Enhancing physiochemical properties and reactivity of landfilled fly ash through thermo-mechanical beneficiation

This study investigates the impact of thermo-mechanical beneficiation techniques on the physiochemical characteristics and reactivity of landfilled fly ashes (LFAs) obtained from power plants in Wyoming and Colorado, USA. Thermo-mechanical beneficiation significantly improved the physiochemical properties of LFAs, leading to a decrease in loss in ignition (LOI) and an increase in fineness. The results revealed improvements in the strength activity index of all LFAs after beneficiation, surpassing the minimum requirement of 75% at 28 days. Beneficiation also enhanced heat release and calcium hydroxide consumption, indicating improved pozzolanic reactivity. The findings demonstrated that as beneficiation temperatures increased, there was a significant reduction in LOI, with levels falling below 3% at temperatures above 450 °C. The relationship between LOI and heat release indicated that reducing LOI could enhance the reactivity of fly ash. However, there was an inflection point at certain LOI thresholds, suggesting that further reductions in LOI may not significantly impact hydration kinetics. The results also showed that the specific surface area of LFA was correlated with heat release and calcium hydroxide consumption, emphasizing the importance of increased fineness for enhanced reactivity. The study also found associations between calcium hydroxide consumption, heat release, and early- and later-age strength activity indices. Higher calcium hydroxide consumption corresponded to increased heat release and reactivity, which in turn contributed to greater strength development over time, particularly at later.