Cementitious properties and hydration mechanism of circulating fluidized bed combustion (CFBC) desulfurization ashes

Self-cementitious properties and pozzolanic reactivity of CFBC desulfurization ashes (CFBCA), modified CFBCAs (MCFBCAs) and pulverized fuel fly ash (PFA) are investigated. The results show that CFBCA and MCFBCAs are self-cementitious, but PFA is not self-cementitious. Self-cementitious strength of MCFBCAs is influenced by the grinding mode and modifiers. Compared with CFBCA and PFA, the pozzolanic reactivity index of MCFBCAs is increased by 23–37% and 15–28.8%, respectively. A higher strength of the cement with the intergrinding MCFBCAs is attained, which is comparable to that of the pure cement paste (C–O) at 28 days. Moreover, MCFBCAs have higher pozzolanic reactivity and can be used as an admixture in cement. By means of XRD, SEM and FT-IR, the main hydration products of the CFBCA and MCFBCAs samples are hydrated calcium silicate (C–S–H), ettringite, gypsum and some portlandite, but no obvious hydration products are detected in the PFA.

► Difference of physical properties between CFBA and PFA are explained.
► Particle size distribution optimized and water demand decreased by modification.
► Intergrinding sample with J and W improves strength and hydration reaction most.
► Pozzolanic reactivity mechanism of CFBA, MCFBAs and PFA are studied.
► Different hydration products are detected by reasonable testing methods.