An NMR Spectroscopic Investigation of Aluminosilicate Gel in Alkali-Activated Fly Ash in a CO2-Rich Environment

The present study investigated aluminosilicate gel in alkali-activated fly ash exposed to a CO2-rich environment by means of NMR spectroscopy. The alkali-activated fly ash was exposed to an atmospheric CO2 concentration of 10% after curing at 80 °C initially for 24 h. Under high concentrations of CO2, highly reactive components Na and Al, which completely reacted within the first few hours, were unaffected by carbonation, while Si, with relatively slower reactivity, behaved differently. Despite a lower degree of the reaction in the carbonated sample, the monomeric silicates rapidly became of higher polymerization, meaning that exposure to high concentrations of CO2 caused Si to form a binding gel phase. Consequently, the carbonated sample possessed a higher amount of binding gel. The obtained results may be useful to understand the fundamental chemistry and behavior of aluminosilicate gel under high concentrations of CO2