The effect of moisture content of water trapped in wood joints

To predict the service life of a structure, a model where the exposure of a structure is compared to its resistance can be used. Which exposure and resistance parameters that are relevant depend on which materials the structure consist of. This approach, with an exposure and a resistance parameter, is similar to the one used in structural engineering where a load (exposure) is compared to the bearing capacity (resistance) of a structural element. For wood outdoors the relevant exposure parameter is a combination of wood moisture content and temperature and the resistance parameter is the ability to withstand decay by rot fungi. This study concerns the exposure parameter of wood outdoors above ground. To predict moisture and temperature conditions in the wood from climate data, the macro climate (precipitation, temperature, RH etc.) needs to be transformed into a micro climate, i.e., the climate at the wood surface. The moisture and temperature conditions in the wood can then be calculated using heat and mass transfer models with the micro climate as boundary condition. The micro climate is influenced by the design of a structure. If water is trapped in joints and stays on wood surfaces, the time during which water is absorbed by the wood increases as well as the risk for decay. The aim of this work is to provide information about the relationship between micro climate and wood moisture content. The study concerns structures exposed to liquid water where high moisture contents are reached. Three different types of joints were exposed to artificial rain in the laboratory. Three different gap sizes between the boards were tested for each joint type to create different micro climates at the wood surfaces. Both the micro climate (the duration of water on surfaces and in gaps) and moisture content profiles were monitored during wetting and drying. The measurements were performed using small glued resistance electrodes