Properties of cement-based materials containing fly ash

Fly ash has been increasingly used in concrete structures due to both environmental and technical benefits. Despite significant past research, our understanding of thermal and physical properties of fly ash mortar and concrete remains incomplete and thus needs further investigation. This paper presents results of a study into important fundamental thermal and physical properties of both fly ash mortar and fly ash concrete. Replacement levels of Portland cement by fly ash investigated were30%, 50% and 60% by mass. In cement-fly ash mortar tests, increasing fly ash content was found to delay setting times, decrease both compressive and flexural strengths and reduce hydration heat. The effect of fly ash on hydration heat evolution of cement binder was quantitatively analysed. The obtained reduction coefficient (k) would allow reasonable prediction of temperature rise in concrete structures, which is of particular interest for mass concrete construction. In cement-fly ash concrete tests, thermal properties, including thermal diffusivity, conductivity and specific heat, were also measured and reported. There also appeared a linear relationship between compressive and flexural strengths of concrete incorporating up to 60% fly ash by mass. In addition, the observed effect of fly ash on ultimate tensile strain, static elasticity modulus and drying shrinkage of concrete was also reported.