Abstract
In this paper, cement combinations based on calcium sulfoaluminate cement (CSAC) were developed and the effect of fly ash and the hemihydrate form of calcium sulfate on the properties of the systems was studied. Fly ash (FA), anhydrite (ANH), flue-gas desulfurization gypsum (FGDG) and plaster gypsum (PL) were used to develop appropriate CSAC/calcium sulfate and CSAC/calcium sulfate/addition systems, the hydration of which was studied. Tested properties of cements were the compressive strength and the setting times. The results suggest that the use of fly ash in the presence of anhydrite accelerates the formation of a strong ettringite-rich matrix that firmly accommodated unreacted fly ash particles, both synergistically contributing to a dense microstructure. At a given sulfate content, the use of anhydrite was shown to be favourable in terms of the setting times, heat patterns and strength development compared to the hemihydrate-based formulations.
Highlights
58 The blending of by-products and additions with Portland cement (PC) is a well established approach to reducing the CO2 emissions associated with the energy-intensive manufacture of cement
Due to rapid setting that occurred in calcium sulfoaluminate cement (CSAC)/plaster gypsum (PL) 241 combinations, preparation and tests were not possible
When calcium sulfate contents reached above 50%, expansion occurred to both combinations with severe cracks forming at a sulfate content of 65% which is a characteristic of ettringite's instability when ye'elimite is introduced in exceedingly high sulfate concentrations
Summary
58 The blending of by-products and additions with Portland cement (PC) is a well established approach to reducing the CO2 emissions associated with the energy-intensive manufacture of cement. The preparation of clinker is achieved by burning the raw materials at temperatures in the range 1300-1350oC in rotary kilns This is 100-150oC lower than PC production and the energy input requirement is lower. By considering the eCO2 emissions of individual cement compounds as given in [7], it can be estimated that the eCO2 of a typical pure CSAC, consisting of ye‟elimite, belite and aluminoferrite, is approximately 600 kg/t. This 74 represents a reduction in eCO2 of approximately 35% when compared to PC
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