Binder chemistry of sodium carbonate-activated CFBC fly ash

Abstract

The use of circulating fluidized bed combustion in coal power plants is dramatically increasing, and the disposal of the resultant ash is a significant environmental concern. The present study investigated the binder chemistry of sodium carbonate-activated CFBC fly ash. Compressive strength tests showed that strength development was relatively faster in samples with 5% sodium carbonate. The main binder gel in samples with and without sodium carbonate was composed of AFt, AFm and C-S-H, while the formation and Al-substitution in C-S-H was enhanced by sodium carbonate-activation. At an excessive dosage of sodium carbonate, the formation of AFt was significantly hindered due to the precipitation of sodium sulfate, and a notable amount of AFm was formed in its place. The results obtained in this study fill a deficit in the understanding of fly ash activated with near-neutral salts, which are used extensively in several industrial applications, including alkali-activated cements.