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 degrees 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 degrees C. At 5 and at 20 degrees C, a similar phase assemblage was calculated to be present, while at approximately 50 degrees 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 degrees C monosulphate and monocarbonate are present. In Portland cements which contain less Al (Al2O3/SO3<1.3), above 50 degrees C monosulphate and small amounts of ettringite are expected to persist. A good correlation between calculated porosity and measured compressive strength was observed. (C) 2007 Elsevier Ltd. All rights reserved.