EVALUATION OF PHOSPHOGYPSUM AS AN ALTERNATIVE OF GYPSUM IN THE FABRICATION OF CEM　Ⅱ/A-M 32.5 R PORTLAND CEMENT

摘要

The production increase of Portland cement CEM Ⅱ/A-M 32 R (European standards) containing up to 5% of gypsum in Senegal having no gypsum deposit is leading to a rise in the need of such imported materials. In order to decrease, these importations, a research on the substitution of gypsum has been conducted. Phosphogypsum is a well-known co-product of fabrication of phosphoric acid from phosphates. The high content of SO3 shows its sulfatating character. Laboratory and industrial tests reveal that the physical and the chemical aspects of the cement with phosphogypsum as sulfatating agent respect Senegalese and European standards. The setting time of this cement is found to be higher than that of the gypsum-based CEM Ⅱ/A-M 32 R cement. This study shows that this increase is linked with soluble P_2O_5 present in phosphogypsum. Production gain is also discussed in term of effective cement cost as a consequence of the decrease of ⅰ) the sulfatating matter, ⅱ) the clinker used, but also ⅲ) the cost of the energy factor. The study also shows that construction materials can sometimes appear as a practical and economical solution to environmental problems. The aim of this paper is to demonstrate the possibility of gypsum substitution by phosphogypsum in the fabrication of CEM Ⅱ/A-M 32 R Portland cement, while keeping the major properties of such standard cement without modification of the directions for use. The impact of this substitution is shown to be economically and environmentally striking.