Influence of Steel Fibers on Creep Damage and Failure Behaviors of UHPC

Abstract:

To study the influence of steel fibers on damage and failure behaviors of ultra-high-performance concrete （UHPC） at short-term high sustained stress loading， an experimental program on creep damage and failure was proposed by using UHPC and normal concrete at the age of 28 days. The stress-strain relationship of each specimen was measured during the whole loading processing. The failure modes， irreversible strain， creep strain， and nominal Poisson’s ratio were analyzed according to the tested results. Based on the non-destructive ultrasonic test and scanning electron microscopy test （SEM）， the expansion of internal micro-cracks within UHPC specimens and the bond damage between steel fibers and matrix were characterized. The results show the high sustained stress of UHPC and normal concrete lead to the development of internal micro-cracks and lateral expansion of specimens， and finally result in the creep failure of specimens. The bridging and confinement effects provided by steel fibers can control the development of internal micro-cracks， and reduce the lateral expansion of specimens. Before sustained loading， UHPC and normal concrete have similar nominal Poisson’s ratios of 0.18~0.19. After sustained loading， the nominal Poisson’s ratio of UHPC becomes 0.28， whereas the normal concrete specimens have a higher nominal Poisson’s ratio of 0.6. When the sustained stress was higher than 0.70 f_c， creep damage of UHPC specimens occurs， which lead to the reductions in strength and elastic modulus at cycle of reloading. With the increment in sustained stress， the bond between steel fibers and matrix is damaged， and the steel fibers fail to confine the development of internal micro-cracks. As a results， the specimens are continuedly damaged and finally fail.

Key words:ultra-high-performance concrete (UHPC);internal micro-cracks;creep damage;creep failure;steel fibers