## 5 Conclusions  
Phosphorous is one of the most common fertilizers used in agriculture. The waste generated from this fertilizer industry is widely used in cement and road construction. An experimental study was carried out to understand the stress-strain behavior of PG in soil stabilization along with mineralogical changes. Lime is added as the primary stabilizer in three combinations: 3, 5.5 and 7% for various combinations of PG. The discussion mainly highlights the combinations of lime with their respective ideal PG combination. The following observations were made;  
1. Addition of lime and PG to the soil for stabilization results in an increase in the peak stress and a reduction in the corresponding strain. Thus, it can be concluded that the stabilization of the expansive soil with a lime-PG combination increases the stiffness of the stabilized composite. The amendment of the lime-stabilized soil with PG further enhances the stiffness of the stabilized soil.
2. The modulus of soil influences the bearing capacity and settlement behaviors of foundations. The stabilization of the expansive soil with increasing lime content resulted in an increasing modulus of the stabilized soil. However, the amendment of the stabilization process using an optimal dosage of PG resulted in a further increase in the modulus of the stabilized soil. However, an increase in the modulus was pronounced when the lime content was less than or equal to the ICL. Thus, it can be concluded that the addition of an optimal dosage of PG to the lime-stabilization process can further enhance the modulus of the stabilized soil, resulting in improved performance and making it more attractive as an engineering material for foundation support.
3. The residual strength of the stabilized soil composites increases with the addition of optimum PG content; However, an increase in its residual strength is not very prominent for lime content beyond ICL. Thus, it can be concluded that optimum PG content is very effective in enhancing the residual strength of lime-stabilized soils for lime contents up to ICL.
4. The addition of an optimum dosage of PG results in a reduction in I\({}_{\text{B}}\) values of the soil for ICL- and OLC-stabilized soils. Thus, it can be concluded that optimum PG amendment favorably improves the brittle behavior of the lime-stabilized composites when minimum lime content is available.
5. XRD investigations reveal the formation of CSH, ettringite and calcite in the P-amended lime-stabilized soils. However, a detailed look reveals that the reduction in intensities of the peaks of soil minerals, coupled with the peaks of new reaction products is very prominent when 5.5% lime is amended with 0.5% PG. This is in line with the other characteristics of the stabilized soil obtained from its stress-strain curves. Thus, it can be concluded that hastening of the lime-soil reactions by PG, in the augmenting of the supply of calcium ions and contribution in the form of ettrinigite is best achieved when optimal dosages of PG are used to modify soils stabilized at their ICLs rather than OLCs.  
Conceptualization: [PERSON]; methodology: [PERSON], S.V. and E.E.; formal analysis: [PERSON] and S.V.; investigation: [PERSON]; resources: [PERSON], S.V. and E.E.; data curation: [PERSON] and S.V.; writing--original draft preparation: [PERSON] and S.V.; writing--review and editing: E.E.; All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
Data Availability Statement: Data are contained within the article.  
The authors are indebted to the Centre for Nano Technology, Anna University, Chennai, India for providing facilities to conduct XRD and SEM tests.  
The authors declare no conflict of interest.