Reinforcing concrete with nano-enhanced bio-additives: a path toward sustainable construction materials

The transition toward sustainable construction materials has intensified interest in bio-derived nanomaterials as multifunctional additives for cementitious systems. This review critically examines the role of Nano-Enhanced Bio-Additives (NEBA) particularly cellulose nanocrystals (CNCs), biochar, chitosan, nano-lignin, and emerging bio-nano compounds such as starch, tannins, and protein-based materials in reinforcing concrete while reducing its environmental footprint. These materials, derived from renewable or waste biomass, exhibit exceptional capabilities including hydration acceleration, matrix densification, internal curing, crack healing, and ion transport regulation. Characterization data (FTIR, DLS, XRD, SEM, TEM) and reaction mechanisms demonstrate how CNCs interact chemically with cement hydrates, enhancing calcium-silicate-hydrate (C-S-H) formation. Biochar contributes to strength gain, porosity reduction, and CO₂ mineralization, while chitosan and nano-lignin function as self-healing agents and natural dispersants, respectively. Despite these advantages, challenges such as nanoscale agglomeration, chemical instability in high-pH environments, scalability, and standardization gaps persist. Strategies including chemical functionalization, hybrid formulations (CNC-biochar blends), smart hydrogel design, and dosage optimization are discussed. Life Cycle Assessment (LCA) data indicates substantial carbon footprint reductions and waste valorization potential, supporting the integration of these additives into circular construction practices. Future research must focus on smart additive development, 3D printing integration, and certification frameworks to facilitate commercial adoption. NEBA offers a viable pathway to high performance, low-carbon, and multifunctional concrete. Their success hinges on interdisciplinary innovation bridging material science, environmental engineering, and regulatory policy to meet the demands of next-generation sustainable infrastructure.