## 5 Experimental Results
### Results from Moist Concrete  
The thermographic observation of a moist surface reveals a striking difference relative to the case of a dry concrete surface, which is demonstrated by Figures 14 and 15. Figure 14: Thermogram of the dry type 1 sample before pulse heating. The black rectangle indicates the region used for extraction of the transient. Figure 13: Measured effusivities with their uncertainties (same data as in Figure 12) in relation to the estimated effect size of moisture influence, as indicated by the blue striped rectangle (expected dynamic range). The initial temperature distribution on the surface of the type 1 sample is displayed in the dry state (Figure 14), as well as in the moist state with 5.4% water content (Figure 15). To enable a useful comparison, the displayed temperature ranges have the same dynamics but are shifted by 2.7 K with respect to each other. The background in both cases has the same temperature of 22.5 \({}^{\circ}\)C. In the case of a moist surface, the temperature is certainly lowered, and features of the grain structure are recognizable without a heat pulse. This is a result of evaporative cooling taking place at the surface of the wet concrete independent of the respective drying phase [9; 14]. In the shown case, the cut clay grains appear colder, probably due to their porous consistency with enhanced capillarity for water transport, leading to an enhanced evaporation. As already explained in Section 2, the reflection coefficient of the investigated surface must be known to correctly determine the absorbed pulse energy. As known from common practice, moist concrete appears darker than when dry. [PERSON] pointed out the possibility of detecting moisture by optical reflection [19], and [PERSON] reported the same effect for pine [18]. Therefore, the reflection coefficient must be known for every specific moisture content in order to apply Equation (1) with the correct value of \(Q\). Figure 16 presents measured reflectivity values of the investigated samples. There is a general trend of a decrease in reflectivity with increasing moisture content. However, the measurement itself is not very accurately indicated by the error bars (determined from 4-5 single measurements at different positions). The respective percentage of the darker inclusions within the analyzed region (2.5 cm diameter) influences the obtained value. The temperature transients for the type 1 sample on the cut side are shown in the following figures as previously shown in Figures 10 and 11, i.e., both include the same datasets but with different axis scales. Both plots contain six datasets of six separate measurements. The transient for 0% is not comparable with the others because the surface was completely free of coating material (see explanation in Section 4.2). Thus, the related curve demonstrates only the general shape and a trend. The obtained transients presented in Figure 17 reveal the expected behavior in principle: the highest moisture content is related to the lowest temperature transient due to the enhanced effusivity. With decreasing moisture content, the surface temperatures during and after the pulse reach higher values. Please note that this is not a simple shift of the curve but a stretching of the curve shape. However, the small difference between Exp. 2 and Exp. 3 (2.4% and 2.0% moisture, respectively) could not be resolved, while the difference between 5.5% and 5.2% moisture was detectable. Figure 18 displays the transients in a log-log plot to compare the curve shape with the prediction of Equation (1), shown as dashed line with an arbitrary intercept. Additionally, the blue rectangle indicates the expected effect size (vertical extent) for a hypothetical concrete, similar to Figure 13.  
Figure 15: Thermogram of the wet (5.4% water content) type 1 sample before pulse heating. The black rectangle indicates the region used for extraction of the transient.