Experimental investigation on the flexural behavior of steel-polypropylene hybrid fiber reinforced concrete

This paper presents an experimental study on the flexural behavior of steel-polypropylene hybrid fiber reinforced concrete (HFRC) using four-point bending tests on 51 samples. Three types of steel fibers, i.e., straight, hooked-end and corrugated fiber, and a type of monofilament polypropylene fiber are considered. The flexural behavior in terms of load-deflection curves, load and deflection characteristics, toughness, cracking properties as well as the synergetic effect of hybrid fibers is studied. The results show that synergetic effect is observed for all the three types of steel fiber with the combination of polypropylene fiber on improving the flexural behavior of HFRC. Specimens with hooked-end fibers show the best flexural performance. However, the combination of straight steel and polypropylene fibers presents the most obvious synergy. Moreover, an increase in volume fractions of both steel and polypropylene fibers leads to an increase in the compressive, splitting tensile and flexural strengths of concrete. The post-peak ductility of concrete is improved and the strength degradation is alleviated with increasing fiber volume fraction and steel fiber aspect ratio. In addition, specimens with corrugated and hooked-end fibers exhibit a better failure behavior than specimens with straight fibers, with multiply micro-cracks induced by mechanical interlocks of deformed steel fibers observed at the main cracks. Finally, based on a comprehensive fiber reinforcing index, analytical equations for flexural loads, deflections, and toughness of HFRC are developed with varying fiber parameters taken into consideration. (C) 2018 Elsevier Ltd. All rights reserved.