Influence of steel fiber content on the rate-dependent flexural performance of ultra-high performance concrete with coarse aggregates

Shaohua Li,Ole Mejlhede Jensen,Qingliang Yu

doi:10.1016/j.conbuildmat.2021.125935

Abstract

Steel fiber is widely used to improve the flexural performance of ultra-high performance concrete (UHPC), yet the synergistic effect of steel fiber and coarse aggregates in UHPC containing coarse aggregates (UHPC-CA) has not been elucidated. Here, the influence of fiber content on the rate-dependent flexural performance of UHPC-CA is investigated from the view of the synergistic effect of steel fiber and coarse aggregates. Results reveal that the increasing pull-out force due to the increase of the crack mouth opening speed at a higher loading rate is responsible for the flexural curve type transition of UHPC-CA. The first crack stress is insensitive to the fiber content. However, the dynamic increase factors (DIFs) of the flexural strength and energy absorption capability of UHPC-CA decrease with increasing fiber content, which is attributed to a lower crack propagation speed of UHPC-CA with a higher fiber content. A model concerning the crack propagation speed and the critical angle for the fracture of coarse aggregates is proposed.

Highlights

Ultra-high performance concrete (UHPC) is considered as a prom ising new cementitious material, which is characterized by its superior flexural strength and excellent post-cracking ductility per formance [1,2]
To deal with the above problems, recently, we introduced coarse aggregates into ultra-high performance concrete (UHPC), while guaranteeing the high mechanical performance of UHPC [10]
Even though the improvement is not considerable, it can be concluded that increasing the steel fiber content shows a pos itive effect on the compressive strength of UHPC containing coarse aggregates (UHPC-CA), which is in line with the previous studies on UHPC without coarse aggregates [30]

Summary

Introduction

Ultra-high performance concrete (UHPC) is considered as a prom ising new cementitious material, which is characterized by its superior flexural strength and excellent post-cracking ductility per formance [1,2]. The excellent mechanical performance makes it potentially competitive for structures which may be subjected to extreme load conditions with different loading rates, e.g. earthquakes [3,4,5]. The ultra-high performance is generally achieved by eliminating coarse aggregates to decrease the size of microcracks, resulting in a dense and homogeneous microstructure [6,7]. To deal with the above problems, recently, we introduced coarse aggregates into UHPC, while guaranteeing the high mechanical performance of UHPC [10]. UHPC with coarse aggregates (UHPC-CA) can be made suitable for specialized structures exposed to extreme loading rates

Objectives

Results

Discussion

Conclusion