Faming Li

Uniaxial Tensile Behavior of Concrete Reinforced with Randomly Distributed Short Fibers

A study was made of the behavior of concrete reinforced with randomly distributed short fibers under uniaxial tension. Five kinds of fibers were used to prepare the fiber reinforced concrete specimens for the uniaxial tension test. These included two kinds of steel fibers, two kinds of polyvinyl alcohol fibers, and one kind of polypropylene fiber. Fiber volume fraction varied from 2% to 6% in most cases. The matrices were normal strength concrete and/or admixture modified concrete. Plain concrete specimens were also prepared as a reference for the purpose of comparison. The adaptive control test method was used in the experimental study to obtain complete stress-deformation responses for both plain concrete and fiber reinforced concrete. Both strain softening and strain hardening behavior was observed in the experiment, and it seemed that a transition point did exist for the composites. It was concluded that strain hardening and multiple cracking responses can be achieved for concrete incorporating short fibers when the parameters are carefully selected.

Continuum damage mechanics based modeling of fiber reinforced concrete in tension

Abstract The tensile properties of concrete can be enhanced substantially by incorporating high strength and small diameter short fibers, which leads to fiber reinforced concrete (FRC). For this reason, FRC has been widely used in infrastructures, where tensile cracks may occur. However, an analytical model for such a material is still lacking. In this article, an attempt was made to model the behavior of FRC, which shows a hardening response in tension, based on the continuum damage mechanics (CDM). In the material, conventional concrete (a cement–sand–coarse-aggregate–water mix) was used as the matrix, and short steel fibers were used as the reinforcement. The quasi-brittleness of the matrix and the fiber–matrix interfacial properties were taken into consideration. Results show that the model-predicted stress–strain curves agree well with those obtained experimentally.

Acoustic emission monitoring of fracture of fiber-reinforced concrete in tension

An attempt was made to experimentally investigate the fracture behavior of fiber-reinforced concrete (FRC) by acoustic emission (AE) characterization during direct uniaxial tensile loading. A previous investigation indicated that conventional concrete incorporating short fibers can produce FRC showing a strain-softening response or a strain-hardening response in tension. These two types of FRCs were further investigated using AE techniques, and the results are reported in this paper. A recently developed uniaxial direct tensile test technique was used to conduct tensile test on specimens without notches. AE monitoring was performed during the entire course of each tensile test. Analyses of AE activities and source locations of AE events were performed to study the damage initiation and propagation in the materials. Results show that nucleation of microcracks can be clearly observed for the FRC that shows a nonhardening response similar to concrete without reinforcement. For FRC showing a hardening response, this phenomenon cannot be observed, which indicates that the fibers were effective in blunting the microcrack nucleation.