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.

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.

Experimental investigation of axially loaded steel fiber reinforced high strength concrete-filled steel tube columns

An experimental study on the compressive behavior of steel fiber reinforced concrete-filled steel tube columns is presented. Specimens were tested to investigate the effects of the concrete strength, the thickness of steel tube and the steel fiber volume fraction on the ultimate strength and the ductility. The experimental results indicate that the addition of steel fibers in concrete can significantly improve the ductility and the energy dissipation capacity of the concrete-filled steel tube columns and delay the local buckling of the steel tube, but has no obvious effect on the failure mode. It has also been found that the addition of steel fibers is a more effective method than using thicker steel tube in enhancing the ductility, and more advantageous in the case of higher strength concrete. An analytical model to estimate the load capacity is proposed for steel tube columns filled with both plain concrete and steel fiber reinforced concrete. The predicted results are in good agreement with the experimental ones obtained in this work and literatures.

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.

Approach for analyzing the ultimate strength of concrete filled steel tubular arch bridges with stiffening girder

A convenient approach is proposed for analyzing the ultimate load carrying capacity of concrete filled steel tubular (CFST) arch bridge with stiffening girders. A fiber model beam element is specially used to simulate the stiffening girder and CFST arch rib. The geometric nonlinearity, material nonlinearity, influence of the construction process and the contribution of prestressing reinforcement are all taken into consideration. The accuracy of this method is validated by comparing its results with experimental results. Finally, the ultimate strength of an abnormal CFST arch bridge with stiffening girders is investigated and the effect of construction method is discussed. It is concluded that the construction process has little effect on the ultimate strength of the bridge.

Flexural Behaviour of High－Strength Steel Fiber－Reinforced Concrete Beams

This paper presents the research results of twelve high strength concrete beams reinforced with steel fibers and bars. Fiber type I and II reduce the deflection by more than 25% and increase the ultimate load by about 10% compared to high strength concr

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

Replacing Stirrups of Self-Compacting Concrete Beams with Steel Fibers

Based on the investigation of fiber influence on workability of self-compacting concrete (SCC), tests were carried out on two series of SCC rectangular simply supported beams, which were made of hooked steel fibers reinforced concrete with or without stirrups, subjected to four-point symmetrically placed vertical loads. The major test variables are steel fiber contents and stirrup ratios. The results indicate that the ultimate load significantly increases with the increase of fiber content; the addition of ...

Durability of Concrete Subjected to the Combined Actions of Flexural Stress,Freeze-thaw Cycles and Bittern Solutions

Freeze-thaw durabilities of three types of concretesnormal portland cement concrete （OPC）, high strength concrete （HSC） and steel fiber reinforced high strength concrete （SFRHSC） were systemically investigated under the attacks of chemical solution, and combination of external flexural stress and chemical solution. Four kinds of bitterns from salt lakes in Sinkiang, Qinghai, Inner Mongolia and Tibet provinces of China were used as chemical attack solutions. The relative dynamic modulus （RDM） was used as an index for evaluating the damage degree during the course of chemical attack and stress corrosion. The experimental results show that the freeze-thaw durability of concrete is visibly reduced in the present of the flexural stress, i e, stress accelerates the damage process. In order to quantify the stress accelerated effect, a stress accelerating coefficient was proposed. The stress accelerating coefficient is closely related with the types of bitterns and the numbers of freeze-thaw cycles is. The more numbers of freeze-thaw cycles is, the greater the stress accelerating coefficient for various concretes will be. In addition, there also exists a critical ratio of external stress to the maximum flexural stress. If the stress ratio exceeds the critical one, the freeze-thaw durability of various concretes will be greatly decreased compared to the responding concretes without applied stress. The critical stress ratio of OPC, HSC and SFRHSC is 0.30, 0.40 and 0.40, respectively, indicating that HSC and SFRHSC have advantages over OPC and are suitable to use in the bittern erosion regions.

Experimental Investigation on the Properties of Recycled Concrete Using Hybrid Fibers

Due to the inherent property of concrete being very weak in tension, efforts have been made to overcome this deficiency by adding various type of fibers like carbon fiber reinforced polymer (CFRP), glass fiber reinforced polymer (GFRP), polypropylene fiber (PPF) and stainlesssteel fiber (SSF) smeared into the concrete mix. The present study involves experimental investigation on the use of GFRP, CFRP and SSF fibers alone or as combination to improve the mechanical properties of concrete. Furthermore, concrete cylinders were cast and tested for compression and tension using 10% fly ash as cement replacement in all specimens. Besides fiber material types, fiber reinforcement ratios of 1% and 1.5% were tested to investigate the mechanical properties of concrete. In all concrete cylinder tests, the fiber reinforcement ratio of 1% had a significant contribution in increasing the tensile strength as oppose to compressive strength. As a result, the tensile and compressive strengths were increased by 26% and 11%, respectively as compared to the control specimen. Increasing the fiber reinforcement ratio from 1% to 1.5%, resulted in diminishing the mechanical properties of concrete. However, reduction in concrete compressive strength was more prominent than the tensile strength. Furthermore, it was observed that, the crack propagation was decreased with the increase of fiber content when compared to the control specimen.

MECHANICAL BEHAVIOUR AND INTERFACIAL PERFORMANCE OF STEEL FIBER REINFORCED SILICA FUME HIGHSTRENGTH CONCRETE

In this paper, the flexural, split tensile, impact and fatigue performance of steel fiberreinforced silica fume high-strength concrete (SIFUMHSC) under static and dynamic loadsare studied. The effect of the amount of silica fume on its performance, the strengtheningeffects of silica fume particle artd steel fiber afld their composite effect are discussed. Testresults indicate to a full extent that different amounts of silica fume substituting for cementcan remarkably improve the static and dynamic mechanical behaviour of steel fiberr einforcedSIFUMHSC with other conditions unchanged and that the main reason for the change is thatthe addition of silica fume brings about a double interfacial strengthening effect of fiber-cement matrix and aggregate-cement matrix, thus improving the structure and characteristicsof the interface. When the addition of silica fume is adequate, the H_v-d, I_a-d and CHAS--dcurves tend to be horizontal, with differences disappearing between the interfacial layer andmatrix, so that the size and number of crack sources in the interfacial zone and the wholematrix become smaller and less, and strengthening effects are better deve1oped. This is thekey to the desired performance of steel fiber reinforced SIFUMHSC.

Mesomechanism of steel fiber reinforcement and toughening of reactive powder concrete

Reactive powder concrete (RPC) is a novel cement-based composite material with ultra-high strength. Embedding a certain amount of short steel fibers in the matrix can improve the RPC’s toughness and overcome the disadvantage of high brittle- ness. In this paper, a number of direct uniaxial tension tests have been carried out with ‘8-shape’ RPC200 specimens. The bond-slip process, mesoscopic structural variation and mechanical characteristics of a fiber pullout of the matrix have been investigated using the real-time SEM loading system and CCD observation tech- niques. The influence of the volume of embedded short steel fibers in matrix on the mesoscopic morphology of attachments on the surface of a pulled individual fiber, the initial cracking force, the ultimate pullout force, interfacial bond strength and the pullout rupture energy have been analyzed. A general formulation relating these quantities to the volume of fibers in matrix has been proposed. The components comprising the interfacial bond strength have been outlined. In addition, the con- tribution that fibers make to enhance and toughen the reactive powder concrete has been discussed. It is shown that there exists an optimal threshold of fiber volume ρv, opt =1.5% at which the bond performance of a fiber pullout of RPC be- haves best.

Determination of shear strength of steel fiber RC beams:application of data-intelligence models

Accurate prediction of shear strength of structural engineering components can yield a magnificent information modeling and predesign process.This paper aims to determine the shear strength of steel fiber reinforced concrete beams using the application of data-intelligence models namely hybrid artificial neural network integrated with particle swarm optimization.For the considered data-intelligence models,the input matrix attribute is one of the central element in attaining accurate predictive model.Hence,various input attributes are constructed to model the shear strength"as a targeted variable".The modeling is initiated using historical published researches steel fiber reinforced concrete beams information.Seven variables are used as input attribute combination including reinforcement ratio(ρ%),concrete compressive strength(f′c),fiber factor(F1),volume percentage of fiber(Vf),fiber length to diameter ratio(lf/ld)effective depth(d),and shear span-to-strength ratio(a/d),while the shear strength(SS)is the output of the matrix.The best network structure obtained using the network having ten nodes and one hidden layer.The final results obtained indicated that the hybrid predictive model of ANN-PSO can be used efficiently in the prediction of the shear strength of fiber reinforced concrete beams.In more representable details,the hybrid model attained the values of root mean square error and correlation coefficient 0.567 and 0.82,respectively.

Moment-curvature relationship of FRP-concrete-steel doubleskin tubular members

Tests were conducted on 3 specimens to study the flexural behavior of fiber reinforced polymer(FRP)-concrete-steel double-skin tubular members(DSTMs).The strip method was used to calculate the section momentcurvature curves of the 3 specimens and 12 models.A theoretical formula is presented for the flexural strength of DSTMs.The test results show that the tension zone of the specimen FRP tubes was in hoop compression while the compression zone was in hoop tension.The load-carrying capacity did not decrease even when the mid-span deflection reached about 1/24 of the span length.The tests,simulation and theoretical analysis resulted in a simplified formula for the flexural strength of DSTMs and a tri-linear moment-curvature model was expressed as a function of the section bending stiffness for DSTMs.

Mechanical Properties of Sustainable,Self-healing Porous Asphalt Concrete

Long lifetime sustainable porous asphalt concrete containing steel fibers was designed. The material is self healing in such a sense that some external stimulus is needed in the form of heating by induction energy. Steel wool was added to porous asphalt concrete to enhance its electrical conductivity and induction heating was applied to increase the temperature to heal the micro-cracks and repair the bonding between aggregate and binder. The main purpose of this paper is to examine the mechanical properties of this sustainable porous asphalt concrete including indirect tensile strength,work of fracture,particle loss resistance and water sensitivity. It is found that adding steel fibers to porous asphalt concrete to increase the healing performance also can improve its overall mechanical properties.

不同钢纤维类型混凝土动静态力学特性试验研究及应用

以云南某深部竖井钢纤维混凝土衬砌支护为背景,利用深部矿山现场使用的水泥、钢纤维及掘进工作面废矸石作为原材料,制作钢纤维混凝土试样,探究了不同钢纤维类型混凝土的动静态力学性能。通过单轴压缩、劈裂拉伸和动态压缩试验获得了钢纤维混凝土动静态力学性能及其破坏特征,结合高速摄像机和数字图像相关技术(DIC),探讨了钢纤维混凝土试样的裂纹演化规律。研究结果表明:双掺、三掺钢纤维混凝土的抗压强度均大于单掺钢纤维混凝土,三掺钢纤维在增强混凝土抗拉强度方面效果最佳,混凝土动态抗压强度随着掺杂钢纤维类型增加而增加;与素混凝土相比,钢纤维混凝土试样表面裂纹出现较晚;掺杂的钢纤维类型越多,试样峰值应变越大;素混凝土表现出脆性破坏特征,钢纤维混凝土则表现出延性破坏特征;将三掺钢纤维混凝土应用于矿山竖井衬砌支护,有效提高了竖井井壁的完整性和稳定性,为深部矿山工程安全高效开采提供了保障。

岩石-钢纤维混凝土复合层动态抗压强度计算模型

为了研究冲击荷载下岩石-钢纤维混凝土(R-SFRC)复合层的抗压强度模型,利用分离式霍普金森压杆对花岗岩、混凝土和R-SFRC复合层进行动态冲击压缩试验,并通过回归试验结果得到R-SFRC复合层的对数型、幂函数型和强度-应变率依赖机制型3种强度模型,同时考虑R-SFRC复合层界面相互作用,基于Mohr-Coulomb强度准则建立复合层动态抗压强度计算模型。结果表明,R-SFRC复合层动态抗压强度随应变率及钢纤维掺量增大而增大;3种回归模型拟合复合层动态抗压强度试验结果的相关系数范围为0.918~0.999,其中依赖机制型模型与试验结果的相关性最大;基于Mohr-Coulomb强度准则的3种模型得到的复合层抗压强度计算值相对试验值的误差范围为-9.23%~3.16%,对数型模型的误差最大值较小。R-SFRC复合层动态抗压强度计算模型可为混凝土支护隧道围岩设计提供理论基础。

钢-PVA混杂纤维高性能混凝土高温后残余力学性能试验研究

为探究3种因素钢纤维、聚乙烯醇(polyvinyl alcohol,PVA)纤维和矿粉对钢-PVA混杂纤维高性能混凝土(hybrid fiber high performance concrete,HFHPC)高温后残余力学性能的影响。对钢纤维、PVA纤维和矿粉3种因素各取3个水平,采用L_(9)(3^(3))方案进行正交设计,测试HFHPC遭受高温作用后的立方体抗压强度、劈裂抗拉强度和抗折强度,并进行极差与方差分析。结果表明:钢纤维体积分数为2.0%时可以有效提高HFHPC的各项强度。PVA纤维能够抑制混凝土爆裂,与钢纤维混杂可体现优势互补。800℃时,当钢纤维体积分数为2.0%、PVA纤维体积分数为0.3%、矿粉掺量为10%时,HFHPC的抗压强度残余率与劈拉强度残余率达到最高,分别为60.23%和74.5%。当矿粉掺量大于10%时,HFHPC抗压强度可显著提高,而劈拉强度与抗折强度略有下降。最后分别建立了HFHPC立方体抗压强度、劈裂抗拉强度和抗折强度的预测模型。

基于堆积密实度的固废活性粉末混凝土配合比设计方法

采用固废掺合料(粉煤灰、矿渣和玻璃粉)进行了活性粉末混凝土(RPC)制备及性能研究,研究了固废种类、掺量和掺入方式对RPC堆积密实度、工作性能、力学性能和微观结构的影响,提出了固废RPC强度模型。结果表明:粉煤灰、矿渣和玻璃粉的替代水泥量分别为15%、10%~15%和20%时,RPC强度更具有优势,工作性能和微观性能更好;固废合理的掺入可使立方体抗压强度最高提高25.8%,而且随着堆积密实度的增大,固废RPC立方体抗压强度先提高后稍有降低;结合鲍罗米公式和密度堆积模型,考虑影响RPC性能的主要因素,提出了固废掺合料RPC配合比的设计方法,为RPC的工程应用提供依据。

基于图像法对自密实超高性能混凝土性能提升的研究

为提升超高性能混凝土(UHPC)的性能,采用改进后的Andreasen&Andersen颗粒堆积模型设计UHPC基体配合比,利用图像法分析UHPC不同基体黏度对钢纤维分布的影响,并通过抗压强度结合纤维分布系数选择合适的基体黏度,研究不同形状、体积掺量的钢纤维对UHPC力学性能的影响,最终得到力学性能最佳的配合比。试验结果表明:良好的UHPC基体黏度在均匀分散钢纤维的同时可以避免内部出现过多气泡,进一步提升UHPC抗压强度;与端钩、长直形钢纤维相比,波纹形钢纤维在相同黏度下分散效果更佳,且对UHPC基体力学性能提升效果更好。UHPC最佳配合比为水胶比0.16,水泥、硅灰、矿渣质量比0.75∶0.2∶0.05,波纹形钢纤维体积掺量3%,减水剂质量分数0.8%,此时粉体颗粒最紧密堆积、钢纤维分布均匀,UHPC性能最佳。