Honors College Thesis


Strength and Composition of Willamette Valley Cob: An Earthen Building Material Public Deposited

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  • Cob is an earthen building material composed of sand, clay and straw. Though cob homes are presently being built in the Pacific Northwest, there is no applicable building code for this material. The purpose of this study is to establish estimates for the major engineering parameters, including both average values and degree of variability between builders from the central and northern Willamette Valley. The secondary purpose of this study is to identify correlations between engineering properties and mixture composition. The results of this study demonstrated that cob has a larger variation in properties between builders than conventional building materials such as concrete or steel. However, the variability is not so large that it cannot be overcome by conservative design. Average values for all parameters were found which would adequately reflect material properties observed in the field. Cob behaves like a combination of concrete and soil, with explanations for observed behaviors found in both theories. Several correlations were found; however, more research is necessary before the structural behavior of cob will be understood well enough to be codified.
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