Insights into the Carbonation of Industrial Slags: The Effect of Al/Si Ratio on the Carbonation of Calcium Aluminosilicate Glass Constituents and Their Role as Supplementary Cementitious Materials

Calcium aluminosilicate glasses are reactive components in industrial slags. To use them for CO2 sequestration, understanding how the glasses’ chemistry influences their carbonation reaction behavior is essential. Here, we investigated the role of aluminum on carbonation of synthesized calcium aluminosilicate glasses with Al/Si ratio = 0.06 to 0.32 through carbonation at low and high water-to-solid ratios (w/s). Overall, Al/Si = 0.11 achieved the highest degree of carbonation (∼72%) while Al/Si ≥ 0.17 achieved the lowest degree of carbonation due to Al-rich regions requiring charge balancing by Ca2+, thus leaving Ca2+ forming Si-NBOs (nonbridging oxygen atoms) to participate in carbonation. Low and high w/s carbonation methods operated via distinct mechanisms, and high w/s carbonation produced a significantly higher degree of carbonation. To test their potential as supplementary cementitious materials, the pozzolanic reactivity of 24 h-high w/s carbonated glasses was tested; it increased with rising Al/Si ratio, which is an opposite trend to carbonation reactivity.