## 2 Materials and Methods
### Results  
#### 2.3.1 Strength Tests  
Table 5 shows the average values of the failure stresses obtained after 7, 28, and 90 days of curing for slag and fly-ashes concretes. In this case, the compressive elastic modulus \(E\), after 28 days of curing and in the stress field 0-\(\sigma_{\mathrm{r}}/3\) is equal to about 25,900 \(\mathrm{N/mm^{2}}\). \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Rubble** & **Sand** & **Water** & **Cement** & **Super-Plasticizer** \\ \hline
1080 \(\mathrm{daN/m^{3}}\) & 700 \(\mathrm{daN/m^{3}}\) & 204 \(\mathrm{L/m^{3}}\) & 340 \(\mathrm{daN/m^{3}}\) & 4.0 \(\mathrm{L/m^{3}}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Composition of ordinary concrete (ORD) mix per unit of volume. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Rubble** & **Microsilica** & **Water** & **Slag** & **Cement** & **Super-Plasticizer** \\ \hline
1080 \(\mathrm{daN/m^{3}}\) & 131 \(\mathrm{daN/m^{3}}\) & 296 \(\mathrm{L/m^{3}}\) & 522 \(\mathrm{daN/m^{3}}\) & 340 \(\mathrm{daN/m^{3}}\) & 7.22 \(\mathrm{L/m^{3}}\) \\ \hline \hline \multicolumn{5}{c}{**Components Ratio**} \\ \hline water/cement & water/(microsilica + cement) & microsilica/cement & super-plasticizer/(microsilica + cement) \\ \hline
0.87 & 0.63 & 0.38 & 0.015 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Composition of slag and microsilica (SF) concrete mix per unit of volume and component ratios utilized. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Curing Days** & \begin{tabular}{c} **Specific Weight** \\ **(daN/m^{3})** \\ \end{tabular} & \begin{tabular}{c} **Compressive Failure** \\ **Stress (N/mm^{2})** \\ \end{tabular} & \
\begin{tabular}{c} **Flexural Failure Stress** \\ **(N/mm^{2})** \\ \end{tabular} &
\begin{tabular}{c} **Tensile Failure Stress** \\ **(N/mm^{2})** \\ \end{tabular} \\ \hline  & & Value & \(\sigma\) & Value & \(\sigma\) & Value & \(\sigma\) \\ \hline
7 & 2222 & 26.0 & \(\pm\)3.74 & - & - & \\
28 & 2185 & 36.5 & \(\pm\)2.12 & 4.4 & \(\pm\) 3.0 & 2.3 & \(\pm\)3.61 \\
90 & 2185 & 43.0 & \(\pm\)3.74 & - & - & - \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Mean values and standard deviations of the mechanical characteristics of slag and fly ashes concrete. Table 6 shows the average values of the failure stresses after 7, 28 and 60 days of curing for slag and microsilica concretes. In this case, the compressive elastic modulus \(E\), after 28 days of curing and in the stress field 0-\(\sigma_{r}/3\) is equal to about 25,140 N/mm\({}^{2}\). In Table 7 the mean values for compression strength of the different concretes are reported. The methods utilized for the mix designs of the concrete utilized in the tests, appropriately refined by the preliminary tests, are shown to be good enough. However, it is evident from the results that the pozzolanic activity, both with fly-ashes, and especially with microsilica, played an important role in getting a good value for compressive strength. The water/cement ratios are both quite high: if utilized to prepare an ordinary concrete, it would have been difficult to reach strength of the order of those obtained from the tests if there was no pozzolanic activity for fly-ashes and microsilica. Therefore, the ratios water/(fly-ashes + cement) and water/(microsilica + cement) are considered more significant in both cases. The higher compressive strength obtained utilizing microsilica instead of fly-ashes is justified by the higher pozzolanic activity of silica fume and, especially, by the dimensions of their granules, which were much smaller than fly-ashes and typical of microsilica. The better behavior is obtained even if, when microsilica are used, it is necessary to add more water and super-plasticizers in order to obtain the same consistency as concrete with fly-ashes (see Table 3). From the tests it seems that higher strengths are obtained for concrete with slag and microsilica, while the specific weight is a little lower than the weight of concretes with slag and fly-ashes.