## 3 Methods
### Measurement of Moisture Content  
The saturation moisture of the cellular walls Us [%] indicates the moisture content level of the wood for which all cellular walls are completely saturated with water. If wood moisture is above the saturation point (U > Us), the water is in the liquid state in the lumen of the cells as the so-called free water or imbibition water. Variations of moisture above Us have very little influence on the physical-mechanical characteristics of the wood [52; 53]. When the wood moisture is below the saturation point (U < Us), diffusion of water vapor in the lumens and bound water in the cell walls takes place. These two phases are not necessarily in local equilibrium and can be coupled via the sorption rate [54]. In this interval, the stored water has a decisive influence on the physical-mechanical characteristics of the wood [34; 52]. Saturation moisture depends on the wood species and for most of them it is in the range 24% \(\leq\) Us \(\leq\) 32%. Wood moisture can be measured or estimated. Direct methods provide for the measurement of the mass of water contained in the sample and the mass of the same in the anhydrous state, while indirect methods exploit the correlations existing between the moisture content of the wood and other physical quantities.  
Among the indirect methods, the electrical resistance method [55] is generally applied. Wood is a very bad conductor of electricity and its resistivity decreases as moisture increases, and vice versa, following by and large an exponential law up to the saturation point, and then continues to decrease less markedly and regularly. This relationship is exploited to estimate the moisture content of the material starting from a measure of its resistivity. The most popular measurement method is based on the use of the hygrometer, an instrument that detects resistivity by means of metal electrodes embedded in the material. When using this equipment, two conditions must be considered: (1) the possible presence of a gradient between the various positions where the electrodes are fixed and (2) the measuring range. Practical experience shows that truly reliable results can only be obtained in the moisture range between a minimum of about 7% and a maximum of about 30% [55]. The wood directly in contact with the electrodes is what affects the measurement of resistivity, which depends on the wood species and the temperature; therefore, the instrument must be suitably calibrated according to the wood species on which the measurements are being made [55]. While direct measurements provide an average moisture value of the entire element, indirect methods return a local average value, and in order to obtain an average measurement it is suggested to repeat the measure at least in three points and at different depths, excluding the extremities and the areas with defects or anomalies (knots, etc.).  
The instrument used for the tests is a Tramex PTM 6005 hygrometer which does not allow pre-calibration but allows the correction of the values according to the wood species, in this case maritime pine, through a conversion table supplied by the producer.  
\begin{table}
\begin{tabular}{c c c} \hline
**Width [mm]** & **Thickness [mm]** & **Length [mm]** \\ \hline
106.0 \(\pm\) 3.0 & 42.6 \(\pm\) 1.4 & 2799 \(\pm\) 1.6 \\ \hline \end{tabular}
\end{table}
Table 1: Average dimensions of the boards.