Evaluating the flexural performance of bio-based concrete with different types of bio-aggregate and binder

This study investigates the influence of bio-aggregate type (hemp, bamboo, and reed) and binder type (CEMIV, LC3, and PNC) on the flexural performance of bio-based concrete, with the objective of identifying optimized formulations for construction applications. The term ‘optimization’ refers to the identification of favorable aggregate–binder combinations based on a comparative assessment of flexural strength, stiffness, deformation behavior, and cracking characteristics. Digital image correlation was employed to analyze deformation and cracking behavior. The results indicate that hemp-based concretes combined with CEMIV exhibit the highest flexural performance, benefiting from effective crack-bridging mechanisms. Reed-based concretes demonstrate a more stable and homogeneous flexural response, particularly when combined with higher-performance binders such as CEMIV and LC3. In contrast, bamboo-based concretes show pronounced interfacial debonding, especially when paired with lower-strength binders (such as PNC), leading to early strain localization. Binders with high fineness, such as PNC, promote the development of finer and more uniformly distributed cracks, despite lower global flexural performance. These findings provide fundamental insights into the intrinsic flexural behavior of bio-based concretes, indicating that the complementary combination of the dimensional stability of reed aggregates and the favorable mechanical performance of hemp shives can form a robust basis for the future development of reinforced bio-based composites, such as fabric-reinforced cementitious matrix (FRCM) systems, where optimized substrate performance is essential. • Flexural behavior of bio-based concretes evaluated using DIC and four-point bending. • CEMIV–Hemp mix achieved the highest flexural strength (0.6 MPa) and rigidity (44 MPa). • Reed concretes showed stable cracking behavior with wider openings but uniform strain. • Bamboo concretes exhibited weak bonding and high strain localization under flexion. • Combined hemp–reed approach offers optimized stiffness, crack control, and stability.