Correlating the reactivity and strength development of coal bottom ash and coal fly ash in cementitious system

Characterizing the reactivity of coal combustion by-products, particularly coal bottom ash (CBA), is crucial for their effective use as cement alternatives, especially when incorporating CBA from various sources in cementitious composites. This study investigates the reactivity of both ground CBA and coal fly ash (CFA) from Class F and Class C using heat of hydration analysis and R3 bound water measurements in the cementitious paste, and their correlation with the compressive strength of cement mortar. Results showed Class F ashes improved early- age properties, while Class C ashes contributed at later-age stages due to higher CaO and sufficient SiO2 contents. Compressive strength results indicated Class F-based cement mortar exhibited 10 % higher strength at 2 days, but Class C surpassed Class F by 3 % and 12 % at 7 and 28 days, respectively. Class F-based cementitious pastes showed a higher peak heat flow (4.46 mW/g) than Class C (3.92 mW/g) and 4 % higher cumulative heat release at 2 days, while Class C exceeded Class F by 2 % at 7 days. R3 bound water measurements revealed Class C ground CBA and CFA outperformed Class F by up to 46 % and 26 % at 7 and 28 days, respectively. Ground CBA exhibited higher bound water content than CFA for both Class C (32.4 > 21.6 g/100 g) and Class F (25.8 > 20.5 g/100 g) at 28 days. All investigated coal ashes demonstrated substantial reactivity and positive strength contributions, with strong correlations supporting the effectiveness of Class F and Class C ground CBA and CFA in cementitious applications.