Low‐Carbon Recycling of Engineering Muck Through Phosphogypsum: Modeling, Optimization, and Durability Performance Investigation

With the rapid development of urban infrastructure in China, engineering muck has emerged as a potential urban risk. The improper disposal of engineering muck not only results in the inefficient occupation of land resources but also poses serious threats to ecological systems and geotechnical stability. Concurrently, the large‐scale accumulation of phosphogypsum in China has resulted in substantial resource wastage and environmental concerns. To address these dual challenges, this study proposes a “waste‐to‐waste” recycling approach by stabilizing engineering muck with phosphogypsum to facilitate low‐carbon reutilization. Response surface methodology (RSM) based on the Box–Behnken design was adopted to evaluate the effects of three critical variables—main stabilizer content, phosphogypsum content, and activator content—on the 7‐ and 28‐day unconfined compressive strengths. On the basis of the optimized formulation, the influence of the composite stabilizer on drying shrinkage behavior and durability, including water stability, wetting–drying cycle resistance, and freeze–thaw performance, was systematically investigated. Additionally, scanning electron microscopy (SEM) was employed to characterize microstructural changes in both untreated and stabilized soil samples. The results demonstrate that the developed quadratic polynomial model exhibits a high degree of accuracy and reliability in representing the experimental data. The optimized mix design is determined to consist of 7.49% main stabilizer, 3.22% phosphogypsum, and 0.30% activator, yielding predicted compressive strength values of 1.48 MPa at 7 days and 1.82 MPa at 28 days. The incorporation of the composite stabilizer facilitates the formation of hydration products, which effectively fills internal pores, enhances particle bonding, and significantly improves the mechanical strength, water stability, and freeze–thaw resistance of the stabilized soil.