Microencapsulated phase change materials (MPCMs) were incorporated into cement pastes of Portland cement (PC). Minislump tests and rheological properties of cement pastes containing three MPCMs with different surfaces (hydrophilic, amphiphilic and hydrophobic) were measured, and the water demand of MPCM in the cement matrix was evaluated. The hydrophilic MPCM was chosen for a more thorough rheological study, since it was found to be more compatible with the cement matrix. The dispersion of a high amounts (45 wt% with respect to the cement content, which corresponds to about 62 vol% of the total solids) of the hydrophilic MPCM in the cement pastes was achieved by optimization of the amount of superplasticizer through rheological measurements. For the viscometer tests, a Power Law model was found to give the best fit to the experimental data. While pastes (with 45 wt% of hydrophilic MPCM) prepared with low superplasticizer contents (<1.2 wt%) were found to be shear thinning, the paste exhibited a shear thickening behavior in the presence of higher amounts of superplasticizer. The shear thickening is probably caused by high water adsorption onto the microcapsules combined with deflocculation of the cement particles at high concentrations of superplasticizer. After the optimization of the superplasticizer content, homogeneous pastes were obtained, where the particles of the hydrophilic MPCM were well dispersed and unaltered after 28 days of hydration.
