Abstract
This study examines how coarse aggregate volume fraction (V(a)) affects the double-K fracture toughness and fundamental mechanical properties of concrete. Wedge-splitting tests were conducted on specimens with six different V(a) values: 19%, 25%, 31%, 37%, 43%, and 50%. The results indicate that compressive strength (f(c)) and elastic modulus (E) consistently increase with V(a), reaching 59.8 MPa and 37.9 GPa at V(a) = 50%, respectively. Conversely, tensile strength (f(t)), double-K fracture toughness (including initiation toughness KICini and unstable toughness KICun), and fracture energy (G(IF)) initially increase before decreasing, peaking at an optimal V(a) of 37%. Specifically, KICini, KICun, and G(IF) reached their maximum values of 0.54 MPa·m(1/2), 1.20 MPa·m(1/2), and 225.0 N/m at V(a) = 37%. The tortuosity of crack paths follows a similar trend, becoming more pronounced up to V(a) = 37% before diminishing. Furthermore, quantitative exponential relationships were established between f(t) and KICini, KICun, and G(IF). A safety warning parameter (δ), derived from the double-K fracture toughness, was proposed to quantitatively assess the pre-peak ductility, with values ranging from 0.88 to 0.72 in this study. The findings offer valuable guidance for optimizing concrete mix design, suggesting that a V(a) range of 25% to 31% provides an optimal balance between high crack initiation resistance and adequate safety warning capacity for critical engineering structures.