Thesis: Fan

Thesis: Jiwen Fan

Psyllium Husk as a Biological Amendment for Soil-based Shelter Coat Protection of Earthen Structures

This research examines the physico-mechanical properties of soils amended with psyllium husk, a commercially available plant polysaccharide-based soil stabilizer, used as a biological amendment and sustainable alternative to synthetic and mineral amendments for soil-based shelter coats.

Earthen heritage is a living record of a global building tradition that has remained viable for millennia. Common to all raw earth-based construction, local availability, low cost in use and reuse, and low environmental impact are all important aspects of building with earth; however, earth is also highly sensitive to climatic factors such as moisture. The increasing intensity of a single rain event due to climate change thus threatens the viability of earthen heritage in traditionally arid areas. For over 5 decades, synthetic organic polymers have been used by conservators and builders to amend earthen materials to provide better protection; however, the success of these materials depends on the composition of the soils and in the presence of moisture. Other issues including incompatibility, irreversibility, and low sustainability have prompted reconsideration for alternatives to better cope with diminishing resources and a changing climate.

Shelter coat and historic plaster finishes on a wall ruin at Fort Union National Monuments (Jiwen Fan, 2024).
Among the possible alternatives are biological materials. Bio-amendments are rooted in traditional building practices. Animal blood and cactus pulp were both used by indigenous and Hispano builders to fortify soil for building and maintaining earthen structures. More recently, biological materials have also been researched to reinforce soil in infrastructure construction and agronomy. Lab-engineered materials such nanocellulose provide further promises for conservation with artificially controlled quality as well as environmental friendliness. This research emphasizes two aspects of biological materials: water erosion resistance in response to climate changes and wide availability and low cost for immediate implication of site implementation. Psyllium husks are a promising candidate for further evaluation and are being explored through laboratory-based testing with a focus on water erosion resistance and rate of sorption. X-ray diffraction and SEM-EDS analysis will also help understand changes to the soil clay mineralogy, plasticity, and other critical performance properties.

Overall, psyllium husk presents high potential in terms of improving the resistance and durability of shelter coating materials against water-related damages. Further research on both psyllium husk and other biological materials is embarked.
Psyllium Husk powder forms a water insoluble gel when mixed with water. It dries out after about 60 hours but can be resumed to a gel through soaking in water (Jiwen Fan, 2024).

Psyllium husk amended (left) and unamended (right) shelter coat samples after Water Erosion Test. The unamended samples show more severe damage from mechanical impacts from the water drop, while the amended samples are barely altered (Jiwen Fan, 2024).