Research and Advances in the Application of Phosphogypsum in Pavement Base Course and Subgrade: A Review

Phosphogypsum (PG) is a secondary material produced during phosphoric acid manufacturing. As the phosphorus‐based chemical industry continues to expand, PG generation has risen steadily. Consequently, ever‐increasing stockpiles of PG pose significant environmental management challenges. At the same time, the road construction sector urgently needs sustainable, low‐impact mineral resources. This review bridges these two concerns by examining integrated strategies for PG valorization. It begins with an assessment of PG's physicochemical characteristics and common impurity removal techniques. Next, it examines PG's use in pavement base course and subgrade layers, focusing on composite systems where PG is blended with inorganic binders, such as cement or lime, or co‐utilized with other industrial solid residues. Additional applications, including soil amelioration, mechanisms underlying strength development, and immobilization pathways for hazardous constituents, are also addressed. A synthesis of current literature reveals that PG's functional performance hinges not on isolated variables but on the holistic integration of pretreatment methods, binder type, particle size distribution, and service conditions. Evidence shows PG can enhance mixture strength through sulfate release, secondary hydration product formation, and pore structure refinement; however, this benefit is highly sensitive to both the inherent composition of raw PG and the formulation of the final blend. For environmentally sound reuse, stringent control over soluble phosphorus, fluoride, heavy metals, and naturally occurring radionuclides is essential. Furthermore, performance validation must encompass realistic stressors, including vehicular loading, alternating moisture exposure, and leaching scenarios, while embedding environmental safeguards at every research stage. By aligning material processing, structural functionality, and ecological risk mitigation, this paper delineates the boundary conditions enabling PG's sustainable deployment in infrastructure. Priority areas for future work include scalable and economical pretreatment approaches, standardized durability testing protocols, long‐term field performance monitoring frameworks, and clearly defined, science‐based environmental acceptance criteria.