## 3 Results and Discussion
### Porosity Distribution of Activated Dry Mortars (Mix 2, Mix 3 and Mix4)
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline  & **BJH Adsorption** & **BJH Desorption** & **Difference** & **Rc (MPa)** & **Specific Surface** \\
**Mix 1** & **Pore Volume** & **Pore Volume** & **(cm\({}^{3}\)/g)** & **(cm\({}^{3}\)/g)** & **Area BET (m\({}^{2}\)/g)** \\ \hline Mix 2 (5% Na\({}_{2}\)CO\({}_{3}\)), w/b = 0.5 & 0.0304 & 0.0436 & 0.0132 & 3.57 & 6.91 \\ Mix 2 (10\% Na\({}_{2}\)CO\({}_{3}\)), w/b = 0.5 & 0.0343 & 0.0477 & 0.0134 & 1.35 & 5.63 \\ Mix 2 (5% Na\({}_{2}\)CO\({}_{3}\)), w/b = 0.6 & 0.0488 & 0.0689 & 0.0201 & 6.10 & 9.41 \\ Mix 2 (10\% Na\({}_{2}\)CO\({}_{3}\)), w/b = 0.6 & 0.0527 & 0.0677 & 0.0150 & 3.32 & 8.75 \\ \hline Mix 3 (3% Na\({}_{2}\)O\({}_{3}\)Si), w/b = 0.5 & 0.0397 & 0.0581 & 0.0184 & 7.71 & 9.01 \\ Mix 3 (6% Na\({}_{2}\)O\({}_{3}\)Si), w/b = 0.5 & 0.0342 & 0.0412 & 0.0070 & 5.02 & 5.88 \\ Mix 3 (3% Na\({}_{2}\)O\({}_{3}\)Si), w/b = 0.6 & 0.0550 & 0.0708 & 0.0158 & 9.02 & 10.64 \\ Mix 3 (6% Na\({}_{2}\)O\({}_{3}\)Si), w/b = 0.6 & 0.0405 & 0.0471 & 0.0066 & 10.55 & 6.43 \\ \hline Mix 4 (2% CaCl\({}_{2}\)), w/b = 0.5 & 0.0402 & 0.0446 & 0.0044 & 12.57 & 4.73 \\ Mix 4 (3% CaCl\({}_{2}\)), w/b = 0.5 & 0.0288 & 0.0304 & 0.0016 & 13.65 & 3.33 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Specific surface area BJH for Mix 2, Mix 3 and Mix 4 (activated samples). The addition of Na\({}_{2}\)CO\({}_{3}\) increases the pore volume. The increase in pore volume is accompanied by a drop in the compressive strength UCS. The UCS value is relatively higher (6.10 MPa) with a w/b of 0.6 compared to 0.5 but an average drop of 3 MPa is recorded on the tested formulations. The addition of Na\({}_{2}\)O\({}_{3}\)Si decreases the pore size. For an w/b ratio of 0.5, a decrease in UCS of 2 MPa is observed. An inverse mechanism occurs with a w/b of 0.6. The gain in UCS is 1.5 MPa. For CaCl\({}_{2}\), the highest compressive strength is recorded among the different activators used. The addition of CaCl\({}_{2}\) seems to close the pores and act positively on the UCS value. A gain of 1 MPa is recorded. Several factors can contribute to the modification of hysteresis. The presence of trapped gas and its ability to exit are the most important; however, the contact angle and geometry of the pores also play a non-negligible role. The hysteresis phenomenon is due to the irregular distribution of the size of the pores, which are generally voids of variable shape interconnected by smaller passages and also the \"ink bottle\" effect retains an amount of fluid/gas not negligible in the pores during desorption. This effect is all the more important as the variation in section in the pore is large. This is the reason why adsorption/desorption isotherms in the form of hysteresis are observed, especially for cementitious materials [42]. The gas retention capacity of the reference samples with the ratio w/b = 0.6 occurs to be higher than those of the ratio 0.5; the loop is larger than those observed with the ratio 0.5. This observation is also confirmed by the specific surface area values determined for each sample (see Table 6). The larger the specific surface area, the more the demand for the quantity of water increases per sample. The values observed are around 11 m\({}^{2}\)/g. Then, the more the number of fluid molecules increases, the more the risk of being trapped in the pores increases; thus, the isothermal effect with hysteresis is more present. The main contribution of the present research work deals with the microstructure modification as the first product of hydration of the binder. The contrasting contribution of microstructure development on the mechanical strength of the material is observed. The different microstructure pattern generated by each mixture and its correlation with the specimen UCS value are intimately linked to the nature of additives and to the hydration mechanism. The mechanical strength of each hydration product depends also to the mechanical properties of the pores structure generated.