Effect of partial substitution of raw gypsum with thermally treated phosphogypsum on the properties of Portland Pozzolanic Cement

For many years of production of phosphate fertilizer very large amounts of phosphogypsum (PG) occupied large area, causing chemical and radiological environmental. Using of PG in building materials represents a good method for lowering the cost of cement production and dispose of phosphogypsum as chemical and radioactive waste. Fresh wet hemihydrate phosphogypsum, cement and pozzolana additive were mechanically activated together and from mixing Portland pozzolanic cement (PPC) with PG, these mixes were prepared at different replacements (by weight) of raw gypsum (RG)with purified PG ranging from 1–5% . The purified PG was obtained by calcining PG at temperatures of 200, 400, 600, 800 and 1000 ᵒC. The compressive strength, bulk density, total porosity, combined water and free lime of different hardened mortars were obtained following 3, 7, 28 and 90 days of curing. In addition, the setting time of cement pastes. The highest percentage increase in strength was found to be for PG calcined at temperatures of 800 and 1000 ᵒC. The incorporation of PG in the cement paste has dramatically increased its initial and final setting times. FTIR spectroscopic analysis and scanning electron microscopy (SEM) were used for investigate the change in structure of mortars after curing and change in morphology and microstructure of some hardened pastes.