Location
University of Leeds
Keywords
low-calcium-silicate cement, aqueous carbonation, sulfate resistance
Abstract
This paper summarizes the results of sulfate resistance study of carbonated mortar specimens made with Solidia CementÔ (SC) and tested for expansion according to ASTM C1012 specification while exposed to three types of soak solutions: sodium sulfate, magnesium sulfate and deionized water. A control set of ordinary portland cement (OPC) mortars was also evaluated. Besides the length change measurements, visual observations of changes in the appearance of specimens were conducted after various lengths of exposure. In addition, microstructural characterization of the specimens was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA) techniques. Finally, changes in the concentration of the chemical species present in the soak solutions in contact with the SC specimens were evaluated using both, the ion chromatography (IC) and the inductively coupled plasma optical emission spectrometry (ICP-OES).
As expected, the OPC mortar specimens started deteriorating early and reached the critical (i.e.0.1%) level of expansion in about 4 months in case of sodium sulfate solution and in about 6 months in case of magnesium sulfate solution. With respect to the SC mortar specimens, those exposed to magnesium sulfate solution showed higher expansion than those exposed to sodium sulfate solution. However, after 18 months of exposure to both types of sulfate solutions the maximum expansion levels of specimens were still only about 33% of the critical (value.
The SEM examination of SC mortar bars indicated that the matrix of the specimens exposed to magnesium sulfate solution showed evidence of formation of gypsum and magnesium-silica compounds. Magnesium and sulfate ions seem to have altered the morphology of the carbonation-generated silica phase and produced gypsum deposits in the air-voids, within the matrix and at the paste – aggregate interfaces. The formation of gypsum in those specimens was confirmed by the results of thermal and XRD analyses. Finally, the ionic analysis of the magnesium sulfate soak solution indicated consumption of sulfate ions whereas the concentration of the sulfates in sodium sulfate soak solution didn’t change during the exposure period.
Included in
Sulfate Resistance Study of Carbonated Low-Calcium Silicate Systems
University of Leeds
This paper summarizes the results of sulfate resistance study of carbonated mortar specimens made with Solidia CementÔ (SC) and tested for expansion according to ASTM C1012 specification while exposed to three types of soak solutions: sodium sulfate, magnesium sulfate and deionized water. A control set of ordinary portland cement (OPC) mortars was also evaluated. Besides the length change measurements, visual observations of changes in the appearance of specimens were conducted after various lengths of exposure. In addition, microstructural characterization of the specimens was conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD) and thermo-gravimetric analysis (TGA) techniques. Finally, changes in the concentration of the chemical species present in the soak solutions in contact with the SC specimens were evaluated using both, the ion chromatography (IC) and the inductively coupled plasma optical emission spectrometry (ICP-OES).
As expected, the OPC mortar specimens started deteriorating early and reached the critical (i.e.0.1%) level of expansion in about 4 months in case of sodium sulfate solution and in about 6 months in case of magnesium sulfate solution. With respect to the SC mortar specimens, those exposed to magnesium sulfate solution showed higher expansion than those exposed to sodium sulfate solution. However, after 18 months of exposure to both types of sulfate solutions the maximum expansion levels of specimens were still only about 33% of the critical (value.
The SEM examination of SC mortar bars indicated that the matrix of the specimens exposed to magnesium sulfate solution showed evidence of formation of gypsum and magnesium-silica compounds. Magnesium and sulfate ions seem to have altered the morphology of the carbonation-generated silica phase and produced gypsum deposits in the air-voids, within the matrix and at the paste – aggregate interfaces. The formation of gypsum in those specimens was confirmed by the results of thermal and XRD analyses. Finally, the ionic analysis of the magnesium sulfate soak solution indicated consumption of sulfate ions whereas the concentration of the sulfates in sodium sulfate soak solution didn’t change during the exposure period.
