Preparation of belite cement from stockpiled high-carbon fly ash using granule-hydrothermal synthesis method

Belite cement was prepared from lime and long-term stockpiled high-carbon fly ash by granulehydrothermal synthesis at 97 degrees C followed by calcination at 800-1000 degrees C. The effects of the lime/fly ash ratio, dosage of Na2O and calcination temperature on the phase compositions of the synthesized precursors and clinkers, and the properties of the cements were investigated. Belite cements with the flexural and compressive strengths at 28-day higher then 6.1 MPa and 32.8 MPa, respectively, were prepared. The results show that the quartz and mullite in the fly ash basically do not take part in the reactions. Adding 0.5-1.5% Na2O promotes the hydrothermal reaction and formation of C-S-H and finally increases the formation of belite. alpha'(L)-C2S and C(12)A(7) are the main cementitious minerals in the clinker calcined at 800 degrees C, while beta-C2S and gehlenite present when the calcination temperature reached 900 degrees C or higher. Replacing ordinary portland cement partly for the belite cement might reduce the water requirement and increase the strengths. (c) 2016 Elsevier Ltd. All rights reserved.