Sulfur anhydride influence on sintering and activity of Portland cement clinker

Resource and energy saving are very important in cement production. It is achieved using industrial waste, that reduces the amount of natural calcium-containing raw materials or the firing temperature of clinker raw mixture. One of these wastes is phosphogypsum, which can replace natural limestone partially or be a mineralizer. However, the sulfur effect on the clinker formation processes and the cement properties is ambiguous. In its presence, the formation of low-active alite is possible; it reduces the cement quality. On the other hand, when a clinker is fired, sulfur in SO2 form emits into the atmosphere with exhaust gases. Acceleration of clinker formation in the sulfur presence is known. The effect of sulfuric anhydride on clinker sintering and the Portland cement activity is investigated in this paper. Using chemically pure materials have been prepared raw mixtures containing 3% CaSO4, calculated for the formation of various mineral composition clinker. All sulfur-containing clinkers contained anhydrite and an increased amount of free lime. The shape and size of alite crystals were unchanged in comparison with the control compositions, which indicates the absence of the CaSO4 mineralizing effect. The sulfur introduction reduces the hydraulic activity of clinkers with modular characteristics corresponding to the factory compositions. To increase the Portland cement strength with the introduction of sulfuric anhydride, it is recommended to reduce the values of saturation coefficient or silicate modulus.