For my senior honors thesis, I decided to study how bio-based materials could help decarbonize the built environment. Buildings and their related construction are responsible for 39% of global energy-related carbon emissions, 28% of which is embodied carbon from processes such as manufacturing and transportation. To mitigate the effects of climate change, the built environment must be decarbonized. I focused on how mycelium could be applied as a novel building material, performing mechanical and thermal properties tests to determine its suitability as a thermal or load-bearing material. Since mycelium can be grown organically on agricultural waste products, it can sequester carbon and waste during growth. As a bio-based material mycelium can also be grown on-site and fill different shapes or forms, further reducing emissions associated with transportation and hazardous materials such as spray-foam insulation.
I focused on the role additives play in mycelial growth and also experimented with novel substrates such as walnut shells, Poly-Lactic Acid (PLA), and foamcore. Due to COVID-19, I lost access to academic resources halfway through my research. While I was able to still complete my mechanical and thermal experiments and draw relevant conclusions, my plans to build a test-wall in a tiny house were affected, and the scope of my experimental substrates had to be reduced.
Scanning Electron Microscopy (SEM) images of several different mycelium strains. (From top to bottom: Oyster, Proprietary Ecovative, Reishi). The growth density and thickness of the different strains informed whether the strain was suited for thermal or mechanical building materials. Compression and tensile tests showed typical stress-strain behavior. While the strengths were within literature ranges, they were too low to be considered for mechanical building materials. Further testing of growth with cross lamination or processing should be pursued.
Insulation testing was based on ASTM-D5334 using a Tempos Thermal Analyser with modulated nutrient additions and growth period. Results indicated that the standard practice of full colonization may not yield the best thermal performance — something that had not been documented before in literature. When exposed to fire, conventional petroleum-based foam insulation tends to melt and burn, producing toxic fumes. In fire resistance tests, a flame was applied directly to the samples and the resulting char thickness was measured. All mycelium samples had less than 0.75 inch charring depth at 10 minutes, while the extruded polystyrene (XPS) sample melted through1 inch within 10 seconds.
Mycelium materials can also possibly sequester industrial waste. While conventionally grown on agricultural byproducts, they are able to grow to some degree on materials such as foamcore, PLA, and XPS. They can also incorporate silica as a fire retardant, opening up a pathway for upcycling glass waste. A test-wall of mycelium bricks and insulation was set to be built in a Tiny House as a part of Dartmouth's Structural Analysis course. However due to COVID-19 the project was postponed indefinitely. With its ability to be grown on-site, and also sequester carbon, agricultural byproducts, and industrial waste, mycelium may very well be the future of building.