Numerical simulation of moisture transport in thermally modified wood exposed to rain

Renewable wooden products exposed to continuously variable outdoor climates are strongly affected by the moisture levels in the material. High moisture contents accumulated in wood during long periods, in combination with favorable temperatures, represent a risk for the durability of thermally modified wood products because of decay development. In this context, numerical simulations can quickly predict the high levels of moisture as well as the related risk
of decay in decking products for buildings. This information can help to optimize the product maintenance, for example, suggesting the use of appropriate coatings. Earlier studies by the first author have shown that the single-phase finite element modelling of moisture diffusion in untreated wood is an efficient tool to simulate the moisture transport in wooden components of buildings sheltered from rain (Fragiacomo et al. 2011). An extension of this approach, which takes into account the effect of rain in thermally modified products, is proposed in the present paper. The sorption isotherms used in the model are measured at different temperatures above zero degrees Celsius within this research. In addition, the diffusion coefficient includes the contribution of free water in wood above the fiber saturation point. A case study of thermally
modified wood is numerically analyzed, and the results in terms of moisture content are compared with data taken from previous research (Metsä-Korteläinen et al. 2011). In future work, the proposed moisture transport model will be combined with well-assessed models for wood decay (Brischke and Meyer-Veltrup 2016).