Steel Fiber Ratio Research Articles

Steel fiber reinforced concrete beams with predetermined failure surface and no stirrups

This paper treats an experimental study of shear problems in steel fiber reinforced concrete beams without shear reinforcement, where a specific groove in the shear span is used to specify the location of diagonal cracks, aiming to reduce the arch effect, controlling the critical crack inclination at 30°, and evaluating the assertiveness of the normative shear strength predictions. The experimental program includes four (4) beams, varying the steel fiber ratio. The results showed that the mechanism was satisfactorily induced shear failure, as expected. Also, it was observed that the ratio av/d did not influence the proposed model significantly, such behavior was expected because the shear cracks observed in the beams were more pronounced after distance av/4, making the arching action and dowel action less effective in the ultimate shear strength value. The proposed model excelled in the accuracy of the normative predictions, with a coefficient of variability between 4 and 8 %, probably to eliminate any arch effect for the ratio av/d = 1.86. However, a simplified calculation model based on the fiber residual stress distribution along the considered inclined section was proposed, and it was noted that the proposal presented better results, with an average value of 1.0 and a coefficient of variation (CoV) of only 3 %. It also showed a mean of 1.02 and a CoV of 8 % compared to the experimental results from the literature. Thus, the proposed predetermined shear failure surface and the calculation model are viable alternatives to evaluate estimates for shear resistance even with shear reinforcement or steel fibers.

Mechanical behavior of steel fiber reinforced recycled aggregate concrete under dynamic triaxial compression

An experimental study of cylindrical steel fiber reinforced recycled aggregate concrete (SFRAC) specimens subjected to hydrostatic pressure and dynamic axial loading in a triaxial cell was performed. A confining stress range of 0–40 MPa and strain rate from 10−5 s−1 to 10−2 s−1 were employed using a servo-hydraulic testing system. In addition, two other control variables – volume fraction of steel fiber and replacement ratio of recycled coarse aggregate were also considered. A series of complete stress-strain curves were obtained, and the results were discussed in the aspects of the failure modes, peak triaxial strength, toughness, octahedral stress and failure criterion. The results indicated that an increase in the confining pressure resulted in a change in the failure modes, a significant increase in the peak strength and ductility. In particular, with an increase in confining pressure, the enhancement of strain rate on the peak strength decreased, indicating that there was a coupling effect between these two. The steel fibers had little influence on the failure modes of SFRAC, but significantly improved its ductility and toughness. The addition of recycled coarse aggregates markedly reduced the peak strength and the reduction reached nearly 20%, which was larger than other reports in uniaxial and true triaxial loading. Finally, a failure criterion for SFRAC specimens subjected to dynamic loading was used for validating the experimental results.

Experimental investigation on the shear performance of UHPC large-keyed epoxy joints subjected to direct shear loading

The joints between precast segments in prefabricated ultra-high performance concrete (UHPC) segmental bridges are of great concern since reinforcements and fibers are disconnected at the interface of joints. To investigate the shear performance of UHPC large-keyed epoxy joints, a series of direct shear specimens were tested to consider three parameters, that is, the confining stress, the depth-height ratio of the shear key, and the steel fiber volume ratio. The cracking patterns, failure modes, and shear capacities of all the UHPC epoxy joints were systematically analyzed to explore the effect of the three parameters. Experimental results showed that the three parameters have significant impacts on the direct shear performance of UHPC large-keyed epoxy joints. Specimens with a depth-height ratio of 0.35 are more beneficial to the shear strength than those of the specimens of 0.2 and 0.5. This phenomenon is quite significant in the situations of low confining stress states. The increase of the confining stress and volume ratio of steel fiber substantially improved the shear strength and the ductility of UHPC epoxy joints, especially when the volume ratio of steel fiber increases from 1% to 2%. The initial crack occurred at 42% ∼ 84% of the ultimate shear load, and the initial stiffness and the residual strength increased greatly with the increase of the confining stress. In addition, a modified theoretical model was proposed to predict the shear strength of the UHPC large-keyed epoxy joint, which exhibited a relatively good agreement with the test data.

Shear Behavior of Reinforced Fiber Concrete Beam Using Steel Lathe Scrap Waste and End Hooked Steel Fiber

Shear behavior of reinforced concrete beams using steel lathe scrap waste and end hooked steel fibers as fully or partially web shear reinforcement replacement was studied. Steel lathe scrap waste is generated from industrial steel waste and can be used as recycled fibers offering additional advantages towards environmental pollution reduction. To investigate their effect of reinforced concrete beam under shear behavior, ten reinforced concrete beam specimens with 1200 mm long, 200 mm wide, and 300 mm high were tested under quasi-static loading (two-point loading). The studied parameters in this investigation were types of fibers such as steel lathe waste fiber and traditional hooked steel fiber ratio and the web shear reinforcement ratio are zero% and 50%. Results observed were initial and post-cracking stiffness, maximum capacity load, vertical displacements, modes of failures, and the ductility of the specimens. It was concluded that using of steel lathe scrap waste and hooked steel fibers in concrete are advantageous, they changed the mode of failure of the beam from a brittle to a ductile mode of failure due to the ductility of steel used, whether traditional steel fiber or steel lathe waste fiber. The optimum ratio of the steel lathe scrap waste was found equal 0.5% while the optimum ratio of traditional hooked steel fiber is 1% as fractional volume.

Experimental investigation on ultra high-performance concrete beams without shear reinforcement

Seven ultra high-performance concrete (UHPC) beams without shear reinforcement are tested in this work to examine their structural behavior as shear failure is a major concern in such members. Coarse aggregate was not used in two of the beams while the other five are made with coarse aggregate as 50% replacement of fine sand. Three longitudinal steel reinforcement ratios (1.14%, 1.64% and 2.46%) and three steel fiber ratios (0, 1% and 2%) are used. Results show that UHPC beams with coarse aggregate show higher ultimate loads (4.7% − 11.5%) than UHPC beams without coarse aggregate and incorporating 1% and 2% steel fiber raises ultimate loads by 60% and 131%, respectively for beams with coarse aggregate. Also, using 2% steel fiber changes failure mode from brittle shear failure by diagonal crack in beams of 0 or 1% steel fiber to ductile flexural failure by yielding of longitudinal reinforcement. Higher stiffness and toughness and lower deflections are observed with the increase of longitudinal reinforcement, steel fiber or coarse aggregate. Using 2% steel fiber highly improved toughness by more than 17 times. Lower rates of improvement are recorded for longitudinal reinforcement and coarse aggregate. However, it is recommended to perform more research to examine more parameters such as fiber types.

Residual strength capacity of reinforced reactive powder concrete two-way slabs subjected to drop weight

This paper presents an experimental investigation of the effect of the impact force on the residual strength capacity of simply supported reactive powder slabs. Eight specimens of reinforced reactive powder concrete slabs with dimensions of 500 x 500 mm and 70 mm in four categories were used. The influences of slab compressive strength (conventional concrete and reactive powder concrete), steel fiber proportion (1, 1.5, and 2%), percentage of reinforcement in the tension zone (ρ1=0.007, ρ2=0.011, ρ3=0.0179), and the number of impacts (two impacts, four impacts, and six impacts) were all investigated in this test. Investigations were carried out to ascertain each slab's residual response, including first cracking load, residual failure load, residual steel reinforcement strain, maximum central deflection, and crack pattern. The results showed that using reactive powder concrete instead of normal concrete increased the mechanical properties of concrete and resulted in a significant increase in failure load. In addition, the central deflection and strain increased. Increasing the reinforcement ratio increased the failure load while simultaneously decreasing the deflection due to the improvement in slab moment resistance. Furthermore, it was discovered through experiments that the addition of steel fiber to the mixture enhanced the slab’s post-cracking reactivity. The presence of steel fiber raised the slab strength resistance by 21.63% as the steel fiber ratio increased from 1% to 2%. This is because the addition of steel fiber increased the slab's tension resistance.

Combined effect of using steel fibers and demolition waste aggregates on the performance of fly ash/slag based geopolymer concrete

Developing sustainable construction products has been showing a rising trend recently. Geopolymer composites are remarkable binding materials fabricated based on recycling and sustainability. In this paper, an experimental investigation was conducted to study some mechanical and durability characteristics of steel fiber-reinforced fly ash/slag-based geopolymer concrete (GPC) with different proportions of recycled coarse aggregate. Steel fiber-reinforced geopolymer concrete mixtures incorporating recycled coarse aggregates of up to 40% at the interval of 10% were prepared, and the mixtures without recycled coarse aggregate were used as reference samples. The steel fiber ratio of 0.3% and 0.6% were used and the combined effect of steel fiber and recycled coarse aggregate on the geopolymer composites’ behavior regarding strength properties, sulfate resistance, elevated temperature resistance, abrasion resistance, and freezing-thawing resistance was addressed. A significant improvement in strength properties was observed in steel fiber reinforced recycled aggregate geopolymer concrete with increasing fiber content; however, the strength properties of geopolymer concrete were decreased with the increase of recycled coarse aggregate amount. Also, the properties such as abrasion resistance, resistance to elevated temperature, sulfate resistance, and freeze-thaw resistance were improved with the addition of steel fiber. It indicates that the synergetic effect of steel fiber and recycled aggregate helps to produce ecologically sound geopolymer concrete with good engineering properties and durability characteristics that will bring sustainability to the concrete sector. Generally, the results show that the recycled coarse aggregate ratio of up to 30% and 0.6% of steel fiber can be considered an ideal combination to make geopolymer concrete with better overall properties.

A novel prediction model of packing density for single and hybrid steel fiber-aggregate mixtures

Steel fiber can significantly improve the tensile strength, toughness, and crack resistance of concrete matrix, but there is limited research on the packing of single steel fiber-aggregate (SF-A) and hybrid steel fiber-aggregate (HF-A) mixtures. To investigate the effect of steel fibers on the packing of aggregates, the loosely-packed packing density (PD) of 36 SF-A mixtures and 36 HF-A mixtures was measured via the high-rigidity container. The results indicated that the PD always decreased with increasing fiber volume regardless of single or hybrid steel fibers and the size ratio of steel fiber to aggregate particle was a crucial parameter affecting this lowering effect. Moreover, a novel prediction model considering the relative size of fiber and aggregate as key factors was developed and the synergistic effect on aggregates by hybrid fibers was also incorporated into the model. Prediction errors less than 1% were evaluated after calibrating the model parameters.

Numerical Simulation of Steel Fiber Pull-Out Process Based on Cohesive Zone Model and Unified Phase-Field Theory

In steel fiber reinforced concrete, the interface is a very complex and weak structure. It is because of the weak interface layer between the steel fiber and the matrix that the reinforcing and toughening properties of the steel fiber cannot be fully exerted. The interface bond performance is the core of the meso-mechanical properties of steel fiber reinforced concrete. To study its influence on the mechanical properties of steel fiber reinforced concrete, three-phase finite element models of steel fiber pull-out are established based on the cohesive zone model and unified phase-field theory by means of FEM in this paper. The interface bond is simulated by a zero-thickness cohesive element, and the pull-out process of steel fiber in the concrete matrix is analyzed to provide a basis for the fracture research of steel fiber reinforced concrete. In this paper, the influence of factors such as the embedment depth, length–diameter ratio, embedment angle, and interface properties of steel fibers on the pull-out mechanical properties of steel fibers are considered, and the relevant finite element models are established to conduct numerical simulations of the pull-out process of steel fibers. The numerical simulation results are in good agreement with the experimental results, and this verifies the reliability of the model. The results show that the steel fiber pull-out finite element model established by the cohesive zone model and phase-field regularized cohesive zone model (PF-CZM) has a certain reliability; the peak pull-out load of the steel fiber increases with an increase in the embedment depth of the steel fiber, and decreases with an increase in the length–diameter ratio and embedment angle of the steel fiber; by controlling the strength of the interface layer and the concrete matrix, the reinforcement effect of the steel fiber on the concrete matrix can be improved; and the PF-CZM has a good characterization of the damage and failure evolution process of the concrete matrix.

Shear transfer strength estimation of concrete elements using generalized artificial neural network models

Abstract Based on published test findings, this article outlines the use of artificial neural networks (ANNs) to forecast the efficiency factor of shear transfer strength in concrete. Backpropagation neural networks with feed-forward have been employed. The ANN model was created by incorporating a huge experimental database and carefully selecting the architecture and training procedure. The presented ANN model offered a more accurate tool to compute R (where R is a measure of the closeness of association of the points in a scatterplot to a linear regression line based on those points) and capture the impacts of five primary parameters: concrete compressive strength, steel reinforcement ratio, steel yield strength, fiber volumetric ration, and steel fiber aspect ratio are given from experimental data. The obtained results reveal that the first important parameter is concrete compressive strength. In addition, ρ y f y parameter represents the normalized tensile force in steel reinforcements of section, whereas the smallest importance parameter L/D is aspect ratio of steel fibers. Also, the current study illustrated the facilities of using generalized artificial neural networks on predicting the shear transfer strength across the concrete sections, whether they are fibrous or not. From the results, the correlation factor (R 2) is estimated to be about 83%, which means it had a good correlation within the input parameters. In addition, the mean absolute percentage error was 2.06.

The Influence of Aspect Ratio of Steel Fibers on the Conductive and Mechanical Properties of Compound Cement Reactive Powder Concrete

The performance of steel fibers reinforced RPC has a great relationship with the aspect ratio of the fibers. It is necessary to systematically study the relationship between the aspect ratio and the mechanical properties of RPC and the force-electricity response. In this paper, the flexural strength, the compressive strength and the flexural toughness and AC electrical resistance and AC impedance spectroscopy of reactive powder concrete are investigated. The flexural strength, compressive strength, and flexural toughness with the curing age of 1 day and 28 days are tested. The cement is the compound cement in this study, and the mass ratio of ordinary portland cement and sulphoaluminate cement is 1:1, and two kinds of steel fibers with aspect ratios of 30(AR-30) and 75(AR-75) are used. The fiber content is 2% of the concrete volume. Scanning electron microscope (SEM) and scanning electron microscope energy spectrum analysis (EDS) are investigated to analyze the composition of the hydration products. It can be obtained from the research results that the flexural strength and the compressive strength of reactive powder concrete decrease with the increase of steel fibers content with an aspect ratio of 30. The decreasing rates of the flexural strength and the compressive strength with the curing age of 1 d and 28 d are 14.93%~83.26% and 0.40%~46.36% with the incorporation of steel fibers with an aspect ratio of 30. The flexural toughness decreases in the form of a quadratic function with the mass ratio of steel fibers with an aspect ratio of 30. The electrical resistance of reactive powder concrete increases with the increase of steel fibers with an aspect ratio of 30. The maximum decreasing rate of electrical conductivity is 91.16%. The AC impedance spectrum is obtained, and the electric circuit of reactive powder concrete accords with the series conduction model, which parallel electrical resistance and capacitance of pore solution, rapid strength RPC and steel fibers respectively connect with a contact resistance of the electrode and specimens. It is found that the steel fibers network with an aspect ratio of 75 is closer by studying the equivalent circuit diagram.

Quantitative analysis of steel fibers on UHPFRC uniaxial tensile behavior using X-CT and UTT

Steel fiber is usually used to improve ultra-high-performance fiber-reinforced concrete (UHPFRC) tensile properties and remedy its brittle failure. X-ray CT scanning (X-CT) was used to observe the orientation and distribution of steel fibers inside UHPFRC. It revealed that the steel fiber inside UHPFRC distribution angle is not equal probability, and the probability is higher along the pouring direction in uniaxial tensile specimen mold. The uniaxial tensile tests (UTT) of 19 UHPFRC specimens with different fiber volume fractions and aspect ratios were performed to analyze the steel fiber on the tensile response and tension failure patterns of UHPFRC. Test results indicated that with an increase in the volume fraction or aspect ratio of steel fiber, the first-cracking strength, tensile strength and peak tensile strain of UHPFRC increase; while they have different growth rates. In addition, with the increase of volume fraction and aspect ratio, the failure patterns of UHPFRC tension specimens gradually changed from brittle failure with single crack to ductile failure with multiple cracks. The stress superposition compositions of tensile strength were different under different failure patterns. Combining mechanical analysis and numerical statistical analysis, prediction equations of the tensile strength of strain softening UHPFRC and pseudo-strain hardening UHPFRC considering the effect steel fiber parameters were respectively proposed. Through the mesoscopic equivalent model analysis of UHPFRC uniaxial tensile specimens, the functional relationships between the effect of steel fiber parameters on the first-cracking strength and peak tensile strain were analyzed, and then their prediction equations were proposed, combined with numerical statistical analysis. The calculation accuracy of the series of prediction equations proposed in this paper were verified by the collected literature data. Meanwhile, comparing the prediction equations proposed in this paper with the existing equations in the literature, the equations proposed in this paper were better.

Analysis and prediction of the compressive and splitting tensile performances for the novel multiple hooked‐end steel fiber reinforced concrete

AbstractIn recent years, the application of the novel multiple hooked‐end steel fiber has gradually become a hot spot in the engineering due to its several excellent properties. In this study, the splitting tensile and compressive properties of the SFRC with 3D single hooked‐end and 4D/5D multiple hooked‐end steel fibers were studied. The variables of the experimental investigation included the concrete matrix strength, steel fiber content, and aspect ratio. The results showed that the compressive strength of steel fiber reinforced concrete (SFRC) increased first and then decreased with the increasing steel fiber content. The concrete matrix, aspect ratio, and end hook number of steel fiber had the significant effect on the optimal steel fiber content. In addition, increasing the content of steel fiber was the most effective way to improve the splitting tensile strength of SFRC, and the splitting tensile strength increased with the increase of the aspect ratio and end hook number of steel fiber. Finally, the splitting tensile strength prediction model of SFRC with novel multiple hooked‐end steel fiber was proposed by introducing the steel fiber number in the SFRC section, and the accuracy of the model was verified by comparison with experimental data.

Study on multi-scale damage and failure mechanism of steel fiber reinforced concrete: Experimental and numerical analysis

The damage and failure behavior of steel fiber reinforced concrete (SFRC) is extremely complex. The reinforcement mechanism of steel fiber to concrete and the meso-failure mechanism of SFRC have not been thoroughly researched. This paper studied the mechanical behavior of SFRC from two perspectives: macro lab experiment and meso-numerical simulation. Firstly, macro-tests were conducted to examine the effects of the volume content and the length-to-diameter ratio of copper coated microfilament steel fiber on the mechanical properties of SFRC. The result shows that when the volume content of steel fiber is 2% and the length-to-diameter ratio of steel fiber is 60, the cubic compressive strength, splitting tensile strength and flexural tensile strength of SFRC are improved the most, which are 33.1%, 121%, and 35% higher than that of plain concrete respectively. Secondly, three empirical formulas of the compressive strength, splitting strength, and flexural strength of SFRC considering the influence of steel fiber parameters were proposed and the characteristics and phenomena of concrete and SFRC in each stage of compression failure were studied. Thirdly, this work proposed a simple and efficient three-dimensional method for modeling SFRC. The simulation accurately predicted the failure mode and mechanical property response of SFRC. In addition, the effects of steel fiber volume content, length-to-diameter ratio, and friction coefficient of contact surface on the mechanical behavior of SFRC composites were discussed by the model.

Experimental Study on the Behavior of Axially Loaded Reinforced Concrete Square Columns Strengthened with SIFCON Shell

Slurry infiltrated fiber concrete (SIFCON) is an advanced generation of fiber-reinforced concrete (FRC) with higher fiber content. SIFCON offers excellent potential for use in areas that require high ductility and impact resistance, particularly when designing seismic retrofits and repairing or strengthening structural reinforced concrete members. This study investigated the behavior of square normal strength concrete (NSC) columns of grade M35 strengthened with SIFCON shell and compared them with unstrengthen NSC. The effect of different SIFCON shell thicknesses (2 and 3) cm, fiber type and volume fraction (4 and 6%), and tie spacing (8 and 16) cm were studied. The fiber types employed were polypropylene and hooked-end steel fiber. Eleven columns were cast and tested for the current investigation in two groups, where the first group (control specimens) consists of two unstrengthen NSC columns and one square NSC column strengthened with a 2 cm SIFCON shell with a 6% steel fiber ratio. The second group comprises eight NSC columns strengthened with a hybrid fiber SIFCON shell. The NSC square columns had dimensions of (8x8x80) cm. 3 cm SIFCON shell thickness was observed to evolve the strengthen columns' load-carrying capacity and energy absorption. The maximum load achieved is about 223% as compared with unstrengthened NSC columns. The energy absorption was about 16 times that of the control. At the same time, the stiffness of strengthened columns is less than that of NSC columns.

SHEAR STRENGTH OF HIGH STRENGTH STEEL FIBER REINFORCED CONCRETE COLUMNS

At present, the highest high-rise RC building in Japan is over 200 meters high. All columns from the first to the 13th floor of the building are applied high strength steel fiber reinforced concrete columns （HSFRC）to control damage under huge earthquake loading. The high strength steel fiber reinforced concrete columns are contain 1.0% steel fiber by volume. It is the first time to apply much steel fiber for high strength concrete columns. Nevertheless, there is no established design equation for high-strength SFRC columns. Therefore, authors have conducted an experimental study of HSFRC columns since 2020. A total of 15 specimens were conducted. In this research, 13 specimens’ experimental data are used. The shear strength equation based on truss arch theory with the volume ratio of steel fibers as a variable factor is proposed as a design equation for high-strength steel fiber reinforced concrete columns.

An Experimental and Numerical Investigation on the Bending Behavior of Fiber Reinforced Concrete Beams

The effects of hooked end steel and polypropylene (PP) fibers on the behavior of large-scale doubly reinforced concrete beams under flexure were investigated using experimental and numeric methods. For this purpose, a total of eight beam specimens consisting in two groups were produced in the laboratory and three-point bending tests were conducted under monotonically increasing load. The beams in the groups were designed to have 0.86 and 1.30% tensile reinforcement ratios leading to either flexural or shear critical sections. Three out of eight were produced to be control samples and did not have any fiber additive while remaining five had 0, 0.5 and 1.0% steel or PP fibers by volume. Experimental results showed that the existence of 0.5% either type of fiber in densely reinforced specimens contributed to shear strength and allowed flexural capacities to be fully used instead of an improvement in the capacity. However, when the steel fiber ratio increased to 1.0% flexural capacity was enhanced by 10% for both type of beams. After the experimental study, the beams numerically modeled using nonlinear finite element method and flexural stiffness before yielding as well as yield strength with load carrying capacities were found to be consistent with that of experiments specifically for the beams having stirrup and steel fibers.

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.

Effect of concrete composition on drying shrinkage behavior of ultra-high performance concrete

The concrete compositions have great effects on the drying shrinkage behavior of ultra-high performance concrete (UHPC). Five factors including water-to-binder ratio (w/b) and contents of steel fiber, superplasticizer, silica fume and fly ash were considered to evaluate their influences on the drying shrinkage behaviors of UHPC in this investigation. Based on the drying shrinkage test results, the effect degrees of these factors were analyzed by the gray relation entropy analysis. Then the microstructure and pore distributions of UHPC samples were measured by scanning electron microscope and mercury intrusion porosimetry for mechanism analyses. The results reveal that a lower w/b or higher content of fly ash is conducive to achieving a reduction in drying shrinkage of UHPC, while the additions of superplasticizer and silica fume have an adverse effect on drying shrinkage, resulting in increased drying shrinkage, and the effect of steel fiber on drying shrinkage is not monotonic, its optimum dosage is 50 kg/m3 in this work and a lower or higher amount will cause an increased DSS of UHPC compared with the one with an optimum dosage. The five factors can affect the drying shrinkage behavior of UHPC by principally changing the microtopography and internal pore structure of the concrete matrix, according to the gray relation entropy analysis, the effect degrees of studied factors on drying shrinkage of UHPC are as follows: w/b > superplasticizer > silica fume > fly ash > steel fiber.

Experimental study on local bond-slip constitutive model between steel and steel fiber reinforced concrete structure of circular cross-section

The interface slip between shape steel and concrete is one of the biggest problems in numerical simulation of composite structures, this paper aims to investigate interfacial bond-slip behavior between steel and steel fiber reinforced concrete. For this purpose, a series of push-out tests on 15 circular section specimens which were designed and fabricated with different steel fiber ratio, interface embedded length and concrete cover thickness have been done. Experimental results show that average bond strength versus free end slip curves of each specimen is similar, and then a basic average bond strength-free end slip constitutive model was proposed in this paper. Meanwhile, considering the distribution regularities of steel strains, local bond strength and relative slip along the interface embedded length at different load levels were obtained through the mechanical derivation, the results show that the maximum local bond strength was located near the free end, and the local bond strength away from free end tended to be steady. Based on the basic average bond strength-free end slip constitutive model, two position functions were proposed to describe the local bond-slip constitutive model considering the variation of positions. Two position functions are of great significance for further research on SSFRC non-linear properties by FEM.