The performance of Posidonia oceanica leaf-based biochar as a partial replacement for cement in concrete: a review of potentials, challenges, and prospects

The rapid growth of industrial activities, particularly cement production, continues to drive annual CO₂ emissions. To address this challenge, biochar, a byproduct of biomass pyrolysis, has gained attention as a sustainable partial replacement for cement in concrete. This study focuses on Posidonia oceanica (PO) leaf-derived biochar, an abundant marine waste that poses significant disposal issues along Mediterranean beaches. PO biochar exhibits a porous microstructure, high surface area, and mineral-rich composition, which contribute to enhanced performance in cementitious composites. Its properties are strongly influenced by pyrolysis temperature, with higher temperatures increasing porosity and channel formation. When incorporated at low dosages (1–2% by weight of cement), PO biochar improves compressive and flexural strengths, particularly with finer particles due to their filler effect. However, excessive replacement levels (> 10%) may reduce strength. In addition, PO biochar enhances water retention and durability, though optimizing pyrolysis conditions remains a challenge. Overall, the review highlights the potential of PO biochar as a sustainable alternative in cement-based materials while identifying key gaps for future research.