## 4 Experimental Design and Procedure
### Testing Process  
Six halogen lamps (500 watts per each lamp) with 3000 watts of total output energy were used as the heat source to heat the specimen surface. The heat source was mounted on a steel frame at a distance of 1.2 m from the surface of the specimen. Figure 4 shows the system of infrared thermography in the laboratory. In every test case, the ambient temperature and relative humidity were measured using the Kestrel 3000 (Figure 4c), of which the accuracy of temperature is 0.1 \({}^{\circ}\)C and of relative humidity is 0.1% [34]. In active IRT, out of several factors (i.e., emissivity, reflected temperature, and distance from the camera to the specimen surface), the ambient temperature and relative humidity are two initial parameters that are set to the IR camera as the input data. These two input parameters are assumed as constant values during each test case and shown in Table 2. The IR camera will automatically calculate the atmosphere transmission and the surface temperature of the specimen [30]. It is noted that a small amount of data of this study can be found in our previous research work [5]. The specimen was heated uniformly in five heating regimes of 15, 20, 25, 30, and 40 min for the front face (depths of 5 to 8 cm), and nine cases of 2, 3, 4, 5, 10, 15, 20, 25, and 30 min for the back face  
Figure 4: System of infrared thermography and equipment: (**a**) System of infrared thermography; (**b**) FLIR SC660 IR Camera (FLIR, Wilsonville, OR, USA); and (**c**) Kestrel 3000 (Nielsen-Kellerman, Chester, PA, USA). Figure 3: Arrangement of artificial delaminations inside the concrete specimen. (depths of 1 to 4 cm). After heating, all lamps were turned off, and the surface temperature in both heating and cooling duration was measured by a long wavelength IR thermal camera (FLIR SC660). With recording intervals of 10 s, thermal images were taken by the IR detector, which was fixed on a tripod at a distance of 3.3 m from the specimen surface, and at an unchanged height of 78 cm from the ground (the height of the camera was nearly the same level as the center of the specimen). Table 3 shows the technical data of the IR camera [35]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline  & & \multicolumn{2}{c}{**Back Face**} & \multicolumn{2}{c}{**Front Face**} \\ \multirow{2}{*}{**Heating Time** **(min)**} & \multirow{2}{*}{**Test Case**} & **(Depth from 1 to 4 cm)** & **(Depth from 5 to 8 cm)** \\ \cline{3-5}  & & **Ambient** & **Relative** & **Ambient** & **Relative** \\  & & **Temperature** & **Humidity** & **Temperature** & **Humidity** \\  & & **(\({}^{\circ}\)C)** & **(\%)** & **(\({}^{\circ}\)C)** & **(\%)** \\ \hline
2 & Case 1 & 19.9 & 63 & - & - \\ \hline
3 & Case 1 & 18.4 & 59 & - & - \\  & Case 2 & 20.8 & 91 & - & - \\  & Case 3 & 19.7 & 64 & - & - \\ \hline
4 & Case 1 & 20.6 & 94 & - & - \\  & Case 2 & 21.2 & 86 & - & - \\  & Case 3 & 17.7 & 62 & - & - \\ \hline
5 & Case 1 & 20.1 & 77 & - & - \\  & Case 2 & 18.2 & 55 & - & - \\  & Case 3 & 17.9 & 84 & - & - \\ \hline
10 & Case 1 & 18.9 & 69 & - & - \\  & Case 2 & 16.9 & 56 & - & - \\  & Case 3 & 21.4 & 73 & - & - \\ \hline
15 & Case 1 & 24.2 & 85 & 10.2 & 59 \\  & Case 2 & 24.8 & 61 & - & - \\  & Case 3 & 17.1 & 66 & - & - \\ \hline
20 & Case 1 & 24.4 & 85 & 14.6 & 73 \\  & Case 2 & 19.2 & 57 & 17.1 & 53 \\  & Case 3 & 18.0 & 76 & 15.8 & 74 \\ \hline
25 & Case 1 & 24.5 & 86 & 12.9 & 35 \\  & Case 2 & 24.5 & 58 & 14.2 & 78 \\  & Case 3 & 21.2 & 73 & 16.1 & 63 \\ \hline
30 & Case 1 & 24.3 & 79 & 12.1 & 48 \\  & Case 2 & 25.2 & 53 & 13.7 & 83 \\  & Case 3 & 17.7 & 84 & 16.8 & 62 \\ \hline
40 & Case 1 & - & - & 15.9 & 52 \\  & Case 2 & - & - & 15.4 & 77 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Environmental conditions for each case of the test.