## 6 Conclusions  
The main conclusions of this study are:  
1. It is possible to avoid dumping \"marginal\" soils and bottom ash residues from thermoelectric power stations so that under specific conditions they can be used for building roads. The use of bottom ashes improves the mechanical properties of pavement subbases and embankments, achieving an infrastructure of greater ecological value and cost savings of sub-industrial materials that are often taken to landfills. 2. The stabilization of soils and gravels with thermoelectric bottom ash and lime gives rise to a modification of the particle size of the original material. Moreover, it implies a reduction in the maximum Proctor dry density compared with the initial reference of the soil, along with an increase in its optimum humidity. 3. From the soils, when using soils S1 and S2, which initially were \"tolerable\" soils, if 15% of ash, and also 1% of lime in the case of S1 is added, a CBR index permitting them to be used in bases and sub-grades can be achieved. Soil S3 can achieve the characteristics of stabilized soil for 15% of ash and 2% of lime, making it suitable for use in sub-grades of road layers. A soil that has no resistance by adding 25% bottom ash becomes a tolerable soil and it can be used in embankments. Very clayy soil, if combined with 15% bottom ash and 1% lime is a high-performance soil. 4. In some cases, the addition of lime appears to have a positive effect on CBR. For example, for soil S1 with 0% lower ash, it is observed that the CBR increases from 0% to 2% lime. However, in other cases, such as for S3 soil, it appears that the lime content does not have a significant effect on the CBR. For soil S1 with 0% ash, it is observed that the UCS increases with an increasing percentage of lime. 5. The effect of the ash and lime enables the conclusion to be drawn that although the soil liquid limit increases, the plastic limit increases even more, which leads to a reduction in the index of plasticity. 6. These improved soils achieve high levels of compaction for 180 s of compaction with a vibratory hammer in the laboratory. From the viewpoint of placement, given that the dry density of the ash is low, it is recommendable that higher compaction is applied than would be applied to natural soil in normal conditions, although this would not require a long time or great cost. 7. For the gravels, the values of the modulus increase significantly after 28 days, showing a rise of 300% between 28 and 90 days, indicating the activation of the ash with lime over an extended curing period. The values of the modulus increase significantly after 28 days, showing a rise of 300% between 28 and 90 days, indicating the activation of the ash with lime over an extended curing period. * In general, it is observed that increasing the bottom ash content can increase strength, although this effect may vary depending on the specific percentage and curing time. For the G-20% mix, it is observed that the strength increases with the bottom ash content, but this increase is more pronounced for the 90-day curing period. * The gravel treated with bottom ash from a thermoelectric plant and lime needs longer curing times than the gravel-cement in order to reach acceptable strengths. The gravel-cement has a high strength under dynamic loading, while the gravel treated with ash and lime demonstrates poor behavior under this loading produced by traffic; therefore, its usage is not recommendable either in layers in which the stresses undergone by the material are of this type or where there are high traction stresses. Conceptualization, A.V.-Z., L.L.-L., E.L.-L. and M.A.C.-P.; Methodology, A.V.-Z., E.L.-L. and M.A.C.-P.; Validation, L.L.-L.; Formal analysis, A.V.-Z. and E.L.-L.; Investigation, A.V.-Z., E.L.-L. and M.A.C.-P.; Resources, A.V.-Z., E.L.-L. and M.A.C.-P.; Data curation, A.V.-Z., L.L.-L., E.L.-L. and M.A.C.-P.; Writing--original draft, L.L.-L. and E.L.-L.; Writing--review and editing, A.V.-Z., L.L.-L., E.L.-L. and M.A.C.-P.; Visualization, A.V.-Z., L.L.-L.; Supervision, A.V.-Z.