Monitoring of Moisture and Dimensional Behaviors of Nail-Laminated Timber (NLT)-Concrete Slab Exposed to Outdoor Air

Abstract

The moisture and dimensional behaviors of a nail-laminated timber (NLT)-concrete slab composed of an NLT-plywood composite and topping concrete are monitored for 385 days. The slab is developed for using as flexural elements such as floors. The humidity control of wood gently introduces significant fluctuations under the ambient relative humidity into the slab, and fluctuations in the relative humidity result in dimensional changes. The equilibrium moisture content of the slab increases from 6.7% to 15.3% during the monitoring period, resulting in a width (radial) strain of 0.58%. The length (longitudinal) strain is negligible, and the height (tangential) strain is excluded from the analysis because of abstruse signal patterns generated. Concrete pouring causes a permanent increase in the width of the NLT-plywood composite. However, the width deforms because the weight of the concrete mixture loosens the nail-laminated structure, not because of the significant amount of moisture in the mixture. The dimensional stabilization effect of the nail-laminated system is demonstrated as the composite strain is lower than the total strain of lumber and plywood, which are elements constituting the nail-laminated structure.

Dimensional behavior of nail-laminated timber-concrete composite caused by changes in ambient air, and correlation among temperature, relative humidity, and strain

“…A canopy was built over the slab to prevent direct contact with sunlight and rain. Because the observation site (37°45'79.03'' N, 126°94'79.62'' E) was located near forests and streams, the RH of the site was somewhat higher than that of the reference point in Seoul (Hwang et al 2022). The climatic conditions of the observation site are harsher than those where TCC is typically used.…”

“…1647 One week after concreting, the width strain increased from 0.1% to 0.43%, corresponding to a strain of 0.28% per 1% EMC. Because the reported shrinkages per 1% MC in the radial direction of Japanese larch lumber and plywood are approximately 0.142% (Kim and Lee 2002;Park et al 2015) and 0.126% (Hwang et al 2022), respectively, it is considered that the moisture and concrete load contributes similarly to the width swelling.…”

“…Another factor to be considered in interpreting the phenomenon is that the gap between the elements caused by the rapid increase in width after concreting offsets the actual swelling of the elements in the Xdirection. Hwang et al (2022) reported that the width strain of an NLT with a flat surface increased 0.23% after concreting. In addition, they stated that the moisture inside the NLT was not significantly affected by concreting and that the load of the concrete dominated the rapid width increase.…”

“…Additionally, the wider gap between the elements created by width swelling may have contributed to the increase in internal moisture. The width swelling immediately after concreting is a permanent deformation that does not recover, even if the RH of the air is sufficiently low (Hwang et al 2022).…”

Effects of Pretreatment for Controlling Internal Water Transport Direction on Moisture Content Profile and Drying Defects in Large-Cross-Section Red Pine Round Timber during Kiln Drying

“…This caused tensile stress on the inner surface and compression stress on the outer surface, by which surface checks were prevented. The speed of moisture movement on the timber interior varies in each direction and across different tree species, and it should thus be assessed in accordance with the given conditions (Hwang et al, 2022;Kim et al, 2020;Sutapa and Hidyatullah, 2023).…”