Influence Of Steel Fibers Research Articles

MODIFICATION OF PROPERTIES OF STRUCTURAL LIGHTWEIGHT CONCRETE WITH STEEL FIBRES / LENGVOJO BETONO SAVYBIŲ MODIFIKAVIMAS PLIENINĖMIS FIBROMIS

Structural lightweight aggregate concrete (SLWAC) is an alternative building material to normal-weight one, due to its ability to reach a relatively high compressive strength at still significantly lower density. Nevertheless, the application of lightweight aggregate instead of normal-weight one to concrete must result in deterioration of some characteristics of the composite. One of the methods of improving SLWAC properties is incorporation of fibers into concrete. This paper focuses on the influence of steel fibres on modification of properties of structural lightweight concrete with sintered fly ash aggregate. Two different concrete mixtures, producing various levels of matured composite density and compressive strength, were modified with three dosages of fibers: 30, 45 and 60 kg/m3. The applied amounts did not result in significant deterioration of the rheological parameters of concrete mixtures. Despite relatively low volume content of fibres, a considerable increase of flexural and tensile splitting strength was observed. Fibres also improved concrete shrinkage as well as post-peak deformability in uni-axial compression. The effect of steel addition on compressive strength proved to be dependent on specimen type. Nevertheless, it was not as crucial as in the case of the above characteristics. However, the modulus of elasticity of SLWAC was not affected by fibre addition. Santrauka Konstrukcinis su lengvaisiais užpildais betonas (SLWAC) yra normalaus svorio statybinių medžiagų alternatyva, turinti mažesnį tankį ir gebėjimą pasiekti gana didelį gniuždomąjį stiprį. Nepaisant to, lengvieji užpildai, naudojami vietoj normalaus svorio užpildų, realiai gali pabloginti kai kurias kompozito savybes. Vienas iš lengvojo betono SLWAC savybių tobulinimo būdų yra plieninių fibrų įterpimas į betono sudėtį. Šiame darbe aptariamas plieninių fibrų poveikis konstrukcinio lengvojo betono su lakiaisiais pelenais savybėms. Tikslui pasiekti buvo parinktos pagal tankį ir gniuždomąjį stiprį dvi skirtingos betono sudėtys su skirtingais (30, 45 ir 60 kg/m3) plieninių fibrų tankiais. Paruošti bandiniai buvo naudoti gniuždomajam stipriui ir kitoms savybėms nustatyti. Tyrimų rezultatai parodė, kad plieninių fibrų priedas nepablogino reologinių betono mišinio rodiklių. Nepaisant palyginti mažo fibrų kiekio, labai padidėjo bandinių lenkiamasis ir tempiamasis stipris. Fibros taip pat pagerino deformacines betono savybes. Gauto kompozito gniuždomasis stipris iš dalies priklausė nuo naudojamų plieninių fibrų charakteristikų. Tačiau plieninių fibrų priedas nepakeitė SLWAC tamprumo modulio.

Study of the influence of microstructural parameters on the ultrasonic velocity in steel–fiber-reinforced cementitious materials

In this paper, the influence of steel fibers on the ultrasonic velocity of steel–fiber-reinforced cementitious materials was studied using a micromechanical model. To this end, a three-phase micromechanical model was extended and generalized to multiphase materials. Firstly, such a model was used to predict the influence of the geometry and volume fraction of steel inclusions on the ultrasonic velocity of steel–fiber-reinforced cementitious materials. Experimental validation was carried out on steel-reinforced and non-reinforced mortar specimens through destructive and non-destructive testing by ultrasound. Comparisons between predicted and measured ultrasonic velocity were in good agreement, with errors less than 1.5%. Moreover, the model was also validated on experimental data obtained from steel–fiber-reinforced concrete specimens [Yazıcı et al. Constr Build Mater 2007;21:1250–3].

Shear Performance of Steel Fibrous Concrete Beams

The influence of steel fibres in shear reinforced concrete beams subjected to monotonic and cyclic loading is experimentally investigated. Seven steel-fibre-reinforced concrete beams and conventionally reinforced beams without steel fibres, used as control specimens, were constructed for the purposes of this study. Hook-ended steel fibres with two different volume fractions (0.5% and 0.75%) have been used in the fibrous concrete beams of the test program as shear reinforcement. Two beams were tested in monotonically increasing four-pointed loading up to total failure of the specimen, and five beams were tested under cyclic deformations. The dimensions and the flexural reinforcement of all the beams examined were the same. Hook-ended steel fibres with an aspect ratio equal to 75 were used. The loading was imposed consistently in low rate, and the values of the load and the corresponding crack widths and deformation at the mid-span of the beams were reported. The conclusions drawn from the experimental results of the tested beams imply that the steel-fibre-reinforced beams exhibited improved shear performance with high shear capacities, enhanced energy dissipation capabilities and ameliorated crack patterns.

Reinforcing Admixtures and their Effectiveness Experiments for Strength and Damping of Polymer Modified Concrete

The relationships between the mechanical properties of modified concrete and the composition of latex blend were studied. Influence of steel fiber and polypropylene fiber on performance of modified concrete was analyzed on that basis. The results indicate that the contradiction between the strength and the damping property of normal concrete will be relieved to some degree by controlling the proportion of latex blend. The adding of fiber can modify the damping property of concrete, while it has a little effects on the compressive strength and elastic modulus of concrete.

Experimental Investigation on the Influence of Steel Fiber on the Compressive and Tensile Strength of Recycled Aggregate Concrete

Experimental Investigation on the Influence of Steel Fiber on the Compressive and Tensile Strength of Recycled Aggregate Concrete

Influence of steel fibers on the development of alkali-aggregate reaction

This work presents the results of an experimental research concerning the use of fibers in mortar specimens subjected to alkali-aggregate reaction (AAR). Two types of steel fibers (0.16 mm diameter and 6.0 mm length, and 0.20 mm diameter and 13.0 mm length) were used with fiber volume contents of 1% and 2%. Besides the expansion accelerated tests, compressive tests and flexural tests have also been carried out to display the main mechanical characteristics of the fiber-reinforced mortars after being subjected to AAR. Moreover, the microstructure of the specimens was analyzed by scanning electron microscopy and energy dispersive X-ray. The results shown that the addition of steel fibers reduced the expansion due to AAR for the experimental conditions studied in this paper. The most expressive benefit corresponded to the addition of 13.0 mm fibers in the mixture containing 2% fiber content. This fiber volume content also corresponded to the maximum increment in the mechanical properties compared to the reference mortar, mainly for the post-cracking strength and for the toughness in bending. It was observed that the fibers have a beneficial effect on the material, without compromising its main mechanical properties.

Influence of steel fibres on strength and ductility of normal and lightweight high strength concrete

This paper presents the results of a series of experiments conducted to investigate the effectiveness of fibre inclusion in the improvement of mechanical performance of concrete with regard to concrete type and specimen size. Lightweight aggregate concrete and limestone aggregate concrete with and without steel fibres were used in the study. The compressive strength of the concrete mixes varied between 90 and 115 MPa and the fibre content was 1% by volume. Splitting tests on prisms and three-point bending test on notched beams were carried out on specimens of varying sizes to examine the size effect on splitting strength, flexural strength and toughness. The experimental findings indicate that the low volume of fibre has little effect on compressive strength but improve remarkably splitting tensile strength, flexural strength and toughness. The increase in splitting tensile strength, flexural strength and toughness index for lightweight concrete seems much higher than that of normal aggregate concrete. The size effect on prism splitting tensile strength is not significant beyond a critical (transition) size. There are apparent size effects on flexural strength and toughness index. As the specimen size increases, splitting and flexural strengths appear to decrease, and fracture behaviour tends to be more brittle.

Parameter-study on the influence of steel fibers and coarse aggregate content on the fresh properties of self-compacting concrete

Self-compacting concrete (SCC) offers several economic and technical benefits; the use of steel fibers extends its possibilities. Steel fibers bridge cracks, retard their propagation, and improve several characteristics and properties of the concrete. Fibers are known to significantly affect the workability of concrete. Therefore, an investigation was performed to compare the properties of plain SCC and SCC reinforced with steel fibers. Two mixtures of SCC with different aggregate contents were used as reference. Each of the concretes was tested with four types of steel fibers at different contents in order to answer the question to what extent the workability of SCC is influenced. The slump flow, a fiber funnel and the J-ring test were used to evaluate the material characteristics of the fresh concrete. This paper discusses the suitability of the applied test methods and the effect of the coarse aggregate content, the content and type of steel fibers on the workability of SCC.

Mechanical properties of steel fibre reinforced lightweight concrete with pumice stone or expanded clay aggregates

This paper presents basic information on the mechanical properties of steel fibre-reinforced light-weight concrete, manufactured using pumice stone or expanded clay aggregates. Results are presented for standard compressive tests and indirect tensile tests (splitting tests on cylinder specimens and flexure tests on prismatic beams using a three-point loading arrangement) under monotonically increasing or cyclically varying loads. The influence of steel fibres and aggregate types on modulus of elasticity, compressive and tensile strength and post-peak behaviour is evaluated. Test results show that compressive strength does not change for pumice stone aggregates, while an increase is observed for expanded clay; tensile strength and fracture toughness are significantly improved for both pumice stone and expanded clay. The results also show that with both expanded clay and pumice stone lightweight aggregates a suitable content of fibres allows one to obtain performances comparable with those expected from normal weight concrete, the important advantage of lower structural weight being maintained.

Influence of Steel Fibers in Fatigue Resistance of Concrete in Direct Compression

The influence of steel fibers on the fatigue resistance of concrete in direct compression, based on experiments, and an assessment of it through neural network modeling have been presented. Both straight and hooked fibers were incorporated in the concrete. The volume fraction was 1% for straight fibers, and both 1 and 2% for hooked fibers. The applied stress levels ranged from 0.55 to 0.95 of the (static) compressive strength. The number of cycles was up to 1,000,000. The neural network was based on a feedforward back-propagation algorithm. Steel fibers enhanced the fatigue strength, distinctly, at all stress levels. Hooked fibers improved the fatigue strength more than the straight ones; the larger the fiber content, the greater was the enhancement of fatigue strength. Strains measured just before failure showed that fiber reinforced concrete could undergo larger strains before failure than plain concrete. Based on strains measured throughout the fatigue cycling, stages of dilation and failure have been apparent. The adopted neural network modeled both the S-N (strength-number of cycles) and strain-N behaviors extremely well. It was considered possible to extrapolate the S-N behavior beyond 1,000,000 cycles in order to estimate the fatigue strength in the super-high cycle ranges of 10 7 and more.

Long-term deflection of high-strength fiber reinforced concrete beams

The paper presents an experimental and theoretical study on the influence of steel fibers and longitudinal tension and compression reinforcements on immediate and long-term deflections of high-strength concrete beams of 85 MPa (12,300 psi) compressive, strength. Test results of eighteen beams subjected to sustained load for 180 days show that the deflection behavior depends on the longitudinal tension and compression reinforcement ratios and fiber content; excessive amount of compression reinforcement and fibers may have an unfavorable effect on the long-term deflections. The beams having the ACI Code\'s minimum longitudinal tension reinforcement showed much higher time-dependent deflection to immediate deflection ratio, when compared with that of the beams having about 50 percent of the balanced tension reinforcement. The results of theoretical analysis of tested beams and those of a parametric study show that the influence of steel fibers in increasing the moment of inertia of cracked transformed sections is most pronounced in beams having small amount of longitudinal tension reinforcement.

Mechanical properties of steel fiber-reinforced, high-strength, lightweight concrete

This paper presents basic information on the mechanical properties of steel fiber-reinforced, high-strength, lightweight concrete with compressive and flexural strengths up to 85.4 MPa and 11.8 MPa, respectively. The influence of steel fiber on modulus of elasticity and Poisson's ratio of concrete are investigated, and flexural fracture toughness is calculated. Test results show that the effect of fiber volume fraction ( V f ) and aspect ratio ( l f d f ) on flexural strength and fracture toughness is extremely prominent, compressive strength is only slightly improved, and tensile/compressive strength ratio is obviously enhanced. It is observed that the flexural deflection corresponded to ultimate load increased with the increase of V f and l f d f , and due to fiber arresting cracking, the shape of the descending branch of load-deflection tends towards gently.

Influence of Steel Fibers on Tension Stiffening

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Influence of Steel Fibers and Compression Reinforcement on Deflection of High-Strength Concrete Beams

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Influence of Steel Fibers on Design Stress-Strain Curve for High-Strength Concrete

To quantify the effect of steel fibers on the stress-strain curve for high-strength concrete under compression, results of compression tests performed in the Magnel Laboratory, were used. Several series of concrete cylinders with and without steel fibers were loaded in axial compression. The available stress-strain curves for design are discussed and the way in which the parabola-rectangle diagram used in most European countries is related to the real diagram, which shows a softening branch, is investigated. A new proposal for the realistic stress-strain curve for high-strength fiber concrete is presented and a proposal to take into account the effect of steel fibers on the design stress-strain curve for the design of high-strength concrete under compression is given. In addition, a comparison is made between high-strength fiber concrete and confined high-strength concrete.

Influence of Steel fibers on the Shear Resistance of Lightweight Concrete I-Beams

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Influence of Steel Fibers on Strain-Softening of High-Strength Concrete

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Shrinkage of steel fibre reinforced cement composites

The paper presents results of an experimental investigation on the influence of steel fibres on the free shrinkage of cement-based matrices. Shrinkage tests were carried out on cement paste, mortar and two types of concrete mixes for a period of up to 520 days. Melt extract, crimped and hooked steel fibres were used for reinforcement at volume fractions ranging between 1 and 3%. The results indicate that fibres restrain the shrinkage of the various cement matrices to a significant extent, resulting in reductions of up to 40%. Crimped fibres are the most efficient in providing shrinkage restraint. The paper also presents a theoretical expression and an empirical expression which can be used to predict shrinkage strains of steel fibre reinforced cement matrices. The analysis requires a knowledge of the values of coefficient of friction, μ, at the fibre-matrix interface, which are also derived in this paper. The μ values for steel fibres in normal concrete, mortar and cement paste range between 0.07 and 0.12.

Influence of steel fibre and stirrup reinforcement on the properties of concrete in compression members

The paper presents the results of an experimental investigation into the combined influence of stirrup and steel fibre reinforcement on the strength and deformation characteristics of conventionally reinforced concrete compression members. Columns, 150 × 150 × 750 mm, were reinforced longitudinally and stirrup reinforcement was provided at spacings of 125, 187 and 375 mm, the former spacing being according to CP 110. Melt extract steel fibres were used for reinforcement at volumes ranging between 0 and 3%. The results indicate that a combination of small stirrup spacing and high fibre volume leads to a marked increase in the ductility of the compression members. This is indicated by an increased energy absorption capacity of the column specimens and high lateral strain capacity and Poisson's ratio of the concrete phase within the columns. In addition, the crack initiation and critical stress levels of the concrete phase decrease with increasing fibre volume indicating thereby a greater degree of inelasticity which leads to a more ductile behaviour. The strength of the compression members is unaffected by either steel fibre volume or stirrup spacing.

FIBRE REINFORCED CONCRETE IN PURE TORSION AND IN COMBINED BENDING AND TORSION.

The paper studies the influence of steel fibres on the torsional and flexural rigidity of concrete beams. Ultimate load tests were carried out on square beams subjected to pure torsion and on rectangular beams subjected to combined bending and torsion. Steel fibres with a length/diameter ratio of 150 were used and the increases in torsional capacity and tensile strength were studied. Fibre reinforced beams were found to have a considerable post-ultimate reserve and pronounced ductility in torsion and in combined bending and torsion. Flexural loads did not cause any reduction in torsional capacity. Satisfactory predictions of ultimate torque were obtained by using sand-heap analogy and a reduced value for the tensile strength of concrete. (a) (TRRL)