Pozzolanic reaction in portland cement, silica fume, and fly ash mixtures

Results of tests on calcium hydroxide and hydrate water contents of silica fume and fly ash mixtures using thermogravimetric analysis are analyzed here. These results indicate that silica fume reacts with calcium hydroxide as early as 12 hours and provides large amounts of hydrates at early ages. Fly ash reduces the calcium hydroxide content at early ages by delaying its production. It can react with calcium hydroxide after 3 days and contribute to hydrate water when the pozzolanic reaction begins. When silica fume is combined with fly ash, calcium hydroxide is also reduced but a significant contribution to hydrate water is found to occur between 3 and 7 days. Reactivity of silica fume with calcium hydroxide is depressed due to the presence of the flying ash.(A)