Utilization of surface-modified fly ash cenosphere waste as an internal curing material to intensify concrete performance

Fly ash cenosphere , as one of the coal-burning related industrial wastes, causes significant negative consequences to the environment. Therefore, it is necessary to explore an ecological way to take full advantage of the cenosphere. In this study, the utilization of the cenosphere as an internal curing material to partially replace cement in concrete was evaluated. An improved surface modification process was proposed to remove the glassy-phase on top of the cenosphere. It was proved to be effective given that excellent water desorption characteristics were obtained in a practical relative humidity variation in the concrete simulated with saturated salt solutions. The surface-treated cenosphere was identified as a performance enhancer to concrete mechanical properties given that an increase of 7.07% and 6.85% in compressive and flexural strength , respectively, was observed. Due to the coupling effect of the internal curing and pozzolanic reactivity of cenospheres, a significant amount of C–S–H gel with a low Ca/Si ratio and tight bond between cenospheres and surrounding pastes were characterized through SEM-EDS and XRD investigations, leading to a strengthened microstructure. This study demonstrated that the surface-modified cenosphere could be utilized as an internal curing material to benefit the concrete performance. • An improved surface modification process for the cenosphere waste is proposed. • Good water desorption properties are identified in the surface-modified cenosphere. • A positive composite effect of internal curing and pozzolanic reactivity is achieved with treated cenosphere. • The surface-modified cenosphere can be used as a partial substitute for the cement. • The surface-modified cenosphere is a performance enhancer to the concrete.