# Assessing the Compaction Quality of Dolomitic Asphalt Pavements Using Ground Penetrating Radar
## 7 Discussion  
The assessment of pavement conditions is essential for efficient transportation infrastructure management. GPR technology provides different alternatives for assessing the dielectric properties of asphalt layers. However, these alternatives may yield significantly different results. [PERSON] and [PERSON] [PERSON] and [PERSON] (2016) found differences between the SR and TOF methods. The present study found that the SR method fits laboratory results better. On the other hand, [PERSON] et al. [PERSON] et al. (2016) found that a certain type of TOF method can provide equally good results. However, the common mid-point (CMP) approach allows for a real-time TOF-accurate estimation method, which involves more complex data acquisition and processing than simpler GPR survey techniques. It requires careful planning and execution and sophisticated processing software, which can increase the overall cost and time needed for the survey. Thus, SR was a simpler method that produced reliable measurements. The study of the relationship between the \(\varepsilon\) and \(\mathrm{G_{mb}}\) revealed a strong linear correlation regarding the wearing course, with a coefficient of determination (R\({}^{2}\)) of 0.85. Similar findings were reported by several other authors, such as [PERSON] et al. [PERSON] et al. (2018) and [PERSON] et al. [PERSON] et al. (2018), using the same antenna frequency (2 GHz) and also by [PERSON] et al. [PERSON] et al. (2018). However, they did not indicate the frequency of the applied antenna. These authors found R\({}^{2}\) values of 0.73, 0.71, and 0.81, respectively. However, the slope of their functions is different from those in the present study (Figure 9). The differences in slope can be attributed to several factors, including the aggregate composition and gradation, asphalt binder content, air voids, and compaction efficiency, as discussed by [PERSON] et al. [PERSON] et al. (2018) in detail. Although the \(\mathrm{G_{mb}}\) was measured using different methods (the density prediction model, non-nuclear density gauge, and nuclear density gauge), the obtained values were within a range of \(\pm\)0.05 g/cm\({}^{3}\), showing high consistency across the studies. The data from the above studies are plotted in Figure 9. It is clear that even though the investigated HMA mixtures have different characteristics (Table 4), most of the data plot to the same region (Figure 9) and provide a means of determining a more general function between the \(\varepsilon\) and \(\mathrm{G_{mb}}\) (Figure 10). We found that in the case of our study (Wearing course, Binder course, Base course) and the survey made by [PERSON] et al. [PERSON] et al. (2018) (AC 13, AC 20, AC 25), the data are located in the same range. However, in the present study, in the case of the sub-base layers, we found that the data fall outside the expected range of dielectric values (\(\varepsilon\)) due to the larger aggregate size (\(\mathrm{d_{max}}\) = 30 mm). Additionally, the asphalt content plays a significant role in these deviations, as a higher asphalt content generally results in lower dielectric values due to the reduced volumetric proportions of mineral filler and aggregate. The impact of the asphalt binder content on dielectric values is particularly important in interpreting the results shown in Figure 8. The asphalt content influences the density and compaction of asphalt mixtures, thereby affecting the dielectric response. As seen in other studies [32; 33], an increase in the asphalt binder content tends to decrease the overall dielectric constant due to the lower permittivity of the binder compared to the mineral aggregate. This relationship must be considered when comparing different datasets and developing generalized functions for dielectric estimation. Therefore, the variations in asphalt binder content should be explicitly analyzed alongside other influencing factors such as air voids, compaction efficiency, and aggregate gradation.