Steel Fiber Volume Fraction Research Articles

Influence of Aggregate Gradation on the Workability, Mechanical Properties and Cost of Steel Fiber–Reinforced Concrete

Abstract Aggregate gradation is an essential concern in obtaining the intended properties in concrete production. The efficiency of this parameter dramatically increases for steel fiber–reinforced concrete (SFRC). Although steel fibers significantly improve the mechanical performance of concrete, they negatively affect the workability. Moreover, steel fibers, as expensive materials, drastically increase the cost of SFRC. For this reason, it is critical to correctly select the aggregate gradation and maximum aggregate size to be used in SFRC. In this study, the aim is to determine the effects of different aggregate gradations on the workability, mechanical performance, and cost of SFRCs. For this purpose, SFRC mixtures were produced with the maximum aggregate size of 16 and 31.5 mm. Vebe tests of fresh SFRCs were performed after the first mixing process and at the end of 30, 60, and 90-min intervals. The effects of test time and fine-to-coarse aggregate ratio on the workability were determined using response surface methodology. The compressive and flexural strengths and toughness performances of hardened SFRCs were also measured. In the last part of the study, to determine the effect of aggregate gradation on the cost, the unit costs of the SFRCs were calculated. The workability of SFRCs increased to a certain degree when finer aggregate gradation and smaller maximum aggregate size were preferred. Additionally, as finer aggregate gradation was used, it was observed that although the volume fraction of steel fibers did not change, the mechanical performance of SFRCs increased for a certain nominal aggregate size. Moreover, the unit cost of SFRCs decreased for a certain nominal aggregate size. As a result, by only selecting a finer aggregate gradation, it is possible to increase the workability and mechanical performance of SFRC and also produce more economic SFRCs for a constant volume fraction of steel fibers.

Behavior of high strength concrete encased steel composite stub columns with C130 concrete and S690 steel

This paper presents an experimental program that studies the structural behaviour of high strength Concrete Encased Steel (CES) composite columns. The structural performance under compression, including the damage pattern, load-carrying capacity, post-peak ductility, and load-displacement response is experimentally investigated. A total of 14 specimens were tested under concentric compression. The parameters studied in this program include concrete compressive strength, steel yield strength, stirrup spacing, incorporation of steel fiber, as well as the shape of the structural steel section. To evaluate the material compatibility between high strength concrete and high strength steel, two concrete grades (C90, C130) and two steel grades (S500, S690) were used to prepare the test specimens. In addition, 0.5% volume fraction of steel fiber was added in concrete mix to minimize the inherent brittleness of high strength concrete. The comparison between test results and analytical predictions reveals the inability of existing design codes to estimate high strength CES columns, unless steel fiber and dense reinforcement are used in combination. The effect of material strength, steel fibers, volumetric ratios of hoop reinforcement, and shape of steel section on both strength and ductility of CES columns was assessed through a comprehensive parametric study. The analysis of test results demonstrates that steel contribution ratio plays a dominant role in the ductility, whereas increasing hoop reinforcement ratio and adding steel fiber has negligible effect. Finally, a simplified formula is proposed to evaluate ductility of high strength CES columns.

Flexural Fatigue Performance of Steel Fiber Reinforced Expanded-Shales Lightweight Concrete Superposed Beams with Initial Static-Load Cracks.

Concerning the structural applications of steel fiber reinforced expanded-shales lightweight concrete (SFRELC), the present study focuses on the flexural fatigue performance of SFRELC superposed beams with initial static-load cracks. Nine SFRELC superposed beams were fabricated with the SFRELC depth varying from 50% to 70% of the whole sectional depth, and the volume fraction of steel fiber ranged from 0.8% to 1.6%. The fatigue load exerted on the beams was a constant amplitude sinusoid with a frequency of 10 Hz and a fatigue characteristic value of 0.10; the upper limit was taken as the load corresponded to the maximum crack width of 0.20 mm at the barycenter of the longitudinal rebars. The results showed that with the increase of SFRELC depth and the volume fraction of steel fiber, the fatigue life of the test beams was prolonged with three altered failure modes due to the crush of conventional concrete in the compression zone and/or the fracture of the tensile rebar; the failure pattern could be more ductile by the prevention of fatigue fracture by the longitudinal tensile rebar when the volume fraction of steel fiber was 1.6% and the reduction of crack growth and concrete strain in the compression zone; the fatigue life of test beams was sensitive to the upper-limit of the fatigue load, a short fatigue life appeared from the higher stress level and larger stress amplitude of the longitudinal rebar due to the higher upper-limit of the fatigue load. The methods for predicting the stress level, the stress amplitude of the longitudinal tensile rebar, and the degenerated flexural stiffness of SFRELC superposed beams with fatigue life are proposed. With the optimal composites of the SFRELC depth ratio and the volume fraction of steel fiber, the controllable failure of reinforced SFRELC superposed beams could be a good prospect with the trend curves of fatigue flexural stiffness.

Experimental Study on Shear Performance of Cast-In-Place Ultra-High Performance Concrete Structures.

In order to study the direct shear properties of ultra-high performance concrete (UHPC) structures, 15 Z-shaped monolithic placement specimens (MPSs) and 12 Z-shaped waterjet treated specimens (WJTSs) were tested to study the shear behavior and failure modes. The effects of steel fiber shape, steel fiber volume fraction and interface treatment on the direct shear properties of UHPC were investigated. The test results demonstrate that the MPSs were reinforced with steel fibers and underwent ductile failure. The ultimate load of the MPS is about 166.9% of the initial cracking load. However, the WJTSs failed in a typical brittle mode. Increasing the fiber volume fraction significantly improves the shear strength, which can reach 24.72 MPa. The steel fiber type has little effect on the shear strength and ductility, while increasing the length of steel fibers improves its ductility and slightly reduces the shear strength. The direct shear strength of the WJTSs made from 16 mm hooked-type steel fibers can reach 9.15 MPa, which is 2.47 times the direct shear strength of the specimens without fibers. Finally, an interaction formula for the shear and compressive strength was proposed on the basis of the experimental results, to predict the shear load-carrying capacity of the cast-in-place UHPC structures.

Effect use of steel fiber on mechanical properties of concrete mixture

In this paper the influence of commercialize steel fiber with properties of hooked end with 60 mm length and 0.75 mm diameter on the mechanical properties of concrete with three varied volumes of steel fiber 0%, 1% and 2% by volume were added to concrete mixes have been investigated. The design compressive strength considered was 25 MPa. Cubes specimens of size 100 mm x 100 mm x 100 mm to test the compressive strength were prepared for the time of 7th and 28th day, and flexural specimens with 100 mm x 100 mm x 500 mm were prepared. In this study, after 28 days of curing, compressive and flexural strength were determined. The use of steel fiber has shown a significant change on the mechanical properties of the concrete, in particular the compressive and flexural strength with the increase of the volume fraction of steel fibers. The test results show that the use of steel fiber improves the compressive strength, moreover change the failure type to ductile failures.

Effect use of steel fiber on mechanical properties of concrete mixture

In this paper the influence of commercialize steel fiber with properties of hooked end with 60 mm length and 0.75 mm diameter on the mechanical properties of concrete with three varied volumes of steel fiber 0%, 1% and 2% by volume were added to concrete mixes have been investigated. The design compressive strength considered was 25 MPa. Cubes specimens of size 100 mm × 100 mm × 100 mm to test the compressive strength were prepared for the time of 7th and 28th day, and flexural specimens with 100 mm × 100 mm × 500 mm were prepared. In this study, after 28 days of curing, compressive and flexural strength were determined. The use of steel fiber has shown a significant change on the mechanical properties of the concrete, in particular the compressive and flexural strength with the increase of the volume fraction of steel fibers. The test results show that the use of steel fiber improves the compressive strength, moreover change the failure type to ductile failures.

Experimental and analytical investigation on flexural behaviour of ambient cured geopolymer concrete beams reinforced with steel fibers

This study investigates the flexural behaviour of geopolymer concrete (GPC) beams reinforced with steel fibers. The effects of the volume fraction and fiber length on the flexural behaviour of GPC beams are investigated. The distinctive behaviour of GPC beams versus ordinary Portland Concrete (OPC) beams is identified and discussed. Based on the experimental results, the GPC beams reinforced with steel fibers showed great improvement in the cracking resistance, serviceability, and ductility compared to the reference beams. The GPC beam without steel fibers failed in a very brittle manner while those reinforced with steel fibers experienced ductile failure. The load capacity of the GPC beams increased with the volume fraction of steel fiber up to 0.75%. Further increasing the fiber content to 1.5% showed a deterioration in the flexural behavior due to poor workability of GPC leading to worse fiber dispersion and orientation. The increase of fiber length up to 60 mm did not improve the moment capacity of the GPC beams owing to premature fiber fracture. An analytical procedure was proposed to estimate the load-deflection curve of the tested beams with good correlation between predictive and experimental results.

Axial compressive behavior of confined steel fiber reinforced high strength concrete

Concrete is brittle in nature which is why different materials have been used to improve this inherent behavior of concrete. In this experimental study, the effect of simultaneous use of steel fibers and confinement on high strength concrete and the corresponding post peak response of fiber reinforced concrete is investigated. A total of 39 high-strength concrete (incorporating varying amounts of steel fibers) cylinders were casted. The steel fiber volume fraction (Vf) was varied as 0.5%, 1.5% and 2.5%. 18 samples were confined with Carbon Fiber Reinforced Polymer (CFRP) sheet, and 9 samples were casted in steel pipe confinement, whereas 12 control specimens (without confinement) were also prepared. The samples were tested under axial compression. The results confirmed that the use of steel fiber had minute effect on the compressive strength, whereas it significantly improved the ductility and enhanced the post peak behavior of concrete. The confinement significantly contributed towards the compressive strength increase. The combined use of steel fibers and confinement in concrete columns can be viewed as extremely beneficial as it not only increases the concrete compressive strength but also solves the issue of brittle failure to an appreciable extent.

Complete Stress-Strain Curves of Self-Compacting Steel Fiber Reinforced Expanded-Shale Lightweight Concrete under Uniaxial Compression.

To expand the structural application of steel fiber reinforced expanded-shale lightweight concrete (SFRELC), a self-compacting SFRELC with high-workability was developed based on previous research. As part of the investigation, the present study focuses on the adaptability of formulas used for the complete stress–strain curves of steel fiber reinforced lightweight-aggregate concrete and conventional concrete under uniaxial compression. On the basis of mix proportion of SFRELC, self-compacting SFRELC was designed with the volume fraction of steel fiber as 0%, 0.4%, 0.8%, 1.2%, 1.6%, and 2.0%. Eighteen cylindrical specimens with dimensions of Φ150 mm × 300 mm were tested to measure the uniaxial compressive stress–strain curves of self-compacting SFRELC. Results indicated that, with the increasing volume fraction of steel fiber, the compressive strain at the peak-stress of the stress–strain curve increased, while the slope of the descending portion decreased. This increased the energy absorption of self-compacting SFRELC with a higher compression toughness. With a comparison of test results between four groups of calculation models, a group of formulas is selected to express the complete stress–strain curves of self-compacting SFRELC under uniaxial compression.

Static Analysis of Properties of a Composite Slab Made from Steel Fibers and a Reinforced Foam Concrete

The effect of reinforcement configuration (steel fibers and a rebar) on the mechanical performance of a multiribbed composite slab (MCS) has been investigated. Four full-scale multiribbed composite prefabricated slabs with different volume fractions of steel fibers and the same total steel content were manufactured using a steel-fiber-reinforced concrete, foam concrete, and normal concrete. Various technical indicators were detected under the same static load, including the crack resistance, yield load, ultimate load, maximum deflection, destruction pattern, and stress of the steel rebar. The MCS exhibited excellent properties, and it is concluded that such slabs can be recommended for use in practice.

Structural Behaviour of Lightweight RC Frames contains Fibres subjected to Lateral Loading

Masonry infilled Reinforced Concrete (RC) framed structure is the utmost common kind of building in which, RC frames contribute in resisting lateral forces. Due to heavy mass and rigid construction, the RC framed buildings performs unfortunate under lateral forces. Practice of Lightweight concrete (LWC) is superlative because the dead load of concrete is massive. Low density materials are chosen in LWC, reduces the mass of the building thus decreasing the influence of lateral forces. However, LWC having a lesser modulus of elasticity has a more rapidly develops the cracks in the RC members. In this investigation, pumice is a naturally available material of volcanic source, has low density, which creates it ideal for production of LWC, likewise steel fibres are employed as an additive to enhance the energy absorption ability and to reduce the possibility of development of the cracks. In the present paper the structural behaviour of Lightweight RC framed structures realized by using steel fibres and subjected to lateral forces, In this study, four RC frames viz., F1-NWC (Control), F2- NWCF (with 1% Volume fraction (Vf) of steel fibres), F3-LWC (with 20% substitute of coarse aggregate instead of pumice aggregate) and F4-LWCF (with 20% substitute of coarse aggregate instead of pumice aggregate and 1% Vf of steel fibres) were casted and tested under in-plane horizontal loading, which are designed according to Indian Standard (IS) code IS 456 (2000). It was observed that the behaviour of F4-LWCF significantly better in comparison to other frames in various parameters such as load carrying capacity, displacement, ductility, stiffness and energy dissipation.

Behavior of Rectangular-Sectional Steel Tubular Columns Filled with High-Strength Steel Fiber Reinforced Concrete Under Axial Compression.

This paper studies the effect of high-strength steel fiber reinforced concrete (SFRC) on the axial compression behavior of rectangular-sectional SFRC-filled steel tube columns. The purpose is to improve the integrated bearing capacity of these composite columns. Nine rectangular-sectional SFRC-filled steel tube columns and one normal concrete-filled steel tube column were designed and tested under axial loading to failure. The compressive strength of concrete, the volume fraction of steel fiber, the type of internal longitudinal stiffener and the spacing of circular holes in perfobond rib were considered as the main parameters. The failure modes, axial load-deformation curves, energy dissipation capacity, axial bearing capacity, and ductility index are presented. The results identified that steel fiber delayed the local buckling of steel tube and increased the ductility and energy dissipation capacity of the columns when the volume fraction of steel fiber was not less than 0.8%. The longitudinal internal stiffening ribs and their type changed the failure modes of the local buckling of steel tube, and perfobond ribs increased the ductility and energy dissipation capacity to some degree. The compressive strength of SFRC failed to change the failure modes, but had a significant impact on the energy dissipation capacity, bearing capacity, and ductility. The predictive formulas for the bearing capacity and ductility index of rectangular-sectional SFRC-filled steel tube columns are proposed to be used in engineering practice.

Development of the strain field along the crack in ultra-high-performance fiber-reinforced concrete (UHPFRC) under bending by digital image correlation technique

The digital image correlation (DIC) technique was applied to the analysis of displacement fields along the surface cracks of ultra-high-performance fiber-reinforced concrete (UHPFRC) under a bending load. Analysis was performed on the fiber bridging forces acting on a unit area of cracked sections belonging to different regions (perfect bonding region, partial debonding region, and full debonding region), according to the fiber distribution characterization and DIC data. By using the DIC technique, the visualization and quantification of the UHPFRC fracture properties could be determined. The length of the uniform zone increased, whereas the fracture process decreased under the external load of the limit of proportionality (LOP). With the appearance of macro-cracks under the external load of the modulus of rupture (MOR), the length of the uniform and fracture process zones increased as the fiber content increased. However, the localization zone decreased. The steel fiber volume fractions had limited influence on the tensile strain at cracking and the complete debonding of fibers.

Autogenous shrinkage behavior of ultra-high performance concrete

This study presents experimental results on the shrinkage behavior of ultra-high performance concrete (UHPC), including the shrinkage development pattern, the calculation of autogenous shrinkage strain and the steel fiber restraining effect. UHPC is found to exhibit a multi-stage shrinkage characteristic. During the first two dormant stages, shrinkage is mainly composed of thermal contraction when limited hydration reaction occurs. Rapid shrinkage development commences once hydration is accelerated, leading to pore moisture depletion and pore refinement. In the later stage, shrinkage gradually levels off due to the decreasing hydration reactivity and the stiffening matrix. Autogenous shrinkage is separated by the removal of thermal strain based on the knowledge of coefficient of thermal deformation (CTD). This leads to the appearance of a transient swelling segment which may be attributed to the formation of Ca(OH)2 and ettringite crystals generating expansive stresses. Addition of steel fibers is found to reduce the shrinkage strain significantly. Its shrinkage restraining effect is a result of the matrix-fiber interfacing bonding and is numerically characterized by a mathematical model with the volume fraction and geometrical features of steel fibers as the major variables.

Toughness enhancement and equivalent initial fracture toughness of cementitious composite reinforced with aligned steel fibres

AbstractBased on theoretical analysis and numerical simulation, the impact of steel fibres on the stress intensity factor (SIF) at the crack tip for cementitious composite was studied. The enhanced toughness of steel fibre reinforced cementitious composite (SFRC) in resisting cracks was explained by the decrement of SIF caused by steel fibre inclusions at the crack tip of the composite. The equivalent initial fracture toughness was used to characterize the crack initiation of SFRC. A simplified method for determining the of SFRC was proposed based on a linear regression method. Fracture tests were conducted on three‐point bending notched beams with different steel fibre volume fractions and specimen sizes to study the crack initiation behaviour of aligned steel fibre reinforced cementitious composite (ASFRC). of ASFRC was calculated, and the size effect of was analysed. The results showed that slightly increased with the steel fibre volume fraction and gradually became stable. For the tested specimens, whose heights varied between 40 and 100 mm, the specimen size had little impact on the .

Effect of steel fibers on the compressive and splitting-tensile behaviors of cellular concrete with millimeter-size pores

A high-performance steel fiber reinforced cellular concrete (SFRCC) with millime-size pore structure is recently suggested as an attractive material in structural engineering because of its desirable engineering characteristics. However, the influence of the steel fibers on the mechanical properties of SFRCC are still very limited in literature. Therefore, before the structural applications, it is necessary to learn the mechanical behaviors of SFRCC under compression and splitting-tension, as well as their relationship. To this end, a detailed experimental program has been performed to research the effect of fibers’ shape (i.e., crimped, straight and hooked end) and aspect ratio (i.e., 33.33, 44.44 and 55.56) on the compressive and splitting-tensile behaviors of the new SFRCC utilizing saturated superabsorbent polymer (SAP) under different volume fraction of steel fibers (i.e., 0.5%, 1.0% and 1.5%). Experimental results show that higher compressive strength and splitting-tensile strength of SFRCC are tightly related to higher volume fraction or aspect ratio of steel fibers, corresponding to the more ductile behaviors and higher loading levels in the post-peak behaviors. Moreover, it is important to consider the influence of fibers’ shape on the mechanical properties of SFRCC. Based on the cracked planes of SFRCC specimens after splitting-tensile tests, it is confirmed that the procedures of specimen fabrication and material characterization significantly influence the distributions of steel fibers and pores and some empirical formulae are proposed to describe the dependence of their distributions on the fiber characteristics.

INVESTIGATION ON FLEXUREL CAPACITY OF RENINFORCED ULTRA HIGH PERFORMANCE CONCRETE BEAMS

4 span-depth ratio of 16 reinforced ultra-high-performance concrete beams were fabricated for the investigation of their flexural behavior and flexural capacity. The variable parameters studied in the test were steel fiber volume fraction and longitudinal reinforcement ratio. Testing results show that increasing steel fiber volume fraction from 3% to 5% could increase the resistance of cracking (cracking load increased by 6.0% to 11%). However, it had little effect on the ultimate load capacity (only increased 1.4%~2.5%). The failure modes of the beams with the longitudinal reinforcement ratio of 3.21% and 6.74% were classified as under-reinforced failure and limited over-reinforced failure respectively. Increasing the reinforcement ratio could enhance the flexural capacity of reinforced UHPC beams (increased by 34.9%~36.5%). A tentative flexural capacity calculation model of reinforced UHPC beams was proposed based on the section equilibrium condition, the assumption of plane section, the material constitutive relation of UHPC, and reinforcement. The calculation results of flexural capacity are found agreeing well with the experimental results.

Experimental Investigation on Compressive Toughness of the PVA-Steel Hybrid Fiber Reinforced Cementitious Composites

In order to achieve the whole process control of crack formation of engineered cementitious composites (ECC) under loading and improve the mechanical properties of ECC, PVA-steel hybrid fiber reinforced cementitious composites (HyFRCC) was proposed by mixing steel fibers with traditional ECC. And the key parameters to affect the HyFRCC performance are PVA fiber content, steel fiber content and aspect ratio of steel fiber. In order to investigate the mechanical properties of PVA-steel HyFRCC such as the compressive toughness, 15 PVA-steel HyFRCC specimens with different volume fraction of steel fiber and PVA fiber, together with 1 non-fibrous cementitious composites specimen and 3 ECC specimens with PVA fiber only for comparison were designed and uniaxial compression tests were conducted. Furthermore, the effect of fiber content, fiber type and fiber geometrical characteristic on the compressive toughness of HyFRCC were analyzed. The results show that PVA fiber content, steel fiber content and aspect ratio of steel fiber have little impact on the uniaxial compressive strength of the PVA-steel HyFRCC, while the peak strain, compressive toughness and the post-peak ductility of PVA-steel HyFRCC are improved significantly due to fiber hybridization. The formation of large scale cracks of ECC specimens after post-peak loading is restrained effectively with the addition of steel fiber. The mixture of PVA and steel fiber has a remarkable effect on the improvement of ECC compression toughness and crack control. It indicates that the energy dissipation and damage control capacity of the structural component with PVA-steel HyFRCC under seismic loading will be enhanced.

Fire flame effect on the compressive strength of reactive powder concrete using different methods of cooling

This research foxed on the effect of fire flame of different burning temperatures (300, 400 and 500)oC on the compressive strength of reactive powder concrete (RPC). The steady state duration of the burning test was (60) min. Local consuming material were used to mixed a RPC of compressive strength around (100) MPa. The tested specimens were reinforced by (3.0) cm hooked end steel fiber of (1100) MPa yield strength. Three steel fiber volume fraction were adopted in this study (0, 1.0and 1.5)% and two cooling process were included, gradual and sudden. It was concluding that increasing burning temperature decreases the residual compressive strength for RPC specimens of(0%) steel fiber volume fraction by (12.16, 19.46&24.49) and (18.20, 27.77 &36.07) forgradual and sudden cooling respectively. This reduction was modified by adding steel fiber, the percentage of (1%) characterized the optimum response. Burning RPC that has non-zero steel fiber content up to 400 oC caused an increase in the residual compressive strength for a case of gradual cooling to be (4.37 & 6.25)% for steel fiber volume fraction of (1 & 1.5) % respectively. Sudden cooling method was improved to be the critical cooling method, the negative influence of this method was directly proportion with both burning temperature and steel fiber volume fraction.

Dynamic modulus of elasticity of geopolymer lightweight aggregate concrete

The production processes of ordinary Portland cement (OPC), accompanying with bad environment influences such as, huge energy consumption, greenhouse gases emissions and natural resource exploitation; but fly ash-based geopolymer concrete is produced without (OPC), yet that has many sustainable environment benefits. In this study locally artificial lightweight aggregate was used to produce lightweight fly ash geopolymer concrete. The dynamic modulus of elasticity for geopolymer lightweight concrete produced by using locally artificial aggregate was investigated. Reference lightweight geopolymer concrete containing natural normal weight fine aggregate without fiber, lightweight geopolymer concrete reinforced with two volume fractions of steel fibers (0.25 and 0.5); in addition to four concrete mixtures containing artificial coarse lightweight aggregate and artificial lightweight fine aggregate with 25, 50, 75 and 100% volumetric replacement to natural normal weight fine aggregate (sand) were prepared. The dynamic modulus of elasticity was tested at 28day age for all specimens using resonance frequency method. The results demonstrate that the incorporation of artificial fine lightweight aggregate as a volumetric replacement to natural fine aggregate in concrete geopolymer lightweight concrete reduces the dynamic modulus of elasticity gradually with the increase of artificial lightweight aggregate content.