Fly Ash for Belite Calcium Sulfoaluminate Cement – Effect of Alkalis on Clinker Formation and Hydration

At present, the cement industry produces about 5% of the global anthropogenic CO2 emissions. Thus a decrease in the CaO content of cement provides an important opportunity to reduce CO2 emissions. Lower amounts of CaO in cement can be achieved by using belite cements. Belite cements are produced by using lower firing temperatures as well as lower CaO contents. The early strength of these cements is reduced in comparison with ordinary Portland cement. To increase early hydration and provide sufficient early strength, cements are usually produced with additional hydraulically active materials, e.g. calcium sulfoaluminates. The aim of the present investigation is to design a suitable raw meal which when burnt yields a belite-rich clinker with calcium sulfoaluminates. The raw meal contains pulverized limestone, anhydrite and hard coal fly ash (instead of bauxite). Since the alkali content of different fly ashes can vary widely, an equivalent raw meal was produced using different carbonates and oxides instead of the original fly ash. In order to investigate the effect of alkalis on the clinker formation and the hydration process of belite calcium sulfoaluminate cement, the content of alkalis in the raw meal was varied. Results are presented for heat flow calorimetry, X-ray diffraction and simultaneous thermal analysis.      «

At present, the cement industry produces about 5% of the global anthropogenic CO2 emissions. Thus a decrease in the CaO content of cement provides an important opportunity to reduce CO2 emissions. Lower amounts of CaO in cement can be achieved by using belite cements. Belite cements are produced by using lower firing temperatures as well as lower CaO contents. The early strength of these cements is reduced in comparison with ordinary Portland cement. To increase early hydration and provide suffi...     »