Effect of modified amino acids on hydration behavior of β-hemihydrate phosphogypsum

In practice, it is often necessary to add retarders to β-hemihydrate phosphogypsum (β-HPG) to prolong its setting time. In this paper, the effects of modified amino acid (XK) on physical and mechanical properties, hydration characteristics, and microstructure of β-HPG were investigated using various methods including fluidity, setting time, strength, hydration heat, X-ray diffraction (XRD), scanning electron microscope (SEM), mercury intrusion porosimetry (MIP), and X-ray photoelectron spectroscopy (XPS). The findings indicate that the addition of XK enhances the fluidity of β-HPG, and as the content of XK increases, there is an occurrence of prolonged setting time but a concurrent decrease in both the compressive and flexural strength. In addition, the incorporation of XK hampers the hydration process of β-HPG, resulting in a reduction in the hydration exothermic rate. Microscopic analysis reveals that while XK does not alter the final hydration products, it does affect the growth pattern of dihydrate gypsum crystals because of surface adsorption, and specifically, the crystals become short and columnar, with a looser crystal structure. Furthermore, XK leads to larger pores and deterioration of the pore structure of β-HPG.