# The Influence of Water on the Heat Loss of Hot Mix Asphalt
## 4 Laboratory Verification of the Value of \(A\) Constant
The actual drops of temperature within the HMA layer as a result of spraying the material with water were determined on specimens compacted in the laboratory (Figure 8). The HMA sample thickness was between 42 to 47 mm. The specimens were insulated on the bottom and side surfaces. As a result, heat was released solely through the top surface which was additionally cooled with water. The measurements were carried out with a pyrometer--for surface temperature and with the use of thermocouples--for the inside temperature of the layer. The thermocouples were placed at an appropriate depth in pre-drilled holes filled with hot-poured mix (bitumen/ fine grain natural crushed aggregate). The measurement of the temperature on the surface of the sample was taken using pyrometer from the distance of 20-30 cm. Standard optics were used, resulting in a measurement area with the diameter of approximately 20 mm (Figure 9). This allowed to precisely place the measured areas on the HMA sample (using laser sight). The measuring equipment had an accuracy of measurement of \(\pm 0.75\%\) with test repeatability of \(\pm 0.50\%\). The measurement of internal temperatures was conducted using thermoelectrical thermometers. Those special devices measure the changes in the temperature by measuring the changes in the thermoelectric force of the thermocouple. The temperature measurements were acquired thanks to the additional setup (by external clamp) of electric measuring equipment: Measuring point change-over switch and digital indicator. Thermocouples and compensating K type nickel-alloy nickel-chromium \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Type of HMA**} & \multicolumn{5}{c}{**Physical and Thermal Properties of HMA**} \\ \cline{2-6}  & \(\rho_{m}\) **[g/cm\({}^{3}\)]** & \(\rho_{b}\) **[g/cm\({}^{3}\)]** & \(V\) **[\%]** & \(\lambda\) **[W/(m-K)]** & \(c\) **[J/(kg-K)]** \\ \hline AC 8 S & 2.705 & 2.644 & 2.26 & 0.938 & 0.815 \\ AC 11 S & 2.715 & 2.606 & 4.01 & 0.857 & 0.817 \\ AC 11 W & 2.757 & 2.609 & 5.37 & 0.870 & 0.816 \\ AC 16 W & 2.775 & 2.601 & 6.27 & 1.151 & 0.818 \\ AC 22 P & 2.795 & 2.608 & 6.69 & 1.057 & 0.821 \\ SMA 8 & 2.669 & 2.601 & 2.55 & 0.723 & 0.819 \\ SMA 11 & 2.681 & 2.581 & 3.73 & 0.684 & 0.822 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Thermophysical parameters of the HMA samples. (Ni-NiCr) thermocouples, class I, were used in the research. The measurement error for this type of thermocouples, within the temperature range from \(-20\) to \(+200\)\({}^{\circ}\)C, is \(\pm 1.5\)\({}^{\circ}\)C.  
The tests were carried out at four ambient air temperatures (0, 5, 15 and 25 \({}^{\circ}\)C) at 80% \(\pm\) 5% RH. The HMA specimens were heated up in a controlled manner in a drying oven to the initial temperature of 150 \({}^{\circ}\)C (measured at the specimen bottom--thermocouple No. 5). Spraying of the surfaces with water (cooled down to ambient temperature) was done by hand at 30 s intervals. The total amount of water used in the test was 200 mL, corresponding to the water film of ca. 3.2 mm in thickness. The test duration was 1 h. The thermal insulation (mineral wool) was additionally protected from the possible migration of water during wetting of the surface. This protection was made with the PTFE sheeting resistant to high temperatures (up to 260 \({}^{\circ}\)C). The flow type was established on the basis of the product of Grashof and Prandtl numbers. The values of Gr and Pr were determined for the properties of water (specific heat, viscosity, density  
Figure 8: Schematic of HMA specimen prepared for temperature drop testing showing measurement locations. Figure 9: The size of the measured area for the used pyrometer using standard optics: D—diameter of measured area, L—distance from the object. and thermal expansion) at the average temperature (\(T_{m}\)) calculated with equation (10). With all the results for all the cases under analysis falling in the range of Gr-Pr \(>\) 2:10\({}^{7}\) we deal with a turbulent flow of heat.