It is beyond the scope of this study to investigate the microstructural origin of the different domains. As we have different domains, we fit the data with a piecewise exponential function composed of two exponential functions of the type discussed above in equation 1. Although the experimental data seems composed of three domains (see above), all three are rarely distinguishable; the data often contains domains I and II or II and III (see below). Consequently, a two-domain model is reasonable for describing the data. In most experimental curves, the missing third domain, either I or III, can be explained by recognizing that it is unlikely to detect phase I for the fast-reacting system. Because the rheology measurement begins after 3 min, we miss the structural development in the first three minutes. For the high concentration of Na 2 SO 4 , the hydration is sufficiently slowed down to reveal the large initial slope of phase I. On the other hand, our data miss the later phase III if the transition to phase III does not occur in the first three hours due to slower hydration. By fitting the piecewise function 2, we also obtain a partition point H p , which separates the domains and use a, b 1 , b 2 and H p as fit parameters (Equation ). The results of the fits are shown in Table , and the graphical representation of the fits is given in Figure . The fit quality is good, which underlines the usefulness of the model.