Optimizing fracture resistance in steel fiber-reinforced self-consolidating concrete: Insights from mode II and mode I fracture energy analysis

Fracture behavior in concrete is critical for structural integrity, especially under shear-dominated loading conditions where mode II fracture prevails. The present investigation examines the fracture resistance of selfconsolidating concrete (SCC) reinforced with steel fibers, with a focus on analyzing both Mode II and Mode I fracture energies. Using the Bazant size effect method, the study explores how compressive strength, fiber content, and specimen size influence the fracture behavior of SCC. The results demonstrate that Mode II fracture energy increases significantly with both compressive strength and fiber content. A pronounced size effect is observed, particularly in larger specimens, where the influence of shear becomes more evident. Even a small addition of 0.3 % fiber volume notably enhances mode I fracture energy by 60 %, while higher fiber volumes affect fracture behavior depending on specimen size. Mode II fracture energy in SCC is found to be over 20 times greater than mode I, although this ratio decreases as fiber content rises. Notably, SCC with or without fibers exhibits lower mode II fracture energy compared to conventional concrete, highlighting the unique challenges and behaviors of fiber-reinforced SCC under shear stress. This investigation provides valuable insights into optimizing fiber content to improve both shear and tensile fracture resistance in SCC.