Combined water fraction (cwf): Theoretical insights, literature data mining, methodological implications and practical use

The combined water fraction (cwf), defined as the ratio of combined (bound) water to mixing water, is a practical and effective indicator for evaluating both conventional and novel cement formulations, with potential to complement existing cement classification methods. This study first revisits the theoretical foundations of the cwf, establishing its relationship with the classical theory proposed by Powers and Brownyard. A meta-analysis of 37 published studies was then conducted, in which combined water content, mixing water, and compressive strength data were used to evaluate 979 cement compositions within the cwf framework. The results demonstrate that the cwf correlates strongly with compressive strength, particularly when individual cement compositions are analyzed. The main methodological factors affecting the cwf–strength relationship were subsequently investigated, including hydration-stoppage procedures, combined water determination methods, the influence of the water-to-cement ratio on combined water content, mortar workability and castability, and differences in phase assemblage. Finally, the practical application of the cwf is demonstrated, including its use as a screening tool for selecting cement formulations capable of meeting specific strength requirements.