This study investigates the mechanical properties and internal pore structure characteristics of raw phosphogypsum–basalt fiber (RPG-BF) cementitious materials with varying raw phosphogypsum (PG) replacement ratios. Specifically, six different PG addition levels (0%, 3%, 6%, 9%, 12%, and 15% by mass of cementitious materials) with a constant basalt fiber dosage of 0.1% (by volume of concrete) were adopted. The mechanical properties of RPG-BF cementitious materials were evaluated by testing the 7-day and 28-day compressive strengths, 28-day split tensile strength, and 28-day flexural strength. Meanwhile, the pore distribution characteristics of the RPG-BF cementitious materials were systematically analyzed using liquid nitrogen adsorption (LNA) tests and scanning electron microscopy (SEM) observations. The experimental results indicate the following: (a) With an increase in PG content, the mechanical properties of RPG-BF cementitious materials exhibit a significant downward trend: the 28-day compressive strength, split tensile strength, and flexural strength decrease by 49%, 44%, and 43%, respectively. (b) The internal pores of the RPG-BF cementitious materials possess excellent fractal characteristics, with fractal dimensions ranging from 2.52 to 2.62. As the PG content increases, the pore structure becomes more intricate and less homogeneous, which is a microstructural factor associated with the degradation of mechanical properties. (c) There exists a strong Pearson’s linear correlation (R > 0.82, with R2 ranging from 0.67 to 0.94) between the pore fractal dimension of RPG-BF cementitious materials and their 7-day/28-day compressive strength, split tensile strength, and flexural strength. (d) SEM observations show that the quantity of micropores and microcracks in the RPG-BF cementitious materials increases with increasing PG content, further confirming deterioration of the material microstructure.
Xu et al. (2026) studied this question.