## 4 Results and Discussion
### Results of the In Situ and Laboratory Tests  
The results obtained using the proposed test method make it possible to plot the mean value of EQ of the specimens (\(Lmean_{lab}\)) vs. the UCS, expressed in MPa (Figure 9), proposing a correlation curve for the evaluation of the mortar compressive strength based on the EQ average values for each site examined. A strong positive exponential interpolation is evidenced by [PERSON]'s coefficient of determination (R\({}^{2}\) = 0.81), and one sample (sample ID 3009-5) could be considered as an outlier. The latter has been visually identified on the plotting since it lies well above the correlation curve obtained by fitting the other experimental measurements. This is related to the fact that this sample furnished a higher UCS value in relation to the associated \(Lmean_{lab}\). Moreover, if this datum is considered in  
Figure 8: Axial stress-strain curves of the samples divided into the classes considered. the fitting process, the coefficient of determination drops significantly from 0.81 to 0.62. The interpolation law presented to correlate EQ values with the UCS is reported in Equation (1):  
\[UCS=0.08*\ e^{0.01*Lmean_{lab}} \tag{1}\]  
Results of the EQ testing on the in situ mortars and on the specimens are reported in Table 4, summarized with the UCS results. It should be noted that \(Lmean_{lab}\)* and UCS* values for each masonry mortar examined have been calculated averaging the values obtained for each specimen. At first, a discrepancy is clearly observed between \(Lmean_{situ}\) and \(Lmean_{lab}\)*, with the site value always lower than the values obtained on the specimens in the laboratory. Based on that, the block volumes of the laboratory specimens have been assessed to see if they influence the rebound of the EQ, excluding its relationship with the inconsistency between \(Lmean_{situ}\) and \(Lmean_{lab}\) values. In Figure 10, the volumes of fourteen blocks of mortar sampled from the eight masonry sites examined were plotted against \(Lmean_{lab}\). The volumes ranged between under 14 cm\({}^{3}\) to almost 200 cm\({}^{3}\). Based on the extremely low [PERSON]'s coefficient of determination (R\({}^{2}\) = 0.095) there is no correlation, or relationship, between the block volume and \(Lmean_{lab}\) (Figure 10), so the discrepancy in mean values cannot be attributed to the different volumes tested. This aspect is in accordance with [23] who tested the influence of block volume and edge effect on the EQ measurements. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Sampling Location**} & \multirow{2}{*}{**Site ID**} & \multicolumn{2}{c}{**Number of Specimens (pcs.)**} & \multirow{2}{*}{\(Lmean_{situ}\)} & \multirow{2}{*}{\(Lmean_{lab}\)*} & \multirow{2}{*}{\(\delta\)} & \multirow{2}{*}{**UCS * [MPa]**} \\ \cline{5-6}  & & & & & & & & \\ \hline  & & & **mean** & **std** & **mean** & **std** & \\ \hline masonry core & 3000 & 1 & 160 & 15 & 221 & 42.1 & 0.72 & 0.33 \\ masonry core & 3002 & 1 & 263.5 & 91.2 & 349.5 & 30.9 & 0.75 & 0.3 \\ masonry core & 3004 & 1 & 143 & 23.5 & 230.6 & 20.5 & 0.62 & 0.19 \\ masonry face & 3006 & 2 & 290 & 54.9 & 372.7* & 34.5 & 0.78 & 0.67* \\ masonry core & 3008 & 1 & 143 & 71.3 & 225.3 & 63.3 & 0.63 & 0.17 \\ masonry core & 3009 & 5 & 143.2 & 74.2 & 250.0* & 107.1 & 0.57 & 0.51* \\ masonry face & 3010 & 1 & 369.6 & 46.5 & 491.4* & 55 & 0.75 & 1.37* \\ masonry face & 3011 & 1 & 375.6 & 37.9 & 523 & 43.8 & 0.72 & 1.29 \\ \hline \hline \end{tabular}
* data referred to the averages data calculated on EQ and UCS for multiple specimens.  
\end{table} 
Table 4: The list of EQ and UCS test results for each masonry examined. \(\delta\) values are reported. Figure 9: Correlation between \(Lmean_{lab}\) and the UCS. [PERSON]’s correlation coefficient is reported.