Modelling of Temperature-Dependent Pozzolanic Reaction of Low-calcium Fly Ash in Blended Cement Paste

摘要

High temperature curing is often used in fly ash concrete to accelerate its pozzolanic reaction. However, current information regarding pozzolanic activity and temperature dependence of fly ash is insufficient to understand the behavior of fly ash and to model its effect in cement systems. In this study, three different types of low-calcium (Class F) fly ashes were selected based on their solubility in NaOH solution at 20°C and 60°C. These three fly ashes were further studied in ordinary portland cement systems by preparing blended cement pastes under sealed curing conditions at 20°C and 60°C. The extent of pozzolanic reaction for these fly ashes were measured by selective dissolution tests. Experimental results showed that pozzolanic activities and temperature dependences of these low-calcium (Class F) fly ashes were different although they have similar chemical and physical properties. A temperature-dependent pozzolanic reaction model considering fly ash material variances was proposed to predict the pozzolanic reaction and therefore degree of reaction at different temperatures. The model was validated by the experimental results. With the help of this model, parametric analyses are presented to show how the pozzolanic activity and temperature dependence of fly ash affects the concrete performance.