Effects of Density, Temperature, Size, Grain Angle of Wood Materials on Nondestructive Moisture Meters

Abstract

The aim of this study was to investigate the effects of density, temperature, size, and grain direction on measurement of moisture contents (MC) of wood materials non-destructively. The MC of different sizes of solid wood, glulam, and CLT from larch (larix kaempferi, $560kg/m^3$) and pine (pinus koraiensis, $430kg/m^3$) were measured using the dielectric type and resistance type meters. The specimens were conditioned in the environmental chamber to be equilibrium moisture content (EMC) of 12 % and 19 %. When density setting in dielectric type meter was increased from $400kg/m^3$ to $600kg/m^3$, the MCs of specimen (S-L-100-E) were decreased from 13.4 % to 11.3 %. However, when wood group (WG) setting in resistance type meter was changed from WG1 to WG4, the measured MCs were increased from 9.2 % to 12.3 %. When temperature setting in resistance type meters was changed from 0 to $35^{\circ}C$, the MC was decreased from 17.0 % to 13.0 %. The MCs measured by dielectric type meter for larger specimens (S-L-100-E_11.3 %, G-L-240-E_11.7 % and C-L-120-E_12.8 %) were higher than those of small size specimens (S-L-30-E_8.7 %, G-L-150-E_10.3 %, and C-L-90-E_9.7 %). The MCs measured by resistance type meter for larger specimens (G-L-240-E_11.6 % and C-L-120-E_13.3 %) were also higher than those of small size specimens (G-L-150-E_10.4 %, and C-L-90-E_11.8 %). The resistance type meter was not affected by the grain direction but the dielectric type meter were affected by the grain direction. The MC measured by resistance type meter for G-L-120-E perpendicular to grain direction was 11.5 % and the measured MC parallel to grain direction was 11.3 %. The MC measured by dielectric type meter parallel to grain direction (12.1 %) was higher than that measured perpendicular to grain direction (10.7 %).

Fig. 1. Types and orientations of specimens.

Fig. 2. Procedures for conditioning and measuring of moisture contents of specimens.

Fig. 3. Schematic diagram to measure the moisture contents of specimens by using portable moisture meters.

Fig. 4. Combinations of specimens for evaluating the detectable depth of meters.

Fig. 5. Moisture contents depending on the contacted grain direction and species, as well as the wood group options in MC-380XCA (Condition of environmental chamber: EMC 12 % Temperature of testing room:20 ℃).

Fig. 6. Moisture contents depending on the contacted surface and grain direction of specimen, as well as the wood group options in MC-460 (G-L-120-E specimen, Condition of environmental chamber: EMC 12 %, Condition of temperature setting of the meter: 20 ℃, Temperature of testing room: 20 ℃).

Fig. 7. Moisture contents of wood materials depending on the temperature option in MC-460 (Condition of environmental chamber: EMC 12 %, Condition of wood group setting: WG3, Temperature of testing room: 20 ℃).

Fig. 8. Moisture contents depending on the specimen volume (Condition of environmental chamber: EMC 12 %, Conditions of density setting for MC-380XCA:500kg/m³, Conditions of wood group and temperature setting for MC-460: WG3 and 20 ℃, Temperature of testing room: 20 ℃).

Fig. 9. Moisture contents detected by dielectric type meters (MC-380XCA) for combinations of specimens which have different moisture content (Conditions of density setting: 500kg/m³, Temperature of testing room: 20 ℃).

Fig. 10. Comparisons of moisture contents depending on measuring methods (Conditions of density setting for MC-160SA and MC-380XCA: 500kg/m³, Conditions of wood group and temperature setting for MC-460:WG3 and 20 ℃, Temperature of testing room: 20 ℃).

Table 1. Nomenclatures of specimens depending on the specimen conditions