Fly ash (FA) is important alternative or supplement to cement to reduce the environmental impact of concrete industry. However, early age strength development of FA is a concern due to the slower reaction rate of FA compared to cement. This paper examines the early age hydration properties of cement paste containing typical Australian FA and establishes correlations between the degree of hydration and the early-age strength development properties of mortar mixes. All mixes have the same mixture proportion of water to binder (w:b) ratio. FA sourced from different power plants are used for the tests. Cement replacement levels of 0%, 10%, 30% and 40% by mass are considered. The degree of hydration was established from the heat production of the mixes by using isothermal calorimetry. The hydration properties were characterized by hydration curve parameters obtained from curve fitting. The results show that both hydration rate and strength of the binder materials (FA and cement) were reduced with higher replacement levels of FA contributing to a reduced hydration rate at early ages. Linear relationship could be obtained between degree of hydration and strength at early ages for all the fly ash binders.
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