PSI - Issue 26

Chiara Bertolin et al. / Procedia Structural Integrity 26 (2020) 147–154 Bertolin et al. / Structural Integrity Procedia 00 (2019) 000 – 000

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P40. Additionally, the propension to contraction or to expansion of samples can be evaluated studying the slope of first derivative curves respect to the point of minimum: a negative slope indicates a certain tendency to shrinkage while a positive one suggests the specimen’s predisposition to swell. The fastest EMC change rate in expansion (clearly highlighted in the grey area of the adsorption branch – Fig. 2c) was found for CS, while the lowest for E. This is probably connected with the continuity and impermeability of the layer formed by the chemicals on the wood radial surface. When considering the shrinkage ( i . e . negative slope towards the minima in adsorption/desorption branch – Fig. 2c and 2d) the highest rate was observed for CS+P40, while the lowest for R, indicating a different behavior of treatments during the two processes, needing more detailed investigation to be completely clarified.

Figure 2: a) Sorption and b) Desorption branches; c) Firsts derivatives of the sorption and d) Desorption (right) branches of the tested samples.

3.3 Specific surface area and water layer thickness. In literature, the water vapor sorption has been used to estimate specific surface area of materials adopting modelling approaches (Tuller and Or, 2005; Arthur et al., 2013; Akin and Likos, 2014; Leao and Tuller, 2014; Arthur et al., 2018). Similarly, in this section the GAB model has been used calculate the thickness of the water layer adsorbed on the samples surface t GAB as in eq. 6: = (6)