Effect of phosphogypsum on physiochemical and mechanical behaviour of cement stabilized dredged soil from Fuzhou, China

Chemical treatment is one of the popular methods dealing with geoenviromental problems related to soil, such as waste dredged materials, soil with heavy metal pollutions, among others. This paper performed a series of laboratory tests to investigate the effect of phosphogypsum on water content, density, pH, unconfined compressive strength and deformation modulus of cement stabilized soil. It is found that the water content and pH value decreased whereas the density increased, as the phophogysum content increased. These changes were attributable to the formation of ettringite related to the chemical reaction between phosphogypsum and cementitious materials (calcium aluminate hydrates). The unconfined compression strengths of the cement stabilized soil with phosphogypsum content of 1.4% to 8.6% were approximately 1.7 to 9.4 times of those without phosphogypsum. Particularly, the earlier strength of the stabilized soil with phosphogypsum cured at 3 and 7 days increased by 1.3 and 2.1 times in comparison with those lacking phosphogypsum. The mineralogical changes revealed that when the cementation bonding was sufficiently formed at 28 days of curing, the increase in ettringite with phosphogypsum content behaved positive influence on strength development of cement stabilized soil. When cementation bonding was relatively low before 7 days of curing, adequate phosphogypsum content might produce moderate level of ettringite, tended to swell and make denser fabric, resulting in the strength increase. It should be also noted that over-dosage of phosphogypsum might cause volume increase and structure disruption, leading to the strength loss. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The addition of phosphogypsum can significantly improve the strength and density of cement stabilized soil, but overdosage may lead to structural disruption. Proper control of phosphogypsum content is beneficial for enhancing the performance of cement stabilized soil.