Mechanical Properties Of Steel Fiber-reinforced Concrete Research Articles

Significance of fiber characteristics on the mechanical properties of steel fiber-reinforced high-strength concrete at different water-cement ratios

The incorporation of fiber reinforcement into concrete is not a new approach to improving its ductility. In the past, research has generally focused on specific parameters, such as fiber type, dosage, slenderness, and the inherent strength of concrete. This study addresses the significant gap highlighted by ACI 544.1R by providing a deeper understanding of steel fiber-reinforced concrete (SFRC). The significance of the study is highlighted by the fact that it fills a crucial gap in research, especially considering the inaccuracy of current models related to flexural strength. The study examines in detail the influence of fiber dosage and length on the mechanical properties of SFRC using hooked-end fibers that range in length from 40 to 60 mm and diameters between 0.62 and 0.75 mm, as well as particular water-cement ratios (0.25, 0.35, and 0.45). The study also thoroughly evaluates the precision of widely accepted equations for predicting SFRC's compressive and flexural strengths. Results show that 0.5 to 1.5 % fibers increase concrete's compressive strength, inherent tensile strength, and peak flexural load capacity by 7–27 %, 11–47 %, and 3–124 %, respectively. However, it should be noted that despite the benefits of extending fiber lengths and increasing fiber content, the opposite has little effect on the flexural strength of SFRC. An original equation, which surpasses the existing models, is presented in this study to calculate the modulus of rupture in SFRC. Compared to independent datasets, this model proves remarkably accurate, boasting a predicted-to-tested ratio of 1.01, emphasizing its potential to advance SFRC research.

Cracking Pattern and Bearing Capacity of Steel Fiber-Reinforced Concrete Single-Layer Tunnel Lining

In recent years, steel fiber-reinforced concrete (SFRC) single-layer linings have been used in tunnel engineering. Compared to plain concrete single-layer linings, SFRC single-layer linings demonstrate enhanced bearing capacity, durability, and sustainability. Existing studies primarily focused on the mechanical properties of SFRC; however, limited investigations have been conducted on the cracking pattern of SFRC linings. This study uses laboratory tests to examine the influence of steel fiber content and aspect ratio on the mechanical properties of concrete, such as compressive strength and elastic modulus. After the recommended content and aspect ratio of steel fiber are proposed through tests, the cracking pattern and safety performance of plain concrete and SFRC linings under surrounding rock pressure are studied using a similar model test. The test results indicate that the recommended steel fiber volume fraction and aspect ratio for CF35 SFRC are 0.58% and 70, respectively. Due to the effect of loose load, cracks initially develop on the inside of arch crowns in both plain concrete and SFRC single-layer linings. Subsequently, new cracks appear on the inside of the lining floor and the outside of the two wall feet. Numerous narrow cracks with rugged and winding expansion paths can be found on SFRC single-layer linings. Conversely, plain concrete single-layer linings exhibit fewer cracks with larger widths along a straighter path. The initial cracking load of a single-layer lining made of plain concrete is 0.027 MPa, whereas for a single-layer lining made of SFRC, it is 0.04 MPa. This indicates that SFRC can effectively enhance the initial cracking load of lining structures. In the event of damage to the lining, the most critical area for the plain concrete single-layer lining is at the two wall feet, where the minimum safety factor is 1.66. However, for the SFRC lining in the same location, the safety factor is 2.7, resulting in a 62.7% increase in safety.

Performance of steel fiber reinforced concrete mixed with chloride solution and exposed to high humidity environment

In order to investigate the performance of steel fiber reinforced concrete (SFRC) suffered from chloride attack, the SFRC specimens were prepared using 9 wt% NaCl solution to accelerate the corrosion, and they were also exposed to the high humidity environment (≥90 % RH); meanwhile, the carbonation was also considered. The performance evolution of SFRC suffered from 14 months of in-situ chloride attack was monitored, including compressive strength, flexural property, splitting-tensile property, and so on. The results show that the SFRC specimens showed no deterioration in the mechanical properties after 14 months of chloride attack, while only some corrosion spots were found on the concrete surface, independently of the water to binder ratios and mineral admixtures. The carbonation accelerated the chloride-induced corrosion of steel fibers in the carbonated zone of concrete, but did not result in the reduction in the mechanical properties of SFRC within 14 months of chloride attack.

Experimental Study on the Performance of Steel-Fiber-Reinforced Concrete for Remote-Pumping Construction.

Remote-pumped concrete for infrastructure construction is a key innovation of the mechanized and intelligent construction technology. This has brought steel-fiber-reinforced concrete (SFRC) into undergoing various developments, from conventional flowability to high pumpability with low-carbon features. In this regard, an experimental study on the mixing proportion design and the pumpability and mechanical properties of SFRC was conducted for remote pumping. Using the absolute volume method based on the steel-fiber-aggregate skeleton packing test, the water dosage and the sand ratio were adjusted with an experimental study on reference concrete with the premise of varying the volume fraction of steel fiber from 0.4% to 1.2%. The test results of the pumpability of fresh SFRC indicated that the pressure bleeding rate and the static segregation rate were not the controlling indices due to the fact that they were far below the limits of the specifications, and the slump flowability fitted for remote-pumping construction was verified by a lab pumping test. Although the rheological properties of the SFRC charactered by the yield stress and the plastic viscosity increased with the volume fraction of steel fiber, those of mortar used as a lubricating layer during the pumping was almost constant. The cubic compressive strength of the SFRC had a tendency to increase with the volume fraction of steel fiber. The reinforcement effect of steel fiber on the splitting tensile strength of the SFRC was similar to the specifications, while its effect on the flexural strength was higher than the specifications due to the special feature of steel fibers distributed along the longitudinal direction of the beam specimens. The SFRC had excellent impact resistance with an increased volume fraction of steel fiber and presented acceptable water impermeability.

Study on multi-scale damage and failure mechanism of steel fiber reinforced concrete: Experimental and numerical analysis

The damage and failure behavior of steel fiber reinforced concrete (SFRC) is extremely complex. The reinforcement mechanism of steel fiber to concrete and the meso-failure mechanism of SFRC have not been thoroughly researched. This paper studied the mechanical behavior of SFRC from two perspectives: macro lab experiment and meso-numerical simulation. Firstly, macro-tests were conducted to examine the effects of the volume content and the length-to-diameter ratio of copper coated microfilament steel fiber on the mechanical properties of SFRC. The result shows that when the volume content of steel fiber is 2% and the length-to-diameter ratio of steel fiber is 60, the cubic compressive strength, splitting tensile strength and flexural tensile strength of SFRC are improved the most, which are 33.1%, 121%, and 35% higher than that of plain concrete respectively. Secondly, three empirical formulas of the compressive strength, splitting strength, and flexural strength of SFRC considering the influence of steel fiber parameters were proposed and the characteristics and phenomena of concrete and SFRC in each stage of compression failure were studied. Thirdly, this work proposed a simple and efficient three-dimensional method for modeling SFRC. The simulation accurately predicted the failure mode and mechanical property response of SFRC. In addition, the effects of steel fiber volume content, length-to-diameter ratio, and friction coefficient of contact surface on the mechanical behavior of SFRC composites were discussed by the model.

Mechanical properties of SFRC: Database construction and model prediction

Dispersing steel fibers into plain concrete has been verified as an effective way to enhance the bearing capacity of structural components. To date, however, the effects of fibers on the basic mechanical properties of Steel Fiber Reinforced Concrete (SFRC) and their uncertainties are not well documented and there are no accurate models that can predict their mechanical properties. This greatly limits the application in real constructions. Considering such a situation, three aspects of works were conducted in this study to alleviate that difficulty, those are, building test database and checking the statistical distribution, reviewing and assessing existing models, and establishing highly-accurate models applied to estimate the compressive, tension and flexural properties of SFRC. To achieve the first two goals, a large database containing 1038 experimental records was compiled from existing publications and 145 predictive expressions were collected from the available literature. The last object was obtained by conducting Bayesian model updating analysis. It was finally found from the present study that: (a) Steel fibers can effectively enhance plain concrete’s compressive, tensile and flexural strengths, but induce greater variability in those indexes. That variability is well described with a lognormal probability distribution. (b) Expressions proposed by Abbass and by Padmarajaiah generally give the most accurate predictions for the compressive strength and elastic modulus, while the formulas of Chinese code JG/T472–2015 and Padmarajaiah give the most accurate tensile and flexural strengths. (c) Because of combining advantages of the experience of the prior model and the accuracy of the test records, Bayesian updating method based analytical model usually possesses an obviously high precision.

Mechanical properties of steel fiber reinforced concrete material in construction of road bridge deck

In order to improve the application effect of steel fiber reinforced concrete (SFRC) in road bridge construction, the mechanical properties of SFRC with different fiber content were analyzed. The SFRC specimens with 0%, 0.5%, 1%, 1.5% and 2% fiber content were designed, and the mechanical properties were tested. The results showed that the compressive strength first increased and then decreased with the increase of fiber content, and the maximum compressive strength of SFRC1.5 reached 40.86 MPa, increasing by 7.19%; the increase amplitude of tensile strength of SFRC1.5 was 73.04%, which was the most obvious; the flexural strength of SFRC increased with the increase of fiber content, and the flexural strength of SFRC2 was 9.78 MPa, increasing by 94.43%. It is concluded from the experimental results of a case study that SFRC1.5 presents the optimal overall mechanical properties and is more suitable for road bridge construction.

Effect of mix composition on the mechanical properties of SFRC

Mechanical properties at the material scale are required for the efficient design of structural concrete members constructed using steel fiber reinforced concrete (SFRC). Simple analytical models are desired which define and correlate the mechanical properties based on the macro-scale parameters for the mix including the density, compressive strength and fiber dosage. This paper describes a study conducted to understand the relationship between the compressive, flexural and direct shear responses for SFRC containing hooked-end steel fibers at 0 to 1% by volume. Three different concrete matrices were considered: a regular concrete, a lightweight aggregate concrete with similar compressive strength, and a high strength concrete that was 2.4 times as strong. Fibers were found to be effective in enhancing the direct shear strength of regular concrete where the cracks progressed around the aggregates. Less improvement in direct shear strength for high-strength and lightweight matrices was observed as cleavage through the aggregates was more prevalent. Further exploration of the flexural test data allowed development of a novel relationship between the residual tensile stresses across cracks relative to the crack opening through a normalization process with key mix composition parameters. The novel relationship is presented in a format that is suitable for use in member-scale structural design.

Experimental study on compressive properties of SFRC under high strain rate with different fiber content and aspect ratio

The dynamic mechanical properties of steel fiber reinforced concrete (SFRC) depend largely on the content and size of steel fibers. This paper presents an experimental study on mechanical properties of SFRC under high strain-rate compressive loading. In order to explore the co-effect of the fiber content and aspect ratio on the dynamic performance of SFRC, the SFRC specimens with three kinds of fiber aspect ratio (30, 50, 60, respectively) and six kinds of fiber content (0%, 0.5%, 1.0%, 1.5%, 2.0% and 2.5% in volume fraction) were tested by Split Hopkinson Pressure Bar (SHPB) device with a diameter of 75 mm. The test strain rate ranged from 30 s−1 to 370 s−1. Test results show that SFRC has obvious strain rate effect. With the same fiber aspect ratio, the optimum fiber content of SFRC shows strain rate sensitivity. And with the increase of fiber content, the dynamic increase factor (DIF) of SFRC decrease gradually. With the same fiber content, SFRC with a fiber aspect ratio of 50 shows the maximum compressive strength at different strain rates. In addition, the study also proposed the expression of DIF, strain rate and fiber content of SFRC to each fiber aspect ratio.

Mechanical properties of SFRC using blended Recycled Tyre Steel Cords (RTSC) and Recycled Tyre Steel Fibres (RTSF)

Processed high-specification steel cords (RTSC) extracted from un-vulcanised rubber belt off-cuts have the potential to substitute (manufactured steel fibres) MSF in concrete, leading to enhanced structural performance and significant environmental benefits. The target of this research is to demonstrate that recycled-only fibre mixes could meet or exceed the performance of MSF-only mixes, at the same total fibre dosage. Direct tensile and single-fibre pull-out tests are carried out, to evaluate the tensile strength of RTSC and the interfacial bond behaviour between RTSC and concrete matrix, respectively. It is found that RTSC have a tensile strength greater than 2600 MPa and their critical embedded length is in the range of 25–40 mm. The flexural characteristics of 8 steel fibre reinforced concrete (SFRC) mixes at fibre dosages of 30 and 45 kg/m3 are examined by using EN 14651:2005 3-point notched prism tests. RTSC with lengths of 60 mm are used on their own, or blended with post-processed steel fibres recovered from end-of-life tyres (RTSF) at varying dosages. The performance of two manufactured steel fibres (MSF)-only mixes and one RTSF-only mix is also examined. Comparisons in terms of flexural performance are made between MSF-only mixes versus recycled-fibre (RTSC on their own or blended with RTSF) mixes at the same total dosage. RTSC are found to be extremely well mobilised at larger crack widths and the post-cracking strength of recycled-fibre mixes is significantly higher (up to 103%) than MSF-only mixes at the same total fibre dosage. In addition, the flexural performance of concrete with recycled-fibre blends improves with increasing amounts of RTSC.

Experimental and analytical study of the fibre distribution in SFRC: A comparison between image processing and the inductive test

The effect of the steel fibre distribution on concrete is significant, studies regarding the distribution characteristics of steel fibre are of great significance for the application of steel fibre-reinforced concrete (SFRC). Based on different mechanical test results, this paper aims to propose a reliable analysis method for more efficient evaluation of steel fibre distribution by using image processing and the inductive test to do comparison analysis on the steel fibre distribution in different concrete specimens. Firstly, the results of image processing and inductive test of different type of SFRC cubic specimens was analysed to obtain the steel fibre distribution, and a formula for rapid calculation of fibre content was proposed. Then, the influence of steel fibre distribution on the mechanical properties of SFRC was analysed by combining double punch test and three-point bending test results. Finally, the high similarity of the spatial distribution of steel fibre is analysed by the inductive test and image processing, which are reflected by the phase coefficient, and the applicability of these two methods are compared and evaluated.

Mechanical properties of SFRC using blended manufactured and recycled tyre steel fibres

This paper investigates the mechanical properties of 10 steel fibre reinforced concrete (SFRC) mixes at fibre dosages of 30, 35 and 45 kg/m3. Manufactured Steel Fibres (MSF) are used on their own, or blended with sorted steel fibres recycled from end-of-life tyres (RTSF). To characterise the flexural behaviour of the mixes, two flexural test methods, BS EN 14651:2005 3-point notched prism tests and ASTM C1550-05 centrally loaded round panel tests are employed. A strong correlation is found in the flexural behaviour of the SFRC prism and round panel specimens, with corresponding conversion equations proposed. The mechanical properties of hybrid mixes using RTSF vary depending on dosages, but are comparable with those of MSF-only mixes at the same fibre dosage. A positive synergetic effect is derived from hybrid mixes containing 10 kg/m3 of RTSF.

구형 비상체에 의한 충격하중을 받는 강섬유보강 콘크리트 패널의 손상특성

This paper investigates the effects of fiber volume fraction and panel thickness on face damage characteristics of steel fiber-reinforced concrete (SFRC) under high-velocity globular projectile impact. The target specimens were prepared with 200 × 200 mm prismatic panels with thickness of 30 or 50 mm. All panels were subjected to the impact of a steel projectile with a diameter of 20 mm and velocity of 350 m/s. Specifically, this paper explores the correlation between mechanical properties and face damage characteristics of SFRC panels with different fiber volume fraction and panel thickness. The mechanical properties of SFRC considered in this study included compressive strength, modulus of rupture, and toughness. Test results indicated that the addition of steel fiber significantly improve the impact resistance of conventional concrete panel. The front face damage of SFRC panels decreased with increasing the compressive toughness and rear face damage decreased as the modulus of rupture and flexural toughness increased. To evaluate the damage response of SFRC panels under high-velocity impact, finite element analysis conducted using ABAQUS/Explicit commercial program. The predicted face damage of SFRC panels based on simulation shows well agreement with the experimental result in similar failure mode.

Stress–Strain Characteristics and Elastic–Plastic Damage Constitutive Equation of Steel Fiber Reinforced Concrete Under Cyclic Compression at Medium Strain Rate

Abstract An experimental investigation was performed on dynamic compressive stress–strain relationships for steel fiber reinforced concrete (SFRC) with various steel fiber volumetric contents under cyclic compression at a medium strain rate. Results indicate that the mechanical properties of SFRC are not only affected by strain rates but are also influenced by loading modes. The envelope curves of unconfined SFRC are different from those of specimens under monotonic compression. Dynamic compressive strength presents a non-monotonic enhancement with increasing steel fiber content. On the basis of the experimental results of cyclic compression at a medium strain rate, the elastic–plastic damage constitutive equations are proposed to describe the dynamic compressive stress–strain relationships of SFRC under cyclic compression at a medium strain rate. These equations match the test results well.

Effects of fibre volume fraction on the compressive and flexural experimental behaviour of SFRC

The purpose of this study is to analyse the effects of fibre volume fraction on the mechanical properties of SFRC (Steel Fibre Reinforced Concrete). The results obtained from compression and four-point bending tests carried out on concrete specimens with fibre volume fraction of 1%, 1.6%, 3% and 5% are critically examined. The experimental behaviour in terms of peak load, post-peak behaviour, and residual strength, are evaluated and compared. The fibre distribution and their contribution in Mode I fracture is also assessed. The effects of steel fibre volume fraction on the strength, ultimate strain and ductility index of SFRC are highlighted in order to give a guide for structural use.

Observations on the electrical resistivity of steel fibre reinforced concrete

Steel fibre reinforced concrete (SFRC) is in many ways a well-known construction material, and its use has gradually increased over the last decades. The mechanical properties of SFRC are well described based on the theories of fracture mechanics. However, knowledge on other material properties, including the electrical resistivity, is sparse. Among others, the electrical resistivity of concrete has an effect on the corrosion process of possible embedded bar reinforcement and transfer of stray current. The present paper provides experimental results concerning the influence of the fibre volume fraction and the moisture content of the SFRC on its electrical resistivity. The electrical resistivity was measured by alternating current (AC) at 126 Hz. Moreover, an analytical model for the prediction of the electrical resistivity of SFRC is presented. The analytical model is capable of predicting the observed correlation between the fibre volume fraction and the electrical resistivity of the composite (the SFRC) for conductive fibres and moisture saturated concrete. This indicates that the steel fibres were conducting when measuring the electrical resistivity by AC at 126 Hz. For partly saturated concrete the model underestimated the influence of the addition of fibres. The results indicate that the addition of steel fibres reduce the electrical resistivity of concrete if the fibres are conductive. This represents a hypothetical case where all fibres are depassivated (corroding) which was created to obtain a conservative estimate on the influence of fibres on the electrical resistivity of concrete. It was observed that within typical ranges of variation the influence of the moisture content on the electrical resistivity was larger than the effect of addition of conductive steel fibres, but also that the relative impact on the electrical resistivity due to conductive steel fibres increased when the moisture content of the concrete was reduced.

Experimental Study on Effects of Steel Fiber Volume on Mechanical Properties of SFRC

In recent years, considerable interest has developed in using fibers to increase the load-carrying capacity of concrete members. Fibers significantly reduce the brittleness of concrete and improve its engineering properties, such as tensile, flexural, impact resistance, fatigue, load bearing capacity after cracking and toughness. However, studies on the exact amount of influence are very limited. Among fibers, steel fibers are one of the most popular and widely used types of fibers in both research and practice. Steel fiber-reinforced concrete (SFRC) has been used increasingly in recent years and has a lot of applications. Previous researchers have mentioned that using fiber as 0.5 – 2.5 % of the volume of concrete can significantly improve the concrete properties. The purpose of this paper is firstly to investigate the effects of fiber volume on the compressive, splitting, and flexural behaviors of SFRC, and secondly to compare modes of failure. Variable items are the steel fiber volume fraction and the curing day. A series of 108 specimens (cube, cylinder and prism) with four different steel fiber volumes are used by a ratio of 0, 0.7, 1.0 and 1.5%. All specimens are cured in a water tank for 7, 14 and 28 days, respectively to provide same conditions. Hooked-ended steel fibers with a length of 30mm and a diameter of 0.75 mm are used.

Correlations among mechanical properties of steel fiber reinforced concrete

In this paper, applicability of previously published empirical relations among compressive strength, splitting tensile strength and flexural strength of normal concrete, polypropylene fiber reinforced concrete (PFRC) and glass fiber reinforced concrete (GFRC) to steel fiber reinforced concrete (SFRC) was evaluated; moreover, correlations among these mechanical properties of SFRC were analyzed. For the investigation, a large number of experimental data were collected from published literature, where water/binder ratio (w/b), steel fiber aspect ratio and volume fraction were reported in the general range of 0.25–0.5, 55–80 and 0.5–2.0%, respectively, and specimens were cylinders with size of Φ 150 × 300 mm and prisms with size of 150 × 150 × 500 mm. Results of evaluation on these published empirical relations indicate the inapplicability to SFRC, also confirm the necessity of determination on correlations among mechanical properties of SFRC. Through the regression analysis on the experimental data collected, power relations with coefficients of determination of 0.94 and 0.90 are obtained for SFRC between compressive strength and splitting tensile strength, and between splitting tensile strength and flexural strength, respectively.

Effect of aspect ratio and volume fraction of steel fiber on the mechanical properties of SFRC

In this study, effects of aspect ratio ( l/ d) and volume fraction ( V f) of steel fiber on the compressive strength, split tensile strength, flexural strength and ultrasonic pulse velocity of steel fiber reinforced concrete (SFRC) were investigated. For this purpose, hooked-end bundled steel fibers with three different l/ d ratios of 45, 65 and 80 were used. Three different fiber volumes were added to concrete mixes at 0.5%, 1.0% and 1.5% by volume of concrete. Ten different concrete mixes were prepared. After 28 days of curing, compressive, split and flexural strength as well as ultrasonic pulse velocity were determined. It was found that, inclusion of steel fibers significantly affect the split tensile and flexural strength of concrete accordance with l/ d ratio and V f. Besides, mathematical expressions were developed to estimate the compressive, flexural and split tensile strength of SFRCs regarding l/ d ratio and V f of steel fibers.