Concrete is one of the most widely used construction materials. However, concrete structures suffer from severe durability issues such as material degradation and reinforcement corrosion due to the ingress of water caused by crack formation, an inherent flaw of concrete. High maintenance and repair costs are therefore unavoidable and pose a burden to the economy. Cement manufacturing and the construction sector account for respectively 8% and 40% of the global CO2 emissions, causing a high impact on the environment as well. In this research, a novel concept of using fungi is introduced, leading to more durable concrete structures where crack formation is no longer a threat for the steel reinforcement thanks to an increased resilience of the material. Very recent research shows that fungi are eligible candidates for this application; they promote the precipitation of calcium carbonate onto fungal hyphae to fill and heal the cracks in concrete. This PhD research aims for the self-healing of cracks larger than 1 mm and targets infrastructure suffering from water and chloride exposure such as tunnels, dams, bridges and marine structures. Making these structures watertight is key to prevent reinforcement corrosion, to reduce repair costs and to extend their lifespan.

Mycelium composites are biodegradable materials made of natural fibres or organic waste bound together by an interconnected network of threadlike hyphae, called mycelium (the roots of mushrooms). These fungal hyphae grow by digesting the substrate and can thus be nourished with waste instead of generating more. These biological materials are very beneficial to the development of a circular economy and have the potential to be integrated in our built environment. Mycelium composites are for example currently developed as packaging materials, insulation panels, acoustic tiles, and are used in architectural and artistic pavilions. 

This master's thesis investigated the mechanical properties of mycelium composites and studied the relation between the structural behaviour of the composite and its constituents. The research aimed to experiment, investigate and analyse different kind of moulds, natural fibres and substrates to obtain a broad range of samples by altering the manufacturing process. Interpretation of the obtained results gave a first idea on the material’s mechanical response in compression, tension and bending, as well as how to optimize it.  

The research was characterized by an on-going evolution in different aspects, referring to the protocol to manufacture and grow the composites, the design of the moulds and the mechanical testing of the material. In a first stage, samples made with loose, chopped and long fibres were manufactured, tested and the obtained results analysed. Secondly, possible enhancements of the material’s behaviour were thought of and executed, such as applying a pre-compression on the samples and a pre-straightening of the fibres.   

Promising results were obtained for the optimizations, but the material however underperformed in the case of structural applications. Nevertheless, potential was certainly witnessed and the hope not given up. Different aspects were found to be influencing factors on the mechanical behaviour and/or revealed to be a problem, such as fibre type, internal growth and mould geometry. Therefore new ideas and solutions already came to mind at the end of the master's thesis. Ongoning research is thus highly encouraged to further investigate the potential of these biodegradable and sustainable materials.