*4.1. Concrete Specimen Design*

In this study, a concrete slab was made with dimensions 125 cm × 105 cm × 10 cm and design compression strength of 30 MPa. The coarse aggregate with maximum size of 25 mm and cement PC40 were employed to make the specimen. The proportion of water, fine aggregate and coarse aggregate to cement was 0.49, 1.48 and 1.90, respectively. The thermal diffusivity of concrete specimen was estimated as α = 1.076 cm2/min in our previous study [20]. Twelve squared artificial delaminations with the same thickness of 1 cm but different sizes ranging from 5.0 cm × 5.0 cm to 15.75 cm × 15.75 cm, and depths of 2, 3, and 4 cm from the back face and 5, 6, and 7 cm from front face were embedded inside the specimen that creates WTDRs from 1.0 to 7.9. Artificial delaminations were made by square pieces of polystyrene with the thermal conductivity of approximately k = 0.027 W/m◦C that is expected to have very similar thermal behavior compared to the air k = 0.024 W/m◦C [26,48]. In addition, artificial delaminations were glued on the stone pieces (made by concrete having same mixture ratio with the specimen) that were attached on the bottom wooden plate of formwork to create defects with exact depths as expected. Therefore, the specimen is anticipated to have similar response under heat transfer in comparison with real concrete bridge deck structure. The arrangement of delaminations and their parameters are shown in Figure 6 and Table 1.

It should be noted that if subsurface defects such as delaminations or voids develop in the concrete bridge, the air fills up inside them. These defects may achieve a similar behavior when receiving a heat flux. Therefore, the results of this study can be applied to not only delamination but also void in concrete bridge deck.

**Figure 6.** Concrete specimen with embedded imitating delaminations: (**a**) arrangement of delaminations; (**b**) formwork to cast the concrete specimen.


**Table 1.** Characteristics of artificial delaminations inside the concrete specimen.
