Journal of Sustainable Architecture and Civil Engineering
DOI link: https://doi.org/10.5755/j01.sace.25.2.22263
This paper focuses on cross-laminated timber (CLT) and how it is affected by the dynamic properties of moisture during installation in the cold climate of Estonia. The moisture safety principles are designed using a case study of comparable activities with 4D principles and on-site water content monitoring. On-site water content monitoring was done on the CLT elements that were installed and a parallel polygon specimen. Polygon testing was arranged with reduced size CLT elements subject to different conditions, with some exposed to the climate, some protected from precipitation, and some covered with film.
The moisture content (MC) of the uncovered horizontal CLT element that was exposed to the climate reached over 25% after higher precipitation and the MC after prolonged direct exposure can reach up to 40% in a week, giving a clear signal of high risk areas for moisture safety. Installing a partly weather protected CLT element without a preliminary roof is a high-risk arrangement, but is essentially possible in a cold climate. Moisture safety pre-planning and a lean strategy must be applied with timber construction.
Current research is focused on crack formation and propagation in cross laminated timber (CLT) panels and its impacts on the water vapour resistance and air permeability of panels. Crack formation was examined by means of climate tests with five layer CLT-panels with a thickness of 95 mm. Results of climate tests showed that decreasing the moisture content (MC) from 11 % to 7 % caused mean crack widths in panels of 0.27 mm and 0.38 mm, and an MC decreasing from 17 % to 7 % caused mean crack widths of 0.89 mm and 2.0 mm. From these test results it was concluded that in CLT panels which were produced and stored in a humid environment there was an approximate 200% increase in the mean maximum width of cracks compared to panels stored in a dry environment. The water vapour transmission increased by about 9 % with smaller cracks (that were imitated with 2 mm holes) and 30 % with larger cracks (6 mm holes). The air permeability of CLT at a maximum air pressure difference of 550 Pa was 2.25 l/(s*m2) with 2 mm holes and 5.56 l/(s*m2) with 6 mm holes. It can be concluded from the afore mentioned test results that cracks significantly influence the hygrothermal properties of CLT. Deeper investigation as to the reasons, formation and propagation procedures are needed to avoid inadvisable cracks in CLT.