Deformed Steel Fibers Research Articles

Recent development of innovative steel fibers for ultra-high-performance concrete (UHPC): A critical review

This paper presents a comprehensive review of recent advancements in innovative high-strength steel fibers for ultra-high-performance concrete (UHPC). Firstly, commercially available ordinary steel fibers for UHPC products are introduced, and the analysis of fiber aspect ratio on the mechanical properties of UHPC follows. Subsequently, the historical development of deformed steel fibers, including hooked, corrugated, twisted, half-hooked, and curvilinear steel fibers for UHPC, is reviewed, accompanied by a discussion of their impact on various properties of UHPC. In response to limitations associated with specific deformed steel fibers in UHPC due to stress concentration, recent development of surface-refined straight steel fibers is presented. The paper further highlights the development of surface-roughened steel fibers through physical and chemical methods aimed at increasing surface roughness and interfacial friction in UHPC, along with an explanation of the benefits of these surface-roughened steel fibers in enhancing both fiber-matrix interfacial bond and tensile performance. Additionally, the adoption of active and inert nanomaterial-based surface coatings on steel fibers for UHPC is explored to intensively reinforce the interfacial transition zone between the fiber and matrix. Hybrid surface refining methods and various chemical treatment techniques for modifying the surface properties of steel fibers in UHPC are reviewed and discussed. Finally, based on the available current database, optimal fiber types as reinforcements for UHPC, in terms of tensile and flexural performances, are suggested.

Combined corrosion and inclination effects on pullout behavior of various steel fibers under wet-dry cycle deterioration

The interfacial bond behavior of corroded fibers in cracked steel fiber reinforced concrete (SFRC) is critical for understanding its structural deterioration performance, while available research focused on aligned straight or hooked-end fibers. This study investigated the combined effects of corrosion and inclination on the pullout performance of various steel fibers bridging artificial cracks exposed to wet-dry cycles of chlorides. Three deformed steel fibers, i.e., hooked-end (H), crimped (C), and milled-cut (M) fibers, with three angles of 0°, 30°, and 45° were examined under both uncorroded and corroded conditions. After corrosion, the average bond strength of H fibers was enhanced due to increased roughness and compact rust layer if the high inclination-induced fracture was avoided, while that of C and M fibers was decreased at various angles because of loose and porous rusts. The highest bond strengths of corroded H, C, and M fibers were discovered at 30°, 30°, and 0°, as a result of the combined mechanisms of snubbing effect, matrix spalling, or corrosion-induced fracture. The ultimate displacement of all fibers increased with angles due to increased matrix spalling area and fiber plastic deformation. The inclination effect of corroded fibers was more significant on energy absorption capacity than average bond strength, regardless of fiber type. A degradation model that describes the snubbing and matrix spalling effects, as well as the corrosion-induced deterioration and fracture was developed, based on which the critical inclination angle was found to decrease with increasing embedded length and decreasing tensile strength.

Punching shear capacity of nonprestressed UHPFRC flat Plates: Evaluation of existing methods

An experimental database of 64 nonprestressed ultra high performance fiber reinforced concrete (UHPFRC) flat plates reported to fail in punching shear was generated and characterized. The selected plates featured round, end-hooked, and deformed steel fibers. All plates have uniform thickness with no shear reinforcement. Trends and correlations between the shear stress at failure and various parameters were investigated. The shear stress at failure was on average four times higher than the shear stress corresponding with the first crack. There was a notable positive correlation between nonprestressed flexural reinforcement ratio and shear stress at failure. Plate ductility at punching shear failure varied significantly. A total of 13 prediction methodologies were considered for final evaluation, 8 of which were developed for UHPFRC, 4 were developed for fiber reinforced concrete (FRC), and 1 was developed for high performance fiber reinforced concrete (HPFRC). The predictive performance of the various prediction models was evaluated using common statistical indicators, as well as a demerit point classification model. The average ratio of measured to predicted punching shear capacity ranged from 0.50 to 2.42. The corresponding coefficients of variation (COVs) ranged from 36% to 58%. Only five out of 13 prediction methodologies underpredicted, on average, the nominal punching shear capacity. The large COV suggests the need for more accurate prediction methods that capture fundamental phenomena observed during tests while being informed by parameters that are practical to obtain. Guidelines for casting methods that produce the desired distribution of fibers are essential in yielding a more predictable plate response.

Effects of fibers on the mechanical properties of UHPC: A review

Ultra-high performance concrete (UHPC) developed rapidly in research and commercial use during the recent decade. Significant progress has been achieved in its material science and technology, including why and how to add discontinuous fiber reinforcement in it. This paper reviews the researches on understanding the effects of various fibers on the mechanical properties of UHPC, focus on the straight steel fibers but involving also deformed steel fibers, non-steel fibers as well as hybrid fibers. It also discusses the research methodology, prediction of mechanical properties by fiber factors, and the classification of UHPC mechanical properties related to this topic. It shows that (1) the experimental research is the main methodology for investigating the effect of the fibers on the mechanical properties of UHPC; the tensile performance of UHPC should be studied by uniaxial tensile tests and its representative indicators should include tensile strength, initial cracking strength, and peak tensile strain; (2) fiber plays an essential role in the reinforcement of the tensile strength, compressive strength, modulus of elasticity, and other material properties of UHPC, but in weakening the flowability of fresh UHPC. The positive and negative effects of fibers on the mechanical properties of UHPC should be considered, and the technology should be developed to maintain the flowability when high volume fraction of fibers is added in the UHPC; (3) the parameters of steel fibers affecting the mechanical properties of UHPC include volume fraction, size, shape, orientation and distribution, average bonding strength and minimum tensile strength, etc., which are mainly studied independently in the existing research. The studies on the combined effect of these parameters are limited but worthy of further investigation; (4) hybrid fibers could efficiently produce reinforcement effects for UHPC. It has great practical and research significance to conduct in-depth studies though the theoretical analysis and quantitative prediction are complex.

Experimental Database on pullout bond performance of steel fiber embedded in ultra-high-strength concrete

The bond strength between the steel fiber and the ultra-high performance concrete (UHPC) matrix plays a significant role in improving the behavior of plain UHPC. This paper compiles the existing experimental research database on the pullout bond performance of steel fibers embedded in UHPC. The variations of key parameters in the database are the steel fiber type and geometry, fiber volume fractions, and fiber embedded length. The effects of these parameters are analyzed and discussed in detail. Based on the analysis of the results, it was found that the deformed steel fibers, i.e., the hooked-end, half-hooked-end, and twisted steel fibers clearly provided higher average bond strengths than that straight fibers. The average pullout bond strength was obtained by increasing of fiber volume fraction in the UHPC matrix up to 2% (11.21MPa) with an increment of 20.4%. When the steel fiber volume fractions increase beyond 2%, the average bond strength decreases. Additionally, it was also found that using smaller embedded lengths in deformed steel fibers could result in the improvement of bond strength. This could be due to the fact that the bond is controlled by the mechanical anchorage of the end-hook rather than the physio-chemical bond in the straight portion. Conversely, increasing the embedded length of steel fiber could greatly contribute to the enhancement of pullout resistance resulting in increased bond strength between the UHPC matrix and steel fibers.

Determination of Single Parameter for Serviceability Requirements of Fibre Reinforced Concrete: Study of Fracture Characteristics

Abstract: This The influence of fibre reinforcement on crack propagation in concrete was studied . Thirty-five double torsion specimens, made with three types of fibres (fibre glass , straight steel fibres and deformed steel fibres ) were tested . The variables were the fibre volume and size of the fibres. The test results indicated that the resistance to rapid crack growth increased somewhat with increasing fibre content up to about 1.25% - 1.5% by volume. The degree of compaction had an enormous effect on the fracture properties .The fracture toughness increased with fibre content up to about 1.25% by volume, and then decreased , due to incomplete compaction. It was found that in this test geometry, fibres did not significantly restrain crack growth. It was also observed that once the crack had propagated down the full length of the specimen, the system changed from a continuous system to a discontinuous system, consisting of two separate plates held together by the fibre reinforcement. Different types of fibres did not significantly affect the fracture toughness. Keywords: Fibre glass, straight steel fibers, deformed steel fibers, fracture toughness.

Synergistic Bond Properties of Different Deformed Steel Fibers Embedded in Mortars Wet-Sieved from Self-Compacting SFRC

Reliable bond of steel fiber in concrete is a key problem relating to the reinforcing effect of steel fiber on concrete matrix and for the guide in significance for the optimal design of the geometry and mechanical properties of steel fiber. In this paper, on the basis of multi-indices of evaluation for the bond properties of single hooked-end steel fiber, the indices for the evaluation of synergistic bond properties of different deformed steel fibers are proposed. The pull-out tests were carried out for different deformed steel fibers embedded in mortar wet-sieved from self-compacting SFRC with manufactured sand. Fourteen types of steel fibers were used, including six hooked-end, two crimped, four indentation, one milling, and one large-end. The bond strength, bond energy, and bond toughness of single and per unit weight steel fiber were evaluated with the correspondence to the loading status of cracking resistance, normal serviceability, and ultimate bearing capacity of concrete. Results show that the deformed steel fibers presented different bond behaviors, hooked-end, and crimped steel fibers with circular cross-sections and a tensile strength of higher than 1150 MPa have excellent effects of strengthening, energy dissipation, and toughening capacity on self-compacting concrete with a cubic compressive strength of 60 MPa at normal serviceability and ultimate bearing capacity. Indentation, milling, and large-end steel fibers are more suitable for reinforcing the concrete strength due to the rigid bond before concrete cracking. The synergistic working of steel fibers with concrete matrix should be concerned to realize the effects of only or simultaneously reinforcing the strength and toughness of concrete.

Flexural Performance of Fibre Reinforced Concrete with an Optimised Spirally Deformed Steel Fibre

In this paper, the flexural performance of Fibre Reinforced Concrete (FRC) with an optimised spirally deformed steel fibre developed by the authors is evaluated experimentally. For comparison purposes, concrete specimens with commercially available steel fibres (hooked-end and crimped) are tested and included in the study. The experiment parameters include two different matrices with 28-day compressive strengths of 35 MPa and 45 MPa and four fibre volume contents (0.2%, 0.35%, 0.5%, and 0.65%). Besides, specimens with plain concrete are also tested as reference. Findings of the research indicate that the spirally deformed steel fibre considerably enhances flexural characteristics of concrete compared with existing fibres on the market (hooked-end and crimped) where the deflection-hardening response (even at the presence of wide cracks) can also be achieved even with low fibre dosages common in practice. Therefore, such a composite, i.e. concrete reinforced with spirally deformed steel fibre, can be deemed as a structural material.

Effects of corrosion level and inhibitor on pullout behavior of deformed steel fiber embedded in high performance concrete

This study investigated effects of corrosion level and inhibitor on the pullout behavior of deformed steel fibers. Two types of deformed (hooked and twisted) steel fiber, were embedded in two different matrices (28 MPa and 84 MPa). The calcium nitrite corrosion inhibitor (CNI) was added at a volume of 25 l/m3. An impressed current technique was used to generate different corrosion levels in the steel fibers. As the corrosion level increased, the pullout resistance of deformed steel fibers increased by maintaining fiber pullout mode and even slip hardening behavior. However, beyond a certain corrosion level, the pullout resistance was deteriorated due to fiber breakage and a sudden drop of pullout load at very small slip. The maximum corrosion level of deformed steel fibers should be limited to 12% for ensuring fiber bridging capacity at the composite level. The addition of CNI was beneficial for maintaining fiber pullout mode even at high corrosion level. By adding CNI, the maximum corrosion level of deformed steel fiber could be limited to 18%.

Benefits of curvilinear straight steel fibers on the rate-dependent pullout resistance of ultra-high-performance concrete

This study examines the effectiveness of using curvilinear steel fibers to enhance the pullout resistance of conventional straight steel (S-) fiber for an ultra-high-performance concrete (UHPC) matrix. Because structures composed of UHPC are subjected to various loading conditions and have random fiber orientations, three different loading rates ranging from static (0.018 mm/s) to impact (up to 906.2 mm/s) and two inclination angles of 0° and 45° were adopted. To fabricate the novel curvilinear steel fibers, five different curvatures were also utilized. Test results indicated that the curvilinear fibers provided a clearly higher pullout resistance than that of the conventional S-fiber, and the effectiveness increased with the curvature, regardless of the inclination angle and loading rate. Higher bond strengths were obtained for the S- and curvilinear fibers when they were inclined at 45° rather than aligned. In general, the bond strengths and pullout energies of the S- and curvilinear fibers in UHPC were improved by increasing the loading rate, and a higher loading rate sensitivity on the bond strengths was observed in aligned fibers than in inclined fibers. The matrix spalling phenomenon was only observed in an inclined state and became more significant with an increasing curvature and loading rate. The developed curvilinear fibers provided noticeably smaller matrix spalling areas than the conventional deformed steel fibers under both static and impact conditions, owing to the mitigated stress concentration. Thus, these may be worthy of attention as a novel reinforcing fiber type for UHPC composites.

Structural performance of optimised spirally deformed steel fibre

The capability of steel fibres in stress transferring across the cracked sections (bridging effect) could be employed to enhance the concrete role (especially in tension zones) in the overall load bearing capacity of Reinforced Concrete (RC) members. However, the structural applications of Fibre Reinforced Concrete (FRC) is limited mainly due to the poor performance of existing fibres on the market (softening response). The continuous pullout load decay, i.e. softening response, cannot result in a major contribution of fibres to the ultimate load bearing capacity of RC members. In this paper, the structural contribution of an optimised spirally deformed steel fibre engineered by the authors possessing hardening response in normal concrete is examined experimentally. To this end, a structural testing programme consists of two sets of RC beams, i.e. shear-critical and flexure-critical, is designed such that the shear and flexural contribution of the spiral fibre can be assessed individually. Various experiment parameters are considered in the testing programme. The test results reveal that such a fibre could be employed as partial/full replacement for conventional reinforcement in RC beams. A shear design equation for RC beams incorporating the new fibre is also proposed.

Enhancing the tensile performance of ultra-high-performance concrete through novel curvilinear steel fibers

This study developed a novel curvilinear steel fiber to improve the tensile behavior of ultra-high-performance concrete (UHPC) and to mitigate the stress concentration observed in conventional deformed steel fibers. To achieve this, four curvilinear steel fibers of different curvatures (0.02–0.10mm range) and a commercial smooth, straight steel fiber were employed. The average and equivalent bond strengths could be improved using the curvilinear steel fibers than the straight fiber from the UHPC matrix. The tensile performance of UHPC was improved by using the curvilinear fibers of curvature (κ) up to 0.04mm. The tensile strength and energy absorption capacity were significantly increased up to 52% and 174%, respectively, by replacing the straight steel fiber to the moderately curved steel fibers with κ=0.04mm, which is the optimum fiber type. The highly curved steel fibers, i.e., with curvatures beyond 0.04mm, slightly deteriorated the tensile performance because of the poorer fiber dispersibility and excessive matrix damage. A comparison of the pullout and tensile parameters showed that the equivalent bond strength of inclined steel fibers in UHPC is the most appropriate indicator for predicting the tensile performance.

Development of ultra-high performance geopolymer concrete (UHPGC): Influence of steel fiber on mechanical properties

This study reports the development of ultra-high performance geopolymer concrete (UHPGC) and overcoming the brittleness feature of geopolymer matrix by using different steel fibers. Four straight steel fibers with different aspect ratios and two different deformed steel fibers were investigated. Flowability, compressive strength and flexural behavior including strengths and deflection, and energy absorption capacity of UHPGC, were systematically evaluated. A deformation ratio of steel fiber was introduced to quantitatively correlate the steel fiber shape and the mechanical performance. The flowability of fresh UHPGC mixtures decreased when the fiber content and length increased, as expected, and was inconspicuously influenced by fiber shape. The increase in fiber content and the decrease of fiber diameter contributed to the improvement of the mechanical strengths of UHPGC. The flexural behaviors of UHPGC improved as the fiber volume and length increased, while the compressive and first crack strengths were affected by both curing conditions and fiber dosages as well. Different from Portland cement-based composites, the corrugated fibers with a higher deformation ratio added in UHPGC, had an inferior strengthening and toughening efficiency, while for straight fibers, those longer and smaller in diameter were more preferred. Finally, based on the previous research, a new one with adjustment and simplification was proposed for that of newly-developed UHPGC, and the fitted results had higher correlation coefficients (r2).

Analysis on enhanced pullout resistance of steel fibers in ultra-high performance concrete under cryogenic condition

This study aims to investigate the implication of cryogenic condition on the pullout properties of straight and deformed steel fibers embedded in ultra-high-performance concrete (UHPC). For this, two environmental conditions, i.e., ambient and cryogenic, approximately −170 °C, were considered along with three steel fiber types, i.e., straight, half-hooked, and twisted, and two inclination angles of 0° and 45°. In order to rationally explain the test results obtained, optical micrograph and scanning electron microscope images were captured and analyzed. The test results indicated that the bond strength of all steel fibers generally increased at cryogenic temperatures, and the effectiveness was higher when they were aligned than inclined. The straight fiber led to a much higher enhancement of the pullout resistance in terms of strength and energy when compared to the hooked and twisted fibers. The matrix damage became more severe as the fiber was geometrically deformed, inclined, and tested under cryogenic conditions. The fiber deformation improved the initial pullout properties but deteriorated the surrounding matrix and later pullout properties due to the fiber rupture or severe matrix spalling. Consequently, a lower efficiency of the deformed fibers as compared to that of the straight fiber was obtained under inclined or cryogenic conditions.

Bond performance of abraded arch-type steel fibers in ultra-high-performance concrete

The feasibility of newly developed abraded arch-type steel fibers as reinforcement in ultra-high-performance concrete (UHPC) is investigated in this study. To this end, twelve abraded arch-type steel fibers with two different curvatures of 0.04/mm and 0.10/mm, three different sandpaper grits of 120, 400, and 800, and two different sanding directions, i.e., longitudinal and transverse, were adopted along with the commercial smooth, straight (plain) steel fiber. To evaluate the effect of surface roughness on the interfacial bond behavior, the surface roughness parameters of plain and abraded steel fibers were quantitatively analyzed with atomic force microscopy. Test results indicate that the surface roughness of plain fiber increased substantially by the sanding process, while smaller grit with coarse particles produced higher roughness on the surface. The abraded arch-type fibers provided better pullout performance than the plain fiber in the same UHPC matrix: the highest bond strengths and energy absorption capacity were approximately two times greater than those of the plain fiber. The higher fiber curvature, smaller sandpaper grit, and longitudinal sanding process were more effective in enhancing the pullout performance of the steel fiber from the UHPC matrix than the counterparts. The abraded arch-type steel fibers generated relatively minor matrix damages during the pulling out process in comparison with conventional deformed steel fibers from the UHPC matrix, thus they can be considered as effective alternatives to the deformed fibers for enhancing the tensile performance of UHPC.

Influence of Steel Fibers on the Account of Permeability Aspects of M20 and M40 Grade Concrete

Steel Fibre Reinforced Concrete is used in a number of applications such as ground slabs, shotcrete, pavements etc to enhance the performance of plain and reinforced concrete. The study on durability characteristics of fiber reinforced concrete is scanty and hence the study on permeability is essential. This paper deals with the study on the permeability of steel fibre reinforced concrete. Deformed Steel fibres with different volume fraction were used in this study. Permeability was observed to decrease significantly with the addition of fibres and it continued to decrease with the increase in fibre content. Permeability tests were conducted using permeability test apparatus as per IS 3085 -1965. Mathematical equations were derived to determine the permeability using the parameters, volume fraction of fibers,and age of curing.

Geometrical and material optimisation of deformed steel fibres: Spirally deformed fibres

This paper presents an optimisation procedure of geometrical and material properties of steel fibres using the validated three-dimensional nonlinear Finite Element (FE) pullout model previously proposed by the authors. The FE model is employed as a virtual laboratory unit to investigate the pullout performance of steel fibres with various shapes such as hooked-end and spirally deformed steel fibres. The preliminary FE pullout analyses imply that the optimisation of the fibre with spiral configuration (adjustment of geometrical and material properties of the fibre) could result in an efficient high-performing steel fibre; hence such a fibre is selected for the optimisation procedure. In order to re-validate the numerical pullout model and further adjust its nonlinear parameters for enhancing the simulations prediction, a set of experimental pullout tests are conducted on four spirally deformed steel fibres with different geometrical properties. Extensive parametric studies are performed on the material and geometrical properties of the fibre to examine their effects on the fibre pullout performance. Moreover, an empirical equation is proposed for the estimation of fibre efficiency and optimum design of spirally deformed steel fibres in which geometrical and material properties are taken into account.

Dynamic pullout behavior of half-hooked and twisted steel fibers in ultra-high-performance concrete containing expansive agents

This study investigates the effects of matrix shrinkage, fiber geometry, and loading rate on the pullout behavior of steel fibers embedded in ultra-high-performance concrete (UHPC). For varying the matrix shrinkage, different quantities of calcium sulfoaluminate-based (CSA) expansive agent (EA) were adopted, ranging from 0% to 8%. In addition, moderately and highly deformed, i.e., half-hooked (HH) and twisted (T), steel fibers were used along with three different loading rates ranging from 0.018 (static) to 793 mm/s (impact). The test results indicated that the addition of the CSA EA is effective in reducing the shrinkage strains of UHPC only when its quantity is greater than 6%. The addition of the CSA EA improved the static average bond strengths of all the HH- and T-fibers; however, its effectiveness on the pullout energy was only valid when these fibers were aligned. The addition of the CSA EA enhanced the dynamic bond strengths of HH- and T-fibers, and the improvement was more obvious in the T-fiber specimens than in the HH-fiber specimens and in the aligned fibers than in the inclined ones. However, its implication on the dynamic pullout energies of the HH- and T-fibers was ambiguous. Both the addition of the CSA EA and a faster loading rate increased the probability of rupture failure of the deformed steel fibers in UHPC. The loading rate sensitivity was the highest in the straight steel fiber in UHPC, followed by the HH- and T-fibers, respectively. Consequently, straight or moderately deformed steel fibers are recommended for use in reinforcing UHPC under extreme loads, such as impact and blast.

An experimental study on pullout and tensile behavior of ultra-high-performance concrete reinforced with various steel fibers

Abstract This study investigates the effects of steel fiber type on the pullout and tensile performance of ultra-high-performance fiber-reinforced concrete (UHPFRC). For this, four different types of steel fibers, i.e., straight, twisted, hooked, and half-hooked, were used. In order to consider random fiber orientation in UHPFRC, various inclination angles, ranging from 0° to 60°, were considered for the pullout tests. Test results indicated that better pullout resistance was obtained in the deformed (twisted, hooked, and half-hooked) steel fibers embedded in ultra-high-performance concrete (UHPC) than that of the straight steel fiber as fiber breakage was prevented. The highest bond strengths of all steel fiber types were found when they were inclined 30° or 45°, while their slip capacities increased with increasing inclination angle. The hooked steel fiber exhibited the highest bond strengths at all inclination angles, while the twisted and half-hooked steel fibers exhibited the highest pullout energies at aligned and highly inclined (45° and 60°) conditions, respectively. In contrast to the pullout test results, the best tensile performance of UHPFRC was achieved by incorporating straight steel fibers, followed by the twisted, half-hooked, and hooked steel fibers. The poorer tensile performance of UHPCs reinforced with the deformed steel fibers was because of the severe matrix damage from excessive mechanical anchorage and fiber congestion, leading to insufficient matrix volume. Similarly, a relatively weak correlation between the fiber pullout and tensile behaviors of UHPFRC was observed. Therefore, a new pullout test method, which is able to consider the fiber random orientation and spacing, is required in order to improve the correlation.

Comparative pullout behavior of half-hooked and commercial steel fibers embedded in UHPC under static and impact loads

This study investigates the pullout behaviors of various steel fibers embedded in ultra-high-performance concrete (UHPC) under static and impact loading conditions. For this purpose, four types of steel fibers, i.e., straight, hooked, twisted, and half-hooked, and three different loading rates applied by static and impact pullout test machines were adopted. To examine the effect of inclination angle on the pullout behavior, four different inclination angles of 0°, 30°, 45°, and 60° were considered. Test results indicate that the highest average bond strengths were found for the hooked and twisted fibers for static and impact loads, respectively, whereas the straight fibers exhibited the lowest bond strength at all inclination angles. The effectiveness of using half-hooked fibers increased when they were inclined, and maximized at an inclination angle of 45° compared to straight and highly deformed fibers. The use of the twisted and half-hooked fibers was also more effective in static pullout energies than the hooked and straight fibers. The pullout resistance of all the steel fibers in UHPC was improved under impact loading conditions, and the order of the loading rate effectiveness regarding both the average bond strength and pullout energy was as follows: straight fibers > half-hooked fibers > twisted fibers > hooked fibers. The change in the failure mode from pullout to rupture, due to the increase in the loading rate, adversely affected the rate sensitivity of the bond strength and energy absorption capacity. Since the deformed steel fibers were easily ruptured under impact loads, their rupture failure needs to be prevented to achieve an excellent bond strength and energy absorption capacity.