## 3 Materials and Methods
Nevertheless, it is clear that although the results of the drilled sample are significantly different from the laboratory test values, they are still within the border of the prediction intervals (Figures 6a, 7a, and 8a). Since a prediction interval describes the uncertainty of a given data point, it can be assumed that the sample taken from the wearing course has a higher sampling error compared to the samples taken from the binder and base courses. In the case of the recommended model, it can be observed that the \(b\) parameter, which influences the \(S\)-shape, is similar for both AC 11 and AC 22 asphalt mixes. Therefore, a conclusion can be drawn that with a suitable amount of data, the \(b\) value can be regarded as constant. Finally, only the \(c\) parameter, which describes the curve shifting, remains unknown. The aggregates of the AC 11 wearing course are mainly from andsite or basalt because of the high abrasion resistance, and the aggregates of the AC 22 binder and base courses are from limestone; hence, the difference in the \(c\) parameter can be explained by the different dielectric characteristics of the aggregates in these asphalt mixes. This fact allows the introduction of a \(k\) correction factor, similar to what was carried out for the Finnish research results, and by multiplying the \(c\) parameter of the model with this correction factor, the results are better fitted to the drilled sample results. In summary, it can be stated that the model recommended in this paper seems to be better at predicting the air void content compared to previous models, and the parameter set of the model can be determined via proper laboratory tests. In the following paragraphs, the results of the GPR measurements performed on the asphalt layers of the residential street are presented, and these results and the experiences gained are discussed. The relative permittivity values exported from the PaveScan device were transformed to air void content values by applying the recommended empirical model, and the RD values were calculated according to Equation (14). The maps of relative compactness were prepared for all three asphalt layers analysed (Figure 9). The desirable domains with RD values between 0.92 and 0.97 are indicated as black contour curves on these maps. In general, it can be stated that a greater proportion of the areas of the analysed layers shows a relative compactness above 0.97, meaning that the air void content at these areas remains below 3%. In the case of the wearing course, the maps of relative compactness are significantly different for the left and right traffic lanes (Figure 9a). The right traffic lane seems to be almost totally homogeneous, with its compactness reaching 100%. Since this is physically impossible, another explanation was sought and identified. Unfortunately, right before the in situ measurements, the contractors sprayed water onto the freshly paved wearing course to accelerate the cooling time. After the watering, the pavement surface became very wet; therefore, the measurements could not be performed immediately after construction. Consequently, the PaveScan testing was shifted to the next day but because of the rather low daily temperature, the influence of moisture on relative permittivity still had to be assumed. Since the PaveScan device uses the SR method, the measured relative permittivity results were distorted by the thin wet layer on the pavement surface. The reason behind this is that the SR method considers only the amplitude of electromagnetic signals reflected from the surface; therefore, it is sensitive to local problems of inhomogeneities. The only cored asphalt sample was obtained from the left traffic lane, which presumably still bears some sampling error, thereby affecting its measured in situ relative permittivity. By analysing the RD map of the AC 22 binder course, it can be observed that on both the right and left lanes, the relative compactness is highest at the middle of the lane, and the values gradually decrease when moving towards the road axis (Figure 9b).