## 3 Results  
### Mechanical Properties  
The decline in flexural strength values of the water-soaked cement and the materials exposed to seawater, sodium chloride (0.5 M NaCl) or sodium sulphate (0.3 M Na\({}_{2}\)SO\({}_{4}\)), was an indication that the effect of the dilution resulting from the lower amount of clinker present in new blends M1 and M2 was greater than the effect of the pozzolanicity of this type of SCMs (U\({}_{\mathcal{K}\&\text{DW}}\) and BA). That finding was consistent with results reported by other authors who recorded declines in strength associated with smaller proportions of C-S-H gel and greater porosity in pastes prepared with SCMs processed from industrial by-products [36; 43; 44]. On the whole, strength rose with exposure time in the pastes exposed to seawater and 0.3 M Na\({}_{2}\)SO\({}_{4}\). That pattern was associated with the formation of salts (see point 3.4) that would initially fill pores to generate a more compact matrix. Subsequent salt expansion, however, would raise inner stress and induce microcracking [41; 45]. The rise in strength in the pastes exposed to 0.5 M NaCl may be attributed to: (i) the formation of more hydration product [46], favoured by the enhancement of Ca(OH)\({}_{2}\) solubility in NaCl solutions; (ii) greater C-S-H gel stability [47] with the uptake of some of the Na\({}^{+}\) into the C-S-H interlayer spaces [48]; or (iii) [PERSON]'s salt precipitation in the pores [49]. A comparison of the behaviour of the blends exposed to the three types of aggressive media is provided in Table 3. OPC and M1 were observed to follow a similar pattern except when soaked in seawater, where the simultaneous inclusion of the new SCMs (BA and U\({}_{\mathcal{K}\&\text{DW}}\)) lowered strength by \(\sim\)5 % relative to the water-soaked 90 d pastes. Of the pastes exposed to sodium chloride, performance declined the least in 90 d M1, to \(\sim\)1 % below its water-soaked counterpart, compared to the \(\sim\)9% decline observed for OPC. Strength rose in the same materials in the 90-d attack by Na\({}_{2}\)SO\({}_{4}\), by 72% in OPC and 13% in M1. The M2 blends (OPC + U\({}_{\mathcal{K}\&\text{DW}}\) + BA + SF) exhibited lower performance than the other two pastes irrespective of the exposure medium. In the samples exposed to seawater, the \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Medium**} & \multirow{2}{*}{**Time (days)**} & \multicolumn{3}{c}{**Paste**} \\ \cline{3-5}  & & **OPC** & **M1** & **M2** \\ \hline \multirow{3}{*}{**Water**} & 21 & 10.04 \(\pm\) 0.71 & 8.09 \(\pm\) 0.85 & 8.87 \(\pm\) 1.01 \\ \cline{2-5}  & 56 & 9.39 \(\pm\) 1.11 & 8.49 \(\pm\) 0.93 & 8.33 \(\pm\) 1.10 \\ \cline{2-5}  & 90 & 10.59 \(\pm\) 1.180 & 9.79 \(\pm\) 1.04 & 9.09 \(\pm\) 1.04 \\ \hline \multirow{3}{*}{**Seawater**} & 21 & 11.29 \(\pm\) 0.83 & 8.38 \(\pm\) 0.26 & 8.12 \(\pm\) 0.32 \\ \cline{2-5}  & 56 & 12.79 \(\pm\) 1.13 & 9.17 \(\pm\) 0.37 & 6.51 \(\pm\) 0.36 \\ \cline{2-5}  & 90 & 13.14 \(\pm\) 0.69 & 9.26 \(\pm\) 0.61 & 5.57 \(\pm\) 0.55 \\ \hline \multirow{3}{*}{**0.5 M NaCl**} & 21 & 9.84 \(\pm\) 0.65 & 8.37 \(\pm\) 0.67 & 8.16 \(\pm\) 0.42 \\ \cline{2-5}  & 56 & 9.73 \(\pm\) 0.93 & 8.91 \(\pm\) 0.63 & 8.44 \(\pm\) 0.48 \\ \cline{2-5}  & 90 & 9.68 \(\pm\) 1.40 & 9.72 \(\pm\) 0.58 & 8.36 \(\pm\) 0.57 \\ \hline \multirow{3}{*}{**0.3 M Na\({}_{2}\)SO\({}_{4}\)**} & 21 & 14.41 \(\pm\) 1.43 & 11.82 \(\pm\) 0.98 & 10.00 \(\pm\) 0.71 \\ \cline{2-5}  & 56 & 17.24 \(\pm\) 1.73 & 10.59 \(\pm\) 1.21 & 9.12 \(\pm\) 0.72 \\ \cline{2-5}  & 90 & 18.24 \(\pm\) 0.50 & 11.09 \(\pm\) 1.03 & 8.91 \(\pm\) 0.54 \\ \hline \end{tabular} Note–OPC: ordinary portland cement; M1: 70%OPC + 20%U\({}_{\mathcal{K}\&\text{DW}}\) + 10%BA; M2: 45%OPC + 20%U\({}_{\mathcal{K}\&\text{DW}}\) + 20%BA + 5%SF.  
\end{table} 
Table 3: Flexural strength (MPa) of pastes soaked in water or aggressive media. 90 d values for M2 were \(\sim\)38% lower than for OPC \(\sim\)8% lower where the medium was 0.5 M NaCl and \(\sim\)2% lower when attacked by 0.3 M Na\({}_{2}\)SO\({}_{4}\).