AIC 53rd Annual Meeting

By drawing inspiration from the traditional practice of amending earthen plaster with natural organic additives, this study explores innovative possibilities of biological amendments inspired by other disciplines for the conservation of earthen built heritage. 

Psyllium husk, a plant-based polysaccharide, is traditionally harnessed for medicinal purposes and has recently gained attention in civil engineering and agronomy as a natural soil stabilizer. This research studies psyllium husk as a cross-disciplinary biological amendment for soil-based shelter coats on earthen structures. Through laboratory testing, we examined the physico-mechanical properties of soils amended with psyllium husk and evaluated its potential as a sustainable alternative to modern synthetic amendments.

Earthen heritage represents a global building tradition that has remained viable for millennia. Key advantages of earthen construction include local availability, low cost, and minimal environmental impact; however, earth is highly sensitive to climatic factors, especially moisture. The increasing intensity of rain events due to Climate Change threatens the stability of earthen heritage in traditionally arid regions. For over five decades, synthetic organic polymers have been used as amendment for the conservation of earthen materials. However, the effectiveness of such materials depends on soil composition and low moisture levels. With clean soil being a dwindling non-renewable resource, they also present issues such as incompatibility, irreversibility, and low sustainability. These limitations have prompted a search for alternative solutions that better address diminishing resources and a changing climate.

Biological materials, rooted in traditional building practices, offer promising alternatives. Historical examples, such as the use of animal blood and cactus pulp by indigenous and Hispano builders in earthen construction, demonstrate the potential of biological materials in enhancing soil stability. Modern lab-engineered materials like nanocellulose offer controlled quality and environmental benefits. Recently, fields like agronomy and civil engineering have developed commercial products that are readily available, cost-effective, and easy to use. Literature research identifies psyllium husk as a promising candidate.

Further evaluation focused on water erosion resistance and compatibility with raw-earth structures. Three stages of laboratory testing were conducted: soil characterization, shelter coat formulation, and performance testing of the amended soil. Testing procedures were designed based on various industry standards, while analytical techniques like X-ray diffraction and SEM-EDS provided deeper insights into the mechanisms of psyllium husk as an amendment and its effects on soil mineralogy and other critical properties.

Results show that psyllium husk performs comparably to synthetic amendments in enhancing the water erosion resistance of soil-based shelter coats. It also demonstrates improved compatibility and potentials of reusability. These findings suggest that psyllium husk could be a viable, sustainable alternative to synthetic materials in the conservation of earthen structures. The study also opens avenues for further research, including field testing, exploring diverse application methods, and investigating synergies with other amendment materials.

Beyond specific findings on psyllium husk, this research highlights the promising implication of applying biological material to conservation. By integrating materials and techniques from other fields, we can develop more feasible, sustainable, and adaptive strategies to address contemporary challenges such as Climate Change and diminishing resources.