Concrete is the most used construction material worldwide due to its abundant availability, structural characteristics and inherent ease of manufacturing and application. However, the material bears several drawbacks such as the high susceptibility for crack formation, leading to reinforcement corrosion and structural degradation. Extensive research has therefore been performed on the use of microorganisms for biologically mediated self-healing of concrete by means of calcium carbonate (CaCO3) precipitation. Recently, filamentous fungi have been recognized as high-potential microorganisms for this application as their hyphae grow in an interwoven three-dimensional network which serves as nucleation site for CaCO3 precipitation to heal the crack. This potential is corroborated by the current state-of-the-art on fungi-mediated self-healing concrete, which, at the beginning of this PhD research, is not yet extensive but valuable to direct further research. This PhD project therefore aims to expand the limited state-of-the-art by exploring various parameters and conditions in a laboratory environment to tackle knowledge gaps and provide insights to the field. Ultimately, the research covers multiple key aspects for the fungal species Trichoderma reesei and Neurospora crassa. Nutritional sources to sustain the fungal species in a cementitious environment are investigated. The influence of alkalinity and different cement types on fungal growth and survival is assessed. Insights on CaCO3 precipitation are gained, optimal biomineralization conditions are discovered and techniques to visualise and analyse the precipitated crystals are grasped and applied. Protection of the microbial spores from the harsh concrete conditions is addressed by looking into the encapsulation of the fungal spores. Finally, the repertoire of potential candidate species is extended by isolating fungal strains from a concrete-relevant environment and screening these on their ability to grow and biomineralize CaCO3 in a cementitious setting. Thanks to the interdisciplinary nature of this research, combining architectural, biological and chemical perspectives, the foundations of the state-of-the-art are reinforced and new ones are built.

Download here Aurélie's doctoral thesis.

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.