Date of Award

Spring 5-12-2017

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Forest Resources

Advisor

Robert W. Rice

Second Committee Member

Douglas J. Gardner

Third Committee Member

Douglas W. Bousfield

Additional Committee Members

Mehdi Tajvidi

Abstract

The primary objective of this research was to assess and to model the hygrothermal properties of CLT panels made from three distinct combinations of spruce lumber and laminated strand lumber (LSL). The hygrothermal performance of these materials both individually and in conjunction in CLT has not been investigated before. Assessment of hygrothermal properties is necessary to evaluate heat and moisture transfer through the panels which in turn helps to determine where problems might occur within the panels because of moisture condensation. To accomplish the primary objective, three secondary objectives were developed. Those included the determination of thermal conductivity and diffusion coefficient values of the constituent elements of the CLT panels lumber and measurements of heat and moisture transfer through three CLT compositions under specific, severe, temperature and relative humidity gradients over extended time periods. LSL had an average thermal conductivity value of 0.103 W/m.K and spruce had an average thermal conductivity value of 0.102 W/m.K at the as-received moisture content. The average diffusion coefficient of LSL as measured by the traditional (upright) diffusion cup method was 5E-07 cm2/s at room conditions which was smaller than that of spruce which averaged 2.24E-06 cm2/s. Thus, CLT panels consisting of spruce as a face layer absorbed moisture more rapidly when that face layer was exposed to higher moisture concentration when compared to CLT panels consisting of LSL as a face layer. The accumulation of moisture between layers increased with placement of the LSL as a core layer. Based on the smaller diffusion coefficient, moisture transport through the CLT panels made of LSL was slower. Among the tested combinations, the prospect of moisture damage increases in the order of LSL-spruce-LSL to spruce-spruce-spruce, to spruce-LSL-spruce in extreme conditions and proper protection measures should be planned accordingly. Modelling with a finite element based program showed that the temperature in the panels when exposed to a severe gradient equilibrated within two days as shown by both experimental and simulated results. For moisture transfer, the diffusion coefficient change with moisture content and temperature based on the Arrhenius equation produced simulation results in agreement with experimental results but the moisture transfer was much slower than the heat transfer.

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