## 5 Discussion  
From the study of the results, it can be concluded that these ashes can be used in subgrades of pavements and embankments for roads to improve gravels and soils that on their own would not be suitable for use under normal conditions of traffic loads.  
The ashes from coal-fired thermoelectric power stations are a residue that is difficult to deal with. The coal in its mineral state contains traces of heavy metals and other elements, and these substances are concentrated in the ash produced by combustion. This makes it necessary to build specific dumps for these sub-products, thus increasing the cost of dumping the material. As well as the costs, it is necessary to occupy an excessive surface of the tip, due to the large volume of the ash. Its current use in roads is practically non-existent, despite its cost being lower than natural aggregates, except for transport and spreading during placement, as with any gravel or soil. The percentage of added lime is low and does  
Figure 7: (a) Graphs of time vs. deformation cycles 200–201 (b) Graphs of time vs. deformation cycles 2600–2601.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**\% Lime**} & \multicolumn{2}{c}{**Gravel-Cement**} & \multicolumn{1}{c}{**G-15\%**} \\ \cline{2-4}  & \multicolumn{2}{c}{**28 Days**} & \multicolumn{1}{c}{**90 Days**} \\ \hline \multirow{2}{*}{0\%} & Breaking Load (KN) & 10.00 & 0.00 \\  & \(\sigma_{\text{F}}\) Stress (MPa) & 1.23 & 0.00 \\ \hline \multirow{2}{*}{2\%} & Breaking Load (KN) & - & 3.00 \\  & \(\sigma_{\text{F}}\) Stress (MPa) & - & 0.37 \\ \hline \multirow{2}{*}{3\%} & Breaking Load (KN) & - & 3.50 \\  & \(\sigma_{\text{F}}\) Stress (MPa) & - & 0.43 \\ \hline \hline \end{tabular}
\end{table}
Table 9: Static flexion test results.  
not significantly affect the cost of the material improved with ash and lime. Nowadays, diverse public administrations are allowing the use of this type of industrial residues (preferentially steel waste), due to the shortage of aggregate from quarries. Moreover, due to the social and environmental drawbacks of opening new aggregate quarries, there are practically no new ones.  
The thermoelectric bottom ash without additives can be used in bases and sub-grades and as filler material. There are real examples in the north of Spain where they have been working correctly for several years [8; 23]. This load-bearing capacity has led to them being used in this study for the improvement of soils and gravels which, through the effect of the lime, can be used in higher layers of roads to support the greater stresses and deformations induced by traffic loads.  
The Aristotle University Department of Transportation's [4] recommendation of 10% ash dosing also relates to the findings of the current study regarding the optimal proportion of ash added to the soil.  
The research is aligned with the results of [PERSON] and [PERSON] [3] on how increasing lime content can negatively affect simple compressive strength in soil-ash and gravel-ash mixtures. The research carried out coincides with the recommendations of the American Coal Ash Association (ACAA) regarding the dosage of bottom ash and lime for treated granular layers [2].