Microstructural and Phase Characteristics of Phosphogypsum-Cement Mixtures

The effects of the tricalcium aluminate (C 3 A) content of the stabilizing cement [Type II (1.3% C 3 A) cement and Type III cement (9.3% C 3 A)], curing time (seven to 90 days), proportion of PG (5-60%), grain size, and impurities in phosphogypsum (PG) (PG compared to gypsum) on the microstructural (by scanning electron microscopy) and phase properties of gypsum PG and cement mixtures, a potential road-base material, were studied (by derivative thermogravimetry). Morphologically, two types of ettringite (well-defined crystals, >2 m in lengths and ill-defined crystals, below 1 m in length) were present in the cement and gypsum PG mixtures. The impurities in PG retarded the initial hydration of cement in direct proportion to its amount in the mixtures. However, gypsum PG increased the degree of hydration of cement in the mixtures in the long term. The reacted gypsum PG produced a large amount of ettringite (within two months) compared to cement only. The amount of carbonation was uniformly low.