Characterization and evaluation of the surface free energy for cementitious materials

• Captive bubble method is designed to test the contact angle of cementitious materials.
• Influence on surface free energy with different dispersion and polar components cementitious materials is analyzed.
• Critical surface energy curve is proposed to state the hydrophilic feature of cement paste.

In this paper, a novel captive bubble method is designed to measure the liquid contact angle on the cementitious material surface. The surface free energy is calculated from the contact angle based on the Young’s equation. The experimental results show that cement pastes with different w/c ratios (0.3, 0.4, 0.5 and 0.6) share a highly similar adhesion work, although the components of surface free energies of samples change with increasing w/c ratio. To estimate the wettability of cement pastes, a critical surface energy is proposed to interpret the hydrophilic feature of the cementitious materials. Moreover, the interaction between sodium chloride solution and surface of the cement pastes is obtained, and the result shows a decline of the dispersion component for each specimen while values of polar components rise.