## 2 Materials and Methods  
### EM Density Gauge Theory  
To measure the density of asphalt mixture in the field was used PQI 380 electromagnetic (EM) density gauge, the operation of nuclear or non-nuclear density meters (non-destructive methods) is generally similar, this process includes calibration, the input value of asphalt mixture density through specimens in laboratory (cores or test pieces), and data collection [33; 34]. The EM density was used, a device that uses electrosopic impedance to measure the electrical response of the asphalt from which you want to calculate its density. The electric field is transmitted through the material by the sensor on the equipment plate [30]. The EM density gauge is a device that uses impedance spectroscopy to make readings of the electrical response of the asphalt, from which the density of the asphalt mixture is calculated directly. The electric transmission field is transmitted from the sensor located in the plate of the EM density gauge through the material (asphalt mixture), to subsequently measure the electrical impedance (Figure 2) and use it within the calculation of the density of the specific rock aggregate [34]. \begin{table}
\begin{tabular}{c c c} \hline
**Device** & **EM Density Gauge** & **GPR** \\ \hline \multirow{4}{*}{Advantages} & Lightweight, easy to use, & \\  & intuitive interface, repeat & \\  & reading, temperature & \\  & correction, low cost & \\  & (USD 14,000), repeatability & \\  & Low performance, & \\  & discontinuous readings, & \\  & reading depth less than & \\  & 100 mm & \\ Special requirements & Core calibration & \\  & & \\ \end{tabular}
\end{table} 
Table 1: Advantages and disadvantages of readings with the EM density gauge vs. GPR. Figure 2: Example of the operation by electrical impedance of electromagnetic density meters for the calculation of the HMA [34]. It has been found that the dielectric constant of a matrix consisting of several materials is proportional to the volume fractions and the dielectric constants of these materials, as shown in Equation (1) [35]. \[\epsilon_{\text{comp}}=\left(\sum_{1}^{n}v_{n}\epsilon_{m}^{x}\right)^{\alpha} \tag{1}\]  
where \(\epsilon_{m}\) are the dielectric constants of the materials constituting the matrix and \(v_{n}\) are the fractions of the volume of the materials involved, \(\alpha\) is a constant that explains the effects of interfacial dielectric polarization for engineering materials, \(\alpha\) = 0.5. Table 2 below shows the usual data for each of the materials making up an asphalt mixture [35]. The value of the dielectric constant for stone aggregates depends on their petrographic and chemical composition; in the case of this research, we used basalt (\(\epsilon_{r}\) = 3.2), but granite (\(\epsilon_{r}\) = 4.5) can also be used. According to the results expected from the equation of the asphalt dielectric constant, it is shown that the temperature coefficient in a mixture having a content of 2% water of \(-1\%\) per 10 \({}^{\circ}\)C, for a temperature of 150 \({}^{\circ}\)C corresponding to 0.025 g/cm\({}^{3}\). If required, a correction of the densities should be made according to the temperature range (at every 10 \({}^{\circ}\)C) in which they are carried out, as shown in Equation (2) [35]:  
\[\epsilon_{w}=78.54\left(1-0.004579\left(T-25\right)\right)+0.0000119\left(T-25 \right)^{2} \tag{2}\]  
There are two common measurement methodologies in the EM density gauge (PQI 380) to obtain the results of the density of asphalt mixtures, which are simple measurements, or with the average measurement of 5 points, the density measurement range of the PQI is 18-2.5 g/cm\({}^{3}\). For optimal results, the calibration of the PQI 380 with the core method is the most accurate and consistent readings; to ensure the methodology is reproducible, the calibration cycle must be monthly or in every change in the aggregate type and size, as well as the changes in the binders, produce a wide variety of electrical properties [36].