## 3 Results
### Flexural Tensile Strength  
The results of the flexural tensile test at 28 days of age showed a slight increase of 0.04% and 0.03% in the strength of the specimens with uncalcined shells, MR-05 and MR-10, respectively, and an increase of 0.05% in the strength of the specimens with calcined shells, MRC-05 and MRC-10, compared to the control specimen MR-00. However, these results do not confirm that the strength is definitively greater in the specimens with shell replacements due to the observed deviations. The detailed results of the flexural tensile strength are presented in Table 3.  
Figure 7a,b shows a graphical representation of the results of the flexural tensile test. From these, it can be seen that calcination did not provide improvements in strength, since this decreases at 28 days of age by 0.21% in the MRC-05 and MRC-10 specimens compared to their MR-05 and MR-10 counterparts, respectively.  
Calcination decreases flexural tensile strength due to changes in the chemical and physical structure of the material resulting from this process. During calcination, the calcium carbonate (CaCO\({}_{3}\)) present in seashells breaks down into calcium oxide (CaO) and carbon dioxide (CO\({}_{2}\)). This change reduces the amount of cohesive material that can contribute to the mechanical strength of the mortar.  
Furthermore, calcination can also generate a more porous and less dense microstructure in the material, which affects negatively its ability to resist tensile stresses. This additional porosity allows more microcracks to form under load, which decreases strength. Overall, the calcination process, if not properly controlled, can reduce the quality of the material in terms of mechanical strength, as demonstrated by the decrease observed in the experimental results.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Specimen**} & \multirow{2}{*}{**\#**} & \multicolumn{3}{c}{**Flexural Tensile Strength [MPa] at Age:**} & \multirow{2}{*}{**Standard Deviation**} \\ \cline{3-3} \cline{5-6}  & & **3 Days** & **7 Days** & **14 Days** & **28 Days** & **at 28 Days** \\ \hline \multirow{3}{*}{MR-00} & 1 & 7.10 & 10.29 & 13.74 & 15.03 & \multirow{3}{*}{0.87} \\  & 2 & 7.05 & 10.20 & 16.92 & 16.55 & & \\  & 3 & 6.41 & 9.36 & 13.14 & 15.03 & & \\ \hline \multirow{3}{*}{MR-05} & 1 & 5.21 & 8.72 & 13.93 & 15.59 & \multirow{3}{*}{0.97} \\  & 2 & 5.53 & 9.68 & 14.33 & 15.47 & & \\  & 3 & 5.31 & 8.98 & 12.76 & 17.21 & & \\ \hline \multirow{3}{*}{MR-10} & 1 & 5.91 & 8.62 & 12.79 & 17.53 & \multirow{3}{*}{1.44} \\  & 2 & 5.21 & 9.39 & 12.79 & 15.58 & & \\  & 3 & 5.94 & 10.78 & 13.19 & 14.72 & & \\ \hline \multirow{3}{*}{MRC-00} & 1 & 3.75 & 8.14 & 9.55 & 11.25 & \multirow{3}{*}{0.81} \\  & 2 & 3.41 & 7.28 & 10.24 & 12.26 & & \\  & 3 & 3.07 & 8.72 & 9.68 & 12.84 & & \\ \hline \multirow{3}{*}{MRC-05} & 1 & 3.15 & 6.57 & 10.51 & 12.92 & \multirow{3}{*}{0.25} \\  & 2 & 3.23 & 7.10 & 9.87 & 12.45 & & \\ \cline{1-1}  & 3 & 2.25 & 6.99 & 10.53 & 12.55 & & \\ \hline \multirow{3}{*}{MRC-10} & 1 & 3.09 & 6.28 & 9.28 & 13.22 & \multirow{3}{*}{0.57} \\  & 2 & 2.83 & 7.22 & 8.16 & 12.08 & & \\ \cline{1-1}  & 3 & 2.47 & 7.22 & 8.87 & 12.53 & & \\ \hline \hline \end{tabular}
\end{table}
Table 3: Flexural tensile strength results.  
The trend of these results is similar to those observed in [43]. The tensile strength at 28 days shows the best results for cement replacements with bivalve clams at 5% and 10%, achieving 2.92 MPa and 2.97 MPa, respectively, which are above the 2.22 MPa presented by the standard. Additionally, the work conducted with the Cardiidae species [56] at 5% and 10% replacements does not reach the strength of 9.9 MPa achieved by the standard sample, obtaining only 8.72 MPa and 8.70 MPa, respectively.