Peculiarities of Formation of Phase Structure and the Hydraulic Activity of High-Calcium Fly Ash
High-lime fly ash (HLFA) obtained from the burning of coal at thermal power stations (TPS) consisting of free CaO can be regarded as a specific class of binding materials as they possess hydraulic activity and harden by forming stone of different hardness. This work is devoted to the study of the mechanisms of the chemical and mineralogical composition of high-lime fly ash formation depending on the industrial way of burning Siberian brown coal. Physical properties, chemical and mineralogical composition, and the hydraulic activity of 16 proper samples of HLFA were investigated: six samples of them were obtained at the Siberian TPS when burning brown coals by a flame burner, and four samples were obtained as a result of the experimental burning of brown coals at the commercial pilot plant with a circular fluidized bed. In addition to experimental research methods, the analysis of the CaO-Al2O3–SiO2 state diagram and the calculation of the Gibbs energy for the estimation of the most probable reactions of phase composition of HLFA formation were performed.
It has been determined that free lime present in low temperature fly ashes obtained by burning in the furnaces with a circular fluidized bed is the product of carbonates of various nature decomposition according to its origin and in all other cases – the product of secondary sulfates decomposition.
KeywordsHigh-lime fly ash (HLFA) Binding materials Phase composition State diagram Gibbs energy Hydraulic activity
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