Micromechanical design strategy for enhancing tensile ductility of strain-hardening basalt fiber reinforced cementitious composites

Despite the environmental and economic advantages of strain-hardening basalt fiber reinforced cementitious composites (BFRCCs), previous studies have reported that their tensile ductility remains limited to below 1%, even under saturated multiple-cracking conditions. This study aims to elucidate the underlying mechanisms responsible for this limited ductility and to propose a micromechanical design strategy for its improvement. First, a strain-hardening BFRCC was developed by investigating a range of mix designs with varying cement content and fiber diameter. The resulting composite exhibited a strain-hardening response under uniaxial tension, achieving a tensile strength exceeding 5 MPa, while the strain capacity was limited to about 0.5% due to small crack openings. Single-crack tests were then conducted to back-calculate key micromechanical parameters required for analytical simulations. Using the calibrated model, sensitivity analyses were performed to quantify the effects of fiber, matrix, and interfacial properties on the tensile performance. The analysis results revealed that, in the investigated case, increasing the fiber diameter is most effective in enhancing ductility; it adequately widens the crack opening and increases the complementary energy required for stable crack propagation, while only slightly reducing the tensile strength. The reduction in tensile strength can be most effectively compensated by improving the shear strength of fibers. The simulation results also indicated that lowing the Young’s modulus of fibers could significantly improve ductility, while the effect of increasing chemical bonding at the fiber–matrix interface was limited. These findings provide a foundational framework for the rational design of strain-hardening BFRCCs with improved ductility. • Tensile ductility of strain-hardening BFRCCs is limited due to tight crack widths. • Increasing fiber diameter is most effective in enhancing composite ductility. • Improving fiber shear strength is critical for composite tensile strength. • Chemical bonding at fiber-matrix interface has limited effect on composite ductility. • Optimization of fiber geometry and properties is vital for BFRCC performance.