A Study on the Uniaxial Compressive Constitutive Characteristics of Phosphogypsum-Based Irregular-Shaped Bricks (PG-ISBs) for Underground Filling Retaining Walls

This study investigated the mechanical properties of a cementitious material used to prepare irregular-shaped brick masonry structures (PG-ISBs) from industrial solid wastes, including phosphogypsum, calcium powder, cementitious agents, and construction brick debris. The hydration products, microstructure, and elemental composition of the system were analyzed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). Based on the experimental stress–strain relationship curves, a constitutive model for the cementitious material was established. The results show that the compressive strength of the PG-ISB cementitious material meets the requirements for filling retaining walls. SEM observations reveal a significant number of micro-pores within the PG-ISB cementitious material, which are important factors affecting its strength. An empirical constitutive model for the uniaxial compression of the specimen was established based on the experimental stress–strain full curves, and the fitting curves showed good agreement with the experimental data.