Moisture conditions in rain exposed wood joints - Experimental methods and laboratory measurements
Fredriksson, Maria LU
(2013)
In Report TVBM
1030.
- Abstract
- This thesis concerns the moisture conditions in rain exposed wood structures, i.e. wood exposed to high moisture levels. The focus was on the microclimate (the climate at the wood surface) and the material climate (the wood moisture content) in joints. Methods for determination of microclimate, i.e. the duration of moisture on a wooden surface and the duration of water trapped in gaps between two boards, as well as a method for moisture content determinations close to surfaces and joints were developed. In addition, a theoretical study was performed to investigate the influence of the distance to a surface and specimen size on resistive moisture content measurements.
The relationship between microclimate and moisture content in... (More) - This thesis concerns the moisture conditions in rain exposed wood structures, i.e. wood exposed to high moisture levels. The focus was on the microclimate (the climate at the wood surface) and the material climate (the wood moisture content) in joints. Methods for determination of microclimate, i.e. the duration of moisture on a wooden surface and the duration of water trapped in gaps between two boards, as well as a method for moisture content determinations close to surfaces and joints were developed. In addition, a theoretical study was performed to investigate the influence of the distance to a surface and specimen size on resistive moisture content measurements.
The relationship between microclimate and moisture content in wood joints was studied by exposing three different types of joints to artificial rain in the laboratory. The microclimate was varied by varying the size of the gap between the two boards. The measurements were performed on Norway spruce (Picea abies (L.) Karst.) heartwood and sapwood. Both slow grown wood from northern Sweden and fast grown wood from southern Sweden were used in the experiments. The duration of high moisture contents was evaluated for all joints. In addition, the measured moisture contents were used to evaluate differences in expected service life for the different joints using three decay models from the literature. End grain water absorption was also studied separately using computed tomography.
Modelling of moisture transport at high moisture levels requires knowledge of sorption properties also in the high moisture range. However, since the method used in the high moisture range was originally designed for desorption experiments there is a lack of absorption isotherm data in the high moisture range. A method for absorption experiments based on the pressure plate technique was therefore developed. Measurements were performed at one pressure level for Norway spruce sapwood and the results were compared to results from absorption experiments at lower relative humidity levels as well as a pressure plate desorption experiment. (Less) - Abstract (Swedish)
- Denna studie behandlar fuktförhållandena i regnexponerade träkonstruktioner, d.v.s. träkonstruktioner som når höga fuktkvoter. Särskilt fokus var på mikroklimatet (klimatet på träets yta) och materialklimatet (träets fuktkvot) i anslutningar. Metoder
för att mäta mikroklimatet, d.v.s. våttider på en träyta och varaktighet av vatten i spalter, utvecklades liksom en metod för att mäta fuktkvot nära ytor och anslutningar. En teoretisk studie gjordes också för att undersöka hur avståndet till en yta samt en
provkropps storlek påverkar mätningen av elektrisk resistans och därmed fuktkvotsmätningar. Tre olika anslutningstyper vattenexponerades i laboratorium och mikroklimat och fuktkvotsprofiler mättes under uppfuktning och... (More) - Denna studie behandlar fuktförhållandena i regnexponerade träkonstruktioner, d.v.s. träkonstruktioner som når höga fuktkvoter. Särskilt fokus var på mikroklimatet (klimatet på träets yta) och materialklimatet (träets fuktkvot) i anslutningar. Metoder
för att mäta mikroklimatet, d.v.s. våttider på en träyta och varaktighet av vatten i spalter, utvecklades liksom en metod för att mäta fuktkvot nära ytor och anslutningar. En teoretisk studie gjordes också för att undersöka hur avståndet till en yta samt en
provkropps storlek påverkar mätningen av elektrisk resistans och därmed fuktkvotsmätningar. Tre olika anslutningstyper vattenexponerades i laboratorium och mikroklimat och fuktkvotsprofiler mättes under uppfuktning och uttorkning. Mikroklimatet varierades genom att variera storleken på spalten mellan de två brädorna i anslutningen. Alla mätningar gjordes på kärnved och splintved av gran (Picea abies (L.) Karst.). Både
material av långsamväxande gran från norra Sverige och snabbväxande gran från södra Sverige användes i försöken. Varaktigheten av höga fuktkvoter utvärderades för alla anslutningar. De mätta fuktkvoterna användes också för att utvärdera skillnader i förväntad livslängd mellan de olika anslutningstyperna. Ändträuppsugning studerades även separat med hjälp av datortomografi.För att kunna modellera fukttransport vid höga fuktnivåer behövs sorptionsegenskaper också i det höga fuktområdet. Eftersom metoden som används i det höga fuktområdet ursprungligen är utformad för desorptionsförsök saknas dock data för absorption. Därför utvecklades en metod för absorptionsförsök baserad på ’pressure plate’ metoden. Mätningar gjordes för en trycknivå för splintved av gran och resultaten jämfördes med resultat från absorptionsförsök för lägre fuktnivåer samt resultat från desorptionsmätningar med ’pressure plate’. (Less)
Please use this url to cite or link to this publication:
https://lup.lub.lu.se/record/4006446
- author
- Fredriksson, Maria
LU
- supervisor
-
- Lars Wadsö LU
- Peter Johansson LU
- opponent
-
- Professor Rapp, Andreas O., Leibniz Universität Hannover, Germany
- organization
- publishing date
- 2013
- type
- Thesis
- publication status
- published
- subject
- keywords
- wood, moisture, durability, service life, microclimate, surface moisture, mositure content, Norway spruce, Picea abies, pressure plate, decay, growth ring width, heartwood
- in
- Report TVBM
- volume
- 1030
- publisher
- Division of Building Materials, LTH, Lund University
- defense location
- Stora Hörsalen, IKDC ( Ingvar Kamprad Designcentrum) Sölvegatan 26, Lunds Tekniska Högskola
- defense date
- 2013-09-27 10:15:00
- external identifiers
-
- other:TVBM-1030
- ISSN
- 0348-7911
- ISBN
- 978-91-7473-637-3
- language
- English
- LU publication?
- yes
- id
- ac0156f1-8fb6-41b8-ab8e-bfd8dc740a01 (old id 4006446)
- date added to LUP
- 2016-04-01 13:43:02
- date last changed
- 2020-07-01 02:15:51
@phdthesis{ac0156f1-8fb6-41b8-ab8e-bfd8dc740a01,
abstract = {{This thesis concerns the moisture conditions in rain exposed wood structures, i.e. wood exposed to high moisture levels. The focus was on the microclimate (the climate at the wood surface) and the material climate (the wood moisture content) in joints. Methods for determination of microclimate, i.e. the duration of moisture on a wooden surface and the duration of water trapped in gaps between two boards, as well as a method for moisture content determinations close to surfaces and joints were developed. In addition, a theoretical study was performed to investigate the influence of the distance to a surface and specimen size on resistive moisture content measurements. <br/><br>
The relationship between microclimate and moisture content in wood joints was studied by exposing three different types of joints to artificial rain in the laboratory. The microclimate was varied by varying the size of the gap between the two boards. The measurements were performed on Norway spruce (Picea abies (L.) Karst.) heartwood and sapwood. Both slow grown wood from northern Sweden and fast grown wood from southern Sweden were used in the experiments. The duration of high moisture contents was evaluated for all joints. In addition, the measured moisture contents were used to evaluate differences in expected service life for the different joints using three decay models from the literature. End grain water absorption was also studied separately using computed tomography. <br/><br>
Modelling of moisture transport at high moisture levels requires knowledge of sorption properties also in the high moisture range. However, since the method used in the high moisture range was originally designed for desorption experiments there is a lack of absorption isotherm data in the high moisture range. A method for absorption experiments based on the pressure plate technique was therefore developed. Measurements were performed at one pressure level for Norway spruce sapwood and the results were compared to results from absorption experiments at lower relative humidity levels as well as a pressure plate desorption experiment.}},
author = {{Fredriksson, Maria}},
isbn = {{978-91-7473-637-3}},
issn = {{0348-7911}},
keywords = {{wood; moisture; durability; service life; microclimate; surface moisture; mositure content; Norway spruce; Picea abies; pressure plate; decay; growth ring width; heartwood}},
language = {{eng}},
publisher = {{Division of Building Materials, LTH, Lund University}},
school = {{Lund University}},
series = {{Report TVBM}},
title = {{Moisture conditions in rain exposed wood joints - Experimental methods and laboratory measurements}},
url = {{https://lup.lub.lu.se/search/files/3548703/4006452.pdf}},
volume = {{1030}},
year = {{2013}},
}