# Utilization of Phosphogypsum and Sediment in Subgrade Material for Pavement Construction
## 4 Conclusions  
This study offers a thorough assessment of the potential of phosphogypsum as a stabilizing agent in sediment mixtures, focusing on its effectiveness in immobilizing heavy metals and enhancing mechanical properties as subgrade material. The analysis of pseudo-total metal content indicates that the initial sediment is highly contaminated, particularly with cadmium, copper, and zinc, which classify it as extremely polluted. This underscores the need for effective treatment of contaminated sediments to mitigate environmental risks.  
The sediment's granulometric composition, dominated by fine particles, enhances its cohesiveness and mechanical properties, making it suitable for construction applications. Thermal analysis via TGA/DTA demonstrates the thermal stability of the sediment mixtures, revealing distinct mass loss phases that correlate with specific thermal reactions. XRF analysis further confirms the predominant presence of clay minerals and highlights the effectiveness of phosphogypsum in reducing the concentrations of heavy metals in treated mixtures. The leaching index (LX) values for the treated sediments, particularly those incorporating phosphogypsum, indicate that they meet the criteria for \"controlled use\" applications, making them suitable for specific environmental remediation efforts. The analysis of leaching mechanisms reveals that surface wash-off is predominant for several metals, while diffusion and dissolution contribute to the release of others, necessitating continued monitoring to mitigate risks. Mechanical testing results indicate that while the uniaxial compressive strength (UCS) of the mixtures with phosphogypsum does not yet meet the minimum requirements for road construction, the California Bearing Ratio (CBR) values demonstrate potential suitability for subgrade material in road embankments. According to the Roads of Serbia's specifications, all tested mixtures can be considered for subgrade material in road embankment construction. This suggests that further optimization of phosphogypsum content is necessary to achieve desired strength characteristics.  
In summary, this study highlights the dual benefits of using phosphogypsum in sediment treatment: it not only aids in the stabilization of heavy metals, thereby reducing environmental risks, but also enhances the physical properties of the sediment for potential engineering applications. Future work should focus on exploring long-term environmental impacts of using these treated sediments in construction and remediation projects.  
**Author Contributions:** Conceptualization, N.S., D.R.V. and V.B.; Formal analysis, N.S., D.R.V., M.S. and V.B.; Investigation, M.S.; Methodology, N.S., D.R.V. and V.B.; Project administration, D.T.P.; Supervision, N.D.; Validation, N.D.; Visualization, M.S.; Writing--original draft, D.T.P.; Writing--review and editing, D.T.P. All authors helped revise the draft of the manuscript. All authors have read and agreed to the published version of the manuscript.  
**Funding:** This research was supported by the Science Fund of the Republic of Serbia, #7753609, BEuSED.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** The datasets during and/or analyzed during the current study are available from the corresponding author upon reasonable request.  
**Conflicts of Interest:** All authors are aware the given information regarding this manuscript is correct. All authors have agreed that there are no conflicts of interest in this manuscript. All authors have declared that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.