Assessing the Carbonation Behavior of Cementitious Materials

The carbonation behavior of six cementitious materials was examined (CSA Type 10 cement, CSA Type 30 cement, fly ash, ground granulated blast furnace (GGBF) slag, electric arc furnace (EAF) slag, and hydrated lime) for applicability to $\mathrm{C}{\mathrm{O}}_2$ sequestration applications. No-slump press-formed compacts and loose powders were subjected to 100% $\mathrm{C}{\mathrm{O}}_2$ at a constant pressure of $5\text{bar}$ for $2\mathrm{h}$ . The $\mathrm{C}{\mathrm{O}}_2$ contents of the as-received and the carbonated materials were measured. It was found that the cements, fly ash, and electric arc furnace slag could each show $\mathrm{C}{\mathrm{O}}_2$ uptake on the order of 12%, while the lime achieved nearly 40%. The blast furnace slag managed 7% uptake. The carbon uptakes achieved were significantly lower than the theoretical maximum as determined by chemistry. The $2\mathrm{h}$ carbonation produced high early age strength in cements and hydrated lime, which can be used as structural materials. The strength gain in fly ash, EAF slag, and GGBF slag was nevertheless not sufficient. X-ray diffraction analysis determined that the primary carbonation product formed was calcite, while ${\mathrm{C}}_3\mathrm{S}$ , ${\mathrm{C}}_2\mathrm{S}$ , and $\mathrm{Ca}{\left(\mathrm{O}\mathrm{H}\right)}_2$ were the phases consumed. Scanning electron microscopy observations considered the morphology of the carbonation products and the degree of reaction in terms of microstructure characteristics.