Proceedings e report - Firenze University Press

SORPTION OF MOISTURE AND DIMENSIONAL CHANGE OF WOOD SPECIES USED IN HISTORIC OBJECTS
Table 1: GAB constants for water vapour adsorption and desorption isotherms for 21 species of wood as well as
their coefficients of tangential and radial dimensional change
Species Adsorption/desorption Dimensional change
coefficients
vm*10 -2
c k tangential radial
Softwoods
pine (Pinus spp.) 7.25/10.07 13.5/8.21 0.49/0.44 0.38 0.13
Japanese cypress (Chamaecyparis
obtusa)
7.58/10.19 4.38/7.41 0.63/0.53 0.23 0.12
spruce (Picea spp.) 6.82/7.96 10.04/12.4
9
0.74/0.70 0.34 0.14
larch (Larix decidua) 7.07/7.33 9.89/9.05 0.74/0.72 0.45 0.13
fir (Abies spp.)
Hardwoods
7.40/11.35 8.90/7.55 0.66/0.50 0.32 0.12
sycamore (Acer pseudoplatanus) 6.67/12.49 9.01/7.01 0.58/0.30 0.38 0.19
oak (Quercus spp.) 6.19/11.1 7.36/7.26 0.72/0.51 0.33 0.19
dark fossil oak wood 7.57/11.13 7.36/12.50 0.45/0.24 0.62 0.39
rosewood (Dalbergia spp.) 6.11/9.84 9.31/7.38 0.66/0.53 0.33
walnut (Juglans spp.) 5.88/10.41 7.35/4.36 0.69/0.56 0.21 0.14
cherry (Prunus avium) 5.91/8.64 9.89/7.01 0.72/0.66 0.25 0.14
lime (Tilia spp.) 4.51/7.69 7.42/4.70 0.79/0.66 0.30 0.19
sour cherry (Prunus cerasus) 6.80/8.15 8.74/9.83 0.69/0.71 0.29 0.16
elm (Ulmus procera) 5.65/9.07 14.16/7.03 0.74/0.66 0.31 0.17
poplar (Populus spp.) 5.95/8.13 9.58/7.88 0.73/0.68 0.27 0.12
mahogany (Swietenia mohagoni) 7.80/11.18 10.00/7.86 0.65/0.59 0.28 0.11
beech (Fagus sylvatica) 6.98/11.92 7.11/4.88 0.70/0.53 0.36 0.17
birch (Betula pendula) 6.67/10.60 7.85/5.64 0.71/0.57 0.30 0.21
willow (Salix spp.) 6.59/9.07 8.03/7.03 0.73/0.66 0.20 0.07
apple (Malus domestica) 6.83/14.95 7.70/5.15 0.73/0.64 0.35 0.20
ash (Fraxinus excelsior L) 6.63/6.54 8.92/8.32 0.68/0.20 0.29 0.21
Average 6.83/9.36 8.61/7.59 0.66/0.57
4. Dimensional change isotherms
The amount wood specimens swell or shrink was measured as relative dimensional change versus RH.
The relationships were described by fitting the polynomial of degree 3 to the adsorption (swelling) and
desorption (shrinkage) data. As for the sorption isotherms, the ‘average’ swelling and shrinking
isotherms were calculated by fitting the data for all 21 wood species and they are shown for the
tangential and radial directions in Fig. 3. The constant coefficients of the polynomial a0 to a3, for the
swelling and shrinkage, are listed in Table 2.
Table 2: The constant coefficients of the polynomial predicting the average swelling and shrinkage isotherms.
a0 a1 a2 a3
swelling tangential -0.0088 4.8412 -5.1062 6.0800
swelling radial -0.0031 3.0628 -3.1238 3.2034
shrinkage tangential 0.0131 5.2690 0.6517 -0.4018
shrinkage radial 0.0051 3.5639 -0.6023 -0.0461
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