## 3 Results and Discussion
### Unconfined Compressive Strength  
Figure 3 shows the UCS values obtained for the tested combinations at 7, 28 and 90 days with three replicates (standard deviations are provided on the curves). The unstabilized samples achieved the same UCS values at all ages, as no chemical reactions occurred in the unstabilized combinations. M1C0, M2C0 and M3C0 achieved 0.6 MPa, 1.5 MPa and 1.4 MPa, respectively. The results obtained for M1C0 were similar to those reported by [PERSON] et al. [10] for clayey soil. However, [PERSON] et al. [11] achieved higher values (1.6 MPa) with clayey soil. The values obtained by [PERSON] et al. [11] were reached by M2C0, which demonstrates that adding by-products to the clayey soil improved the UCS values. In fact, M2C0 showed an improvement of 250% compared to the mixture without by-products (M1C0). Additionally, the clayey soil contributed to greater cohesion in the mix, as combination M2C0 achieved a higher UCS value than combination M3C0. In the CEM-stabilized specimens, a direct relationship was observed between UCS values and CEM dosage. This was related to the fact that a higher cement dosage allows for the generation of a greater amount of cementitious gel, and therefore, stronger specimens are obtained [38]. Additionally, a direct relationship was found between UCS values and curing time, with a generally faster increase in UCS between days 7 and 28 compared to the period between days 28 and 90. This was related to the rapid hydration of the cement to generate hydration products, in accordance with the literature [11; 39]. M1C2.5 \begin{table}
\begin{tabular}{c c c} \hline \hline  & **OMC (\%)** & **MDD (g/cm\({}^{3}\))** \\ \hline M1C0 & 18.5 & 1.76 \\ M1C2.5 & 19.8 & 1.72 \\ M1C5 & 21.4 & 1.65 \\ \hline M2C0 & 7.1 & 2.27 \\ M2C2.5 & 7.6 & 2.24 \\ M2C5 & 8.4 & 2.22 \\ \hline M3C0 & 6.9 & 2.29 \\ M3C2.5 & 7.3 & 2.25 \\ M3C5 & 7.7 & 2.21 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: OMC and MDD of all combinations. achieved 2.1 MPa, 2.3 MPa and 2.8 MPa at 7, 28 and 90 days, improving the UCS value of the unstabilized M1 mix (MIC0) by 383% at 28 days, in accordance with the literature [12; 39]. The improvement in combination M1C5 was greater, achieving UCS values of 4 MPa, 4.1 MPa and 4.2 MPa at 7, 28 and 90 days respectively, which represented a 700% increase compared to the values of M1C0 at 28 days. These values were consistent with the literature, where similar UCS values are reported for cement-stabilized SRE samples [12; 39; 40]. The UCS values obtained for combinations M1C2.5 and M1C5 exceeded the typical requirements found in the literature, which are between 1.3 MPa and 2 MPa [9; 41]. Combination M2C2.5 achieved 4.3 MPa, 4.5 MPa and 5.9 MPa at 7, 28 and 90 days respectively, improving the UCS values of M2C0 by 300% at 28 days. Similarly, M2C5 reached 7.9 MPa, 9.3 MPa and 9.6 MPa at 7, 28 and 90 days, respectively, representing a 620% improvement over M2C0 at 28 days. Additionally, both M2C2.5 and M2C5 outperformed combinations M1C2.5 and M1C5 at 28 days by 196% and 227%, respectively. This demonstrated that the addition of by-products with gravel- and sand-sized PSD to a clayey soil enhanced the UCS of the SRE mixtures. As cement generated calcium silicate hydrate gels, these gels were capable of binding the by-product aggregates, resulting in a stronger specimen than if only clay were used [23; 24]. Both combinations M2C2.5 and  
Figure 3: UCS values of the tested combinations at 7, 28 and 90 days. (**a**) M1 mix, (**b**) M2 mix, (**c**) M3 mix. M2C5 achieved higher values than those reported in previous studies [12; 39; 40]. This was attributed to the fact that the soil had not been improved in those studies, whereas in the case of Mixture 2, the clayey soil was modified by adding by-products that modified and enhanced the mix's properties. Combination M3C2.5 achieved 5.5 MPa, 6.2 MPa and 6.5 MPa at 7, 28 and 90 days respectively, improving by 443% over combination M3C0 at 28 days.