Synthesis of Sustainable Subgrade Geocomposite Material Using Phosphogypsum Stabilized with Red Mud

The utilization of industrial waste as a construction material has become imperative in the era of sustainable engineering. In this context, the present study delves into the performance and behavior of two commonly discarded waste materials: phosphogypsum (PG) and red mud (RM), when employed in subgrade soil applications. PG is highly acidic, with a pH of 2.83, while RM is highly alkaline, boasting a pH of 10.12. Consequently, RM is introduced in varying proportions to neutralize the acidity of PG, and the engineering characteristics of the resulting mixture are thoroughly investigated. The study encompasses the evaluation of fundamental properties such as specific gravity and Atterberg's limits, alongside engineering properties including unconfined compressive strength (UCS) and California bearing ratio (CBR) tests. These assessments aim to determine the suitability of the PG–RM blend for use as a construction material. Additionally, the study demonstrates that the addition of RM to PG effectively mitigates its acidity through neutralization. Results from the UCS tests highlight that the highest strength is achieved with a 40% replacement of PG, after which the UCS value decreases. Furthermore, a 40% replacement of PG with RM yields a higher CBR value of 9.13%. This comprehensive study instills confidence in the use of PG blended with RM as a subgrade material in road construction projects, contributing to sustainable engineering practices.