Freezing of Water in Hardboard: Absence of Changes in Mechanical Properties
Keywords:
Hardboard, mechanical properties, moisture content, freezingAbstract
One-eighth-inch dry process and two species mixes of 7/16 in. wet process hardboard roofings plus 1/8 in. dry process and 7/16 in. wet process standard hardboards were examined using differential thermal analysis to ascertain the maximum moisture content that exterior hardboard could attain without exhibiting significant freezing. All samples with moisture contents greater than ≈20% exhibited high temperature freezing near - 10 C. Additionally, dry process materials with moisture contents near or above 30% had a distinct low temperature freezing event near -35 C. Integration of the area under the freezing curves indicated that ≈ 3% of the water contained in these samples froze at low temperature. During thawing, this fraction of water melted above -10 C. This type of thermal hysteresis is characteristic of the freeze/thaw behavior expected for supercooled water. Mechanical strength tests performed on dry process (4.1 and 41.1% moisture content) and wet process (4.4 and 34.3% moisture content) standard hardboard exposed to freeze/thaw cycling to -50 C revealed no consistent changes in the modulus of elasticity, modulus of rupture, tensile strength parallel to surface, or internal bond strength.References
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