Improved insulation with fibres in heavy cob for building walls

Earth construction promises to reduce the carbon dioxide impact of building materials, and more investigations are needed to define regions where the latter are suitable. This work aims to formulate clay materials reinforced with plant fibres in a traditional manner to determine their thermal properties for applications in modern wood-frame structures. The main objective is to manufacture cob using different types of clay, disregarding the clay/sand ratio, and to achieve a solid cob material characterized by an absence of cracks, low volumetric shrinkage, and thermal properties like those of a normal cob. The Atterberg limits of each clay and the absorption coefficient of the fibres were determined before the samples were made. Formulation of 93 samples was carried out with 15, 20, 25, and 30 % water and 0 %, 3 %, and 6 % wheat fibers by mass. Subsequently, 18 samples produced with 25 % water and 0 %, 3 %, and 6 % wheat fibres by mass were retained and used for testing. The thermal conductivity (λ), specific heat capacity (Cp), thermal diffusivity (D), and thermal effusivity (E) were measured after sample drying. The study showed an improvement in thermal properties with increasing fibers in the mixtures, leading to a significant improvement in thermal performance. The clay and cob samples showed a thermal conductivity (λ) of 1.16 W/(m K) and 0.55–0.2 W/(m K), respectively. An increase in thermal capacity was observed with the samples containing fibre, while the thermal diffusivity and thermal effusivity decreased with increasing fibres in the mixtures. Single-factor ANOVA tests were used to show no significant difference between the thermal properties of red and beige clay samples. Our observation supports the idea that beige clay can be used as a finishing coating material for cob walls formulated with red clay.