The Double-K Fracture Toughness of Concrete with Different Coarse Aggregate Volume Fractions

Abstract

This study examines how coarse aggregate volume fraction (Va) affects the double-K fracture toughness and fundamental mechanical properties of concrete. Wedge-splitting tests were conducted on specimens with six different Va values: 19%, 25%, 31%, 37%, 43%, and 50%. The results indicate that compressive strength (fc) and elastic modulus (E) consistently increase with Va, reaching 59.8 MPa and 37.9 GPa at Va = 50%, respectively. Conversely, tensile strength (ft), double-K fracture toughness (including initiation toughness KICini and unstable toughness KICun), and fracture energy (GIF) initially increase before decreasing, peaking at an optimal Va of 37%. Specifically, KICini, KICun, and GIF reached their maximum values of 0.54 MPa·m1/2, 1.20 MPa·m1/2, and 225.0 N/m at Va = 37%. The tortuosity of crack paths follows a similar trend, becoming more pronounced up to Va = 37% before diminishing. Furthermore, quantitative exponential relationships were established between ft and KICini, KICun, and GIF. 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 Va range of 25% to 31% provides an optimal balance between high crack initiation resistance and adequate safety warning capacity for critical engineering structures.

Affiliated Institutions

• Hebei University of Engineering CN
• Hebei GEO University CN
• China University of Mining and Technology CN

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