Rheological Behaviour of Cement Paste with Fly Ash in the Formulation of Self- Compacting Concrete (SCC)

Abstract

The use of Self-Compacting Concrete (SCC) is growing rapidly due to its ability to compact solely under its own weight. But, due to the unavailability of a universally approved mix design procedure, the industry uses trial and error methods to proportion mixes leading to high material and time wastage. Unlike traditional concrete, SCC possesses a very high workability. Thus, it is worthwhile to be evaluated through a rheological point of view. But, to facilitate high workability, SCC requires a sufficient amount of paste to fill the voids and confine its aggregates. However, if the binder or the cement content is raised to achieve this purpose, it will result in many negative structural and non-structural impacts. It will not only increase the cost, but will also lead to cracks due to the increased heat of hydration. It will also harm the environment through excessive use of resources, while contributing to the emission of large amounts of carbon dioxide, a greenhouse gas. Therefore, Supplementary Cementitious Material (SCM) such as fly ash could be identified as a better supplement to overcome these problems. This study focuses on determining the yield shear stress and plastic viscosity (Bingham constants) of paste having varying constituent proportions, by using coaxial type rheometer. Both individual and combined effect of water/cement (w/c) ratio and fly ash content on the rheological behaviour is observed and analysed to determine the optimum SCM composition for a mix for two common w/c ratios. The results for optimum material quantities could be used as a guide for initial trial mixes, minimizing the time and material wastage.