Research on the pretreatment and mechanical performance of undisturbed phosphogypsum

In this study, dehydration process of original phosphogypsum (PG) was firstly studied by differential thermal analysis method, and the optimal heat treatment temperature was obtained. Subsequently, the effects of dehydration time and ageing time on compressive and flexural strengths of PG pastes were studied. Additionally, the influence of blast furnace slag, silica fume and Portland cement on compressive strength of PG were determined. Results showed that CaSO4·2H2O in PG were dehydrated at three steps and the related dehydration temperatures were 80 ℃, 140 ℃ and 160 ℃. When the dehydration duration at 140 ℃ was 9 h and the ageing time was 5 d the PG paste obtained the best flexural and compressive strength. The addition of blast furnace slag and cement behaved a positive effect on the mechanical strength of PG. The 28 d compressive strength of PG mixture was increased by 97.8 % when the dosage of cement was 40 % by the mass ratio of total binder. Unfortunately, fly ash led to the decreasing mechanical strengths of PG mixture.