Moisture distribution in glulam beams with natural cracks observed with CT Scanning before and after rain

IRG/WP 13-20534

K Sandberg

The way cracks in outdoor wooden constructions affect durability is an interesting topic, since a certain amount of cracks can always be found naturally in wood and glued laminated wood. The question in this was, can cracks lead water into the wood and thereby increase the risk for decay and reduce strength and service life. Moisture balance, i.e., water absorption and water distribution were studied in two 2-meter-long glulam beams after exposure to rain. For the experiment, computer tomography and image processing were used. The beams were X-ray scanned on four occasions during one year: August (CT1), September (CT2), June (CT3) and the following August (CT4). One red-painted spruce beam 215 x 315 mm and one oiled pressure-treated pine beam 140 x 315 mm were studied. The study shows that water can enter a crack for many millimeters by capillary forces, but that this does not necessarily occur. How and to what extent water enters into a crack or delamination depends on material, surface treatment, position and size of the crack or delamination and the quantity of rain and wind. The sizes of the cracks depend on the climate, that is, moisture and temperature variation over time. Some of the cracks become invisible during this movement, and the variation can be as much as 2.5 mm over a 36-hour period. Under certain conditions, small cracks disappear as the woods swells.

Keywords: glulam beam, cracks, durability, moisture content, surface treatment, CT-scanning, outdoor test, service life.1. introduction

Conference: 13-06-16/20 Stockholm, Sweden

Download document (985 kb)
free for the members of IRG.

Order document from secretariat