## 4 Tests Results and Discussion
Judging, for example, these two specimens, No. 2 and 5, investigated under the same mean effective stress, the difference between statistical parameters is up to 90%. In Figures 9-11, a graphic variation of the \(V_{S}\) values with a predetermined wave's propagation period at different specified stress level is shown. Besides, it is also a graphic comparison between the time domain and frequency domain techniques of BEs results interpretation. It is important, that for these figures, only the data when the ratio \(L_{\text{TT}}/  
Based on these figures, and in particular, Figures 9 and 11, the conclusion regarding zero crossing method from the statistical analysis is confirmed. Most differs this method from the others. Therefore, in the analysis of the results for \(p^{\prime}=45\) kPa and \(p^{\prime}=180\) kPa it was removed, completely or partially. In all the figures, the values of shear wave velocity for compositions of RCA with rubber chips are distinctly lower and less consistent in comparison to pure RCA specimens. A great dispersion of these results is strongly remarkable. The exact values of the spread of the results, comparing two tested materials, are given in Table 7.  
Subsequently, for further discussion, from each figure (Figures 9-11) certain wave's periods were chosen, for which wave velocities were nearly identical at given mean effective stress. The selected periods differed slightly, depending on whether pure RCA or mixtures of RCA with rubber chips were analyzed, and what was the level of \(p^{\prime}\) Then, from these wave periods finally one (marked by  
Figure 11: Variation of \(V_{S}\) with period for \(p^{\prime}=180\) kPa. Diamond symbols: pure RCA specimens; rectangle symbols: compositions of RCA with rubber chips. Figure 10: Variation of \(V_{S}\) with period for \(p^{\prime}=90\) kPa. Diamond symbols: pure RCA specimens; rectangle symbols: compositions of RCA with rubber chips. rectangle in Figures 9-11) was chosen, for which the difference between the \(V_{S}\) values from different methods was the lowest, from 1% up to maximum 16%. There are the following periods: \(T=0.20\) ms for \(p^{\prime}=45\) kPa, specimens No. 1 and 4, \(T=0.13\) and 0.14 ms for \(p^{\prime}=90\) kPa, specimens No. 2 and 5, \(T=0.13\) and 0.12 ms for \(p^{\prime}=180\) kPa, specimens No. 3 and 6. Based on the selected periods, the characteristic shear wave velocities were eventually received. In Figure 12, the above-mentioned \(V_{S}\) values are shown as a function of mean effective stress, in order to compare with the reference method. The shear wave velocities vary between 180.2 and 302.1 m/s, as well as between 95.3 and 150.0 m/s (Figure 12). In the case of modified concrete recycled aggregate, the test results are again more scattered. This can be explained, e.g., by the properties and behavior of rubber themselves. Rubber chips do not absorb water and behave differently that grain of soil. Hence, they cannot be saturated with water when the specimen is being saturated and can be very mobile during wave's propagation. They can move simply inside the specimen. Two identical measurements are performed, but the conditions inside the specimen tested are already different, because of various arrangements of rubber grains. Therefore, in the case of this modified material, it is difficult to get consistent results. It is evident that, regardless of the type of a test material, the \(V_{S}\) values increase with the increase in the \(p^{\prime}\) values. As far as pure RCA specimens are concerned, this is an increase of an average of 29% when \(p^{\prime}\) changes from 45 to 90 kPa, and of 14% with an increase in \(p^{\prime}\) from 90 to 180 kPa. At first, \(V_{S}\) changes are greater, than smaller, with higher \(p^{\prime}\). In the case of modified RCA, the \(V_{S}\) values increase of about 10% and 23%, when mean effective stress increases respectively from 45 to 90 kPa and from 90 to 180 kPa. Here, the trend of \(V_{S}\) changes is reverse, first there are smaller, than greater changes.