Electrical conductivity, physico-chemical and mechanical characteristics of fly ash pozzolanic cement

The effect of partial substitution of sulphate resisting cement (SRC) or ordinary Portland cement (OPC) with 10, 20 and 30 mass % by fly ash (FA) on the properties of fly ash-pozzolanic cement pastes was investigated. The early hydration reaction was studied by electrical conductivity prior addition of water to cement pastes to monitoring the change occurring during the setting and hardening. The change in phase composition was investigated by differential thermal analysis (DTA) and FT-IR spectroscopy. The effect of FA on the hydration progressing up to 90 days was studied by the determining chemically combined water, free lime contents, total porosity, degree of hydration gel/space ratio, reaction ratio and compressive strength. The results show that FA extended the initial and final setting times. The free lime of pozzolanic cement pastes increases up to 7 days, and then decreases up to 90 days, due to the pozzolanic reaction of FA. As the FA content increases the reaction ratio increases up to 30 mass%. However, the increase of FA content leads to decrease the compressive strength and increase the total porosity in comparison with SRC and OPC control pastes.