## 3 Results  
A total of 48 prismatic mortar specimens were tested in the laboratory. The ultrasonic pulse velocity and compressive strength of each were obtained, which are shown in Table S1 (supplementary material). Table 2 shows the average value of compressive strength for each specimen, the measurement of the propagation time, and the ultrasonic pulse velocity. From the statistical analysis of exponential regression of the results, the equation to determine the trend of the data obtained, with a determination coefficient (R\({}^{2}\)) of 0.8921, is as follows:  
\[\text{Compressive strength}=0.0538\times e^{1.5767\times UIPV} \tag{5}\]  
Based on the expression determined in this study and on the experimental data, an upper and lower limit of reliability was calculated considering a 95% confidence level. \[\text{Upper limit}=0.1207\times e^{1.4072\times UPV} \tag{6}\]  
\[\text{Lower limit}=0.0193\times e^{1.7955\times UIPV} \tag{7}\]  
Figure 2 shows the results obtained, the exponential trend, and the calculated limits. The estimated compressive strength is calculated by the exponential regression for the UPV values obtained, as shown in Equation (5). In addition, the relative and absolute errors between the real and calculated values were obtained and shown in Table 3.  
The 95% confidence limits can be used to preliminarily estimate the compressive strength of mortars, quickly and inexpensively, from a UPV measurement. Therefore, if we were to obtain a UPV of 4.15 km/s, we would know with 95% confidence that the compressive strength value was 33.35-41.39 MPa. The absolute and relative errors of the results obtained by exponential regression were also calculated based on the values of the compressive strength test, ranging from 0.21 to 7.23 and from 0.51 to 17.81%, respectively. These errors represent an acceptable approximation for an estimate, for example, in a standard quality study. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Specimen’s Name** & **Addition of 25\%** & **Cured Time (Days)** & \begin{tabular}{c} **Average Value of** \\ **Compressive Strength** \\ **(MPa)** \\ \end{tabular} & \
\begin{tabular}{c} **Propagation Time** \\ **(μs)** \\ \end{tabular} &
\begin{tabular}{c} **Average Value of** \\ **UPV (km/s)** \\ \end{tabular} \\ \hline
1(A-B-C) & Z-7 & 7 & 19.23 & 42.16 & 3.79 \\
2(A-B-C) & Z-9 & 7 & 28.58 & 40.56 & 3.94 \\
3(A-B-C) & Z-12 & 7 & 28.34 & 40.56 & 3.94 \\
4(A-B-C) & Z-26 & 7 & 27.46 & 40.53 & 3.95 \\
5(A-B-C) & Z-7 & 28 & 43.05 & 38.10 & 4.20 \\
6(A-B-C) & Z-9 & 28 & 41.47 & 38.26 & 4.18 \\
7(A-B-C) & Z-12 & 28 & 39.64 & 38.36 & 4.17 \\
8(A-B-C) & Z-26 & 28 & 40.67 & 38.30 & 4.18 \\
9(A-B-C) & PM-1 & 28 & 40.59 & 39.23 & 4.08 \\
10(A-B-C) & PM-3 & 28 & 29.73 & 39.60 & 4.04 \\
11(A-B-C) & PMT-4 & 28 & 31.21 & 39.00 & 4.10 \\
12(A-B-C) & ZEO-1 & 28 & 39.77 & 37.70 & 4.24 \\
13(A-B-C) & CVM & 28 & 38.56 & 37.60 & 4.26 \\
14(A-B-C) & ZSA M-1 & 28 & 41.87 & 37.87 & 4.23 \\
15(A-B-C) & GM-1 & 28 & 36.59 & 38.53 & 4.15 \\
16(A-B-C) & \(-\)1 & 28 & 57.06 & 36.33 & 4.40 \\ \hline \end{tabular}  
* Specimen number 16 was composed of 100% of cement type II 42.5 R.  
\end{table} 
Table 2: Results obtained for specimens prepared with the mixtures in the compression resistance and ultrasonic pulse velocity tests. However, sometimes greater accuracy is required when performing an analysis of the physical properties of mortars. Therefore, the trend in four of the study samples from the same deposit was further tested to see if the correlation remained reliable, as the chemical composition would be almost the same. The results obtained from the natural mordenite from the San Jose-Los Escullos site were isolated following the same process mentioned before. The equation determined from the statistical analysis of exponential regression of the results, with a determination coefficient (R\({}^{2}\)) of 0.9801, is as follows:  
\[\text{Compressive strength}=0.0212\times e^{1.8125\times UPV} \tag{8}\]