# Mechanical Behavior of a Mine Tailing Stabilized with a Sustainable Binder
## 4 Mechanical Behavior of Mine Tailing after Stabilization  
### Preparation  
For all alkaline activation processes, an activator/fly ash ratio of 0.4 was used based on reports by [PERSON] et al., 2017 [PERSON] et al., 2017 [PERSON] et al. (2017). The concentration of NaOH used was 10 molal [PERSON] et al. (2017); [PERSON] et al. (2017). As shown in Table 5, three mixtures were defined, varying only in the amount of waste added to determine which mixture revealed a better mechanical performance.  
Uniaxial compression tests were performed according to the BS standard (1990). The tests were carried out with a constant displacement speed of 0.009 mm/s, using the triaxial compression test press with a 5 kN load cell. The displacements were measured using a linear variable differential transformer (LVDT). Three specimens were constructed for each of the three mixtures to evaluate the mechanical results in average terms. All specimens were tested on the same day, with a curing period of 7 days. This curing time does not allow a precise evaluation of the evolution of geopolymer reactions and characteristics of alkaline-activated mixtures in the long term. However, at this stage, it was only intended to determine which of the mixtures revealed a better mechanical performance.  
The evolution of the compressive strength as a function of the axial strain of the specimens corresponding to mixtures M1, M2, and M3 was evaluated, as shown in Figure 15. In the first mixture (M1), the three specimens tested resulted in mechanical strengths of 482.8 kPa, 556.3 kPa, and 550.6 kPa, respectively. On average, the M1 mix resulted in a compressive strength of 529.9 kPa.  
Regarding mixture M2, it was only possible to assess the behavior of one of the specimens since the two remaining were damaged during the test because the equipment used had supports with hinges, which caused the destabilization of the specimens seconds after the beginning of the test. For the M2 specimen, a compressive strength of 385.4 kPa was obtained.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Total Stresses** & \multicolumn{2}{c}{**Effective Stresses**} \\ \hline c & \(\phi\) & c\({}^{\prime}\) & \(\phi^{\prime}\) \\
0 & 27\({}^{\circ}\) & 0 & 31\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table}
Table 4: Shear strength parameters of the mine tailing.  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline  & **FA (g)** & **MT (g)** & **Activator (g)** & **Water (g)** & **NaOH (g)** & **FA (\%)** & **MT (\%)** & **Activator (\%)** & **Water (\%)** \\ \hline M1 & 500 & 500 & 200 & 142.9 & 57.1 & 50.0 & 50.0 & 16.7 & 11.9 \\ M2 & 500 & 400 & 200 & 142.9 & 57.1 & 55.0 & 45.0 & 18.2 & 13.0 \\ M3 & 500 & 600 & 200 & 142.9 & 57.1 & 45.0 & 55.0 & 15.4 & 11.0 \\ \hline \hline \For the last mixture defined (M3), the mechanical strengths achieved were 853.1 kPa, 875.2 kPa, and 895.4 kPa, resulting in an average strength of 874.6 kPa. Among the mixtures studied, this was the most efficient. The mixture with the lowest amount of activator (M3) was the one that showed the best mechanical performance, meaning that the specimens of the two other mixtures (M1 and M2) were compacted with moisture contents higher than the optimum. In addition to demonstrating values with lower mechanical resistance, as they contain a greater amount of activator, mixtures M1 and M2 are less economical since  
Figure 15: Evolution of compressive strength vs. axial strain for mixtures M1, M2 and M3.  
the cost associated with the production of the alkaline-activated cement resides in the cost of activating solutions.