EVALUATION OF WHEAT STRAW, HAMMER-MILLED HEMP, RICE HULLS AND CELLULOSE SETTLEMENT BEHAVIOUR FOR LOOSE- FILL INSULATION APPLICATIONS

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Authors
Butt, Erin
Keyword
Straw Bale , Insulation , Loose-fill , Low Embodied Carbon , Hemp , Rice Hulls , Cellulose
Abstract
Straw bale construction has gained attention in the building industry for its purported sustainability and its low embodied carbon footprint. Research on straw bale construction has examined its thermal and structural performance, as well as the influence moisture and the environment have on long-term performance. Most of this work has examined straw in a baled configuration. The following thesis examines the use of loose-fill fine and coarse cut wheat straw, hammer-milled hemp, rice hulls and cellulose as insulation alternatives. To effectively evaluate the thermal and long-term performance of these loose-fill materials, the installation density and physical behaviour needs to be better understood. The following thesis addresses: 1) the vertical settlement behaviour and stable volume densities under S1 classification following the EN-14064-1 standard for the five materials when exposed to vibrational loading (18 Hz); 2) the vertical settlement of fine cut wheat straw for static and vibrational loading (18 Hz) when exposed to high humidity conditions of 80% relative humidity and 23 oC; and, 3) the design of large-scale wall assemblies for experimental long-term testing of loose-fill straw and cellulose in a double-stud wall cavity. The relationship between density and settlement follows a comparable trend across all materials, where an increase in density decreases the settlement. A decrease in void frequency and size was observed with increasing density in wheat straw and hemp specimens. Wheat straw with longer average fibre length was correlated with a decrease in the density needed for stable behaviour. A minimal change in settlement was observed for wheat straw subjected to high humidity, which led to fibre moisture content of 12-14.5% (this is below the 20% moisture content typically believed to lead to decay of straw). The lowest density meeting S1 classification for each of the materials are as follows: fine cut wheat straw (75.1 kg/m3), coarse cut wheat straw (50.7 kg/m3), hammer-milled hemp (113.4 kg/m3), rice hulls (155.1 kg/m3), and cellulose (49.1 kg/m3). The study provides evidence for the importance of density on the stability of bulk loose-fill material for its long-term performance and provides density values for installing these materials in large-scale wall panels.
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