# Mechanical Behavior of a Mine Tailing Stabilized with a Sustainable Binder
## 5 Conclusions  
The deposition of tailings resulting from the mining operation in landfills must be better managed since these tailings, in contact with erosive agents such as air and water, release chemical elements forming acid mine drainage. Additionally, their mechanical properties must be improved many times for safer disposal in landfills. These tailings are normally stabilized with Portland cement. However, there are very high environmental impacts associated with the production of Portland cement, and more sustainable solutions are needed. This study evaluated the improvement of the mechanical characteristics of a mine tailing using a sustainable binder obtained through the alkaline activation of fly ash. The mine tailing was initially submitted to a series of geotechnical characterization tests. Based on the results obtained, the mine tailing was classified as lean clay (CL). Based on the theory of critical states, the parameters that allow the delimitation of the NCL, k-line and CSL were defined. The obtained results indicated that the critical state parameters of the mine tailings are reasonably similar to the typical values of Santa Clara clay. Concerning the process of improving mine tailings using an alkaline activation technique, the composition of tailing-binder mixtures was defined. Through uniaxial compression tests, it was concluded that the mix with the best performance had the lowest moisture content (55% tailing + 45% fly ash). The most promising mixture was evaluated using triaxial compression tests in both unstabilized and stabilized samples. The stabilization process by alkaline activation significantly influenced the shear strength of the tailing. In  
Figure 22: Failure envelopes of the mine tailing in peak deviatoric stresses (stabilized specimens). \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{2}{c}{**Total Stresses**} & \multicolumn{2}{c}{**Effective Stresses**} \\ \cline{2-4}  & **c** & \(\Phi\) & \(\mathbf{c^{\prime}}\) & \(\Phi^{\prime}\) \\ \hline Natural MT & 0 & 27\({}^{\circ}\) & 0 & 31\({}^{\circ}\) \\ Stabilized MT & 0 & 58\({}^{\circ}\) & 0 & 46\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Shear strength parameters of the mine tailing before and after stabilization (peak deviatoric stresses). fact, even for a short curing period (7 days), a significant increase in friction angle was observed even though cohesion maintained zero value since this period is not enough to develop measurable bonds between the binder and the solid particles. In this sense, the shear strength is expected to increase significantly with the curing time, namely with the increase in cohesion. From the theory of critical states, there was a notable reduction in the parameters that define the NCL, k-line, and CSL, showing a considerable reduction in compressibility and recompressibility for the stabilized specimens. In short, this study characterized the mechanical behavior of the mine tailing before and after stabilization with a sustainable binder based on the alkaline activation of fly ash. The mechanical properties increase due to the development of a binder due to the alkaline activation of the fly ash that reacted with the activator. The results showed the efficacy of the stabilization treatment in the increase in the shear strength of the mine tailing, even for a short-term curing period. Conceptualization, H.R.M., J.P., E.K.N., C.A., N.A., N.C. and T.M. ; methodology, H.R.M., J.P., E.K.N., C.A., N.A., N.C. and T.M. ; formal analysis, H.R.M., J.P. and T.M. ; investigation, H.R.M., J.P., C.A. and T.M. ; resources, N.A., N.C. and T.M. ; writing--original draft, H.R.M. ; writing--review and editing, H.R.M., J.P., E.K.N., C.A., N.A., N.C. and T.M. ; supervision, N.A., N.C. and T.M. ; project administration, N.C. and T.M. ; funding acquisition, N.C. and T.M. All authors have read and agreed to the published version of the manuscript.