Combined Water Fraction: A Practical Method to Evaluate Composite Cements Considering Chemical Reactivity and Water Demand

Abstract Portland cement compositions are becoming increasingly complex due to the use of different types and amounts of supplementary cementitious materials. Therefore, there is a need for alternative methods to evaluate the current and novel cements. These methods should consider not only the chemical reactivity of the cement but also their mixing water demand. In this context, a reference methodology based on the combined water fraction (cwf)—defined as the ratio between combined (bound) water and mixing water—was presented and applied to evaluate six composite cements formulated with the two most promising supplementary cementitious materials: calcined clay and limestone filler. The cwf, which reflects key aspects of the microstructure of the hardened material, showed a strong correlation with both the calculated capillary porosity and the compressive strength of the mortars. Finally, the practical use of the methodology is exemplified for the screening and choosing eco-efficient binders.