## 4 Concrete Samples
### Moist Samples  
Similar to [PERSON] and Pascal, different moisture contents were obtained by simply soaking the concrete samples in water and estimating the moisture content by weighing [6]. However, the existing samples were partially coated (see above), and the coating reduces the water absorption by covering and closing micropores on the surface. Thus, the coatings had to be removed. Figure 5 shows the appearance of the prepared samples after the coating was removed. Here, only type 1 and type 3 were further investigated. The type 1 sample is shown from both sides, which have different appearances. Regarding an on-site application, the formwork side (Figure 5b) represents the more realistic case. The type 3 sample was cut as a slice from a cylinder; thus, there is no formwork side on this sample. Please note that certain pores seem to contain residues from the coating; thus, the water penetration might be influenced in comparison to the original state of the concrete.  
Both samples were soaked in pure water at room temperature. Starting with a long-term soaking of 19 days, further cycles of drying and soaking were carried out to obtain different water contents. However, the water content was sometimes not stable within a few hours; thus, a series of mass measurements was necessary, and gaps between measurements were interpolated. Figure 6 shows the measurement results for the first soaking experiment.  
\begin{table}
\begin{tabular}{c c c c} \hline \multirow{2}{*}{**Property**} & **Type 1** & **Type 2** & **Type 3** \\  & **(Lightweight Concr. Red** & **(Repair Mortar)** & **(Lightweight Concr. Black** \\  & **Expanded Clay)** & **Expanded Clay)** \\ \hline Density (g/cm\({}^{3}\)) & 1930 & 2125 & 1800 \\ \hline Thermal conductivity from TPS & & & \\ (W/(m \(\cdot\) K) & 1.37 & 2.54 & 1.6 \\ \hline Thermal conductivity according & & & \\ to the German standard DIN & & & \\  4108-4 (W/(m \(\cdot\) K) & & & \\ \hline \end{tabular}
\end{table}
Table 2: Density and thermal conductivity of the investigated concrete samples.  
Figure 4: **(a)** Partially coated concrete sample type 1 (side length: 10 cm); **(b)** partially coated concrete sample type 2 (diameter: 10 cm); **(c)** partially coated concrete sample type 3 (diameter: 10 cm).  
Most of the moisture was absorbed within the first two days. The two materials exhibited different absorption dynamics, although they are very similar (appearance and material properties reported in Table 2). The difference is even more pronounced during drying; the type 3 sample lost around one-third of the water content within 5 h.  
Figure 7 illustrates the chronology of several soaking/drying cycles. Please note the different starting levels in spring 2022 due to different sample storage conditions. Here, the drying of the sample type 1 sample began 21 days earlier. The numbers of days in the boxes refer to the type 3 sample. Table 3 lists the treatment data again to provide a better overview of the samples' histories. It is clear that the estimated water content is an average over the whole volume. Due to drying out through the surface, lower values for moisture content would be expected in the near-surface region. However, the averaged values are used as an indicator of moisture content.  
Figure 5: (a) Concrete sample type 1, cut side (after removing the coating); (b) concrete sample type 1, formwork side (after removing the coating); (c) concrete sample type 3 (after removing the coating).  
Figure 6: Increase in water content (moisture) during a period of 19 days of soaking and a sudden drop after 5 h drying in air.