Moisture uptake in CLT during the construction phase real construction conditions versus specimens exposed to environment

Abstract

The rapid growth in the use of Cross-Laminated Timber (CLT) in construction highlights the need to address durability concerns, particularly in regions with less experience in Mass Timber Construction and favourable climatic conditions for the biological degradation of wood, such as Mediterranean countries. A lack of awareness and deficient construction management can negatively impact the public perception of wood as a sustainable and durable material. Furthermore, the wood species commonly used for CLT production are softwoods, which have low natural durability and are not pre-treated against biological agents such as fungi and insects. This study investigates CLT moisture uptake during the construction phase through 8-month hygrothermal data (air temperature, air relative humidity, and wood moisture content) from a Mass Timber Building case study and 8-month hygrothermal data from CLT specimens directly exposed to weather. For this purpose, more than 80 pairs of insulated electrodes were installed in the case study, which were distributed in different layers of 26 CLT panels (12 floor panels, 12 wall panels and 2 balcony panels). Regarding the specimens exposed to the environment, 25 pairs of insulated electrodes were installed in each of the 6 specimens, totalling 150 pairs. Additionally, measurements of the wood moisture content and exposure to potential sources of contamination, including water, soil, and dust were used as parameters for a qualitative evaluation of mould growth risk. Results obtained reveal that, although climate exposure plays a significant role, visual mould growth was absent in natural exposure tests even after 11 months of exposure. Meanwhile, on-site CLT panels presented visual mould growth within two months, even in a dry season with limited rainfall. These findings demonstrate the difficulty to accurately replicating real construction exposure and underline the necessity of good construction practices, incorporating a more integrated approach that goes beyond weather protection measures, such as improved site cleanliness and organisation, and adoption of rigorous moisture management measures to mitigate biological risks and enhance the durability and sustainability of Mass Timber Construction.