Effect of carbonation on alkali-activated slag paste

Carbonation on waterglass- and NaOH-activated slag pastes was analyzed and compared with carbonation in Portland cement pastes to determine possible differences. Thermogravimetry-differential thermal analysis (TG/DTA), Fourier-transform infrared spectrometry, and nuclear magnetic resonance were used to determine the effects on the main reaction products. According to the TG/DTA results, carbonate precipitation following carbonation is much more intense in Portland cement pastes than in alkali-activated slag pastes. This may be attributed to the fact that in Portland cement paste both the portlandite and the C-S-H gel can be carbonated, whereas in alkali-activated slag pastes, only the C-S-H gel is carbonated directly. In both systems, carbonation leads to the formation of CaCO3, Si-rich C-S-H gel, silica gel, and alumina. The carbonation of waterglass-activated slag pastes is not altered by the presence of either of the organic additives used in the study.