Effects of pH and Fineness of Phosphogypsum on Mechanical Performance of Cement–Phosphogypsum-Stabilized Soil and Classification for Road-Used Phosphogypsum

This article investigates the effects of phosphogypsum (PG) pH and particle fineness on the mechanical properties of cement–PG-stabilized soil. Using solutions of calcium hydroxide (Ca(OH)2) and sulfate (H2SO4) to adjust pH value of PG from 2 to 8. The key pore size used to characterize PG fineness was determined to be 200 μm based on the Grey relational analysis (GRA), and the fineness of PG was controlled from 12.31% to 56.32% by grinding different time. Cement–PG cementitious materials (CPCM) and cement–PG-stabilized soil with different mixture ratios were formed at an optimum moisture content; following this, the unconfined compressive strength and California bearing ratio values of the samples were tested. Results show that the increased pH or the decreased fineness leads to continuous increases in the unconfined compressive strength of CPCM and cement-PG stabilized soil as well as the CBR value of cement–PG-stabilized soil. However, once PG pH value exceeded 5 or fineness was less than 20%, the mechanical properties of cement–PG-stabilized soil remained stable. A classification standard for road usage PG was established based on the analyses regarding cement-PG stabilized soil’s mechanical properties, which has great significance of selecting or disposing road-used PG.