Cement-Based Composites with Biochar for Shielding Effectiveness in the Construction Sector

The partial substitution of non-renewable materials in cementitious composites with eco-friendly alternatives presents a promising approach to cost reduction and enhancement of shielding properties. In this study, the electromagnetic shielding effectiveness of cement-based composites incorporating biochar as a conductive filler is investigated in the X-band (8.2–12.4 GHz), a frequency range widely used in radar and satellite communication. A commercial lignin-based biochar derived from wood (CB) is analyzed, focusing on its composition, dispersion within the cement matrix, and impact on shielding performance. The water and carbon content of the biochar are examined through thermogravimetric analysis (TGA), revealing a high carbon content of 74%. Cementitious composite samples with 12 wt.%, 14 wt.% and 18 wt.% biochar are fabricated to fit a rectangular waveguide for shielding effectiveness measurements. SEM analysis shows a homogeneous dispersion of CB particles within the matrix. Shielding effectiveness (SE) values above 20 dB are achieved for composites containing 18% of CB biochar at 10 GHz. Additionally, the influence of water content, arising from different curing and ageing conditions, is examined. Results indicate that extended wet curing enhances shielding effectiveness, whereas prolonged ageing in ambient conditions reduces it, with a decrease of approximately 5 dB after 10 weeks. This behavior is attributed to variations in physically adsorbed water, which should be considered when designing cement-based composites for electromagnetic shielding applications. Overall, lignin-based biochar emerges as a promising candidate for partial cement replacement, significantly improving the shielding performance of cementitious materials.