Effects of Steel Fiber and Specimen Geometric Dimensions on the Mechanical Properties of Ultra-High-Performance Concrete

Abstract

Ultra-high-performance concrete (UHPC) is an advanced concrete with superior mechanical strength, ductility and durability properties. However, the influence of steel fiber on its constitutive laws and the specimen geometric dimension effect on its strength had not been paid enough attention. To investigate the effect of steel fibers on the properties of UHPC, specimens with different fiber volume contents and fiber types were tested. Meanwhile, the mechanical properties of UHPC at different ages from 3 days to 28 days were conducted. Moreover, specimens with various geometric dimensions were also prepared to study the effect of specimen geometric dimensions (dog-bone-shaped, prism and cylinder specimens) on the properties of UHPC. The results indicated that elastic modulus, tensile peak stress and the corresponding strain increased as the fiber volume content and curing age increased. Specimens with hooked-end fibers exhibited better tensile performance than those with straight fibers. Furthermore, different geometric dimensions of specimens significantly influenced the tensile properties of UHPC. Based on the experimental results, conversion factors were suggested for the transformation of strength obtained from specimens with different geometric dimensions to reference specimens. In addition, both compressive and tensile constitutive laws were proposed to generate the stress–strain relationship of UHPC.

Effect of Steel Fibers on Tensile Properties of Ultra-High-Performance Concrete: A Review

“…Figure 6 a summarizes the influence of the steel fiber content on the improvement index of the direct tensile strength. All the studies agree that the direct tensile strength increases with an increase in the steel fiber content (up to 5 vol.% [ 88 , 93 ]), even reaching 3.2 times that of a UHPC without fiber reinforcement [ 79 ]. The size of the dog-bone specimen affects the improvement of the direct tensile strength by the fiber content [ 45 , 75 , 80 , 93 ].…”

“…Some studies have found that hooked-end fibers with a fiber length of 13~30 mm do not significantly improve the direct tensile strength [ 64 , 79 ]. Park et al [ 52 ] also obtained similar findings when studying the effect of ultra-long hooked-end fibers on the direct tensile strength of UHPC.…”

“…Most prediction formulas mainly study a fiber volume fraction of 1.5~3 vol.%, and the fiber shape is straight and hooked steel fiber (as shown in Table 4 ). Some studies have used the linear tensile model to represent the direct tensile constitutive equation [ 57 ], some have used nonlinear models [ 84 ], and some have combined linear and nonlinear models to propose three-stage and four-stage constitutive models [ 79 , 103 , 104 , 105 ]. These models have a high fit to the pre-strain-hardening part, but a relatively poor fit to the post-strain-hardening part, which depends on the crack growth process of the UHPC.…”

Development of Concrete Mixture for Spun-Cast Full-Scale Precast Concrete Pipes Incorporating Bundled Steel and Polypropylene Fibers

“…Xue et al [ 28 ] suggested that the seawater–sea-sand concrete can be utilized to conserve river sand and fresh water by using polyoxymethylene fibers for improved resistance to early age cracking and enhanced mechanical properties. Fang et al [ 29 ] studied the effects of steel fibers having various geometries and shapes on the mechanical performance of ultra-high-performance concrete (UHPC). It was found that hook-ended steel fibers resulted in better improvement in the tensile performance compared with straight steel fibers.…”

Early Age Shrinkage and Mechanical Effect of Ultra-High-Performance Concrete Composite Deck: A Case Study with In Situ Test and Numerical Simulation

“…UHPC has nearly three times the strength of normal concrete and high constructability, and it has been applied in the structural joint, bridge deck, or even the entire pedestrian bridge [ 10 , 11 , 12 , 13 ]. However, since they are mixed from different material components, the physicochemical properties of UHPC are quite different from normal construction materials, and the common construction characteristics remain to be investigated, especially the early age shrinkage behavior [ 14 , 15 , 16 , 17 ]. Due to the high content of binder and low water-to-cement ratio, the autogenous shrinkage of UHPC is much higher than normal concrete, and with the potential shrinkage crack, the material strength can be reduced over time [ 18 ].…”