Multiscale correlation mechanism between pore structure and tensile ductility of high ductility cementitious composites: Fiber distribution state and fracture damage characteristics

The tensile ductility of High Ductility Cementitious Composites (HDCC) was influenced by the interactions between pores of various sizes; however, the underlying mechanisms of this influence were not yet fully understood. In this study, High-Strength High Ductility Cementitious Composites (HS-HDCC) with controlled multi-scale pore structures were designed by optimizing the cementitious mixture composition. A systematic investigation was then conducted to determine the relationship between pore structure at multiple scales and the tensile ductility of HDCC. Results indicated that nanopores ranging from 10 to 50 nm promoted the formation of microcrack pathways at the interfaces between C-S-H and other hydration products. These pathways lowered crack-tip toughness (J tip ), enabling saturated multi-seam cracking behavior. At a larger scale, air bubbles measuring 2000–3000 μm improved the spatial distribution of fibers within the matrix. This improved distribution led to optimal fiber orientation during pull-out, maintaining high fiber bridging efficiency. Optimizing the pore structure resulted in HS-HDCC composites achieving compressive strengths and tensile ductility as high as 100.3 MPa and 10.2 %, respectively. These values represented improvements of 15.2 % and 18.6 % compared to the Control group (SF10). Furthermore, the optimized composites demonstrated a reduction in average crack width by 23.5 % and a decrease in permeability by 31.4 %, compared to the Control group (SF10). The results offer a theoretical foundation and technical guidance for the design and engineering application of next-generation HDCC. • Optimized the pore structure of HS-HDCC by adjusting the composition of cementitious materials. • Explored the correlation mechanism between different pore structures and tensile ductility of HS-HDCC. • Revealed the dual effect mechanism of bubble pore size on the 3D orientation and interfacial properties of fibers.