property assessment of hybrid fiber-reinforced ultra-high-performance concrete

The purpose of this study was to determine the effect of steel/polypropylene hybrid fibers on the mechanical properties and microstructure of ultra-high-performance concrete (uhpc). tests were carried out on uhpc without and with fibers (steel and/or polypropylene in amounts of 0.25–1%). in this study, granite or granodiorite coarse aggregate with a grain size of about 2/8 mm was employed. the three-point bending tests displayed prolonged post-peak softening behavior. in addition, increasing the content of polypropylene fibers reduced the fracture energy. moreover, the sem results illustrated that adding a certain amount of fibers to concrete considerably changes the microstructure. it was observed that the smallest micro-cracks in the interfacial transition zone between the paste and aggregate occurred in the concrete containing steel fibers.