Effect of Shrinkage Reducing Agent and Steel Fiber on the Fluidity and Cracking Performance of Ultra-High Performance Concrete

Due to the low water-cement ratio of ultra-high-performance concrete(UHPC),fluidity and shrinkage cracking are key aspects determining the performance and durability of this type of concrete.In this study,the effects of different types of cementitious materials,chemical shrinkage-reducing agents(SRA)and steel fiber(SF)were assessed.Compared with M2-UHPC and M3-UHPC,M1-UHPC was found to have better fluidity and shrinkage cracking performance.Moreover,different SRA incorporation methods,dosage and different SF types and aspect ratios were implemented.The incorporation of SRA and SF led to a decrease in the fluidity of UHPC.SRA internal content of 1%(NSRA-1%),SRA external content of 1%(WSRA-1%),STS-0.22 and STE-0.7 decreased the fluidity of UHPC by 3.3%,8.3%,9.2%and 25%,respectively.However,SRA and SF improved the UHPC shrinkage cracking performance.NSRA-1%and STE-0.7 reduced the shrinkage value of UHPC by 40%and 60%,respectively,and increased the crack resistance by 338%and 175%,respectively.In addition,the addition of SF was observed to make the microstructure of UHPC more compact,and the compressive strength and flexural strength of 28 d were increased by 26.9%and 19.9%,respectively.

Effect of Steel Fiber on Concrete’s Compressive Strength

The general goal of this research is to investigate whether steel fiber has a significant “positive” or “negative” influence on concrete compressive strength, as well as the optimal steel fiber ratio that delivers best result. Manually, cement, fine aggregates, coarse aggregates, steel fibers, and water were mixed together properly. A slump test was carried on the mixed concrete. After determining the workability, the mixed concrete was poured into cubes dimension 150 mm × 150 mm × 150 mm and left for 24 hours. After 24 hours, the samples were removed from the mold and placed in a water tank to cure for 7 to 28 days. The cube was tested for compressive and flexural strength in a universal testing machine after the samples had cured for the required 7 - 28 days. This study focuses on how to obtain high strength concrete using with steel fiber in the Conventional mix ratio to enhance concrete strength. Concrete reinforcement using steel fibers alters the characteristics of the concrete, allowing it to withstand fracture and hence improve its mechanical qualities. This study reports on an experimental study that reveals the effect of steel fiber on concrete compressive strength and the optimal steel fiber ratio that produces the best results. Steel fiber reinforcing improved the compressive strength of concrete. The average compressive strength of normal M25 concrete with 0% steel fibers and curing ages of 7 and 28 days was determined to be 22.97 N/mm2 and 25.78 N/mm2, respectively. The steel fibers are then added in various concentrations, such as 1%, 2%, and 3%, with aspect ratios of 70. The compressive strength of concrete with 1%, 2%, and 3% steel fiber with an aspect ratio of 70 was examined at 7 days and found to be 23.96, 24.80, and 26.14 N/mm2 correspondingly.

Mechanical Properties of Layered Steel Fiber and Hybrid Fiber Reinforced Concrete

To explore a new structure form of fiber reinforced concrete, namely, the layered steel fiber and layered hybrid fiber reinforced concrete （LSFRC and LHFRC）, the mechanical properties of LSFRC and LHFRC, such as compressive strength, tensile strength, flexural strength, fatigue and durability were focused on. The experimental results show that LSFRC and LHFRC can improve the flexural strength of concrete by 20%-50%. In the aspect of improving the flexural strength of concrete, adulterant rate has more obvious effect than length/diameter ratio. Double logarithmic fatigue equation considered liveability was founded. The impermeability of LHFRC is superior to LSFRC and plain concrete （C）. However, the porosity of LHFRC is lower than LSFRC and C. The shrinkage of LHFRC at every age is obviously lower than C. The antifreeze durability of LHFRC is also better than C.

Effect of Acid Rain Erosion on Steel Fiber Reinforced Concrete

Acid rain can deteriorate the performance of reinforced concrete structure.Combined with the characteristics of acid rain in China,the properties of steel fiber reinforced concrete subjected to acid rain were studied.The effects of steel fiber content and pH value of acid rain on the mass loss,erosion depth,neutralization depth,and splitting tensile strength of tested concrete were investigated.The mercury intrusion pore（MIP） test was used to analyze the influence of steel fiber on the acid rain resistance of concrete matrix.The results show that the corrosion of steel fiber reinforced concrete subjected to acid rain results from the combined effect of H^＋ and SO4^2- in the acid rain,and steel fiber can improve the acid rain resistance of the tested concrete by improving the pore structure and enhancing the tie effect of the concrete matrix.The experiment further indicates that the optimum content of steel fiber is 1.5%compared to the various mixing proportion in this tests.The tested concrete mass loss and splitting tensile strength decrease followed by increasing as a function of corrosion time when the pH value of the simulation solution is 3 or 4,while they decrease continuously in the simulation solution at pH 2.Thanks to the tie effect of steel fiber,the spalling of concrete matrix is significantly improved,and the erosion depth and neutralization depth are less than those of conventional concrete.

Charactersitics of Stress-strain Curve of High Strength Steel Fiber Reinforced Concrete under Uniaxial Tension

A whole of 110 specimens divided into 22 groups were tested with varying the volume fraction of steel fibers and the matrix strength of these specimens. The stress-strain behaviors of four types of steel fiber reinforced concrete （SFRC） under uniaxial tension were studied experimentally. When the matrix strength and the fiber content increase, the tensile stress and tensile strain vary differently according to the fiber type. The mechanisms of reinforcing effect for different types of fiber were analyzed and the stress-strain curves of the specimens were plotted. Some experimental factors for stress or strain of SFRC were given. A tensile toughness modulus Re0.5 was introduced to evaluate the toughness characters of SFRC under uniaxial tension. Moreover, the formula of the tensile stress-strain curve of SFRC was regressed. The theoretical curve and the experimental ones fit well, which can be used for references in construction.

Mesoscopic Modeling Approach and Application for Steel Fiber Reinforced Concrete under Dynamic Loading:A Review

Steel fiber reinforced concrete(SFRC)has drawn extensive attention in recent years for its superior mechanical response to dynamic and impact loadings.Based on the existing test results,the highstrength steel fibers embedded in a concrete matrix usually play a strong bridging effect to enhance the bonding force between fiber and the matrix,and directly contribute to the improvement of the post-cracking behavior and residual strength of SFRC.To gain a better understanding of the action behavior of steel fibers in matrix and further capture the failure mechanism of SFRC under dynamic loads,the mesoscopic modeling approach that assumes SFRC to be composed of different mesoscale phases(i.e.,steel fibers,coarse aggregates,mortar matrix,and interfacial transition zone(ITZ))has been widely employed to simulate the dynamic responses of SFRC material and structural members.This paper presents a comprehensive review of the state-of-the-art mesoscopic models and simulations for SFRC under dynamic loading.Generation approaches for the SFRC mesoscale model in the simulation works,including steel fiber,coarse aggregate,and the ITZ between them,are reviewed and compared systematically.The material models for different phases and the interaction relationship between fiber and concrete matrix are summarized comprehensively.Additionally,some example applications for SFRC under dynamic loads(i.e.,compression,tension,and contact blast)simulated using the general mesoscale models are given.Finally,some critical analysis on the current shortcomings of the mesoscale modeling of SFRC is highlighted,which is of great significance for the future investigation and development of SFRC.

Structural Behavior of Continuous Prestressed Steel Fiber Reinforced High Strength Concrete Beam

The flexural behaviors of continuous fully and partially prestressed steel fiber reinforced high strength concrete beams are studied by experiment and nonlinear finite element analysis. Three levels of partial prestress ratio （PPR） are considered, and three pairs of two-span continuous beams with box sections varying in size are designed. The major parameters involved in the study include the PPR and the fiber location. It is concluded that the prestressed high strength concrete beam exhibits satisfactory ductility; the influences of steel fiber on the crack behaviors for partially prestressed beams are not as obvious as those for fully prestressed ones; steel fibers can improve the structural stiffness after cracking for fully prestressed high strength concrete beams; the moment redistribution from mid-span to intermediate support in the first stage should be mainly considered in practical design.

Complete splitting process of steel fiber reinforced concrete at intermediate strain rate

The complete splitting process of steel fiber reinforced concrete （SFRC） at intermediate strain rate was studied by experiment. The basic information of a self-developed SFRC dynamic test system matching with lnstron 1342 materials testing machine was given, and the experiment principle and the loading mode of cubic split specimen were introduced. During the experiment, 30 cubes of 150 mm×150 mm×150 mm and 36 cubes of 100 mm×100 mm×100 mm, designed and prepared according to C20 class SFRC with different volume fractions of steel fiber （0, 1%, 2%, 3%, 4%） were tested and analyzed. At the same time, the size effect of SFRC at intermediate strain rate was investigated. The experimental study indicates that SFRC size effect is not influenced by the loading speed or strain rate. When the steel fiber content increases from 0 to 4%, the splitting strength of SFRC increases from 100% to 261%, i.e. increasing by 161% compared with that of the common concrete. The loading rate increases from 1.33 kN/s to 80.00 kN/s, and the splitting tensile strength increases by 43.55%.

Properties of High Strength Steel Fiber Reinforced Concrete under Compression

This paper mainly discusses the properties of high strength steel fiber reinforced concrete under compression. Steel fibers with volume content of 1% do not display significant effect on the strain at peak stress and the area of the ascending portion of

Nonlinear Finite Element Analysis of Steel Fiber Reinforced Concrete Deep Beams

By the nonlinear finite element analysis （FEA） method, the mechanical properties of the steel fiber reinforced concrete （SFRC） deep beams were discussed in terms of the crack load and ultimate bearing capacity. In the simulation process, the ANSYS parametric design language （APDL） was used to set up the finite element model; the model of bond stress-slip relationship between steel bar and concrete was established. The nonlinear FEA results and test results demonstrated that the steel fiber can not only significantly improve the cracking load and ultimate bearing capacity of the concrete but also repress the development of the cracks. Meanwhile, good agreement was found between the experimental data and FEA results, if the unit type, the parameter model and the failure criterion are selected reasonably.

Fatigue tests of composite beam by steel fiber reinforced self-stressing concrete in the hogging bending

Through the experiments of 7 T-section composite beams, steel fiber reinforced self-stressing concrete （SFRSC） as the composite beam in the composite layer was studied under the hogging bending. The tests simulated composite layer tensile strain under the hogging bending of inverted loading composite beams, giving the relationship under the different fatigue stress ratios between fatigue cycles and steel bar’s stress range, crack width, stiffness loss and damage, etc., in composite layer. This article established fatigue life equation, and analyzed SFRSC reinforced mechanism to crack width and stiffness loss. The results show that SFRSC as the composite beam concrete has excellent properties of crack resistance and tensile, can reinforce the fatigue crack width and stiffness loss of composite beams, and improve the durability and in normal use of composite beams in the hogging bending zone.

The Influence of Steel and Basalt Fibers on the Shear and Flexural Capacity of Reinforced Concrete Beams

To improve the shear and flexural capacity of flexural members, the steel and basalt fibers were used in model beams tested under flexure. Three series of single span free supported model beams were prepared from SFRC （steel fiber reinforced concrete） with longitudinal steel reinforcement （steel ratio of 1.2 %） and varied spacing of steel stirrups and they were tested till failure. Another three series of BFRC （basalt fiber reinforced concrete） double-span model beams with a span of 2 mm~ 1,000 mm and cross section 180 mm ~ 80 mm were tested. During the tests till to the failure the beam reactions, vertical deflections and horizontal strains in concrete were registered, to clarify the range of redistribution of bending moments and shear forces over the span of the beams. Almost all the tested model beams failed in shear, showing visible influence of steel and basalt fibers on the shear capacity of the tested beams. The tests results confirmed that steel and basalt fibers in reinforced concrete beams can partially replace （in certain cases） the traditional steel stirrups calculated for shear.

Performance of Steel-fiber Reinforced Concrete Exposed to High Temperature

Effects of high temperature on the compressive and splitting strength of the steel-fiber reinforced concrete (SFRC) with different content of steel-fiber were investigated and its mechanism was simply analyzed.Results indicate that the compressive and splitting strength of SFRC decrease slowly within 400 ℃ and they decay a little faster when over 400 ℃.The residual compressive and splitting strength rate of SFRC (2% fiber) increase about 27.6% and 9.3% of that of the control concrete without steel-fiber,respectively.The finite element software ANSYS was adopted to analyze the temperature field and stress field of the steel-fiber reinforced concrete at 400 ℃.The simulation results can further explain the effects of fiber content on the thermal field and stress field in SFRC and forecast the crack tendency of SFRC during heating process.

Toughness of Polymer Modified Steel Fiber Reinforced Concrete

An experimental investigation is carried out to study the toughness of polymer modified steel fiber reinforced concrete. Volume fraction of steel fibers is varied from 0% to 7% at the interval of 1% by weight of cement. 15% SBR latex polymer was used by weight of cement. Cubes of size 150 × 150 × 150 mm for compressive strength, prism specimens of size 150 mm × 150 mm × 700 mm for flexure strength and, specimen of size 150 × 150 × 150 mm with 16 mm diameter tor steel bar of length 650 mm embedded in concrete cube at the center for bond test were prepared. Various specimens were tested after 28 days of curing. Area under curve (toughness) is measured and mentioned in this work.

Experimental and Numerical Analysis of High-Strength Concrete Beams Including Steel Fibers and Large-Particle Recycled Coarse Aggregates

In order to study the performances of high-strength concrete beams including steel fibers and large-particle recycled aggregates,four different beams have been designed,tested experimentally and simulated numerically.As varying parameters,the replacement rates of recycled coarse aggregates and CFRP(carbon fiber reinforced polymer)sheets have been considered.The failure mode of these beams,related load deflection curves,stirrup strain and shear capacity have been determined through monotonic loading tests.The simulations have been conducted using the ABAQUS finite element software.The results show that the shear failure mode of recycled concrete beams is similar to that of ordinary concrete beams.The shear carrying capacity of high-strength concrete beams including steel fibers and large-particle recycled coarse aggregates grows with an increase in the replacement rate of recycled coarse aggregates.Reinforcement with CFRP sheets can significantly improve the beam’s shear carrying capacity and overall resistance to deformation.

STUDIES ON STRESS TRANSFERENCE MECHANISM OF STEEL FIBRE REINFORCED CONCRETE

The stress transfer mechanism of steel fibre reinforced concrete is studied. The solutions for the stress and displacement were regarded as the superposition of ' the elementary solutions' and ' the improved solutions'. The elementary solutions were found by using two-dimensional elastic theory and the improved solutions were found by using the Love displacement function method. The calculated results indicate that the solutions possess good convergence. By comparing the three-dimensional solutions with the shear-lag solutions, evident difference may be found.

Effects of Steel Fibers and Iron Filings on Thermal and Mechanical Properties of Concrete for Energy Storage Application

An experimental study on the thermal properties of iron filings and steel-fiber-reinforced concrete for solar/thermal energy storage application is presented in this report. It takes into account the results of measurements of thermal conductivity, thermal resistivity, thermal diffusivity and the results of compressive strength, density as well as energy storage capacity calculated from the knowledge of the above measured parameters. The experimental testing method is described as well: based upon the linear heat source theory, it requires the use of a special probe to be inserted into the sample. The experimentation was forwarded to test concrete aggregate mixtures with three different sizes and same quantity of steel fibers;two different quantities of iron filings and one plain concrete. The measurements were carried out from the pouring time of cubic samples and were ended up when hardened conditions were achieved. The results indicate that the steel fibers and iron filings have influence on the thermal and mechanical properties of the concretes tested, thus the iron filings and steel fibers reinforced concrete is suitable for better solar/thermal energy storage due to an increase in storage capacity over plain concrete.

Punching and Local Damages of Fiber and FRP Reinforced Concrete under Low-Velocity Impact Load

In recent years, the development and application of high performance fiber reinforced concrete or cementitious composites are increasing due to their high ductility and energy absorption characteristics. However, it is difficult to obtain the required properties of the FRCC by simply adding fiber to the concrete matrix. Many researchers are paying attention to fiber reinforced polymers (FRP) for the reinforcement of construction structures because of their significant advantages over high strain rates. However, the actual FRP products are skill-dependent, and the quality may not be uniform. Therefore, in this study, two-way punching tests were carried out to evaluate the performances of FRP strengthened and steel and polyvinyl alcohol (PVA) fiber reinforced concrete specimens for impact and static loads. The FRP reinforced normal concrete (NC), steel fiber reinforced concrete (SFRC), and PVA FRCC specimens showed twice the amount of enhanced dissipated energy (total energy) under impact loadings than the non-retrofitted specimens. In the low-velocity impact test of the two-way NC specimens strengthened by FRPs, the total dissipated energy increased by 4 to 5 times greater than the plain NC series. For the two-way specimens, the total energy increased by 217% between the non-retrofitted SFRC and NC specimens. The total dissipated energy of the CFRP retrofitted SFRC was twice greater than that of the plain SFRC series. The PVA FRCC specimens showed 4 times greater dissipated energy than for the energy of the plain NC specimens. For the penetration of two-way specimens with fibers, the Hughes formula considering the tensile strength of concrete was a better predictor than other empirical formulae.

Flexural fatigue strength of steel fibrous concrete containing mixed steel fibres

This paper reports investigation conducted to study the fatigue performance of steel fibre reinforced concrete (SFRC) containing fibres of mixed aspect ratio. An extensive experimental program was conducted in which 90 flexural fatigue tests were carried out at different stress levels on size 500 mm×100 mm×100 mm SFRC specimens respectively containing 1.0%, 1.5% and 2.0% volume fraction of fibres. About 36 static flexural tests were also conducted to determine the static flexural strength prior to fatigue testing. Each volume fraction of fibres incorporated corrugated mixed steel fibres of size 0.6 mm×2.0 mm×25 mm and 0.6 mm×2.0 mm×50 mm in ratio 50:50 by weight. The results are presented both as S-N relationships, with the maximum fatigue stress expressed as a percentage of the strength under static loading, and as relationships between actually applied fatigue stress and number of loading cycles to failure. Two-million-cycle fatigue strengths of SFRC containing different volume fractions of mixed fibres were obtained and compared with plain concrete.

Axial Bearing Capacity of Short FRP Confined Concrete-filled Steel Tubular Columns

The bearing capacity of FRP confined concrete-filled steel tubular （FRP-CFST） columns under axial compression was investigated. This new type of composite column is a concrete-filled steel tube （CFST） confined with fiber-reinforced polymer （FRP） wraps. Totally 11 short column specimens were tested to failure under axial compression. The influences of the type and quantity of FRP, the thickness of steel tube and the concrete strength were studied. It was found that the bearing capacity of short FRP-CFST column was much higher than that of comparable CFST column. Furthermore, the formulas for calculating the bearing capacity of the FRP-CFST columns are proposed. The analytical calculated results agree well with the experimental results.