workability over time is concerned, citric acid performed better at the dosages considered in the project, producing qualities comparable to those of Portland cement. Borax and phosphoric acid, however, were more effective in reducing the rate of exothermic heat release and also the total heat released.