## 3 FWD and Test Site  
Figures 1 and 2 are an aerial photograph and a top-view schematic of the FWD test site constructed by Taiwan Freeway Bureau, respectively. Four types of cross-section which are commonly used in Taiwan freeway pavement structures were constructed at the test site. The length of the test road is 50m, while the width of each pavement cross-section is 5 m. Figure 3 illustrates the schematic for each cross-section. For all cross-sections, an aggregate-type subbase with 30 cm thickness was constructed on a well-compacted subgrade. For cross-sections 2 and 3, a 22-cm-thick bitumen-treated base (BTB) was paved on the aggregate subbase, whereas the thicknesses of BTB layer were 20 cm and 30 cm on the aggregate subbase for cross-sections 1 and 4, respectively. A dense-graded asphalt concrete (DGAC) layer with 15 cm thickness above BTB and 1.5 cm thickness of open-graded asphalt concrete (OGAC) on DGAC layer were constructed for both cross-sections 1 and 2. In cross-sections 3 and 4, DGAC layer with 10 cm thickness and 5 cm thickness of stone mastic asphalt (SMA) were laid on the top of BTB layer. Then, 1.5 cm thickness of OGAC and 3-cm-thick porous asphalt concrete (PAC) were constructed above the SMA layer in sections 3 and 4, respectively. Table 1 details the asphalt binder type and the percentage of binder content for DGAC, OGAC, PAC, SMA, and BTB. The PAC and SMA were made from Type-III modified asphalt binder, whereas the binder types of remaining materials were AC-20.  
Figure 1: Aerial photograph of the test site.  
Figure 3: Cross-section and the thermometer configuration.  
Figure 2: Top view of the test site.  
In order to develop the temperature-evaluation model and to conduct the temperature correction for FWD back-calculation, thermometers were installed in the FWD test site for the measurements of temperature. Figure 4 shows a photograph of the thermometers buried in the road section. The locations and depths of the buried thermometers are indicated in Figures 2 and 3, respectively. The specific depths of thermometers were buried 3.5, 5.5, 7.5, 9.5, 11.5, 13.5, 15.5, 18.5, 20.5, 22.5, and 24.5 cm below road surface, 11 depths in total. The surface and atmospheric temperature at the test road were also recorded in the test site using a data miner at a frequency of one record per hour.  
A PRIMAX 1500 FWD device as shown in Figure 5 was employed in this study. The FWD device applied an impact loading and the surface deflections were measured at 12 locations such as 0, 200, 300, 400, 500, 600, 700, 900, 1200, 1500, 1800, and 2100 mm away from the center of the falling-weight disk. Afterwards, the measured deflections can be entered into the back-calculation software to obtain the modulus of each pavement layer. This research conducted the FWD test at different temperatures (i.e., in the morning, at noon, and in the afternoon) to investigate the effect of temperature on the FWD test and back-calculation results.  
To determine the modulus and the relationship between temperature and frequency of the asphalt material layers such as the DENSE and BTB layers, this study performed in situ core drilling on the test roads. The drilled cores were then subject to dynamic modulus tests in a laboratory to obtain a master curve of the dynamic modulus and frequency-temperature shift factors. Subsequently, the 'frequency-temperature shift factors were used in FWD back-calculation to conduct the temperature correction. Through comparison of the shifted modulus and the dynamic modulus master curve, the effectiveness of applying the frequency-temperature shift factors in FWD back-calculation can be evaluated. In addition, a temperature-evaluation model for different depths of pavement was established by a regression analysis using the atmospheric temperature data and temperature data of various depths at the test site.  
Figure 4: Thermometers placed at the test site.