Thermodynamic modeling of Portland cement pastes exposed to sodium sulfate and magnesium sulfate

Abstract

Sulfate attack in concrete structural elements can lead to the precipitation of expansive products, such as ettringite and gypsum, compromising the service life and durability of the material. This study aimed to investigate, through mineralogical (XRD) and thermal (TG/DTG) analyses combined with thermodynamic modeling, the behavior of two paste compositions (CP V-ARI and 90% CP V-ARI + 10% silica fume (SF)) when exposed to sodium sulfate and magnesium sulfate attack. Thermodynamic modeling was also used to determine the crystallization pressure of ettringite and gypsum. The XRD and TG results indicated that the incorporation of silica fume into the cement pastes reduced the precipitation of secondary ettringite under sodium sulfate exposure. However, this behavior was not observed under magnesium sulfate attack. The thermodynamic modeling showed good agreement with the experimental results. Regarding crystallization pressure, both pastes exhibited similar internal stresses. Finally, the results indicate that thermodynamic modeling is an effective tool for identifying and explaining the phases formed during sulfate attack in cementitious composites.