By adjusting the content of geopolymer in geopolymer stabilized phosphogypsum (GSP) as roadbed filler, along with the mixing ratio, this paper mainly explores tendencies in the mechanical properties and water stability of GSP. This research is based on macro-mechanical properties such as unconfined compressive strength, resilience modulus, California bearing ratio and shear strength. It is also based on water stability tests, such as the water soaking test, dry and wet cycle test and expansion test, to explore changes in water stability. As for the durability of GSP, this paper is mainly based on the realization of a long time observation of mechanical properties and water stability. In the existing research, most of the stabilized phosphogypsum (PG) base material or roadbed filler consists of cement, lime, etc. In this paper, a new exploration is carried out on the composition of stabilized PG material, realized without the participation of cement. The 28 d compressive strength of GSP reaches 2.5 MPa, and over time this strength grows, which prevents the phenomenon of strength inversion that may occur in conventional cement-stabilized PG. In addition, a long-term soaking experiment was designed in this study based on the material after the strength was stabilized for up to 90 d. After the strength was steady, the GSP with the best water stability still had a softening coefficient of 80% after experiencing water immersion for 7 d. After determining the feasibility of the mechanical properties and water stability of GSP as roadbed filler, we further explored the strength formation mechanism of GSP by microscopic tests (XRD and SEM). This shows that geopolymer can stabilize PG in two main ways: one is the hydration reaction with PG to generate C-S-H gel and ettringite, and the other is to connect PG not involved in the chemical reaction to form a dense whole through generated hydration products. Geopolymer, stabilizing a high amount of PG, not only provides a new method for the consumption of PG, but also has more stable performance than cement, and has certain advantages in economy. In addition, the advantage of this study is that good performance can be achieved by simply sieving PG and adjusting the geopolymer ratio in practical engineering projects.

Comprising a relatively large amount of industrial solid waste, the high-value utilization of phosphogypsum (PG) is closely related to the sustainable development of resource materials and the protection of the ecological environment. PG can improve some of the shortcomings of geopolymers, but there is a lack of systematic research on the specific influencing factors as well as the mechanism of the two in a hydration reaction. In this study, the effects of the Si/Al, Na/Al and Ca/Al ratios on the micropores as well as the hydration products of phosphogypsum-modified geopolymer material (PMGM) are systematically explored via macroscopic and microscopic tests from the molar ratios of the raw material’s target components. By changing the molar ratio, the generation of hydration products is affected, thereby altering the properties of the material. The effects of each molar ratio on paste workability, capillary water absorption, drying shrinkage and self shrinkage are systematically analyzed, while the types, productions, and micropores of hydration products are analyzed via XRD and SEM. This study provides a new idea for the large-scale recycling of PG and makes a systematic investigation of its hydration mechanism, which can provide a reference for the reaction principle of PG with geopolymers.