To better understand how these anions might influence the hydration kinetics, we have thermodynamically modeled the equilibrium phase composition as a function of CA conversion in the presence of the maximum acid concentration for HCl, HNO 3 , and H 2 SO 4 (see Figure ). The modeling reveals a three-step increase in pH in all cases. At very low CA conversion (approx. 1 %), no new phase is forming due to the very low pH of the pore solution (below 4). Above 1 % CA conversion, gypsum and microcrystalline Al(OH) 3 form first in the presence of H 2 SO 4 , followed by the re-dissolution of gypsum and the formation of the ettringite at larger reaction degrees. Finally, the monosulfate AFm phase and CAH 10 form. In the presence of HCl and HNO 3 , the formation of microcrystalline Al(OH) 3 occurs first, followed by Friedel salt (in HCl) and mononitrate (in HNO 3 ), and CAH 10 (both cases). The model for the hydration of pure CA in water is also calculated (see Figure ). Minimal microcrystalline Al(OH) 3 formation is predicted at 25 °C, and the formation of CAH 10 is expected in a much larger amount as the pH immediately reaches pH 12 even at low CA conversion. We can therefore assume that the enhanced formation of microcrystalline Al(OH) 3 at initially low pH in the presence of acids is, at least in part, responsible for the retardation of the main hydration peak. At the same time, this process is likely influenced by the additional formation of small amounts of different hydrate phases, as suggested by modeling. Depending on the used acid, the observed retardation difference might result from Friedel's salt, monosulfate, mononitrate, and potentially monoperchlorate formation, although this phase has not been studied so far to the best of our knowledge. On the other hand, the anions certainly have different surface affinities for the CA phase and, additionally, kosmotropic effects, such as that observed at w/s 100 (see section 3.2), might play a role on early phase dissolution. However, the mechanistic details of the acid-caused retardation are beyond the scope of this investigation.