Fiber-reinforced Concrete Specimens Research Articles

A comparative study of flexural and shear behavior of ultra-high-performance fiber-reinforced concrete beams

In this research, the flexural and shear behavior of five locally developed ultra-high-performance fiber-reinforced concrete beams was experimentally investigated. Four-point loading tests were carried out on concrete specimens which were further compared with five normal-strength concrete beams constructed at the laboratory. The objective of this study is to assess the flexural and shear behavior of ultra-high-performance fiber-reinforced concrete beams and compare them with that of normal-strength beams and available equations in the literature. Results indicate underestimation of shear (up to 2.71 times) and moment capacities (minimum 1.27 times, maximum 3.55 times) by most of the equations in beams with low-reinforcement ratios. Finally, results reveal that the experimental flexural and shear capacities of ultra-high-performance fiber-reinforced concrete specimens are up to 3.5 times greater than their normal-strength counterpart specimens.

The effect of age and testing method on the added fracture energy of fibre reinforced concrete

The use of Fibre Reinforced Concrete (FRC) is widely accepted in the tunnelling industry. The generally accepted method to determine the material parameters of FRC is the standard 3-point beam test. The effect of age can be relevant for tunnels, because these structures are usually designed for life cycles over 100 years. In this paper the test results of FRC specimens with different fibres using different testing methods (beam and square panel) at different ages will be presented. FRC changes its properties over time in case of both fibre types. The post crack capacity of steel FRC increases in beam tests, while it decreases in panel tests, which yields the conclusion that steel fibres work better at smaller crack width. This changes only a small amount over time. The energy absorption measured from panel tests reduces in case of steel fibre, but stays at a constant level for synthetic fibre.

Residual mechanical properties of polypropylene fiber-reinforced concrete after heating

This paper presents results from experimental studies on residual mechanical properties of fiber-reinforced concrete specimens exposed to elevated temperatures. Seven series of concrete mixes, including six series of polypropylene fiber-reinforced concrete and one series of plain concrete specimens, were tested after exposure to various heating temperatures and cooled down. The residual mechanical properties including compressive and tensile strengths, modulus of elasticity and cracking modes, as well as ultrasonic pulse velocity of fiber-reinforced and plain concretes are evaluated after heating-cooling cycle. The effect of temperature level, length and amount of polypropylene fibers content on residual mechanical properties is studied. Results from the experiments show that polypropylene fiber-reinforced concrete exhibit better performance compared to plain concrete. Different strategies, through varying amount of polypropylene fiber content (1–2 kg/m3) and fiber length, proposed to enhance residual compressive and tensile strengths and also minimize the splitting and cracking in concrete after exposure to fire.

A study of test and statistical damage constitutive model of multi-size polypropylene fiber concrete under impact load

To investigate the effects of mixing polypropylene fiber of different sizes and the effect of fiber size on the impact characteristics of concrete, two sizes of polypropylene fine fiber and one size of polypropylene coarse fiber were selected to design and fabricate nine groups of polypropylene fiber-reinforced concrete test specimens by controlling the fiber mixing ratio and conducting a split Hopkinson pressure bar test to obtain the stress–strain curves of the test specimens in various groups, and their parameters such as the elasticity modulus, peak strength, and peak strain. The incorporation of fiber improved the pre-peak impact properties of concrete to different extents. Strain hardening did not occur in the post-peak curves, and different types of fibers exhibited different characteristics. Thus, the fine fiber could significantly improve the peak strain, while the coarse fiber could more significantly improve the elasticity modulus and peak strength. The improving effects exerted by incorporating three types of fiber were better than those exerted by incorporating two types of fiber. Moreover, the statistical damage model was used to obtain the parameters by fitting and analyzing their variation rules based on the statistical damage constitutive model and the particle swarm optimization algorithm.

Steel fiber-reinforced concrete under impact loading dynamic constitutive equation

This study presents the experimentation of dynamic impact tests on steel fiber-reinforced concrete (SFRC) specimens to analyze dynamic constitutive equation. The dynamic compression experimentation of SFRC with a fiber volume ratio of 0%, 0.75%, and 1.5% was conducted using a Φ75 mm-diameter split Hopkinson pressure bar experimental system. Thus, different steel fiber contents and stress–strain curves under different strain rates are obtained. Results showed that the peak strain value and peak stress of SFRC increase with fiber content and strain rate concurrently. On the basis of the definition of Holmquist–Johnson–Cook constitutive strain rate effect and the stress–strain curves of different strain rates, a dynamic damage constitutive model of SFRC composite under compression is proposed. The proposed concrete material dynamic constitutive model depends directly on the strain, strain rate, material strength factor, and steel fiber content factor. Through simulation and experimental curves, the corresponding material parameters are obtained and show that using this constitutive model allows the fitting results to correspond accurately with the experimental data.

Direct tension behaviour of steel fibre reinforced concrete measured by a new test method

A new direct tension test method of applying tension to a dumbbell-shaped specimen through side-glued steel plates at the end blocks for measuring the tensile stress-strain characteristics of fibre reinforced concrete (FRC) was developed. Finite element analysis of the test setup revealed substantially reduced stress concentration in the specimen. The new method was applied to test FRC specimens made with four different types of hooked steel fibres. It was found that both the first cracking strength and post cracking strength increased with the fibre volume but at different rates for the different types of steel fibres. From the stress-strain curve, two different values of tensile strain capacity, one defined as the tensile strain at maximum tensile stress and the other defined as the tensile strain at which the tensile stress dropped to 80% of cracking stress, were obtained. Regression analysis of the test results yielded good correlations to the fibre factor and empirical formulas for estimating the minimum fibre factor for strain hardening and the tensile strain capacities.

Performance Evaluation of Metallic and Synthetic Fiber Hybridization on the Cyclic Behavior of Exterior Beam-Column Joint

Abstract The influence of different fiber profiles and fiber hybridization on the cyclic behavior of an exterior beam-column joint is experimentally studied and compared with conventional specimens. In the beam-column joint, the joint region concrete is substituted with fiber-reinforced concrete (FRC)/hybrid fiber-reinforced concrete (HyFRC) and tested under reverse cyclic loading to examine the inelastic response. The physical properties of composites employed are examined using cylindrical specimens under uniaxial compression. The stress–strain behavior shows tremendous difference in peak and post-peak strength and strain with respect to the volume and type of fibers in the composites. The test results of joint specimens validate that the hybridization of polypropylene fiber with metallic fiber offers better shear resistance and also improves the damage tolerance capacity like high-volume FRC specimens without critical joint detailing. The damping and energy dissipation response of FRC/HyFRC specimens clearly show that the need for seismic detailing can be eliminated using FRC/HyFRC.

Fiber geometrical parameters of fiber-reinforced high strength concrete and their influence on the residual post-peak flexural tensile strength

The mechanical behavior under flexural tensile stress of fiber-reinforced concretes is strongly conditioned by fiber density and orientation; in particular, the residual strength values under tensile stress forces. However, although a lot of research has been conducted to understand how the casting and type of compaction affects the fiber distribution and orientation, up to date neither fiber location nor fiber orientation can be controlled during the concreting process. The uncertainty of fiber distribution within the material implies scatter results, in such a way that apparently identical fiber-reinforced concrete specimens can show very different results, in terms of mechanical behavior. The use of CT-Scan technology means that the exact location and orientation of the fibers within a concrete specimen may be depicted. In addition, as a non-destructive test, it can be done prior to mechanical testing.This paper studies the relation between fiber density and orientation and behavior under flexural tensile stress, through the use of CT-Scan technology. To do so, a high-strength steel-fiber reinforced concrete wall was constructed and 8 100 × 100 × 350 mm prismatic specimens were extracted from different sections of the wall, with the intention of revealing different fiber density and orientation values. First, the specimens were scanned using a CT-Scan, to obtain the real fiber density and orientation values. Subsequently, they were tested in a three-point-bending test, to obtain the curves tension –CMOD, and LOP values and residual strength under tension. Finally, empirical relations are shown between those values and fiber density and orientation.

Behaviour of UHPFRCs in compression under high stress-rates

The paper presents the results obtained on cylindrical Ultra High Performance Fibre Reinforced Concrete specimens with diameter of 30mm and a height of 60mm under compression at high stress rate (1.7–2.3 TPa/s). Four different percentages of fibre reinforcement are considered (1, 2, 3, and 4% fibre content) and compared with the results of the matrix (UHPC). A slight reduction of the strength and fracture time with the introduction of fibres is observed. The experimental results are analysed and discussed with the intent to better understand the mechanical behaviour of UHPFRC materials in case of dynamic event under service loading conditions.

Mode I fracture toughness of fibre reinforced concrete

Low fracture toughness of concrete represents a serious shortcoming. An effective way to improve the concrete toughness is represented by the dispersion (during mixing) of discontinuous fibres into the concrete mix. The principal beneficial effect of fibres is the crack bridging in the cementitious matrix, providing resistance to crack propagation before fibre debonding and/or pulling out or failure. In the present paper, the fracture behaviour of FRC (fibre reinforced concrete) specimens is examined, with micro-synthetic polypropylene fibrillated fibres being randomly distributed in concrete. The modified two-parameter model, proposed by the authors to calculate Mode I plain-strain fracture toughness for quasi-brittle material, is able to take into account the possible crack deflection (kinked crack) during stable crack propagation.

Estimation of Population Standard Deviation for Post-Crack Performance of Fiber-Reinforced Concrete

Abstract The post-crack performance of fiber-reinforced concrete (FRC) is widely reported to exhibit a high degree of variability. Several reasons exist to explain this problem, most notably the small area of crack surface involved in most beam tests. Of less widely recognized significance to variability is the relationship between the sample standard deviation and the population standard deviation for this material. Standard statistical theory can be used to estimate the relationship between the variance in a sample of observations and the variance in the population from which the observations are drawn, but this critically depends on the observations being drawn from a population displaying a normal distribution. Moreover, the observations must also exhibit covariant stationary characteristics. In this investigation, it is shown that neither of these assumptions are necessarily true for FRC specimens produced using standard mixing procedures. Instead, the distribution of post-crack performance parameters obtained from standard beam and panel-based tests exhibit inconsistent characteristics that possibly require an empirical approach to effective estimation of the population standard deviation.

Rate Effects of Fiber-reinforced Concrete Specimens in Impact Regime

A study of the rate sensitivity of prismatic specimens of steel fiber-reinforced concrete (FRC) is carried out in this contribution. Experimental results are analyzed from impact tests carried out with an instrumented drop weight testing machine. FRC mixes with two types of fibers have been studied, namely short straight fibers and long hook-ended fibers. The experiments have included two amounts of fibers (volumetric fractions of 0.5% and 1.0%), and also companion unreinforced plain concrete specimens are studied. The analysis has focused on the bending properties of the studied mixes, i.e. bending strength and absorbed energy. The study shows that each particular mix of FRC has different rate sensitivity because the dynamic behavior is a consequence of the rate dependence of the mechanisms governing the interaction between fibers and matrix. For the impact strain-rate domain achieved in the tests (1-10 s-1), it is shown that the study has to be done in terms of the energy absorption capacity of FRC. According to the results, the rate sensitivity decreases as the amount of fibers increases and, furthermore, the rate sensitivity of FRC mixes with hook-ended fibers is smaller than that of FRC mixes with straight fibers.

A proper infill sampling strategy for improving the speed performance of a Surrogate-Assisted Evolutionary Algorithm

In the present paper, an improved Surrogate-Assisted Evolutionary Algorithm is proposed. It combines the Differential Evolution algorithm with a quadratic surrogate approximation and a proper infill sampling strategy to choose appropriate sample points. The selection of the new candidate points is arranged to enhance both the local accuracy and the global optimum search. A comparison between performances of different evolutionary algorithms is carried out by searching the global minimum of two benchmark functions, by solving a dynamic identification problem of a three floor frame and by calibrating the non-linear stress-crack opening relation for Fibre-Reinforced Concrete specimens starting from experimental data.

Reliability assessment of confinement models of carbon fiber reinforced polymer-confined concrete

This paper presented a review of 84 confinement strength models developed for predicting the ultimate compressive strength of carbon fiber-reinforced polymer-confined concrete subjected to uniaxial compression. Among these models, 64 design-oriented models and 12 analysis-oriented models were selected and evaluated by a comprehensive database including the experimental results of 1475 carbon fiber-reinforced polymer-confined concrete specimens through three statistical indicators: the mean ( μ), the coefficient of determination [Formula: see text], and the root mean square error ( σ) of the predicted ultimate compressive strength [Formula: see text] and the experimental ultimate strength [Formula: see text]. Based on the results of evaluation, 27 design-oriented models were further considered for reliability assessment and structural reliability analysis. Given the performance of strength predictions and the reliability assessment, it was found that for the design purpose, the 27 design-oriented models are reliable for practical predictions of carbon fiber-reinforced polymer-confined concrete structures subjected to uniaxial compression.

Components of Fracture Response of Steel Fibre Reinforced Concrete Specimens

Records of fracture tests on steel fibre reinforced concrete notched specimens in a three-point bending configuration are evaluated in detail and selected results are discussed in the paper. The values of fracture parameters are determined using work of fracture method and double-K fracture model. Primarily, the role of plain concrete as a matrix in steel fibre reinforced concrete specimens is studied with regard to the recorded fracture response.

High-Strength Fiber-Reinforced Concrete Beam-Columns with High-Strength Steel

A series of reinforced concrete (RC) components with high-strength materials were tested under pure flexural monotonic and cyclic quasi-static loading protocols. The specimen materials included high-strength concrete (HSC), ultra-high-strength steel (UHSS), and steel fibers to create high-strength fiber-reinforced concrete (HSFRC) specimens. The replacement of conventional steel with UHSS increased the specimen’s ultimate flexural capacity more than 60%, but reduced its ductility. The addition of steel fibers to HSC specimens increased the peak strength by an additional 10%, and greatly reduced cracking and spalling of HSC specimens. However, the energy dissipation capacity of the specimens did not increase due to the presence of fibers.

Investigation of Punching Behaviour of Steel and Polypropylene Fibre Reinforced Concrete Slabs under Normal Load

Punching is among the most important risks leading to abrupt and brittle fracture in reinforced concrete structures. Punching effect at the end-parts of columns takes place during the transmission of loads from the slab to the columns and this effect is as important as the resistance of slab against bending. In this paper, punching performances of plain, steel fibre and polypropylene fibre incorporating reinforced concrete slabs were compared experimentally. Research program involved testing of three specimens. One specimen was cast as reference specimen and normal load were applied. One steel fibre and one polypropylene fibre-reinforced concrete specimens were produced as flat slab and normal load were applied. For comparison with other studies, the dimensions of test specimens were 1000 x 1000mm and slab thickness was selected as 100mm. Reinforcing bars were placed in only bottom parts of the slabs in all specimens. Ø10 S-335 steel reinforcement were used in the study. It was decided to locate the column in the middle part of the slab for providing formation of punching. The column shape was selected to be circular with a diameter of 150mm.In the first phase of the experimental study, results of load-displacement curves were interpreted. In the second phase, the punching performances of specimens under normal loads were compared and some suggestions were made.

Containment performance evaluation of prestressed concrete containment vessels with fiber reinforcement

Abstract Background Fibers in concrete resist the growth of cracks and enhance the postcracking behavior of structures. The addition of fibers into a conventional reinforced concrete can improve the structural and functional performance of safety-related concrete structures in nuclear power plants. Methods The influence of fibers on the ultimate internal pressure capacity of a prestressed concrete containment vessel (PCCV) was investigated through a comparison of the ultimate pressure capacities between conventional and fiber-reinforced PCCVs. Steel and polyamide fibers were used. The tension behaviors of conventional concrete and fiber-reinforced concrete specimens were investigated through uniaxial tension tests and their tension-stiffening models were obtained. Results For a PCCV reinforced with 1% volume hooked-end steel fiber, the ultimate pressure capacity increased by approximately 12% in comparison with that for a conventional PCCV. For a PCCV reinforced with 1.5% volume polyamide fiber, an increase of approximately 3% was estimated for the ultimate pressure capacity. Conclusion The ultimate pressure capacity can be greatly improved by introducing steel and polyamide fibers in a conventional reinforced concrete. Steel fibers are more effective at enhancing the containment performance of a PCCV than polyamide fibers. The fiber reinforcement was shown to be more effective at a high pressure loading and a low prestress level.

Dynamic Properties of Concrete at Moderately Elevated Temperatures

Reinforced concrete is widely used to not only provide structural support but also to mitigate the effects of radiation, malevolent attacks, and dynamic accidents. Dynamic tests were performed on 102 x 203 mm (4 x 8 in.) normal weight concrete (NWC) and fiber-reinforced concrete (FRC) cylinders using a drop hammer. Dynamic splitting tension and dynamic compression tests were performed at room temperature and at 204°C (400°F). The dynamic increase factor (DIF), which is the ratio of dynamic to quasi-static strength, and the strain rate were compared to existing models. The DIF for tension and compression increased with strain rate. For compression, a DIF up to 3.2 was recorded for strain rates up to 12 s⁻¹. For tension, a DIF up to 4.1 was recorded for strain rates up to 1.8 s⁻¹. Heated NWC and FRC specimens had lower DIFs compared to room-temperature specimens for dynamic compression and tension. The experimental DIFs followed closely the Modified Comite Euro-International du Beton (CEB) model for tension.

Compressive Behavior of Fiber-Reinforced Concrete with End-Hooked Steel Fibers.

In this paper, the compressive behavior of fiber-reinforced concrete with end-hooked steel fibers has been investigated through a uniaxial compression test in which the variables were concrete compressive strength, fiber volumetric ratio, and fiber aspect ratio (length to diameter). In order to minimize the effect of specimen size on fiber distribution, 48 cylinder specimens 150 mm in diameter and 300 mm in height were prepared and then subjected to uniaxial compression. From the test results, it was shown that steel fiber-reinforced concrete (SFRC) specimens exhibited ductile behavior after reaching their compressive strength. It was also shown that the strain at the compressive strength generally increased along with an increase in the fiber volumetric ratio and fiber aspect ratio, while the elastic modulus decreased. With consideration for the effect of steel fibers, a model for the stress–strain relationship of SFRC under compression is proposed here. Simple formulae to predict the strain at the compressive strength and the elastic modulus of SFRC were developed as well. The proposed model and formulae will be useful for realistic predictions of the structural behavior of SFRC members or structures.