Material Characterization and Fire Performance of Clay Boards

Sammanfattning

Clay boards are emerging as a sustainable alternative to gypsum boards for fire protective linings in timber structures. However, their fire behaviour is still not well understood. Most existing studies focus on full scale systems, which show when a board fails but not why it fails. This thesis addresses this gap by investigating two commercial clay board variants with different compositions, densities, and thicknesses using a multi scale experimental approach. First, the material-level behaviour was investigated, including microstructure, thermal properties, and thermal degradation. This knowledge was then used to interpret fire performance in small-scale cone calorimeter tests and intermediate-scale furnace tests. The results show that the performance of clay boards depends on both material composition and thickness. Under constant heat flux, both 22 mm clay board variants give comparable fire performance to a 13 mm Type F gypsum board. Organic components such as straw, wood, and miscanthus have little effect on thermal insulation.However, they play key role in maintaining structural integrity by binding the clay matrix together.Once these binders degrade, the clay board loses its strength and becomes prone to fall-off Performance parameters obtained from cone calorimeter tests at 50 kW/m$^2$ showed good agreement with intermediate scale furnace tests conducted for 30 minutes. Comparison with the Eurocode 5 design model showed that current equations, which are valid for higher density boards, give similar but slightly conservative estimates of basic protection time when used for low density boards. Overall, this study improves the understanding of clay boards at the material level. It helps relate material level knowledge of clay boards to their fire performance at small and intermediate scales. It also highlights the need for future full scale tests to better investigate board fall off, while considering the effects of orientation, material composition, jointing, and mechanical fixtures.