It is important to emphasize that the pH jump to the alkaline pH observed here is unrelated to the setting reaction of calcium aluminate cement. First, the system under study is too diluted anyway to form a stiff solid, and second, in low w/s ratios, the pH jumps a second time after a few hours from approx. 12 to 13. This second jump coincides with the setting and strength development, while the first increase in pH corresponds to the initial dissolution of CA. In our case, we predict a final pH of around 11.3 when considering the formation of amorphous Al(OH) 3 , and around 12.0 when considering the formation of microcrystalline Al(OH) 3 (Figure and S4). Therefore, it is expected that the pH of 11 reached after 60 minutes will increase to approx. 12 during the main hydration step.