Calcium Carbonate and Ettringite Induced Efflorescence in CAC- Anhydrite Binary Systems

We focused on the efflorescence induced microstructural evolution of ettringite-rich systems prepared with calcium aluminate cement (CAC) and anhydrite. The effects of anhydrite on the visible efflorescence, and the corresponding capillary absorption of CAC-anhydrite mortars were revealed. The composition and microstructure of efflorescence-causing substances were investigated by optical microscope, in-situ Raman spectroscopy, scanning electron microscope, energy dispersive spectrometer, thermogravimetric analysis, and differential scanning calorimetry, at multi-scales. Results indicate that, besides the calcium carbonate, ettringite is another main component of efflorescence-causing substances. Compared with the neat CAC mortars, the addition of anhydrite has a significant effect on the degree of efflorescence by acting on the composition of hydration products and pore structure. In addition, methods are proposed for the prevention of efflorescence of CAC-anhydrite binary system.