# Assessing the Compaction Quality of Dolomitic Asphalt Pavements Using Ground Penetrating Radar
## 1 Introduction  
The dielectric properties of pavement materials are crucial in GPR investigations [1]. The dielectric permittivity (\(\varepsilon\)) of a substance refers to its ability to store the applied electric field, with the dielectric constant (\(\varepsilon_{\mathrm{r}}\)) representing the ratio of its permittivity to that of the vacuum (\(\varepsilon_{0}\)) [2]. Previous studies, such as those by [PERSON] and [PERSON] [3, 4], proposed three calibration methods: core calibration, laboratory \(\varepsilon\) determination, and reflection amplitude calibration, all suitable for pavement evaluation. This paper distinguishes itself by using horn antennas and the surface reflection method to indirectly determine the specific gravity (Gmb) of dolomitic asphalt mixtures, developing a general function applicable to similar asphalt compositions and offering a more streamlined and widely applicable approach than the methods discussed. The \(\varepsilon\) of asphalt pavement can be measured using the time-of-flight (TOF) and the surface reflection (SR) methods. The TOF method determines permittivity by analyzing the electromagnetic (EM) wave travel time, or TOF, within the asphalt layer, using in situ core samples to derive the dielectric constant based on the known layer thickness and GPR signal properties. The SR method estimates permittivity by measuring the SR amplitude from the GPR signal and comparing it with a calibration signal amplitude obtained from the EM reflection off a metal plate on the pavement's surface [5]. The main reason for variations in asphalt dielectric constants is related to the composition of the material and its physical properties [6; 7; 8], such as its aggregate type, bulk density, bitumen content, and air void content [9; 10; 11; 12]. Among these constituents, the aggregate type has the greatest versatility concerning the \(\varepsilon\)[13]. A wide range of rock types are used as aggregates, though certain types are preferred due to their resistance to fragmentation and polishing. Two widely used rock types are dolomite and limestone [14], with a density similar to that of volcanic and crystalline rocks but with a notably different \(\varepsilon\)[15; 16]. Besides aggregate properties, the density of the asphalt mixture is also a key factor in the performance of flexible pavements. The air void content should range between 3% and 8% [17]. A high air void content leads to moisture damage, binder oxidation, pavement raveling, and cracking. Conversely, a low air void content increases stiffness and reduces the rutting potential and possible bleeding [18]. In dense-graded asphalt mixtures, if the air void content falls below 3%, it can lead to significant permanent deformation and shoving [17; 18]. Asphalt pavements' \(\mathrm{G_{mb}}\) and air void ratios are inversely related: as the air void ratio increases, the \(\mathrm{G_{mb}}\) of asphalt decreases. Thus, the air void ratio is also used to assess the asphalt density. Both parameters are largely influenced by the degree of asphalt compaction. Compaction of the asphalt layer minimizes the presence of low-\(\varepsilon\) air in the asphalt mixture, while the volumetric ratios of high-dielectric asphalt and rock are augmented. Consequently, this process leads to elevated \(\varepsilon\) values [19; 20]. Compaction is critical for achieving the desired density of the asphalt layers; in other words, the quality of the newly constructed pavement depends mostly on the quality of the compaction. In the process of asphalt pavement construction, the paver initially places the asphalt mixture on a bound or unbound base. Subsequently, compactors traverse the loose asphalt mat, eliminating air voids from the mixture. With each pass of the compactor, the air void content decreases. Previous work has demonstrated that inadequate asphalt compaction can result in excessive rutting, cracking, raveling, potholing, and water seepage [21].