The composition of the aqueous phase significantly influences the rheology and hydration of fresh cement paste in the presence of PCE superplasticizer. In addition, the molecular structure of PCE has a decisive role on its performance in cementitious materials. It is found that the charge density of the backbone has a minimal effect on the interparticle force, and the length of the side chain plays a more significant role in determining the interparticle force. In addition, the dosage of PCE affects both the strength and the decay length of the interparticle force. In the PCE-free sample, the higher ionic strength of the aqueous phase contributes to a higher yield stress. The effect is thought to be caused by the different influences of the cations and PCE interactions. Calcium seems to support the polymer adsorption and potassium seems to affect the depletion forces. The yield stress increases with resting time when high dosages of PCE are used in pore solutions, although the surface becomes more negatively charged. The adsorbed PCE at rest tends to bridge the particles rather than disperse them. The experimental results suggest that the polymer and the ion can form complexes in the liquid phase, leading to size changes. This would increase the depletion forces and an increased bridging effect between the particles at rest, thus affecting the rheological properties.