Experimental investigation on the mechanical behavior of hybrid steel-polypropylene fiber reinforced concrete under conventional triaxial cyclic compression

Abstract

Hybrid fiber reinforcing technology has gained a wide recognition in concrete built infrastructure. The cyclic stress–strain relation of hybrid fiber reinforced concrete (HFRC) plays a crucial role in the elastoplastic analysis of HFRC that further determines the structural damage progression and hysteretic behaviors. This paper investigates the mechanical behavior of HFRC subjected to conventional triaxial cyclic compression. A total of 48 HFRC cylindrical specimens are tested for different fiber volume fraction, fiber aspect ratio and confining pressure. The acoustic emission behavior of HFRC is analyzed with an elaboration of failure pattern transition as well as the mechanism analysis of fiber effects, and the macroscopic mechanical properties evolutions in terms of triaxial compressive strength, plastic behavior and stiffness deterioration were also investigated. It is clearly indicated from the test results that the incorporation of hybrid fibers together with the applying confinement can significantly enhance the mechanical property of concrete with the failure pattern transformed from a tensile failure to a shear failure mode. An increment in the strength of HFRC is observed as the steel fiber dosage increases. The polypropylene fiber contributes largely on improving the plastic behavior of HFRC at an expense of a slight decrease in the compressive strength. It is noted that the effect of confinement outweigh the fiber inclusion in restriction of damage degradation whilst the fiber effect is more pronounced as the confinement is low. Thereafter, the stiffness deterioration in terms of Young’s modulus, shear modulus, bulk modulus and Poisson’s ratio are investigated. The results show that the Young’s modulus and shear modulus of HFRC monotonously reduce during the damage process, whilst the Poisson’s ratio would monotonously increase and the bulk modulus exhibits a hyperbolic evolution form. Applying confinement and adding fibers can restrain the deterioration process of the stiffness, and the influences of fibers on stiffness deterioration are more significant under a low confinement level than that under a high level.