The effects of phosphogypsum on the setting and mechanical properties of Portland cement and trass cement

Abstract Phosphogypsum, the by-product of phosphoric acid industry, consists of CaSO 4 .2 H 2 O and contains some impurities such as P 2 O 5 , F and organic substances. These impurities seriously restrict the industrial use of phosphogypsum in cement industry as a retarder. In this study, the effects of phosphogypsum and purified phosphogypsum on the hydration of Portland cement and trass cement were investigated by measuring setting time, strengths of pastes, and chemical analysis as well as the electron microscopic (SEM) observation of the hydration products. It was concluded that untreated phosphogypsum can be used as a retarder directly in trass cement, whereas Portland cement requires purified phosphogypsum.