Durability and ductility of concrete structures are very important issues; especially because concrete is a brittle material with a low tensile strength and straincapacity. Both “D’s” can be achieved by using steel fibers2-5. However, to have a durable construction, small crack widths (0.2 to 0.3 mm) are required in the serviceability limit state. Short straight steel fibers can serve as bridging mechanisms during cracking. As a consequence, the use of short steel fibers, especially those with a high aspect ratio, is beneficial for that. Ductility, on the other hand, refers to large deformations, i.e. a good bridging effect of the fibers at large crack widths is necessary. To perform this task, long deformed fibers are more obvious. So, to achieve both durability and ductility, the application of multiple fiber types, i.e. a mixture of short and long fibers, is logical. The application of different types of fibers together in a concrete mixture, was proposed for the first time by Rossi6, as the so- called multi-modal fiber reinforced concrete.

This paper describes the mechanical performance of hybrid fiber concrete with a maximum fiber dosage of 0.75 Vol.%. Two types of fibers were used: short straight steel fibers and long hooked-end steel fibers. The concrete compressive strength (fc,cub150) varied between 55 and 65 MPa, dependent on the fiber mixture. Several dosages of the two types of fibers were examined. Three-point bending tests] using notched prisms were performed. The obtained results confirm that the flexural strength at small crack widths and the ductility of the hybrid fiber concrete with rather low fiber content is remarkably improved in comparison with plain concrete. Moreover, the postcracking behaviour of the hybrid fiber concrete is not only dependent on the total fiber content but also on the fiber mixture.