High-Volume Phosphogypsum Cement Stabilized Road Base: Preparation Methods and Strength Formation Mechanism

This study investigated the potential for efficient and resourceful utilization of phosphogypsum (PG) through the preparation of a High-volume Phosphogypsum Cement Stabilized Road Base (HPG-CSSB). The investigation analyzed the unconfined compressive strength (UCS), water stability, strength formation mechanism, microstructure, and pollutant curing mechanism of HPG-CSSB by laser diffraction methods (LD), X-ray diffraction (XRD), fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and inductively coupled plasma-mass spectrometry (ICP-MS). The optimal mix ratio of HPG-CSSB was 4% cement, 1% CA2, 35% PG, and 60% graded crushed stone. The UCS reached 6.6 MPa, 9.3 MPa, and 11.3 MPa at 7, 28, and 60 d, respectively. The alkaline curing agent stimulated cement activity and accelerated the release of Ca²⁺ and SO₄^2- from the PG. This formed many C-S-H gels and ettringite (AFt). The curing agent converted Ca²⁺ to C-(A)-S-H gels due to high volcanic ash activity. The diverse hydration products strengthened HPG-CSSB. The HPG-CSSB exhibits favorable water stability, demonstrating a mere 7.6% reduction in strength following 28 d of immersion. The C-S-H gel and AFt generated in the system can carry out ion exchange and adsorption precipitation with F^- and PO₄^3- in PG, achieving the curing effect of toxic and hazardous substances. HPG-CSSB meets the Class A standard for integrated wastewater discharge.