## 4 Numerical and Experimental Comparison  
### Thermal Comparison  
To provide cross-sectional temperatures and to validate the thermal numerical model, six coordinate systems were created at the same points where the thermocouples were placed in the experimental tests (A, B, C, D, E, F zones).  
Figure 14 shows a temperature comparison between the experimental tests and the numerical simulation at the steel decking. The temperature measured in the interface of steel decking and concrete is very similar in the four numerical models, with the temperature in NC being slightly lower in the first time steps. Figure 14 shows that the numerical model can qualitatively represent the physical phenomena in zones C and D of the slabs. Initially, despite the numerical model temperature evolution being slower than the laboratory results, it is possible to simulate the experimental heat transfer phenomenon. The increase in temperature in the experimental results shows a slope reduction after 450 s due to the endothermic process of free water vaporization. Numerical models simulate that effect by changing the slope at around 100 \({}^{\circ}\)C. At the end of the numerical simulation, around 1300 s, there is a large divergence between the experimental and numerical results, due to the absence of free water in the composite slab at the end of the endothermic process.  
The temperature within the concrete is highly influenced by its thermal conductivity. The temperature results in the numerical model in zones E and F are shown in Figure 15. In these zones, the numerical and experimental temperatures are in good agreement for the first 300 s. After that, the movement and diffusion of water, caused by vaporization, makes it difficult for the numerical models to follow the experimental values. For zone E, although the numerical models for LWC-1 and LWC-2 (see Figure 15a) are unable to simulate the rapid increase in temperature that occurs in the interval from 300 s to 500 s, they can replicate the trend of temperature increase correctly. This difference between the numerical and experimental results is due to part of the free water mass escaping from the specimen at the heating surface, with the rest moving to the inner core characterized  
Figure 13: FEM vertical displacement (mm) at 1800 s: (**a**) LWC-1; (**b**) LWC-2; (**c**) LWC-3; (**d**) NC.  
by a lower temperature, where vapor condensates into water. It is found that the existing model does not realistically account for pore structure, and thus is not capable of properly predicting thermal conductivity as a function of liquid saturation. However, the numerical model quantitatively simulates the thermal behavior for LWC-3 and NC slabs in zone E during the entire thermal analysis (see Figure 15b). Figure 15 also shows that the numerical results in zone F are closer to the experimental results.  
On the non-exposed side, the numerical model results in Figure 16 show the evolution of the temperature as a function of thickness and time, in zones A and B. In addition, the numerical results range from 20 to 32 \({}^{\circ}\)C, inside the maximum and minimum limits of the experimental results, respectively. As shown in Figure 16, the insulation criterion is fulfilled.  
The thermal flux at the thin part of the slab (zones B and F) is one-directional and perpendicular to the upper flange of the steel docking. The thermal flux at the thick part (zones A and E) is perpendicular to the lower flange and the web of the steel docking. The evolution of temperature for zones B and F in the numerical models is close to that measured experimentally in zones A and E.  
Figure 14: Comparison between experimental (solid lines) and FEM (dashed lines) temperatures in the contact zone between the steel docking and the concrete: zones C and D.  
Figure 15: Comparison of experimental (solid lines) and FEM (dashed lines) temperatures at zones E and F: (**a**) LWC-1 and LWC-2; (**b**) LWC-3 and NC.