Thermodynamic Modeling and Experimental Study of Carbonation of Alkali-Activated Slag Cements
Solmoi Park, Barbara Lothenbach, Jeong Gook Jang, Hyeong-Ki Kim, Namkon Lee
Abstract
The present study investigates the carbonation of slags activated by NaOH, Na 2 SiO 3, Na 2 CO 3, and Na 2 SO 4 . The main hydrates in those activated with NaOH or Na 2 SiO 3 were C-(N-)A-S-H, strätlingite, and MgAl-layered double hydroxide phases as observed using different experimental characterization techniques and thermodynamic modeling. The use of a Na 2 CO 3 activator led to the formation of calcium carbonate and monocarbonate instead of strätlingite, and Na 2 SO 4 to ettringite formation. Carbonation of the alkali-activated slags in a powdered form at 1 vol % concentration of the CO 2 environment proceeded rapidly, while little change was observed after 7 d. The main carbonation products commonly identified were calcium carbonate, carbonate containing-MgAl-layered double hydroxide, and N-A-S-H. In Na 2 SiO 3 - and Na 2 SO 4 -activated slags, M-S-H formation was predicted, which destabilized the MgAl-layered double hydroxide phases. Strätlingite and monocarbonate, which were initially present or formed as a transient phase, were transformed to N-A-S-H during carbonation, while C-(N-)A-S-H was only partially decalcified and destabilized.