Microstructure of Ettringite Binder Exposed to Natural Carbonation

Abstract

Ettringite binder which composes of Calcium Aluminate Cement (CAC), Ordinary Portland Cement (OPC), and Calcium Sulfate (Anhydrite - CaSO4 or Hemihydrate -CaSO4.0.5H2O or Gypsum - CaSO4.2H2O) is one of the recent cementitious materials The main advantage of this type of binder is the rapid hydration that leads to extremely rapid development of mechanical strength. This feature is obtained by the production of large amount of early ettringite during the hydration process. In this research work, the carbonation process of ettringite phases is analysed and discussed by means of infrared spectroscopy, X-ray diffraction. The goal of this work was to study the evolution of developed carbonated phases due to the action of CO2 over the AFt phases developed in the CAC/PC/CaSO4 system. After 1 year, the total carbonation depth of the samples stored outdoors is approximately 4 mm and there is no carbonation for the samples stored in endogenous condition. The carbonation process of ettringite gives gypsum, calcium carbonate and aluminum hydroxide. These phases are detected by both X-ray diffraction and Infrared spectroscopy method.