where t (in mmol/L) is the calcium concentration measured at time t (in h), [Ca] s (7.85 mmol/L) is the equilibrium calcium concentration, and k (0.122/h) is the rate constant of dissolution (see Figure ). The goodness of fit is evaluated with the coefficient of determination (R 2 ) and the mean absolute percentage error (MAPE). The calcium concentration is then translated into a CA reaction degree by comparison with the expected calcium concentration from full dissolution of the CA fraction (see Table ) within CAC1 (40.5 mmol/L). It is thus possible to infer that the reaction degree reached in 35 min in HCl (∼1 %) would be reached in only ∼27 s in water. Hence, the increase in time to reach the pH swing (i.e., 35 min instead of 27 s) observed experimentally is not caused by a larger reaction degree required to achieve the pH increase, but instead denotes a true reduced reactivity of CA, as demonstrated by the CAC dissolution rate (r, in mmol/(L min)) estimated from Ca concentration using equation 1see Figure (right). Note that we use calcium as a dissolution tracer because it is not expected to precipitate in any phases below pH 10.75. Above pH 10.75, CAH 10 may start forming.