## 3 Results and Discussion
### Mechanical Properties of Mortars  
The mechanical properties of the mortar specimens were determined by uniaxial compressive strength tests. Table 5 and Figure 6 show the uniaxial compressive strengths of the mortar specimens 0 MS, MS, M5, M10, M15, M20 and M25 mixtures at 2, 7, and 28 days of curing. In Figure 7, the uniaxial compressive strengths measured on 0 MS mortar sample are compared with those obtained on mortars made by using pozzolanic materials (G = garnet) FF = diatomaceous earth) instead of marble powder. The number of the alphanumeric abbreviation indicates the percentage of cement replacement. \begin{table}
\begin{tabular}{c c c c c} \hline
**Mean SD = 2.0 MPa** & **Cement Replacement** & \multicolumn{3}{c}{**Compressive Strength (\(\sigma\), MPa)**} \\ \cline{2-5}
**Sample** & **(r, wt.\%)** & **2 dd** & **7 dd** & **28 dd** \\ \hline
0 MS & 0 & 31.5 & 42.3 & 55.9 \\ \hline MS & 0 & 29.8 & 43.5 & 58.6 \\ M5 & 5 & 26.4 & 38.7 & 53.9 \\ M10 & 10 & 28.5 & 35.7 & 52.7 \\ M15 & 15 & 34.8 & 41.1 & 49.8 \\ M20 & 20 & 25.7 & 35.5 & 48.1 \\ M25 & 25 & 20.9 & 30.7 & 43.3 \\ \hline G10 & 10 & 29.5 & 44.3 & 62.3 \\ FF10 & 10 & 34.6 & 46.7 & 61.4 \\ FF20 & 20 & 26.9 & 36.2 & 48.2 \\ \hline \end{tabular}
\end{table} 
Table 5: Compressive strength of the specimens 0 MS, MS, M5, M10, M15, M20, and M25 mixtures, at 2, 7, and 28 days of curing. Figure 6: Compressive strength histogram of the specimens MS, M5, M10, M15, M20, and M25 mixtures at 2, 7, and 28 days of curing. The comparison with mortars containing garnets and diatomaceous earth is useful to demonstrate that substitution of cement in increasing percentages does not necessarily lead to a decrease in the mechanical properties of the mortar. This is true if the aggregate is made up of a substantially inert material (_marmettola_), the addition of which inevitably leads to a decrease of the physical-mechanical properties. Regarding the addition of pozzolanic materials (G and FF) that can react with the binder, it leads to an increase of the uniaxial compressive strength for relative low cement replacement (10 wt.%), and the maintenance of the physical-mechanical properties up to quite high substitution levels (about 20 wt.%). The use of pozzolanic materials in manufacturing mortars and their hydraulic effects are well known since ancient times, and several examples can be found in the literature, in which different pozzolanic materials are used to make mortars with high mechanical strength [50, 51, 62, 63, 64, 65, 66, 67, 68, 69, 70]. At 2 days of curing, the values of the compressive strengths of the specimens of both the reference mixture (MS) and the specimens of the mixture made without the superplasticizer additive MasterGlenium SKY 698 (0 MS) are quite similar, 29.8 MPa in respect to 31.5 MPa. Even after 7 days of curing, very similar compressive strength values are observed, 43.5 MPa in the reference mixture (MS) and 42.3 MPa in the mixture made without additive (0 MS), respectively. At 28 days of curing, the compressive strength of the specimens of the MS reference mixture is 58.6 MPa, while that of the mixture made without additive (0 MS) is 55.9 MPa. Considering the standard deviation value of 1.5 MPa, no significant differences are observed in the uniaxial compressive strength of the specimens MS and 0 MS at 2, 7, and 28 days of curing. This result indicates that the superplasticizer additive MasterGlenium SKY 698 does not change the mechanical properties of the samples. At 28 days of curing, the highest values of compressive strength were measured on specimens of the reference mixture (MS, 58.6 MPa), while the lowest values were found in the mixture containing 25 wt.% of marble powder (M25, 43.3 MPa) as cement replacement. From the data reported in Table 5, it can be observed that, at 28 days of curing, there is a decrease in compressive strength due to the increase in the percentage of marble powder used to replace the cement.