Application of the double-K fracture model and identification to evaluate the fracture-mechanical properties of concrete with a dose of recycled and industrially produced fibers

The growing volume of tire waste in illegal landfills motivates the scientific community to develop applications for it across various sectors of the economy. Recycled steel fibers (RSF) from tires can be a promising candidate for use as dispersed reinforcement in concrete, offering an environmentally and economically advantageous alternative to industrially produced steel fibers (ISF). The results presented in this study were obtained by experimental verification of samples, the double- K fracture model, and an identification method in the virtual laboratory. Using experimental testing, it determined workability, concrete compressive strength ( f c ), splitting tensile strength ( f ct,sp ), elastic modulus ( E c,EXP ), concrete flexural tensile strength ( f ct.fl ), and fracture energy ( G F ). The concrete mix design with RSF showed the deterioration in workability compared to the mix design without fibers (42.5%). In results obtained using the double- K fracture model, a dosage of 40 kg of fibers per 1 m 3 of fresh concrete improved the fracture toughness by 45% and the resistance to stable crack propagation by 177% compared to concrete without fibers. By demonstrating the reliability of fiber concrete under static short-term loading and the ability to develop a functional material computer model of fiber action in concrete, this study aims to break the stereotypical negative views of investors and designers regarding its use in civil engineering structures. If the identification method is successfully verified in subsequent research, it will be possible to produce a smaller number of samples to determine the same number of fracture-mechanical properties, making testing methods more efficient and reducing time in practice.