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Non‐destructive methodologies for the evaluation of moisture content in sawn timber structures: ground‐penetrating radar and ultrasound techniques
Author(s) -
RodríguezAbad I.,
MartínezSala R.,
GarcíaGarcía F.,
CapuzLladró R.
Publication year - 2010
Publication title -
near surface geophysics
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.639
H-Index - 39
eISSN - 1873-0604
pISSN - 1569-4445
DOI - 10.3997/1873-0604.2010048
Subject(s) - water content , ground penetrating radar , moisture , perpendicular , anisotropy , geology , acoustics , radar , geotechnical engineering , soil science , materials science , composite material , engineering , optics , telecommunications , geometry , mathematics , physics
ABSTRACT The moisture content ( M C ) is a critical parameter for most physical and chemical pathologies of timber and, in the case of structural wood, a M C > 20 % can be dangerous for any load‐bearing construction. The complexity of evaluating M C while timber is in use by means of the current methods (oven‐drying and resistance wood meter) led us to test non‐destructive techniques to evaluate this parameter on site. With this in mind, measurements with two non‐destructive techniques, ground‐penetrating radar (GPR) and ultrasound, were carried out on joists of Pinus pinaster Ait. from their initial green state until the point of hygroscopic equilibrium moisture content. In particular, the analysis presented in this paper focuses on the capacity of each technique to register the velocity variations of their waves during the timber drying process. Prior to the GPR analysis, it was necessary to distinguish between differences in the propagation velocity of electromagnetic waves( v E M)attributable to the wood anisotropy and those due to variations in M C . The propagation velocity of the electromagnetic waves was always found to be lower when the electrical field was parallel to the grain of the wood than when it was perpendicular to it. However, when the field was perpendicular, its direction whether radial or tangential, did not significantly affect thev E M. The direct measurements illustrate the ability of the GPR technique to characterize the M C of timber as a clear decrease in the M C resulted in an increase in thev E M. A strong correlation was obtained between the two parameters with coefficients of determination,R 2 > 90 % . Longitudinal elastic wave velocities( v P )were assessed by means of a ultrasound technique during the timber drying process. Despite the fact that thev Pincreased with the decreasing M C of each joist, the determination coefficient between these two variables was very low. The analysis presented in this paper is a successful application of the GPR technique to the study of wood’s physical properties and has a promising future for the non‐destructive, on‐site analysis of timber M C .