Modelling Water Sorption Gradients in Spruce Wood Using Ct Scanned Data*

Liquid water sorption in the longitudinal direction in wood samples of Picea abies (L.) Karst. (Norway spruce) was measured with computed tomography (CT) scanning and image processing and then evaluated using multivariate discriminate analysis. The purpose was to determine if there were any differences in liquid water sorption that could be dependent on the vertical position within the tree (0.8, 5.8, and 9.5 m from the butt cut), the growing site (dry or wet), and the type of tree (suppressed or dominant). Test pieces were CT scanned after 1, 3, 7, and 14 days of water sorption in end grain and during desorption at room temperature. The objective was to find wood suited to exterior use that is durable because it takes up water poorly. The conclusion was that heartwood of spruce absorbs less water than sapwood. Heartwood gradients were generally steeper, with a markedly lower moisture content than sapwood. The moisture content gradient profiles differed between the wet and dry sites during sorption and desorption in heartwood and sapwood. Whether or not the trees had been suppressed or dominant had no impact on the moisture content gradients. There was an indication that moisture content gradients in heartwood differed between the first and the second logs, but in sapwood there was no difference.