# Binary Mixes of Self-Compacting Concrete with Municipal Solid Waste Incinerator Bottom Ash
## 3 Results and Discussion
### Mechanical Performance
#### 3.4.2 Splitting Tensile Strength  
The splitting tensile strength was carried out on cylindrical specimens after 28 and 91 days, the results of which are shown in Table 6 and Figure 4. This property followed the same trend as that of the compressive strength, i.e., increasing the MIBA content led to a decline in splitting tensile strength, the causes of which are those laid out in the previous section. Furthermore, it is possible that the quality of the interfacial transition zone (ITZ)  
Figure 3: Compressive strength in cubes at 7, 28 and 91 days (**left**); Relationship between compressive strength in cubic and cylindrical specimens at 28 and 91 days (**right**). \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Mix**} & \multicolumn{3}{c}{**7 days**} & \multicolumn{3}{c}{**28 days**} & \multicolumn{3}{c}{**91 days**} \\ \cline{2-11}  & \(\mathbf{f_{\text{cm,cube}}}\) & \(\mathbf{\sigma_{\text{fem,cube}}}\) & \(\mathbf{\ell_{\text{cm,cube}}}\) & \(\mathbf{\sigma_{\text{fem,cube}}}\) & \(\mathbf{\ell_{\text{cm}}}\) & \(\mathbf{\sigma_{\text{fem}}}\) & \(\mathbf{\ell_{\text{cm,cube}}}\) & \(\mathbf{\sigma_{\text{fem,cube}}}\) & \(\mathbf{\ell_{\text{cm}}}\) & \(\mathbf{\sigma_{\text{fem}}}\) \\ \hline RC & 50.3 & 5.3 & 57.6 & 4.2 & 55.4 & 12.5 & 80.1 & 2.9 & 65.6 & 12.4 \\ C208A & 33.7 & 2.0 & 35.7 & 5.5 & 20.6 & 0.3 & 41.3 & 0.8 & 22.1 & 3.7 \\ C308A & 23.9 & 1.3 & 24.2 & 2.5 & 11.2 & 0.7 & 32.6 & 2.9 & 15.3 & 1.4 \\ C40 BA & 18.1 & 1.0 & 21.8 & 2.1 & 9.1 & 0.1 & 24.8 & 0.6 & 10.6 & 0.7 \\ C50 BA & 12.9 & 0.3 & 16.8 & 0.8 & 6.3 & 0.4 & 16.0 & 0.5 & 6.8 & 2.1 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Compressive strength in cylindrical at 28 days and 91 days and in cubes at 7 days, 28 days and 91 days. may have declined due to the higher MIBA content and increased \(w/c\) ratio. Mixes C20 BA, C30 BA, C40 BA and C50 BA showed reductions in the 91-day splitting tensile strength of 30%, 52%, 54% and 62%, respectively, when compared to the RC. All specimens practically reached their total splitting tensile strength after 28 days, with coefficients of variation between 2% and 9%. Contrary to that expected, the splitting tensile strength of the RC and C50 BA specimens after 91 days was slightly lower than the 28-day splitting tensile strength, thus showing no strength development from the continuous hydration of cement. [PERSON] et al. [45], when testing mortars with partial replacement of cement with MIBA (i.e., 0%, 10%, 20%, 30% and 50%), reported a comparable trend concerning the decline in tensile strength with increasing replacement level. Table 6 also shows the results of a calculation for the predicted change in splitting tensile strength as a function of the uniaxial compressive strength in cylindrical specimens according to Eurocode 2 [46]. For normal structural uses, the mean tensile strength is related to the cylinder strength using the following equations:  
\[f_{ctm}=0.30\cdot{f_{ck}}^{2/3},\text{ for concrete classes }\leq\text{ C50}/60 \tag{4}\]  
\[f_{ctm}=2.12\cdot ln\left(1+\frac{f_{cm}}{10}\right),\text{ for concrete classes }>\text{ C50}/60 \tag{5}\] \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Mix**} & \multirow{2}{*}{\
\begin{tabular}{c} **f\({}_{\text{cm},28}\)** \\ **(MPa)** \\ \end{tabular} } & \multicolumn{2}{c}{**f\({}_{\text{cm},28}\) (MPa)**} & \multirow{2}{*}{
\begin{tabular}{c} **f\({}_{\text{cm},91}\)** \\ **(MPa)** \\ \end{tabular} } & \multicolumn{2}{c}{**f\({}_{\text{cm},91}\)**} & \multicolumn{2}{c}{**f\({}_{\text{cm},91}\) (MPa)**} \\ \cline{2-6}  & **EC2** & **Measured** & & **EC2** & **Measured** \\ \hline RC & 55.4 & 3.98 & 5.03 & 65.6 & 4.29 & 4.88 \\ C20 BA & 20.6 & 2.37 & 3.09 & 22.1 & 2.48 & 3.40 \\ C30 BA & 11.2 & 1.60 & 2.32 & 15.3 & 1.97 & 2.36 \\ C40 BA & 9.10 & 1.37 & 2.19 & 10.6 & 1.53 & 2.24 \\ C50 BA & 6.28 & 1.03 & 1.96 & 6.85 & 1.11 & 1.87 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Splitting tensile strength versus compressive strength determined according to EC2 at 28 and 91 days.