Experimental screening of growth behaviour and flexural performance of hemp-mycelium composites for construction applications using local residual feedstocks.

The construction industry is responsible for 34% of global energy demand, 21% of greenhouse gas emissions, and nearly 40% of the EU’s total waste. Hemp-mycelium composites offer a renewable, carbon-storing and biodegradable alternative to conventional materials, applicable in insulation, packaging, and lightweight building components. However, many supplements used to stimulate mycelial growth overlap with food production, raising concerns about resource competition and sustainability. The potential of locally available residual streams as low-impact nutrient sources remains insufficiently explored. This study presents an experimental screening of four residual streams (coffee grounds, cow manure, brewery residues and cardboard), both individually and combined with yeast, wheat, oats, and MgCO₃. These supplements were mixed with hemp shives and inoculated with Ganoderma lucidum and Pleurotus ostreatus to assess differences in mycelial surface coverage and measured flexural strength. Rather than determining optimal formulations, the study identifies relative trends and promising substrate-fungus interactions for future investigation. Results show that responses depend on both fungal species and supplement combination. Within the tested conditions, Ganoderma lucidum is associated with higher and more consistent surface coverage and measured flexural strength compared to Pleurotus ostreatus . For both strains, formulations containing brewery spent grains and a manure–cardboard mixture exhibited measured mycelial surface coverage and flexural strength above the species-specific overall averages obtained from samples with sufficient structural integrity for measurement. In Ganoderma lucidum , these substrates yielded strengths of 0.65-0.71 MPa (vs. 0.50 MPa) and surface coverage of 82.29-89.62% (vs. 71.89 %). For Pleurotus ostreatus , strengths were 0.27-0.37 MPa (vs. 0.23 MPa) and coverage 75.98-87.94 % (vs. 49.75 %). The results provide a comparative overview of how supplement composition and fungal species relate to variations in growth and mechanical response. Given the exploratory nature of the study, findings should be interpreted as indicative patterns and inform further investigation under controlled conditions.