Untreated phosphogypsum as a set retarder for slag cement production

The utilization of large amounts of by-products and waste materials plays a very important role in solving ecological problems. Phosphogypsum is a waste product of the phosphoric acid. About to 200,000 tons of phosphogypum are annually produced in Egypt and cause serious storage and environmental problems. Phosphogypum is a rich source of calcium sulphate carrying impurities of phosphates and fluorides. This work aimed to evaluate the effect of substitution of natural gypsum by phosphogypsum on the hydration behavior as well as the physico-mechanical properties of slag cement. The natural gypsum was partially substituted by phosphogypsum in the ratios 2.0,4.0 and 6.0 wt., \%.The different prepared were hydrated up to 90 days. The hydration was followed and the physico-mechanical properties were estimated. The results revealed that, poshgypsum accelerates the rate of hydration and enhances the mechanical properties of the investigated mixes, especially at later ages of hydration. It can be concluded that, phosphogypsum is more effective set retarder than natural gypsum and can be successfully used for slag cement.