Fracture study of concrete composites with synthetic fibers additive under modes I and III using ENDB specimen

Abstract

This paper investigates the mode I (i.e. tensile) and mode III (i.e. tearing) fracture behavior of concrete composites containing synthetic forta-ferro (SFF) fibers. By employing a simple and suitable test specimen called edge notched disc bend (ENDB) specimen, the effect of adding different percentages of SFF additive on fracture load, fracture toughness and work of fracture was studied experimentally under both pure mode I and pure mode III. A number of unique and useful experimental results were obtained in this research for crack growth resistance of plain and fiber reinforced composite concretes subjected to pure modes I and III loading conditions. It was observed that the fracture initiation and propagation stages are significantly affected by the SFF content. In comparison with the ordinary and plain cement concrete which is manufactured with no fiber additive, the SFF fiber reinforced concrete composite showed higher fracture toughness and work of fracture values. This demonstrates the improved performance of SFF fiber reinforced concretes against cracking under both tensile and tear loads. However, the fracture behavior of tested ENDB specimens made of concrete composites was dependent on the loading mode type (i.e. I or III) and also the SFF content. According to the experimental results the influence of SFF fibers on enhancing mode III fracture toughness was noticeably greater than the pure mode I case and for both loading modes the highest fracture toughness values (i.e. KIc and KIIIc) were obtained for those concrete composites containing 0.3% SFF. In addition, while the magnitude of KIc was greater than the corresponding value of KIIIc for all tested concrete composites, the fracture energy (or work of fracture) of mode III specimens were significantly higher than the mode I specimens. Indeed, the SFF fiber reinforced concrete composites exhibited excellent post peak failure response such that due to resistance of SFF fibers agains applied loads significant amount of energy was required for overall breakage of tested concretes. This ability can be considered as an advantage of SFF fiber reinforced concrete materials for designing earthquake-resistant structures.