Thermodynamic Modeling of Compositional Variations of an Ordinary Portland Cement and Their Effect on the Phase Changes Under Sulfate Attack

摘要

The resistance against sodium sulfate attack of an ordinary Portland cement with different calcium sulfate and silica fume contents is investigated. Mortar and paste samples were produced and exposed to a sodium sulfate environment. In the cements, which contain silica fume, less ettringite and gypsum precipitate and less expansion of the mortar bars is observed. Thermodynamic calculations support these experimental findings. The moderate addition of gypsum to the ordinary Portland cement also results in less ettringite formation during sulfate attack and in a reduced expansion as was expected from thermodynamic calculations.