Mechanical Behavior and Formation Mechanisms of Hyphae-Based Lightweight Geomaterials

As the main by-product of wheat, wheat bran is mostly used as animal feed or incinerated, which adversely affects the environment. Mycelium-based biocomposites, which are mixtures of agricultural by-products (e.g., wheat bran) and fungi, minimize wheat bran wastage and have attracted attention as building materials owing to their high strength, low density, and environmental friendliness. Nonetheless, the practical application of mycelium-based materials in geotechnical engineering remains rudimentary. Building on mycelium-based biocomposites, this study develops lightweight sand-mycelium soil (LSMS), consisting of soil, substrate materials (wheat bran), and hyphae (P. ostreatus), as an eco-friendly lightweight backfill material in geotechnical engineering. The impact of substrate material content, effective confining pressures, and hyphae on the mechanical properties of P. ostreatus-based LSMS was studied. In addition, a detailed investigation of the formation mechanisms of P. ostreatus-based LSMS was conducted. The results indicated that increased substrate material content reduces the strength but increases the ductility of P. ostreatus-based LSMS. The presence of hyphae alters the structure of P. ostreatus-based LSMS, reducing volumetric contraction and improving strength, although this depends on confining pressure. The formation of P. ostreatus-based LSMS involves biophysical mechanisms (hyphal network bundling and filling of void spaces) and biochemical mechanisms (self-bonding, secretion bonding, and aragonite deposition). Biochemical mechanisms may provide a more prolonged effect on the stability of P. ostreatus-based LSMS compared to biophysical mechanisms. P. ostreatus LSMS shows great potential as an eco-friendly alternative to conventional lightweight backfill materials in geotechnical engineering.