Recycle of fired phosphogypsum waste product as a cement replacement and its role on the hydration and strength development of pastes

The effect of Partially up to fully substituted of treated phosphogypsum x(PG) for natural gypsum on the physico- mechanical as well as kinetic of hydration of ordinary Portland cement has been discussed . The results show that by increasing PG % the water to cement ratio decreased while the initial and final setting times increased So PG acts as a retarder and water reducer . The retardation effect may be attributed to formation of ettringite layer which formed on the surface of C3A of cement pastes . The chemically combined water, free lime content and bulk density increased with curing time and with PG content for all cement pastes up to 90 days due to increasing of the rate of hydration. The compressive strength increased by increasing of PG % due to formation of anhydrite , changes in major oxides content and reduction of impurities . X-Ray Diffraction, SEM and DTA of some samples have been studied