Additives that influence the nucleation and crystal growth of portlandite can be expected to impact the morphology of the precipitates significantly . Therefore, we analyzed the precipitates obtained from the portlandite nucleation experiments via SEM (Figure ). The precipitates were collected immediately after stopping the titration experiments (last point of the curves for the reference and 2 mmol L -1 concentrations in Figure ) by vacuum filtration of the whole reaction mix over a 0.22 µm polystyrene filter. To avoid further reaction, the obtained solid was washed two times with isopropanol and dried under a constant flow of nitrogen overnight. XRD analyses of the precipitates confirmed the formation of pure portlandite for all experiments (Figure ). The shape of the portlandite particles of the reference experiment without additive (Fig ) can be described as hexagonal prisms with irregular pyramidal bases. As reported in the literature, the observed morphology is typical for portlandite crystals derived from homogenous salt solutions and highly alkaline conditions .