Wetting-drying effect on the strength and microstructure of cement-phosphogypsum stabilized soils

Phosphogypsum has often been used as an effective and environmentally friendly binder for partial replacement of cement, improving the engineering properties of slurries with high water content. However, the in fluence of phosphogypsum on the physicomechnical properties of stabilized soil subjected to wetting-drying cycles is not well understood to date. In this study, the effect of phosphogypsum on the durability of stabilized soil was studied by conducting a series of laboratory experiments, illustrating the changes in mass loss, pH value and uncon fined compressive strength ( q u ) with wettingdrying cycles. The test results showed that the presence of phosphogypsum signi ficantly restrained the mass loss in the early stage (lower than the 4th cycle), which in turn led to a higher q u of stabilized soil than that without phosphogypsum. After the 4th cycle, a sudden increase in mass loss was observed for stabilized soil with phosphogypsum, resulting in a signi ficant drop in q u to a value lower than those without phosphogypsum at the 6th cycle. In addition, the q u of stabilized soils correlated well with the measured soil pH irrespective of phosphogypsum content for all wetting-drying tests. According to the microstructure observation via scanning electron microscope (SEM) and X-ray diffraction (XRD) tests, the mechanisms relating the sudden loss of q u for the stabilized soils with phosphogypsum after the 4th wetting-drying cycle are summarized as follows: (i) the disappearance of ettringite weakening the cementation bonding effect, (ii) the generation of a larger extent of microcrack, and (iii) a lower pH value, in comparison with the stabilized soil without phosphogypsum. (c) 2024 Institute of Rock and Soil Mechanics, Chinese Academy of Sciences. Production and hosting by Elsevier B.V. This is an open access article under the CC BY -NC -ND license (http://creativecommons.org/ licenses/by-nc-nd/4.0/).