Location
University of Leeds
Keywords
Calcium aluminate cement; Calcium sulfo-aluminate cement; Calcium sulfo-aluminate belite cement; Alkali activated binder systems.
Abstract
Understanding the rate and implications of carbonation on strength and durability in alternative cementitious materials (ACMs) is critical in designing ‘green’ concretes for intended service lives. In this paper, three commercially available ACMs, including one calcium aluminate cement (CAC), one calcium sulfoaluminate belite cement (CSA), and one alkali-activated binder using class C fly ash (AA), were evaluated against one portland cement (OPC). Thermogravimetric analysis (TGA) and x-ray diffraction (XRD) techniques were used to understand the effect of carbonation on ACM paste composition. Water sorption tests on both carbonated and uncarbonated cement mortar showed a significant reduction in porosity of this OPC and CAC system with carbonation, whereas no significant change in this CSA and AA system. In addition, the carbonation front in concrete made with these ACMs was measured using phenolphthalein and rainbow indicators at regular intervals of exposure to 7% CO2, and these results are compared to companion concretes made with this OPC. The rate of carbonation in this CAC, CSA and AA system were significantly higher than that of OPC. The carbonation in the systems made with the ACMs in this study results not only in a decrease in pH, which may lead to depassivation on embedded metal reinforcement but is also found to cause decomposition of main strength giving hydration products. Further research is required to understand the effects of carbonation on steel passivation and chloride threshold levels in the ACM systems.
Included in
Carbonation in Alternative Cementitious Materials: Implications on Durability and Mechanical Properties
University of Leeds
Understanding the rate and implications of carbonation on strength and durability in alternative cementitious materials (ACMs) is critical in designing ‘green’ concretes for intended service lives. In this paper, three commercially available ACMs, including one calcium aluminate cement (CAC), one calcium sulfoaluminate belite cement (CSA), and one alkali-activated binder using class C fly ash (AA), were evaluated against one portland cement (OPC). Thermogravimetric analysis (TGA) and x-ray diffraction (XRD) techniques were used to understand the effect of carbonation on ACM paste composition. Water sorption tests on both carbonated and uncarbonated cement mortar showed a significant reduction in porosity of this OPC and CAC system with carbonation, whereas no significant change in this CSA and AA system. In addition, the carbonation front in concrete made with these ACMs was measured using phenolphthalein and rainbow indicators at regular intervals of exposure to 7% CO2, and these results are compared to companion concretes made with this OPC. The rate of carbonation in this CAC, CSA and AA system were significantly higher than that of OPC. The carbonation in the systems made with the ACMs in this study results not only in a decrease in pH, which may lead to depassivation on embedded metal reinforcement but is also found to cause decomposition of main strength giving hydration products. Further research is required to understand the effects of carbonation on steel passivation and chloride threshold levels in the ACM systems.
