Mechanical Strength, Water Resistance, and Microstructure of Cold-Bonded Phosphogypsum-Based Lightweight Aggregates

The extensive accumulation of phosphogypsum (PG) poses significant environmental challenges, necessitating its efficient utilization. This study investigated the mechanical properties, water resistance, and microstructural characteristics of cold-bonded phosphogypsum-based lightweight aggregates (PLAs) with various contents of ordinary portland cement (OPC). A minimal OPC content of 3% yielded the highest cylinder compressive strength (16.3 MPa at 28 days), which is attributed to an optimal synergy between hydration product formation and densification. A comprehensive microstructural analysis using scanning electron microscopy (SEM), X-ray diffractometry (XRD), and thermogravimetric (TG) analysis demonstrated clear correlations between porosity, hydration products (ettringite and C─ S─ H gel), and mechanical performance. Furthermore, the study emphasized the water resistance of PLAs. Due to the continuous hydration reaction and the wrapping of hydration products, the PLAs had strong water resistance and immobilized hazardous phosphate ions, thereby enhancing both environmental safety and material stability. Economic and environmental assessments further highlighted the feasibility and sustainability of utilizing low OPC dosages, aligning with global sustainability goals. These findings provide actionable strategies for scaling industrial applications of PLAs while mitigating environmental impacts.