A High-Performance Wood Strand Composite Material for Building Envelopes

V. Yadama, M. Mohammadabadi
Washington State University,
United States

Keywords: wood strand composite, sandwich panel, building envelope, renewable material, small diameter timber

Summary:

Finding a solution for small diameter timber from hazardous fuel treatments contributes to forest health as well as rural economic development. The issue is with lower wood quality of the wood derived from these trees as well as lower rate of conversion into higher value products such as lumber and veneer. Wood strand technology, such as OSB, can offer a solution. However, can we produce a wood strand composite panel of greater performance than OSB with improved functionality and with less materials (wood and resin)? To this aim, wood strand composite sandwich panel with biaxial corrugated core(s) was developed to serve as a material for construction of building envelopes. The presentation will focus on the design and evaluation of a panelized wood strand composite sandwich panel with biaxial corrugated core(s) that was developed to serve as a material for building envelopes such as walls, floors, or roofs. Thin wood strands with an average thickness of 0.36 mm were produced from ponderosa pine logs ranging in diameter from 191 to 311 mm, blended with liquid phenol formaldehyde (PF) resin to a target content of 8% by wood weight, oriented unidirectionally to fabricate a wood strand mat, and hot-pressed into a corrugated core using a matched-die mold. Single or multiple cores can then be bonded with flat wood strand panels on the faces to fabricate a sandwich panel. Single or multiple cores can then be bonded with flat wood strand panels on the faces to fabricate 1.2 m by 2.4 m sandwich panels. This sandwich panel has a higher structural performance than comparable construction materials with the same applications. For instance, wood strand sandwich panels with one corrugated core is one-quarter the weight of an OSB panel of the same dimensions (length, width, and height) and same density of the core and outer layers. Also, the bending stiffness is 42% higher than an OSB panel of the same density, or over 2.5 times stiffer when normalized for their actual density. When used in walls, these panels can be subjected to gravity loads from the roof and other floors, and transverse wind loads. Presentation will focus on performance evaluation of wood strand sandwich panels in compression and bending conducted following the standard testing guidelines in ASTM E72-15. Additionally, changing resources and demand for reduced energy dependency have led to consideration of combining energy and structural performance codes for construction of sustainable buildings with low embodied energy materials and reduced operational energy (residential and commercial buildings account for almost 39% of the total U.S. energy consumption and 38% of U.S. carbon dioxide emissions). To improve the energy performance, the cavities in the sandwich panel resulting from the corrugated geometry of the core were filled with two-part closed-cell foam. Prefabricated wall panel filled with insulation foam and instrumented was evaluated for its hygrothermal performance at Washington State University’s Natural Exposure Testing (NET) facility, and compared with the performance of a structurally insulated panel installed and evaluated at the NET facility as well.