## 5 Discussion and Conclusions  
From the outputs of the statistical analyses on the effect of rain on in situ measurements, it seems that the effect of water content in the test specimen on the measured values of the speed of ultrasound velocity is more or less negligible. When the simplest measure, such as a coefficient of variation, was used, it indicated that the slabs would show very similar behavior. Namely, the first testing slab (V1 SFRC) provided the least different results in the sense of its variability. Nevertheless, from a technical point of view, it can be deduced that this testing slab was apparently poorly compacted and therefore it had a different porosity than Slabs V2 and V3. Unfortunately, it was not possible to test another test sample with the same mixture, especially with the same value of the water ratio. The water ratio has a great influence on the resulting porosity of the internal structure of the composite. The amount and size of the pores affect the time of water penetration through the composite and its amount needed for full saturation. Basically, it was needed more water to fully saturate Slab V1, which could slow the rate of the ultrasound signal penetration. It can be said that according to laboratory tests, the effect of the evaluated composite saturation degree on the resulting values of the rate of ultrasound propagation is negligible. However, for a more complex evaluation of this issue,  
Figure 13: The comparison of results of measuring of ultrasonic testing method and radiography for Slab A2-3: (**a**) Slab A2-3, the steel fibers are distributed homogeneously, areas with locally higher or lower concentration are negligible. The predominant unidirectional orientation of the steel fibers occurs only in the lower part of the slab, as a marginal effect during concreting; (**b**) isovels distribution the SFRC tested Slab A2-3. It indicates no significant discontinuity in the slab. further experiments will be performed. The question is whether it is necessary for the methodology of assessment of the condition of the protective structure in situ to include the moisture of the structure caused by rain in the factors influencing the assessment result. This question arises from the assumption of the formation of cracks and microcracks in the internal structure of the composite after dynamic loading, when there is no full destruction. A larger amount of water would be needed to saturate the loaded structure, which could have a more significant effect on the speed of the ultrasound. Due to the overall result of the statistical test, a larger statistical data set will be needed for verification, i.e., to perform further measurement on more samples. Based on the analysis of the acquired radiographs, it can be stated that the structure of the distribution of steel fibers in concrete is very homogeneous in testing slabs, with only slight deviations of the locally increased or decreased concentration. Based on the results of ultrasonic measurement and subsequent validation of measurement results by radiography, it can be stated that the ultrasonic method is suitable for detecting discontinuities of cement-based material in field conditions. Therefore, it is appropriate to include it in the set of NDT methods designed to assess the condition of military protective structures in the field. What needs to be worked out on this method is a set of measures and possibly aids that would eliminate the effects on the accuracy and repeatability of measurements. Another part of the research will take place in the Bouletice Military Training Area. After transport, the boards will be measured ultrasonically to check for structural changes. Following this, they will be loaded with an explosion so that microcracks form. The charge size for each testing slab will be mathematically simulated using ANSYS-AUTODYN software. Conceptualization, Z.E. and K.T. ; methodology, Z.E. and K.T. ; software, S.P., H.K. and A.O. ; validation, Z.E., S.J. and K.T. ; formal analysis H.K., S.P., K.T. and A.O. ; investigation, Z.E.