A practical model to predict the flow of water-powder mixes and its application to mix design of cementitious blends

This paper addresses the prediction of the spread-flow of water-powder mixes, which is of particular interest in the mix design of cementitious pastes, mortar and concrete. The model introduced, splits the total water demand which is necessary to achieve a specific spread of water-powder mixes into three parts: (i) water to fill the voids between the solid particles, (ii) water to reach the onset of flow and (iii) water to reach a specific spread. An algorithm developed allows the systematic calculation of the total water demand of mixes with varying proportions of powders after the individual characterization of the source materials regarding their void volume and spread-flow coefficients (i.e. retained water ratio and deformation coefficient). With this approach it is possible to optimize the proportion of mixture in cement-based binders (blended cements) with regard to a minimum water demand for a target spread. An example for the optimization of blends of ordinary Portland cement (OPC) and supplementary cementitious materials (SCM) in terms of clinker-efficiency is given leading to improved strength with reduced environmental impact in comparison to OPC based mixes.