Inclusion Of Steel Fibers Research Articles

Ductile and brittle effects of fibre reinforcements in low calcium cementitious matrix

The motivation of the present investigation has analyzed the engineering properties of discrete fibre addition in conventional concrete. A comparative evaluation was studied systematically in the performance of concrete with the addition of two different fibres such as polypropylene (pp) and steel fibres. The laboratory test results lead the conclusions that the brittle matrix provided a maximum strength up to 45.30 MPa was noticed at 28 days moist curing by the inclusion of steel fibres (1% Vf). However, in the case of maximum strength up to 42.50 MPa was noticed when the addition of polypropylene fibres (0.1% Vf) at 28 days moist curing. It can be subsequently proved either high strength (steel) or high deformability fibres (pp) improve the composite matrix when the addition of discrete fibres in conventional concrete.

Repeated drop-weight impact tests on self-compacting concrete reinforced with micro-steel fiber

Steel fiber has become a proven material that can significantly alter the behavior of different types of concrete mixtures from brittle to more ductile ones. Rich literature is currently available on the mechanical properties of steel fiber-reinforced self-compacting concrete. However, the investigation of the impact resistance of this material to drop weight is still required to enrich the knowledge about its behavior under different loading conditions. An experimental work was conducted in this research to evaluate the performance of steel fiber-reinforced self-compacting concrete under repeated impact loading using the repeated blows test recommended by ACI 544-2R. The tests investigated the effect of drop weight and drop height in addition to fiber content. Straight micro-steel fibers were incorporated in three volumetric contents of 0.5, 0.75 and 1.0% and were compared with a similar plain mixture. The test equipment was adjusted to conduct repeated impact loading from different drop-heights and using different drop-weights. The adopted drop-heights were 450, 575 and 700 mm, while the adopted drop-weights were 4.5, 6.0 and 7.5 kg. The combination of the adopted drop-heights and weights composes four loading cases in addition to the standard loading case with a drop-weight and drop-height of 4.5 kg and 450 mm. The inclusion of micro steel fiber was found to significantly increase the impact resistance of self-compacting concrete with percentage developments ranging from 150 to 860% compared to plain samples. The specimens tested under 4.5 kg and 450 mm drop weight and height exhibited the highest percentage improvement in impact resistance among the five loading cases. The results also showed that the impact ductility of fibrous specimens was up to 24% higher than that of plain specimens.

Numerical analysis on displacements of steel-fiber-reinforced concrete beams

abstract: This work deals with parametric analyses of the structural behaviour of steel-fiber-reinforced concrete using a Damage Constitutive Model and homogenization technique. This approach is contemporary once Brazil has not a standard procedure for the design of this type of material. The present study performs a parametric analysis of rectangular beams subjected to flexion at four points, with height variations (h), reinforcement area (As) and span (L) are used to verify the influence of each parameter on the numerical study of the deformability of beams composed by this material. Fiber volume concentrations of 2.00% and 2.50% have been used on the modelling. It is observed that the obtained results were mainly affected by height and span. It is noticeable that the inclusion of steel fibers leads to an increase in the maximum load and ductility of the analyzed beams in this work.

Effect of steel fibers over the Self Compacting Concrete

The introduction of self-compacting concrete in the construction industry overcomes the flaws caused due to the improper compaction of concrete. Fibers are proved to increase the properties of conventional concrete. This research focuses on the performance of self-compacting concrete after augmenting steel fibers. The steel fibers are added in proportions such as 0.25 percentage, 0.5 percentage, 0.75 percentage and 1 percentage. After casting the self- compacting concrete, the strength was assessed for 7 days and 28 days and its compressive strength and split tensile strength was analyzed. The inclusion of steel fibers yielded good outcome in the tests and it is proved to yield better engineering properties.

Steel Fiber Use as Shear Reinforcement on I-Shaped UHP-FRC Beams

In the presented paper, the effectiveness of steel fiber use on the shear and flexure behaviors of ultra-high performance concrete (UHPC) beams and the feasibility of steel fibers in place of shear reinforcement were investigated experimentally. In this framework, a total of four I-shaped UHPC beams were produced for a high tensile reinforcement ratio of 2.2%. While two of them were non-fiber UHPC beams with and without the shear reinforcement to show the contribution of steel fibers, the remaining beams were made from the ultra-high performance steel fiber-reinforced concrete (UHP-FRC) having the short straight fibers with 1.5% and 2.5% by volume. The shear and flexural parameters, such as the load–deflection response, cracking pattern, failure mode, deflection, and curvature ductilities were discussed based on the four-point loading test results. While the reference beam without fiber and shear reinforcement failed by the shear with a sudden load drop before the yielding of reinforcement and produced no deflection capability, the inclusion of steel fibers to the UHPC matrix transformed the failure mode from shear to flexure through the fibers’ crack-bridging ability. It might be deduced that the moderate level of steel fiber use in the UHP-FRC beams may take the place of shear reinforcement in practical applications.

Constitutive models for nonlinear analysis of SFRC corbels

In this paper, nonlinear constitutive models are proposed for steel fiber reinforced concrete (SFRC) in compression and tension. The models were implemented in the finite element computer program ANSYS for 3-D nonlinear analysis of SFRC corbels under monotonic static loading. Several validation studies have been performed for normal-strength and high-strength SFRC corbels with constant or variable depth. Good agreement is generally achieved between experimental and numerical results for the load-deflection curves and crack patterns. Additionally, parametric studies have been performed in order to investigate the effect of structural parameters on the performance of SFRC corbels. It was found that: (1) increasing the concrete compressive strength (fc’) improves corbel shear capacity and toughness, (2) the inclusion of steel fiber (Vf) delays premature shear failure for corbels and enhances strain ductility, (3) an enhancement in shear capacity and strain ductility is noticed by increasing the ratio of horizontal stirrups (ρh), and finally, (4) increasing the shear span-to-depth ratio (a/d) reduces the shear capacity of SFRC corbels. Corbel shear capacity increases by 27% due to a 33% increase in (fc’), by 31% due to Vf = 1% inclusion, by 20% due to a 1% increase in (ρh), and by 20% due to a 39% decrease in (a/d) ratio. The proposed nonlinear finite element approach is efficient in determining the expected enhancement in shear capacity and ductility of SFRC corbels, and consequently in optimizing design parameters for such elements.

Flexural response of hollow high strength concrete beams considering different size reductions

In this work, 14 reinforced concrete solid and hollow beams were tested under four-point bending test to evaluate the flexural behavior of hollow concrete beams. The experimental program focused on two main variables which are the size reduction percentage and the inclusion of steel fiber. In addition, the longitudinal reinforcement ratio and the presence of lateral stirrups were also within the investigated parameters. Four solid beams in addition to 10 hollow beams with central square holes with side lengths of 60, 80, and 100 mm were fabricated to evaluate the test parameters. These beams were either reinforced with 1% steel fiber or contain no fiber. The flexural performance of the beams was evaluated using the load–deflection behavior, flexural ductility, stiffness and toughness. In addition to the experimental work, analytical formulas were introduced to evaluate the cracking and peak loads of the hollow beams. The test results showed that ductility of hollow beams with size reductions of 16% and 28.4% was higher than that of the reference solid beam, while the ductility of the hollow beam with 44.4% size reduction was quite comparable to that of the solid beam. Moreover, the toughness values of the hollow beams were higher by 19 to 37% than that of the reference solid beam. Based on the obtained results, it can be concluded that hollow reinforced concrete beams with 1.0% steel fiber and with size reduction up to 44.4% can replace solid beams without suffering significant reductions in strength, ductility and toughness.

Comparative study on shear failure behavior of squat high-strength steel reinforced concrete shear walls with various high-strength concrete materials

The shear failure behavior of four squat shear walls with high-strength steel (HSS) and high-strength concrete (HSC) was experimentally investigated in this study. The experimental variables are the steel grade, namely SD420 and SD785, and the type of HSC materials, namely commercially available HSC with the inclusion of steel fibers and ultra-high performance concrete (UHPC) with or without steel fibers. The squat walls were tested under displacement reversals and their cyclic responses were extensively compared using various performance measures. The results indicate that the addition of steel fibers in the squat walls transformed the shear critical damage pattern from significant concrete spalling to localized diagonal cracks. The HSS reinforced squat wall made using commercially available HSC with the addition of a 0.75% volume fraction of steel fibers had a load-displacement response, energy dissipation capacity, and shear strength comparable to those of the squat walls made using specially mixed UHPC containing a 1.5% volume fraction of steel fibers. Moreover, while the high-strength horizontal reinforcement in the squat non-fiber HSC did not yield until the end of the test, its yield strength was fully utilized when it was used in the fiber-reinforced HSC walls. In addition to the experimental study, the applicability of existing design codes and the softened strut-and-tie model for assessing the shear strength of the high-strength squat walls was evaluated.

Review on Fly Ash and Alccofine Based Self-Compacting Fiber Reinforced Concrete

The modern civil engineering constructions have their own structural and durability requirements related with concrete to better suit the intended function of the structure. It is necessary to develop the concrete with special properties, so that the structure continues to perform its intended purpose. The inclusion of fly ash, alccofine and steel fiber could be a solution for the demand in concrete for the modern construction. Based on the research done on the concrete containing these materials, it is observed that, the replacement of cement by fly ash reduces the workability and strength of concrete, but 25% replacement can be used as an optimum dosage for the structural concretes which reduces the cost by 7%. Inclusion of fly ash also increases durability of concrete by enhancing resistance to drying shrinkage and freezing and thawing action in the concrete. It is found that replacement of cement by alccofine in the concrete increases the strength and workability and can be used up to 15% as an optimum dosage. Hence, alccofine along with super-plasticizers can be used to develop high strength self-compacting concrete. Addition of fibers has a great advantage in improving both strength and durability properties. Especially the steel fibers up to 1% addition can increase inherent tensile strength, flexural strength and resistance to drying shrinkage and freezing and thawing of concrete. Hence, the environment friendly concrete with self-compacting ability, high strength and better durability properties can be manufactured using industrial waste as mineral admixtures along with steel fibers.

Behavior of fiber reinforced concrete members under sustained axial/flexural load

AbstractThe inclusion of steel or polypropylene fibers in the concrete mix can substantially improve the serviceability characteristics of reinforced concrete members. For fiber reinforced concrete (FRC) members, the fibers enhance the postcracking stiffness, thereby reducing the short‐term and long‐term deflections, and very significantly reducing the width of cracks and the spacing between them. Relatively little experimental and analytical research has been undertaken on the effects of creep and shrinkage on the long‐term performance of FRC structural members after cracking. Failure to account for creep and shrinkage of the concrete and creep of the fibers can lead to a serious under‐estimation of the extent and severity of cracking, as well as long‐term curvatures and deformations. This paper describes a method of analysis and the material modeling required to determine the time‐dependent behavior of cracked, steel or macro‐synthetic FRC members containing conventional bar reinforcement and subjected to a sustained bending moment and/or axial force. The model is versatile in that it can handle a range of inputs (fiber type, specimen geometry, loading conditions, etc.) and is simple enough for routine use. The model is validated against available test data and is shown to produce satisfactory correlations.

Strength Characteristics of Slag Based Steel Fiber Reinforced Concrete with Partial Replacement of Steel Slag in Coarse Aggregate

The current research work represents the various test results from an experimental program for the influence of mineral admixture, stone dust, steel slags and rapid hardening (accelerator) type of chemical admixtures along with the inclusion of steel fibers for various mixture proportions on the mechanical properties of concrete. The different strength properties considered the cubical size for compressive strength, prism for flexural rigidity and monitored the ultrasonic pulse velocity test including water absorption (sorptivity) test for different curing days was evaluated. The outcome results for concrete shows that when the percentage of steel slag is increased then there will be a good workability in fresh concrete than normal aggregates. In overall 100% of stone dust, if the portion of steel slag is more than 40% with replacement of coarse aggregate and binding material as slag will lead to minimum workability, there is no change in the proceding workability area in the further addition of super plasticizer. Also, the study indicates that the crimped steel fiber matrix interaction gives considerable results to enhance the bending stress in flexural rigidity caused by the introducing of steel fibers.

Experimental and statistical analysis of hybrid-fiber-reinforced recycled aggregate concrete

Although concrete is the most widely used construction material, its deficiency in shrinkage and low tensile resistance is undeniable. However, the aforementioned defects can be partially modified by addition of fibers. On the other hand, possibility of adding waste materials in concrete has provided a new ground for use of recycled concrete aggregates in the construction industry. In this study, a constant combination of recyclable coarse and fine concrete aggregates was used to replace the corresponding aggregates at 50% substitution percentage. Moreover, in order to investigate the effects of fibers on mechanical and durability properties of recycled aggregate concrete, the amounts of 0.5%, 1%, and 1.5% steel fibers (ST) and 0.05%, 0.1% and 0.15% polypropylene (PP) fibers by volumes were used individually and in hybrid forms. Compressive strength, tensile strength, flexural strength, ultrasonic pulse velocity (UPV), water absorption, toughness, elastic modulus and shrinkage of samples were investigated. The results of mechanical properties showed that PP fibers reduced the compressive strength while positive impact of steel fibers was evident both in single and hybrid forms. Tensile and flexural strength of samples were improved and the energy absorption of samples containing fibers increased substantially before and after crack presence. Growth in toughness especially in hybrid fiber-reinforced specimens retarded the propagation of cracks. Modulus of elasticity was decreased by the addition of PP fibers while the contrary trend was observed with the addition of steel fibers. PP fibers decreased the ultrasonic pulse velocity slightly and had undesirable effect on water absorption. However, steel fiber caused negligible decline in UPV and a small impact on water absorption. Steel fibers reduce the drying shrinkage by up to 35% when was applied solely. Using fibers also resulted in increasing the ductility of samples in failure. In addition, mechanical properties changes were also evaluated by statistical analysis of MATLAB software and smoothing spline interpolation on compressive, flexural, and indirect tensile strength. Using shell interpolation, the optimization process in areas without laboratory results led to determining optimal theoretical points in a two-parameter system including steel fibers and polypropylene.

Efficiency of Fiber Reinforced Concrete Containing Waste Marble dust and Waste Foundry Sand

The study focused on the effect of marble dust 0-10% (MD) by weight of cement content, waste foundry sand 0-30% (WFS) replaced by normal river sand and inclusion of glued steel fibres 0-1.5% (GSF) by volume fraction and also 1.5% of chemical admixture(SP) by weight of binding materials produced the excellent quality of structural concrete. Conversely, the replacement level of WSF can be limited up to 30%, Further, add into the concrete will affect the strength. From the test results observed that the 10% of MP, 20 % of WFS with 1.5% of GSF along with 1.5% of SP in concrete produced the higher compressive strength was 34.20, 39.90 and 42.50 N/mm2 at 7, 28 and 56 days respectively, the strength was increased up to 7.40% than compared to controlled concrete. Also, a higher amount of bending stress was measured from 3.30 to 4.57 MPa at 28 days for various mixes of concrete and the ultrasonic pulse velocity values are recorded between 3630 to 4030 m/sec for various mixes at 28 days. Finally, the durability measurement of RCPT and also material characteristics test on the modulus of elasticity of concrete were studied systematically.

Experimental study on high strength concrete encased steel composite short columns

This paper investigates on the axial compressive behavior of high strength Concrete Encased Steel (CES) composite short columns. Six column specimens made of high strength concrete were tested under monotonic pure compression. The structural performance was investigated including failure pattern, load-carrying capacity, load-deformation response, and post peak ductility. The major parameters affecting the ultimate strength of such composite columns are studied including concrete strength, spacing of transverse reinforcement bars, and the inclusion of steel fibers in the high strength concrete. Based on the experimental work, it is found that the failure mode of CES columns with high concrete strength C120 is characterized by concrete cover spalling, which triggers a sudden drop of compression capacity once the peak resistance is reached. With the decrease of transverse reinforcement spacing, the ultimate load capacity of high strength CES columns can be enhanced due to better concrete confinement but the failure is still brittle with abrupt unloading from the peak load. The test results also indicated that the provision of 0.5% volume of steel fiber is able to prevent the concrete cover spalling, and hence the load-carrying capacity can be enhanced. Finally, the test results together with additional test data collected from the literature are used for comparison with codes’ prediction using the EN 1994-1-1 and JGJ 138-2016. The code methods give excellent prediction of CES columns with normal strength steel and concrete grade up to C90, but they over-estimate the maximum resistance of CES columns with concrete strength higher than 90 MPa. To extend the current design methods for CES members with higher strength concrete, two analytical methods were proposed which shows good correlation with test results, thus enabling the design of CES members with higher strength of concrete.

Experimental analysis of longitudinal shear between the web and flanges of T-beams made of fibre-reinforced concrete

The longitudinal shear between the web and flanges of T-beams is an Ultimate Limit State contemplated by technical codes. For this reason, the longitudinal shear must be compared with the longitudinal shear resistance of the flange. Longitudinal shear strength can be increased by including steel fibres in the concrete mass. This article shows the experimental results of 13 T-beams mounted on two supports subjected to two central loads. Four of these beams were made with conventional concrete and nine with fibre-reinforced concrete. The direct instrumentation results are discussed and the failure process is described. Longitudinal shear cracking load is studied on the basis of both a theoretical approach and experimental results. An analysis is performed to evaluate each specimen’s longitudinal shear, not only in the ultimate state, but also throughout the loading process evolution, based on load and strain records. This process involves determining each beam’s effective width. The experimental data confirm an increase in longitudinal shear strength caused by adding steel fibres to concrete.

Stepwise Regression for Shear Capacity Assessment of Steel Fiber Reinforced Concrete Beams

Inclusion of steel fibers to concrete progresses the flexural and tensile capacities of concrete. Consequently the shear capacity of concrete flexural members improve. Predicting the shear capacity of concrete beams containing steel fiber is an important issue not only in structural design but also to retrofitting of existing structures. Since there are several variables to assess the shear capacity of steel fiber reinforced concrete (SFRC) beams, presenting a suitable equation is a complicated task. The aim of the present paper is to evaluate an empirical formulae based stepwise regression (SR) method for shear capacity of SFRC beams. A series of reliable experimental data has been provided from literatures for model development. The obtained results based SR model were compared with experimental data in training and testing state. A practical formulae based SR method has been developed for shear capacity assessment of SFRC beams. Besides, several equations based models also presented to compare with the equation based SR model. The comparison showed the SR formulae gives the most exact accuracy than others in terms of shear capacity assessment of SFRC beams.

Effects of blast furnace slag and steel fiber on the impact resistance of railway prestressed concrete sleepers

This study aims to investigate the effects of ground granulated blast furnace slag (GGBFS) and steel fibers on the flexural behavior of railway prestressed concrete (PSC) sleepers under static and impact loads. For this, two types of railway PSC sleepers with 14 or 16 prestressing strands were fabricated, and two different hammers with weights of 400 and 500 kg dropped at a height of 2 m for providing two potential energies of 7.85 and 9.81 kJ for the impact resistance. The structural integrity of the sleepers after impact damage was examined by evaluating their residual flexural performance. Test results indicated that the addition of 0.75 vol% hooked steel fibers was effective in improving the flexural performance of the sleepers at both static and impact loads, while the inclusion of GGBFS led to an improvement in the static flexural performance only. Based on our analysis of cracking behavior, enhancements in static and impact resistance of the sleepers with steel fibers were caused by the limited formation of cracks and a decrease in maximum crack width. Higher flexural strengths of all tested sleepers were also obtained under the impact load than under the static load, and the increase was higher for higher potential energies because of the strain-rate effect. The enhanced residual capacity (i.e., higher strength and stiffness) of the PSC sleepers was obtained by including steel fibers and increasing the number of strands. In addition, slightly lower dynamic load factors were observed for the fiber-reinforced PSC sleepers than those without fibers, meaning that the sleepers with steel fibers were less sensitive to the strain-rate than their counterparts without fibers.

Effect of aggregate size and inclusion of polypropylene and steel fibers on explosive spalling and pore pressure in ultra-high-performance concrete (UHPC) at elevated temperature

This paper investigates the individual and combined effects of polypropylene (PP) fibers, steel fibers, and aggregate size on spalling behavior and pore pressure build-up of ultra-high-performance concrete (UHPC) exposed to elevated temperature. Simultaneous measurements of pore pressure and temperature were conducted at different depths in UHPC specimens under one-sided heating with a heating rate of 2 °C/min. Compressive, tensile, and permeability tests were performed to analyze spalling behavior. Addition of PP fibers fully prevented spalling and they are much more effective in increasing permeability than steel fibers and larger aggregates. The combined use of PP and steel fibers, and PP fibers and larger aggregates showed strong synergistic effect on increasing permeability. The higher the permeability, the lower was the maximum pore pressure measured in the samples. Two plateaus were observed from the temperature history due to vaporization of liquid water (between 115 and 125 °C inside the specimens) and release of water vapor (starting from 180 °C), respectively. The second plateau was identified as the functional temperature of PP fibers. Maximum pore pressures in spalled specimens were much lower than their tensile strengths, which could imply the contribution of hydraulic pressure in the region of moisture clog on spalling.

Flexural behavior of fiber reinforced lightweight concrete

DOI: 10.7764/RDLC.18.3.536 In this research the flexural behavior of lightweight aggregate concrete with inclusion of steel and glass fiber was investigated. Pumice aggregate was used for the replacement of normal weight aggregate to reduce the density of concrete in order to achieve lightweight concrete. The methodology consisted of comparing the results of conventional reference concrete, plain. Light Weight Aggregate Concrete (LWAC) and fiber reinforced LWAC. The beams were produced with two types of fiber reinforced LWAC, plain LWAC and conventional concrete with similar compressive strength to allow for the comparison of structural performance of the beam. The fibers were added in the LWAC to reduce the brittleness of the concrete in order to increase the energy absorption capacity and to control the faster rate of crack development. In this research steel and glass fibers were added separately in three percentages of 0.5, 1.0 and 1.5 based on the weight of concrete. The hybrid combinations of steel and glass fibers were not adopted in this study. The beam specimen with 20% LWA and 0.5% steel fiber has the increase in load carrying capacity by 28% as compared to control beam.The ductility ratio of the same beam is 85% more than that of control specimen.

Flexural performance of steel fibre reinforced concrete beams designed for moment redistribution

This paper presents an experimental study to investigate the flexural and moment redistribution performance of six full-scale two-span continuous reinforced concrete beams with and without steel fibres. The beams were reinforced with conventional bar reinforcement with longitudinal steel reinforcement ratios of between 0.0069 and 0.0138; four of the six beams also contained either 30 kg/m3 or 60 kg/m3 of steel fibres. The specimens were tested under monotonically increasing displacement-controlled loading. The primary variables within different test specimens were the arrangement of longitudinal steel bar and the dosage of steel fibres. The beams were designed for 30% of positive and negative moment redistribution with respect to the linear-elastic condition, the maximum allowed by different codes and standards. Test results showed that the inclusion of steel fibres increases the load carrying capacity of the reinforced concrete beams. Furthermore, the addition of steel fibres increased the number of cracks and decreased the crack spacing. For the steel reinforcement ratios tested, the RC-SFRC beams were found to have good ductility. It was shown that the RC-SFRC beams achieved full moment redistribution demand to form the collapse mechanism, and maintained their load carrying capacity for large plastic-hinge rotations. The guidelines of AS 5100.5-2017 were found to give a good prediction of the load carrying capacity of the tested RC-SFRC beams.