1. Fachkongress Konstruktiver Ingenieurbau - Mai 2022 259 Building materials from wood and fungal mycelium for loadbearing structures Dana Saez M. Sc. RWTH Aachen University, Faculty of Architecture, Chair of Structures and Structural Design (Trako), Aachen, Germany Denis Grizmann M. Sc. RWTH Aachen University, Faculty of Architecture, Chair of Structures and Structural Design (Trako), Aachen, Germany Univ.-Prof. Dr.-Ing. Martin Trautz RWTH Aachen University, Faculty of Architecture, Chair of Structures and Structural Design (Trako), Aachen, Germany Dr.-Ing. Dipl.-Ing. Anett Werner TU Dresden, Faculty of Mechanical Science and Engineering, Institute of Natural Materials Technology, Bioprocess engineering, Dresden, Germany Abstract Towards an imminent transformation of the construction industry into a more sustainable one, the investigation of fungal mycelium composites has gained ground among researchers in recent years. This research, aligned with the circular economy principles, proposes replacing conventional construction materials with novel mycelium-based materials. Although most of the published research of fungal materials for construction focuses mainly on their favorable isolation properties, we further explored their load-bearing capacity. The virtual growth of fungal mycelium, combined with a lignocellulosic material as wood, yields a promising scenario for a material that allows being shaped into any given form. Moreover, the fungal hyphae develop a network among the chipped-wood substrate connecting it into a matrix. This process also highlights mycelium’s binding capacity. Both properties, rapid virtual growth and binding, served as a basis for this ongoing research. We focused not only on determining the basics for defining the load-bearing capacity of the material but also on two possible case studies. 1. General overview on fungal mycelium research Figure 1: Circular economy in the construction industry, re-interpretation of the Life Cycle Assessment (LCA) from (LETI) Fungi have the capacity to transform organic waste, like by-products from agriculture and forestry, into composites that offer similar or superior properties compared to oil-based materials. Also, they can play a crucial role in the circular economy due to their low embodied energy and cradle-to-cradle capacity. Fungal biotechnology has a great potential due to the natural metabolic properties of filamentous fungi. There are currently about 60,000 basidiomycetes in culture, all of which have their ecological niches and specialize in particular services that must be exploited in a very targeted manner. They are often used mostly for edible mushroom production (mushroom, oyster mushroom and shiitake) although they are interesting research objects for medicine (metabolic pathways), pigments or active substances. Their technical use hardly goes beyond the production of packaging material, like the one patented by Ecovative [Ecovative, (3)]. In the construction industry, the application focus of fungal biotechnology is currently still on an experimental level. Recent studies on the physical and technical properties of fungal mycelium composites with a view to technical ap- 260 1. Fachkongress Konstruktiver Ingenieurbau - Mai 2022 Building materials from wood and fungal mycelium for load-bearing structures plication were carried out worldwide [Ziegler et al., 2016 (4)], [Lelivelt et al., 2015 (5)], [Elsacker et al., 2019 (6)]. These studies include elementary investigations on mycelium composites in combination with lignocellulosic substrates. Here, the physical properties such as thermal conductivity, water absorption capacity, and also mechanical properties such as strength and Young’s modulus of mycelial composites with natural fibers such as grass, hemp, and straw as well as with wood chips were tested and documented. Some elementary properties such as the high thermal insulation resistance, but also the limited moisture absorption is filtered out, according to which mycelium is definitely suitable as thermal insulation. The construction industry is responsible for 30% of global CO² emissions [BMBF, 2019 (1)]. The lifespan of a building includes both, embodied and operational energy (KgCO2e). The embodied energy refers to the carbon emissions of building materials, their transportation and on-site application, and their final deposition. The operational energy is the amount of energy required for the functioning of a building. This is generally associated to the comfort requirements of a building like, heating, cooling, ventilation, lighting conditions, but we should also include home appliances [LETI, 2018 (2)]. Mycelium composites address the problem of embodied energy emissions since it fit in the circular economy presenting a great opportunity to replace oil-based building materials. 1.1 Fungal mycelium research precedents at Trako Figure 2: a) brick developed for the LimyBrick project; b) small and c) large cylinders for compression test; d) sandwich with mycelium core; and e) single element for bonding wall developed for the MycoMatrix project Besides the research activities in the field of classical timber engineering [Trautz, 2019 (7)], [Trautz, 2017 (8)], Trako has been dealing with bio-based materials, their technical and mechanical properties, and their structural usability, among others, as load-bearing, i.e., statically functional materials in architecture and civil engineering since 2014. The project ‘LimyBrick’ (BMBF) was dedicated to investigating fungal mycelium matrix materials and exploring the possibilities to produce modular building elements such as bricks (Fig. 2, a). Propper colonization and biomass production of fungal mycelium is directly influenced by substrate selection, environmental cultivation conditions (temperature, humidity, and pH), and its specific genetic composition [Meyer et al. 2020 (9)]. Hence, basic investigations considering the production of solid, technically, and statically usable mycelial matrix materials were conducted. Therefore, different combinations of fungi and wood substrate were investigated to determine the substrate’s influence on the strength capacity, the ideal climatic and nutrient conditions for growth, and the manufacturing steps for the prototype production (scale 1: 1) [Moser et al., 2017 (10)]. The research team analyzed several influencing parameters like the influence of growth on the volume to oxygen supply ratio to optimize the manufacturing process. Despite autoclaving the substrate mixture, during the growing process, environmental conditions for cultivation are also conducive to the growth of parasitic fungi. The moisture content of the living matrix was measured and reduced while maintaining a practicable growth rate to avoid the growth of parasitic fungi. Regarding strength behavior, the LimyBrick research team conducted a series of experiments on the filling or packing density of the test specimens and their effect on the compressive strength of the test specimens. Also, the influence of the substrate grain size based on three different grain sizes and their combination on the compressive strength of the test specimens was investigated. Subsequently, experiments on the alignment of the substrate chips and their effect on the compressive strength of the test specimens were conducted. A systematic combination and matching of the components resulted in enhancing the strength capacity from 0.3 N/ mm2 to 1.2 N/ mm2 under compressive stress. The experience gained during the LimyBrick project served as the foundation for developing the consecutive project: MycoMatrix, also supported by BMBF. Myco- Matrix aims to establish foundational research on the structural capacity of mycelium and wood-based composites. In this context, similar tests as in the LimyBrick project were carried out, but this time, following two different directions: one focusing on the binding capacity (see point 3.1 MycoWall), and the other on the combination of the mycelium-based composite and wood panels (see point 3.2 Mono-material binding). Figure ii a) illustrates the mycelium brick prototype develop during the LimyBrick project. Compared to commercially available perforated bricks [Ytong porenbeton silka kalkstein (11)], which have a compressive strength of 3.9 to 10.3 N/ mm² depending on the brick strength class, the determined strength of the material is considerably lower at a value of approximately 0.5 N/ mm². This served as a motivation to investigate the mechanical pro- 1. Fachkongress Konstruktiver Ingenieurbau - Mai 2022 261 Building materials from wood and fungal mycelium for load-bearing structures perties of Mycelium and wood-based composites further. Whereas in the LimyBrick project a series of cylinders for compression tests were carried out [Fig. 2 b)], during the MycoMatrix project compression tests continued with cylinders in two formats, small [Fig. 2 b)] and large [Fig. 2 c)], in combination with full density and cultivation time variation. The test program was also completed with shear [Fig. 2 d)] and bending tests [Fig. 2 e)]. 2. Case studies on load-bearing structural components Figure 3: Adapted from Brand, Layers of Change [12] In his book How Buildings Learn [Brand (12)], S. Brand divides the parts that conform a building into six categories with different longevity during its life cycle. Some categories, like the skin, are more susceptible to change, while others, such as the load-bearing structure, remain immanent, mainly, due to its long lifespan. Moreover, aaccording to a report of the German Sustainable Building Council (DGNB), the building sector is responsible for the 30% of global CO² emissions, 40% energy consumption in Europe, and 30% of resource consumption worldwide, where 80-90% is used in the load bearing structures of buildings [Saez et al., 2021 (13)]. We understand this situation as a key opportunity to further investigate load-bearing capacity of fungal mycelium-composites. Therefore, we focused our research on two different case studies MycoWall and Mono-material binding. The case studies consist on 1-to-1 scale prototypes. The prototype manufacturing allows us to observe scale-related construction problems, and implement design solutions to be developed during the process. Also, we can conduct a series of empirical tests highly influenced by the construction complexity and final geometry of the prototypes. 2.1 MycoWall MycoWall is a prototypical building system consisting of sandwich construction elements formed by a mycelium core and wood plates. The prototypes were developed in a feasibility phase of the MycoMatrix project with the aim to apply the mycelium and wood-based composite to traditional construction systems as timber frame construction. The establishment of the material mentioned above into the building practice requires an application scenario adapted to the standards of the corresponding mechanical properties. The proposed sandwich building system is based on the classic timber frame construction method that is suitable for one-to-three-story residential building. The mycelium-bonded sandwich panels are connected by the sides of the frame made of solid timber profiles (see Fig. 4 ). The size of mycelium-bonded sandwich panels is limited by some manufacturing constrains like the size of the drying cabinet required for the denaturation stage. In the case of this constrain, it could be solved by segmenting the sandwich panels resulting on a modular system, as showed on Fig. 4, 1/ 2 or 1/ 3 sandwich panel. Moreover, this segmentation also allows easy transport and montage. In contrast to the classical wooden panel construction, the mycelium sandwich panels have a continuous static bond between the two timber planking panels. It is created by the mycelium layer in contact with the surface of the plank, which has an advantageous effect especially on the horizontal and the stiffening load-bearing effect. Also, as a floor slab, the sandwich core of mycelium transmits the shear stresses and replaces, in terms of volume, a considerable volume of wood, which would have been underutilized statically at this point and would only add weight. From a technical point of view, the envisaged sandwich wall and ceiling elements thus combine several favorable characteristics: Lightweight construction and weight savings; thermal insulation, especially with sides subjected to different thermal loads; and sound insulation, due to the sound-absorbing effect of the mycelium core. MycoWall is an ongoing research project that includes the development and optimization of the building system, its technical production requirements, and the determination and evaluation of its structural and physical properties. 262 1. Fachkongress Konstruktiver Ingenieurbau - Mai 2022 Building materials from wood and fungal mycelium for load-bearing structures Figure 4: schematic illustration of timber frame construction system with sandwich panels. Adapted from Saez et al. 2021. 2.2 Mono-material binding Existing research on mycelium-based materials recognizes the binding capacity of fungal hyphae. It digests and bonds to the substrate’s surface, forms entangled networks, and provides mechanical strength to the mycelium-based composites [Sun et al. 2019 (14)]. As mention before (see point 3) This research was driven by some results of our ongoing project MycoMatrix. After observing the results obtained during the ongoing project, we decided to explore mycelium and chipped wood composites’ bonding capacity further with a series of experiments that combine mechanical interlocking and fungal hyphae networks. Although the bonding capacity of the matrix material was explored on a micro-scale at the laboratory conducted by Dr. Werner [Löser, 2020 (15)], the samples were developed on a meso-scale. On a micro-scale level, we can observe a strong bonding of the mycelium hyphae between the wood substrate as illustrated in Fig. 5. As in the case of the MycoWall, by exploring the meso-scale prototypes we aimed to enhance the bonding surface’s geometrical parameters. Figure 5: REM photo of Ganoderma Lucidum mycelium and chips of spruce wood as substrate. 3. Material challenges and opportunities In order to successfully develop mycelium and woodbased materials with load-bearing capacities for their application in construction we should first optimize the material stability and fabrication. Some of the difficulties we faced during the project are as follows: low compression strength, shrinkage after denaturation, and manufacturing time. When comparing the results of the behaviour under compression of the test specimens with those of the literature, similar values could be observed (0.41 N/ mm²). Yet, as pointed out in point 1.1 these values do not meet the standards of other structural materials used in construction like Perforated bricks for masonry [Ytong porenbeton silka kalkstein (11)]. On this respect, one of the most important values to be investigated is the mixture between fungal mycelium and wood substrate. Within this project, four basidiomycetes species were investigated, namely Ganoderma Lucidum (GL), Trametes Hirsuta (TH), Picnoporus Sanguineus (PS), and Fomes Fomentarius (FF). All of the fungal mycelium species were studied with two different types of wood substrates: beech and spruce. Spruce was chosen due to its availability as a construction by-product in the german market, and Beech was chosen because it represents one of the natural habitats of the tested fungi. [Saez et al., 2021 (13)] For all basidiomycetes investigated, beech turned out to be the most suitable substrate for the production of mycelium-based composite materials. Likewise, GL is potentially one of the most suitable fungi for use in the production due to its fast growth, albeit its strength capacity appears to be comparatively lower that that of TH, which presented a much lower growth under same environmental conditions. Once the optimal mixture was stablished, a series of test to prove optimal cultivation time and packing density were conducted. A series of test specimens were cultivated under same conditions for 1. Fachkongress Konstruktiver Ingenieurbau - Mai 2022 263 Building materials from wood and fungal mycelium for load-bearing structures three, four, and five weeks. The results showed an improvement on the stiffness capacity of the tests cultivated during four weeks in comparison with the three-week cultivation ones. Additionally, no difference between fourweek and five-week cultivation specimens were found, in consequence we decided to continue the experiments based on a four-week growing period. After determining the optimal growth period for GL and beech wood on the formworks, the packing density was analyzed. All test specimens were produced accordingly with 80%, 100%, and 120% packing density. This was mechanically introduced while filling the formworks. These series of test resulted on a positive influence on the strength for the specimens with a 120% packing density. The shrinkage that occurred during denaturation [Fig. 6] leads to a change on the geometry of the test specimens. However, this is dependent on the initial water content during the cultivation in the bags, for an approximately 75% amount of water, the volume reduction is 20%. We also observed that the volume reduction is not homogeneous in all the axis of the produced species, it is always related to the geometry. The greatest volumetric reduction is observed in the axis that prevails over the others, i. e. in the zaxis when it prevails over the xand y-axis. This phenomenon should be considered on the product’s design process. Figure 6: Development of mass in the denaturation process. Finally, one of the biggest problems presented by the biofabrication of mycelium-based composites, is the time requirements. Where the inoculation time was considerably reduced from 10 to 7 days, the minimal amount of time required for the cultivation in bags is 5 days, the cultivation in formworks resulted much slower, requiring a at least 24 days for its optimal development. Leading to a total of 41 days for the production of the mycelium and wood-based composite material. Although, there are parameters to be considered that still have scope for optimization, as the substrate geometry to formwork geometry ratio, or permeability to form ratio (Fig. 7), bio-fabrication seems to be quite time intensive in comparison to similar materials used traditionally in the building industry. To sum up, we can state that all the problems aforementioned, present an opportunity to develop the research on mycelium and wood-based composites further. Figure 7: Permeability of the surface layer. Shape and size of the formworks. My1.4.4 - 3 one-sided, My 1.4.4 - 6 two-sided. 4. Conclusion and Outlook Figure 8: Integration of Mycelium and wood-based composites in the circular economy of the construction industry. Nowadays, the most of the products used in construction are designed for single use only. As illustrated in Fig. 8, the implementation of building materials in circular economy like the mycelium based described in this research would not only strongly improve the LCA of buildings using them, but also, find a second life for by products of the carpentry industry and timber construction systems, as well as, recycling of old wood used in buildings that reach the end of their service life. For this reason, we find the MycoMatrix project relevant enough to be further developed. Due to the large availability of basidiomycetes, there is still scope to conduct a large-scale screening to find the best possible combination of fungus and wood substrate. Further on, the cultivation parameters for the respective fungi would have to be optimized and the resulting bio composites would have to be analysed with regard to their mechanical and physical properties. As previously described, the production of 1: 1 scale prototypes, as the MycoWall or the Mono-material binding ex- 264 1. Fachkongress Konstruktiver Ingenieurbau - Mai 2022 Building materials from wood and fungal mycelium for load-bearing structures periments, is fundamental to understand complex physical and mechanical material properties to be empirically determined. 5. Acknowledgements Colleagues from the Institute for Building Research Aachen (ibac) at RWTH: Clarissa Glawe and Hendrik Morgenstern; Student assistants from Trako at RWTH: Raman Suliman, Lea Scholz, Helena Krapp, and Steliyana Yancheva. Master Student Tina Löser at TU-Dresden and collaboration partners from AG Enzymtechnik also TU-Dresden. Literature [1] German Federal Ministry of Education and Research, “National Research Strategy Bioeconomy 2030. Our Route towards a bio-based economy”, Federal Ministry of Education and Research (BMBF) Public Relations Division, Berlin, 2019. [2] London Energy Transformation Initiative, 2018. LETI Climate Emergency Design Guide How new buildings can meet UK climate change targets. 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Dresden University of Technology, Faculty of Mechanical Engineering, Institute of Natural Materials Engineering, Chair of Bioprocess Engineering. Dresden.