Chemical properties of pore solution of hardened cement pastes with mineral additions

Abstract

This paper presents the influence of mineral additions in blended cement, or ‘green’ concrete, on the divalent ions of the cement paste pore solution. Because of the lack of data concerning the direct comparison between the pore solution of cement and mineral additions-based material, six types of hardened cement pastes were tested. For this purpose, Portland cement (CEM I or CEM V) and mineral additions (limestone filler, fly ash, blast-furnace slag and silica fume) were used. Results from chemical analyses by ionic chromatography show significant concentrations of divalent ions, such as sulfates and calcium, in the pore solution. In fact, the reference cement paste based on CEM I contains about 1.8 mmol/l of calcium and 1.6 mmol/l of sulfates. However, the use of mineral addition significantly modifies the pore solution. In particular, a substitution of cement by 10% of silica fume increases the calcium and sulfates concentrations to 12.2 mmol/l and 6.7 mmol/l, respectively. This change in the chemical composition, the pH and the ionic strength should be taken into account in multispecies transfer modelling and the thermodynamic equilibrium. The time evolution of the chemical composition, pH and ionic strength of the pore solutions was also investigated.