Bio-based fiber–reinforced cementitious composites: durability mechanisms, fungal susceptibility and research gaps

This review synthesizes recent research on the durability of bio-based fibers in cementitious composites with secondary emphasis on fungal colonization risks. It considers the most widely studied natural fibers (e.g., bast, seed, and animal-derived fibers such as flax, hemp, jute, coir, and wool) and highlights how fiber chemistry and microstructure affect moisture uptake, bonding, and aging behavior. Key degradation mechanisms are identified: alkali-induced hydrolysis of cellulose, hemicellulose, and lignin; mineralization of fiber cell walls by calcium hydroxide; swelling–shrinkage of fibers during moisture transport; weakening of the fiber–matrix interface (increased porosity, decalcification, adhesion loss); and damage from cyclic wetting–drying and freeze–thaw events. The roles of fiber pretreatments (e.g., alkali extraction, polymer coatings) and supplementary cementitious additives (e.g., metakaolin, silica fume) in mitigating these effects are also discussed. Fungal contamination is addressed by presenting environmental drivers (prolonged moisture, temperature, organic nutrients) and material factors (organic fiber content, porosity, pH) that favor mold growth, along with biodeterioration pathways (enzymatic hydrolysis, organic acid production, biofilm formation) and current testing gaps. Major knowledge gaps and future needs are identified: the lack of standardized accelerated aging and mold-challenge protocols for biofiber–cement systems, limited long-term field performance data, absence of predictive degradation models incorporating biological factors, and the need for systematic evaluation of treated fibers’ durability. The discussion clarifies how chemical, physical, and biological processes collectively affect biofiber–cement composites and outlines priorities for future research.