Similar to portlandite nucleation, the titration of a solution containing Na 2 SiO 3 and NaOH with CaCl 2 leads to a linear increase of the calcium concentration until a maximum occurs, which marks the onset of nucleation. Recent literature has shown that C-S-H also follows the non-classical crystallization pathway . According to Picker et al., the amount of PNC formed at a pH of 13 is very low due to the electrostatic repulsion of negatively charged silicate monomers . In our data, this is evident from the near-congruency of the reference curve with the added calcium concentration until nucleation begins (Figure , black curve). As the amount of silicon and hydroxide is fixed at the beginning of the experiment, no plateau is reached after the nucleation for all C-S-H experiments. A local minimum is reached after the nucleation.