The hydration properties of blended cement containing ultrafine fly ash with particle size less than 17 μm from the circulating fluidized bed combustion of coal gangue

Abstract

This paper presents the proposal of the particle size range of circulating fluidized bed fly ash (CFA) that was positively associated with properties of blended cement by gray correlation analysis. Then, the hydration characteristics of blended cement containing ultrafine CFA (UCFA) with the above-suggested particle size distribution are studied from the physical and mechanical properties, hydration heat, non-evaporable water content, morphologies and pore structure. The results show that there is a positive association between CFA particles of less than 17 μm (especially 3–8 μm) and property of blended cement, while there is a negative association for particles of more than 17 μm, so the particles content of less than 17 μm should be improved in CFA as much as possible. The industrial UCFA, whose particle content of less than 17 μm reaches 98.18%, is prepared. The blended cement containing 10% UCFA possesses excellent properties, which ever surpasses pure portland cement. Furthermore, the physical and mechanical properties of blended cement containing no more than 30% UCFA meets the Chinese cement standard of 42.5 grade. With increase in the addition amount of UCFA, the hydration rate and degree of blended cement are gradually decreased and the influence is small at the addition amount of no more than 30%. The addition of 10% UCFA can optimize the pore structure of cement system, and the effect of 30% UCFA on the microstructure of cement gradually decreases with ages.