The workability kinetics of phosphogypsum binder

Abstract

The dihydrate phosphogypsum (PG) based binder workability kinetics were investigated regarding to water-binder ratio (W/B) and chemical admixtures added to the composition of PG paste. PG was dried at 60 °C and homogenized to powder like particles with collision milling in disintegrator and calcium sulphate hemihydrate was obtained by heating PG at 180 °C. The obtained binder chemical, mineralogical and technological properties were tested and compared to commercial gypsum plaster. Early age (2 h) and 14 d compression strength was determined. The workability and setting time of both – PG and commercial gypsum was investigated with viscosimeter, ultrasonic pulse velocity and Vicat apparatus and correlation between testing methods was obtained. Results indicate that binder based on PG has slightly lower pH (pH 6.3) than commercial binder (pH 6.8) and finer particle size grading leading to increased W/B ratio and more rapid initial setting time. The set retarder could efficiently increase the setting time of PG binder giving extra workability time which is positive factor for prolonged treatment of binder slurry, i.e. to prepare porous gypsum binder. Such approach would give a safer alternative to PG disposal, closing the materials loop and enhancing the circularity of this material.