## 3 Results
### Mechanical Strength  
The flexural strength test results for the different mortar formulations incorporating wash fines are presented in Table 7. The values correspond to the average strength measured for three specimens at 14 and 28 days, with the associated standard deviation.  
A decrease in flexural strength is observed as the rate of substitution of cement by washing fines increases. At 28 days, the unadded reference mortar had a flexural strength of 6.7 MPa. The incorporation of 10% washing fines results in a slight drop to 5.8 MPa. This decrease becomes more pronounced for P20 and P30 formulations, with strengths of only 5.1 and 2.9 MPa, respectively.  
This downward trend in flexural performance with the incorporation of washing fines can be attributed to several factors. Firstly, the greater porosity of these mixes [35], as highlighted above, weakens the compactness of the cementitious matrix and creates stress concentration sites. Secondly, the very nature of wash fines, composed mainly of fine particles of low reactivity, does not allow for the development of a microstructure as dense and resistant as Portland cement [29; 37; 38].  
On the other hand, Table 8 presents the results of compressive strength tests carried out on the various mortar formulations incorporating the washing fines. The values correspond to the average strength measured for three cubic specimens at 14 and 28 days.  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Total Shrinkage [\(\mu\)m/m]** & **Ref** & **L10** & **L20** & **L30** \\ \hline
1 day & 509 & 1054 & 1203 & 1637 \\
3 days & 603 & 1451 & 1504 & 2162 \\
28 days & 713 & 1473 & 1624 & 2222 \\
70 days & 800 & 1608 & 1684 & 2362 \\ \hline \hline \end{tabular}
\end{table}
Table 6: Total shrinkage of mortar incorporating washing fine.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Formulation**} & \multicolumn{3}{c}{**Flexural Strength**} \\ \cline{2-3}  & **14 Days [MPa]** & **28 Days [MPa]** \\ \hline Ref & 6.4 \(\pm\) 0.4 & 6.7 \(\pm\) 0.2 \\ L10 & 5.4 \(\pm\) 0.2 & 5.8 \(\pm\) 0.3 \\ L20 & 4.7 \(\pm\) 0.3 & 5.1 \(\pm\) 0.4 \\ L30 & 2.5 \(\pm\) 0.3 & 2.9 \(\pm\) 0.2 \\ \hline \hline \end{tabular}
\end{table}
Table 7: Flexural strength of mortar incorporating washing fines.  
A significant decrease in compressive strength is observed as the rate of substitution of cement by washing fines increases. The reference mortar with no added fines shows a strength of 51 MPa after 28 days of curing. The incorporation of 10% washing fines (L10) results in a moderate decrease to 36 MPa. However, this reduction becomes more marked for formulations L20 and L30, with strengths of just 29 MPa and 21 MPa, respectively, at 28 days.  
This drop in compressive performance with an increasing substitution ratio can be attributed to several factors. Firstly, as previously observed, the incorporation of washing fines increases the total porosity of the mortar, thus weakening its compactness and density [35]. This more porous and less dense microstructure does not allow the mortar to develop as high mechanical strength as the reference mortar. Secondly, the very nature of the wash fines, composed mainly of fine particles of low reactivity, does not contribute significantly to the development of a dense, resistant microstructure [29; 37; 38].  
These results of a compressive strength decrease with increasing substitution rate are consistent with those of [PERSON] et al. (2023) [29], who observed a similar trend in their study on waste powders as cement mortar components.