Thermodynamic modelling of the effect of temperature on the hydration and porosity of Portland cement

The composition of the phase assemblage and the pore solution of Portland cements hydrated between 0 and 60 °C were modelled as a function of time and temperature. The results of thermodynamic modelling showed a good agreement with the experimental data gained at 5, 20, and 50 °C. At 5 and at 20 °C, a similar phase assemblage was calculated to be present, while at approximately 50 °C, thermodynamic calculations predicted the conversion of ettringite and monocarbonate to monosulphate. Modelling showed that in Portland cements which have an Al2O3/SO3 ratio of > 1.3 (bulk weight), above 50 °C monosulphate and monocarbonate are present. In Portland cements which contain less Al (Al2O3/SO3 < 1.3), above 50 °C monosulphate and small amounts of ettringite are expected to persist. A good correlation between calculated porosity and measured compressive strength was observed.