Investigating the Effect of Micro and Macro Fibers on the Fracture toughness of Concrete in Notched Bending Beam Specimens under Symmetric, Ant Symmetric and Combined Loading Conditions

During the last few decades, various types of fibers have been widely used to reinforce concrete. Considering the properties of fiber-reinforced concrete, the production and use of fibers in the industrialized countries of the world have a wide range, and currently all types of fibers with technical specifications and various applications are mass-produced industrial. Considering the need to develop the production and use of fiber concrete technology. In this research, considering the variety of fibers in terms of material, shape, size, etc., to investigate the effect of metal and synthetic fibers (polypropylene) in micro and macro form, to one of the most important fracture parameters of concrete, i.e., fracture toughness, was studied in 100 mm x 100 mm x 500 mm Single-Edge Notched Bending (SENB) beam samples under symmetrical (I), antisymmetric (II) and combined (I/II) loading conditions. Also, considering the favorable performance of micro fibers on increasing the modulus of rupture of concrete and also the desired performance of macro fibers in improving the concrete rupture module and increasing the bearing capacity of concrete in the post-cracking area of concrete, by using these two types of fibers simultaneously, their superposition effect on the characteristics concrete failure was evaluated in different loading modes (tensile mode, shear mode and combined mode). To analyze the failure probability of the samples, we used metal and synthetic fibers in micro and macro form, with volume percentages of 0.2% and 0.5%, respectively. Using two-parameter Weibull statistical distribution, it was observed that the use of fibers in both micro and macro form has a agreeable effect on the probability of failure of the samples based on the fracture toughness of the samples obtained in the laboratory.