## 3 Results and Discussion
### About Concrete
#### 3.2.3 Compressive Strength Tests  
In Table 11, the results of the compressive strength tests are summarized. The results obtained for three samples of each mixture (R1, R2, R3), the average (Rm), and the standard deviation (\(\sigma\)) are reported. The sample S4, where the sand is entirely replaced by R-EPS, has the lowest strength value (5.12 MPa). Similarly, among the mixtures involving the replacement of parts of the sand granulometric mix with R-EPS, sample S10, which replaces all three identified parts of the mix, has the lowest mechanical strength (15.35 MPa), although higher than sample S4 due to the presence of a certain amount of sand. From the comparison between the achieved mechanical performances and the content of R-EPS in the mixture (Figure 22), it is evident that the compressive strength of the specimens decreases with the increasing content of R-EPS in the mix. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Specimen Code** & **R1 1** & **R2 1** & **R3 1** & **Rm 1** & \(\sigma\) \\  & **[MPa]** & **[MPa]** & **[MPa]** & **[MPa]** & **[MPa]** & **[MPa]** \\ \hline S0 & 50.42 & 44.86 & 48.77 & **48.02** & 2.019 \\ \hline S1 & 31.28 & 28.11 & 27.81 & **29.07** & 1.360 \\ \hline S2 & 13.25 & 13.58 & 13.42  
In analogy to what was done for the mortars, an ANOVA test was also conducted for the concrete. In this case as well, the results confirm that the differences in means are not due to natural statistical fluctuation but because, as the composition of the mixture varies, the measured quantities also vary (Tables 12 and 13). With regard to the formulation of concretes, it is highlighted that for all mixtures, except for S6, it was possible to achieve the S5 consistency class, according to UNI EN 206:2021 [75]. Thermo-hygrometric tests generally showed (Figure 18) that the decrease in density, generated by the use of R-EPS (Figure 18) replacing sand, corresponds to a significant improvement in the thermal properties of concretes, caused by the increase in air voids within the base mixture. Based on the compression strength and density values, a comparison was made with the classification of concretes from UNI EN 206:2021 and NTC2018 [76], as outlined in Figure 23. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Source of Variation** & **SS 1** & **Df 1** & **MS 1** & **F** & **_p-Value_ & **F Crit** \\ \hline Between groups & 5640.797 & 10 & 564.0797 & 224.6765 & \(9.38832\times 10^{-20}\) & 2.296696 \\ \hline Within groups & 55.23387 & 22 & 2.51063 & & \\ \hline Total & 5696.031 & 32 & & & \\ \hline \hline \end{tabular} \({}^{1}\) SS = sum of squares; Df = degree of freedom; MS = mean square.  
\end{table} 
Table 13: Cements. ANOVA test for compressive strength. Figure 22: Concrete. Trend of mechanical strength values in relation to the content of R-EPS. This allowed the evaluation of which mixtures can be considered lightweight concretes (LC) (800 kg/m\({}^{3}\)\(\leq\)\(\rho\)\(\leq\) 2000 kg/m\({}^{3}\)) and non-lightweight concretes (NLC) (\(\rho\) \(>\) 2000 kg/m\({}^{3}\)), as well as structural concretes (SC) (Rck,cube \(\geq\) 15 MPa) and non-structural concretes (NSC) (Rck,cube \(<\) 15 MPa). Out of the eleven samples, three do not fall into the lightweight concrete category, including the reference concrete (S0, S6, S7). Among the lightweight concrete samples, four are suitable for structural purposes (S1, S5, S8, S9), while the remaining four (S2, S3, S4, S10) are suitable for non-structural purposes (Figure 24). Furthermore, it is observed that the volumetric percentage replacement of sand with R-EPS for the entire grain size distribution (S1, S2, S3, S4), although more advantageous  
Figure 23: Trend of mechanical strength values in relation to density with identification of concrete classifications. Figure 24: Concrete. Classification of mixes based on mechanical strength and density.