## 3 Results and Discussion
### Compressive Strength, E-Modulus and UPV  
Table 7 shows the results obtained from the compression tests performed directly on blocks. Unlike more conventional cubic or cylindrical samples, this is a common practice in CEBs, notwithstanding the lack of standardised aspect ratio correction factors, and this leads to an effective strength overestimation [51]. The displacement control has been chosen instead for better control of the failure pattern. From the results obtained, the expected linear relationship between bulk density and compressive strength was not found [7]. Nevertheless, compressive strength values align in an almost constant range (1.5-3 MPa), as shown in Figure 9a. The elastic modulus indicates that both batches of blocks are stiffer at 180 days. As for the UPV test results, Figure 9b shows the data collected. Interestingly, the data show that the compressive strength of both batches of blocks decreases slightly from 28 to 180 days, especially in finer-textured R1 CEBs. In fact, at 180 days, R1 CEBs exhibit 30% lower strength than at 28 days, and CEB R2 is 11% lower. It should be noted that the coefficients of variation of the 28-day results are higher than those at 180 days. Moreover, the values do not show a well-defined trend. This result could, therefore, be attributed to a mere dispersion in the data. However, specific studies need to be carried out to ascertain whether this was an actual degradation of bond strengths, especially in the finer-grained CEBs, and the reasons behind it. Concerning the results of the UPV test, in both mixtures, at 28 days, the results were not indicative. They fell in the same range and were practically superimposable. At 180 days, \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{4}{c}{**R1 CEBs**} & \multicolumn{4}{c}{**R2 CEBs**} \\ \hline  & \(\gamma\) & \(\sigma_{\epsilon}\) & **E-Modulus** & **UPV** & \(\gamma\) & \(\sigma_{\epsilon}\) & **E-Modulus** & **UPV [m/s]** \\  & [kg/m\({}^{3}\)] & [MPa] & [MPa] & [m/s] & [kg/m\({}^{3}\)] & [MPa] & & \\ \hline  & 1720.47 \(\pm\) & 2.54 \(\pm\) 0.33 & 55.65 \(\pm\) & 1018.65 \(\pm\) & 1945.79 \(\pm\) & 2.27 \(\pm\) 0.34 & 53.61 \(\pm\) & 1004.57 \(\pm\) \\
28 days & 14.50 (0.84\%) & (13.01\%) & 21.22 (38.13\%) & (10.29\%) & (2.16\%) & (15.00\%) & 1.69 (3.15\%) & 87.21 (8.68\%) \\  & 1727.49 \(\pm\) & 17.8 \(\pm\) 0.11 & 40.46 \(\pm\) & 974.71 \(\pm\) & 1848.36 \(\pm\) & 2.03 \(\pm\) 0.23 & 46.21 \(\pm\) & 1113.33 \(\pm\) \\
180 days & 15.47 (0.90\%) & (6.42\%) & (5.25\%) & (2.89\%) & (0.58\%) & (11.49\%) & 1.86 (4.02\%) & (5.70\%) \\ \hline \hline \end{tabular}  
* This table shows the average data with its standard deviation and, in brackets, the coefficient of variation.  
\end{table} 
Table 7: Compression test and UPV test results 1. Figure 9: (a) Bulk density vs. compressive strength; (b) Bulk density vs. UPV. however, the propagation speed was higher in R2 blocks (denser, less porous, but also less humid) and lower in R1 blocks (less dense, more porous, and more humid), as predicted by theory (in theory, the ultrasonic pulse should propagate faster in denser media. The pores, in fact, tend to obstruct the path of the wave). The results obtained could be attributed to the moisture content, which, let us recall, at 28 days in both batches was 1.40% and at 180 days in the R1 blocks was 0.80% and in the R2 blocks 0.60%. However, further studies are needed to confirm this hypothesis. To the best of the authors' knowledge, the few studies available on the subject have found a direct relationship between wave propagation speed and compressive strength [32; 52; 53]. According to this, faster waves correspond to denser and, in general, more resistant media. [PERSON] et al. [54] refer to an inverse correlation between porosity and UPV, like the fact that as porosity increases, density decreases and with-it resistance. [PERSON] et al. [28] agree with the common assumption that faster waves are related to denser blocks.