Characterisation of cement pastes by inverse gas chromatography

Two cement pastes, commonly used in concrete formulations, were characterised by IGC at 35–80 °C before and after coating with an epoxy resin and a hardener. The cements are mixtures of hydrates in various proportions, such as calcium silicate hydrate (CaO–SiO2–H2O) and calcium hydroxide Ca(OH)2. Apolar and polar probes were used to determine the dispersive and acid–base characteristics of the cement pastes. These materials have high surface energy as judged from the dispersive contribution to the surface free energy (γSd) values lying in the 50–70 mJ/m2 range at 60–80 °C. Examination of the specific interactions permitted to show that the cement pastes are strongly amphoteric species with a substantial predominant Lewis basicity that is in line with the basic pH of their aqueous suspensions. Following coating with an epoxy resin (DGEBA) and a hardener (triethylene tetramine), the surface energy of the cements decreases substantially with the mass loading of the organic material. The surface thermodynamic properties were also correlated with the surface chemical composition as determined by X-ray photoelectron spectroscopy.