Steel Fiber Concrete Research Articles

Effect of nitric acid on Rice Husk Ash steel fiber reinforced concrete

Concrete is globally used construction material and nowadays its durability is the main concern. Acid is one of the chemicals influencing the durability of concrete. Nitric acid (HNO3) is one such acid. Several mineral admixtures are used to improve the durability of concrete. Rice Husk Ash (RHA) is one of such admixtures. This paper make known the results of an experimental programme intended to explore the durability aspects of Normal Concrete (NC) and Steel fiber Rice Husk Ash Concrete (SFRHAC). M25 grade of concrete using normal constituents was designed and used for referral. The RHA was used for partial replacement of Ordinary Portland Cement (OPC). The different replacement levels considered were 10, 15, 20 and 25%. It is found that workability of concrete decreased with increase in the replacement level. The optimum replacement level was found to be 15%, with respect to the compressive strength. The hooked steel fiber was added (by volume) to the RHA and Steel fiber concrete. The cubes of both NC and SFRHAC were cured in Tap water as well as in 5% Nitric acid solution till 90 days. Nitric acid is based on acid rain, sewage and industrial waste etc. The compressive strength of cubes was determined after 7, 28, 56, and 90 days. The compressive strength of water cured SFRHAC is higher than the NC. The compressive strength of both NC and SFRHAC was found to decrease in acidic solution for all the exposure periods; however, the decrease was lower in case of SFRHAC. The XRD analysis was carried out to estimate the effect of nitric acid on the constituents of concrete. The higher peaks of Calcium Silicate Hydrate (C-S-H) are detected in SFRHAC samples.

Изменение водонепроницаемости при нагреве сталефибробетонов с высокопрочной цементно-песчаной матрицей

The paper considers the effects of high temperatures in case of fire on the change in impermeability of steel fiber reinforced concrete having a high-strength cement-sand matrix and various content of fiber of different types, sizes, and strength. It is shown that in the temperature range from 20° to 1100° C in the diagram “Heating temperature - impermeability class», the matrix and steel fiber concrete(SFC) have a S-shaped character, and in case of heating temperature of over 100 °C, there comes a distinct decrease in impermeability.

МЕТОД ПОСТРОЕНИЯ ДИАГРАММ-ИЗОХРОН ВЫСОКОПРОЧНОГО СТАЛЕФИБРОБЕТОНА И ЕГО МАТРИЦЫ

High-strength steel fiber concrete, made on the basis of fine-grained high-strength concrete, is a quite promising building material, in particular, for the construction of high-rise buildings and structures of increased massiveness. The introduction of steel fiber into the concrete matrix can significantly reduce the influence of such shortcomings of fine-grained concrete as increased fragility and explosive nature of fracture, and also positively affects the tensile properties of concrete. However, the widespread use of high-strength steel fiber concrete is currently limited, among other things, by the lack of an experimentally relied normative framework for this material. The proposed article aims to bridge this gap. Modern engineering trends are aimed at introducing into practice diagram methods of calculation based on real diagrams of material deformation under load. This article describes the technique of constructing isochron diagrams for fine-grained high-strength concrete and steel fiber concrete with disperse reinforcement in the amount of 1.5% by weight, made from Russian-made components. Isochron diagrams allow you to calculate the deformation of the material depending on the level of load at any time, including during prolonged loading. There have been made changes to the existing methodology, allowing to take into account the nonlinearity of both current and ultimate creep characteristics depending on the level of loading. The proposed theoretical dependences give good convergence with the experimental data.

Changes in the Prismatic Strength and Elastic Modulus of High-Strength Steel Fiber Concrete and its Matrix Depending on the Age

Changes in the Prismatic Strength and Elastic Modulus of High-Strength Steel Fiber Concrete and its Matrix Depending on the Age

Dispersed reinforcement of columns of a high-rise building

The article deals with the application of combined reinforcement of concrete with steel and basalt fibers. A model of a high-rise building was calculated in the LIRA-SAPR 2013 software. Design and characteristic strength of steel fiber and basalt fiber reinforced concretes to compression and tension and the initial elastic modulus were determined to calculate the model. Comparison of the effect of B40 concrete steel fiber reinforced concrete (SFRC) and basalt fiber reinforced concrete (BFRC) on column reinforcement was performed by comparing the required areas of reinforcement, as well as the percentage of reinforcement, taking into account crack resistance. The total area of reinforcement decreased with the addition of steel fiber by 36.9% and basalt fiber by 39.9%. The percentage of reinforcement also decreased, taking into account crack resistance, from 0.694 for columns with concrete B40 to 0.437 for SFRC columns and to 0.417 for BFRC columns. The addition of fiber increases the strength characteristics of concrete: compressive strength increased by 35.8% and 77.2%, tensile strength by 150.2% and 75.7%, crack resistance by 37% and 39.9%, the initial modulus of elasticity of the material increased by 8.7% and 3.7% for SFRC and BFRC respectively compared with concrete B40.

Technological and construction features of modular reinforced concrete foundation designing for various high-rise structures

The paper proposes a new type of modular collapsible reinforced concrete foundation for steel support of various types of structures: power lines, wind power plants, billboards, traffic lights, etc. The foundation has the shape of a cross-hammer in the plan and consists of separate modules manufactured at the factory and connected to each other by concrete dowels and tie bolts on the construction site. At the same time, this technological approach makes it possible to obtain more stable (uniform) strength and deformation properties of both the individual module and the assembled foundation as a whole. Reducing the material consumption is achieved by creating a cavity in each typical module and filling it with local inert material (soil). The Central module has an anchor device for joining with the support according to the type of flange connection. This device, along with the use of conventional anchor bolts, involves filling the Central module with non-shrinkable fast-hardening steel-fiber concrete. Thus, the positive result of the proposed solution is to increase the bearing capacity of the Foundation as a whole, increase the strength and stiffness of its main joints, and simplify installation in comparison with traditional approaches to construction. A comparative calculation of the foundations of the proposed and standard known solutions showed the effectiveness of the first one by at least 17.2%.

Експериментальні дослідження роботи стержневої арматури в перерізах комбіновано-армованих нерозрізних залізобетонних балок

Проведено аналіз експериментальних досліджень особливостей роботи стержневої арматури в перерізах двопролітних залізобетонних балок. При їх конструюванні в якості армування використовується класична сталева арматура у вигляді каркасів, та дисперсне армування бетону сталевою фіброю.

Дослідження властивостей опору сталефібробетону

На основі теоретичних досліджень прийнятої моделі проаналізовано основні теоретичні дослідження опору сталефібробетону – зв’язок між напруженнями і деформаціями. Визначена ефективність фібрової арматури залежно від довжини і розташування фібр в просторі. Доведено, що в’язкість сталефібробетону приблизно в 10...12 разів більша за в’язкість бетону та залізобетону.

Flexural behavior of RC beam strengthened by stay in place SFRC sheet formwork

The paper presents results of experimental and numerical modeling of flexural behavior of RC beam strengthened be stay in place SFRC sheet formwork in a tensioned zone. Analysis of influence of the SFRC on crack propagation. As a result monolithic concrete provides the perception of tensile forces before the formation of main cracks in the steel fiber concrete.

Study of high-strength steel fiber concrete strength characteristics under elevated temperatures using mathematical modelling methods

This article presents the study of the various factors influence on the high-strength steel fiber concrete strength characteristics using a mathematical model that was obtained on the basis of experimental data. At the same time, the steel-fiber concrete reinforcement, the scale factor, the temperature and the duration of heating are related to the factors under study. A fundamental approach to building a model is to use exponential functions. This function allows to move from the product of the studied factors to their sum, which greatly simplifies the further use of the dependencies obtained in engineering practice. Separately, it should be noted that one of the studied factors (the duration of exposure to temperatures) is set by the result of its impact on the final response function. That is, taking into account the destructive processes in the structure of concrete with short-term heating and structural – with long-term. In addition, the optimization of the proposed mathematical model is performed, as a result of which it is established that the maximum values of the strength of the steel fiber concrete is achieved at the values of the percentage of reinforcement of HSFRC.

Nonlinear Large Deformation Mechanism and Stability Control of Deep Soft Rock Roadway: A Case Study in China

Improving the safety and stability of soft surrounding rock with nonlinear large deformation gives a strong guarantee for the safe mining and sustainable development of deep coal mines. In order to control the nonlinear large deformation of the surrounding rock in a deep soft rock roadway, this paper discusses the nonlinear large deformation mechanism and coupling support countermeasures of a typical engineering application at Xin’an coal mine in Gansu province, China. The series of experiments and theoretical analysis described in this paper reveal the phenomena, properties, and reasons for the nonlinear large deformation of soft surrounding rock in detail. Then, the type of nonlinear large deformation mechanism is determined and transformed from a composite one to a simple one. Based on experimental results and mechanism transformation, a suitable coupling support countermeasure, which contains the Constant Resistance Large Deformation (CRLD) bolt, steel mesh, floor hollow grouting cable, and steel fiber concrete, is proposed to reduce the nonlinear large deformation and the potential risk during mining. The application shows that the coupling support countermeasure can effectively reduce the nonlinear large deformation of the surrounding rock and help to maintain the stability of the deep soft rock roadway at Xin’an coal mine.

Mechanical properties of mixed steel fiber reinforced concrete with the combination of micro and macro steel fibers

AbstractThe paper intends to analyze and study the features of steel fiber reinforced concrete (SFRC) and plain concrete that contains combined fibers of various aspect ratios. Experiments on works are held to examine the features of the new combination of concretes. Simultaneously, the characteristics of the concretes that are hardened are examined by performing tests on compressions, flexural strength tests, and split tensile strength (STS). It further verifies the effects of fibers when they are distributed in the hinged zone of structural components to obtain financial benefits by minimizing the ingredients in steel fiber in the concrete mix. The result shows that the combined reinforced concrete steel fiber can be employed as the better combination to be applied in SFRC for achieving strength in STS, and flexure. Anyhow, enhanced ability for working was achieved as more amounts of microfibers in mixed with concrete. And there is slight variation in the features of concrete between beam of fibers with full length and fibers which are available in hinged zone. Similarly, the categorization of neural network such as Neural Network–Levenberg–Marquardt (NN‐LM) and Neural Network‐Gradient Descent (NN‐GD) is further used to perform the experimentation in an intelligent manner, which comes close to the actual values while calculating the mean absolute error (MAE) and root mean square error (RMSE) values.

Application of fibro concrete mixture at construction of bases and coatings automobile roads

Fiber concrete – concrete with the inclusion of fibers (fibers) from inorganic or organic materials (steel, glass, polyethylene, etc.). Fiber concrete reinforced with fibers, has a high resistance to shock loads and abrasion, well perceives tensile stresses. An important issue in the preparation of fiber-reinforced concrete is its mobility. One of the difficulties encountered in practice when working with fiber reinforced concrete, reinforced by steel wire, is its lack of workability. To ensure the required workability of the concrete mixture and to achieve a uniform distribution of wire segments in it, it is necessary, in addition to the wire segments and the core, to control their ratio. Tests of fiber reinforced concrete showed that the larger the aggregate size, the lower the flexural strength. The use of granite crushed stone with a size of 20 mm allows to obtain better results than when using crushed stone from gravel or limestone. While in ordinary concrete, the quality of rubble increases the flexural strength, in fibrous concrete, the flexural strength increases the effectiveness of the fibers. The use of fiber-reinforced concrete in the construction of road pavements is determined by technical and economic efficiency, which is caused by the most complete use of the positive properties of fiber-reinforced concrete as compared to conventional cement concrete. Fiber concrete has several advantages compared to conventional cement concrete: a) increased crack resistance, impact toughness, wear, – frost and fire resistance, thermodynamic resistance, etc.; b) the possibility of use without conventional rod or wire steel reinforcement; c) reducing labor costs for reinforcement works, increasing the degree of mechanization and automation of road and airfield pavement construction. In recent years, the use of concrete (cement concrete) foundations and pavements of highways and industrial sites has begun to revive in road construction. The use of various types of cement concrete and fiber concrete (steel fiber concrete, glass fiber concrete, fiber concrete on synthetic fiber) will increase the durability of road and airfield pavements, increasing resistance to shock loads, abrasion and tensile stresses.

Evaluation on the Mechanical Properties of Steel-Fiber Concrete at Elevated Temperatures

This paper presents experimental results on mechanical properties of steel-fibre concrete burned at high temperatures, which consists of tensile strength, modulus of elasticity and flexural modulus. The steel-fibre usage is limited to 0.5% of concrete volume. The reviewed parameters in the evaluation include compressive strength of normal to high-strength concrete, and temperature (normal, 300°C, 600°C, 900°C). The specimens are heated up after it reached 120 days of age. Experimental results toward mechanical behaviour indicate that tensile strength tends to decline linearly at 300°C and 600°C respectively. The value of modulus of elasticity and flexural modulus of fibre-reinforced concrete heated at 300°C, 600°C and 900°C tend to decline linearly. The results of the experimental evaluation also proposed a model for tensile strength degradation equation, modulus of elasticity and flexural modulus against temperature.

Flexural strength at high temperatures of a high strength steel and polypropylene fibre concrete

Concrete is a widely used material in building construction. In case of fire concrete is subjected to high temperatures exhibiting thermal instability for certain temperatures. The phenomenon leads sometimes to degradation of the concrete compromising the safety of the structures. This paper reports the results of an experimental investigation for assessing the fracture energy at ambient and high temperatures of a high strength polypropylene and steel fibre concrete. The experimental program was designed to evaluate the influence of various parameters that may influence the fracture energy of the fibre concretes in study. Five concrete compositions were tested with different steel fibre dosages and types: one without steel fibres (reference composition), two with Dramix 3D steel fibres and two with Dramix 5D steel fibres (45 and 75 kg/m3). All compositions had 2 kg/m3 of polypropylene fibres that were used to avoid spalling on the specimens. The results indicated that the addition of steel fibres improving the fracture energy of the concrete increasing its ultimate flexural strength and ductility at ambient temperature. However, at high temperatures a deterioration in the fracture energy and ultimate flexural strength with the increasing of temperature was observed. Concrete compositions with Dramix 5D steel fibres lead to higher fracture energy and flexural strength comparing to compositions with Dramix 3D steel fibres. The same happens when using higher dosages of steel fibres in the concrete composition.

Experimental Studies of Reinforced Concrete and Fiber-Reinforced Concrete Beams with Short-Term and Long-Term Loads

Experimental studies of the stress-strain state of reinforced concrete and fiber-reinforced concrete beams under short-term and long-term loads were carried out. The tests were carried out on three series of beams of different types - from ordinary concrete, steel fiber concrete and combined section, when the lower zone of the beam with a height of0.5his made of steel fiber concrete, and the upper one is made of ordinary concrete. During short-term loading, the load was applied in steps with a 10-minute exposure at each step to failure or to a predetermined level of a continuously acting load. In the interval between the steps, the process of cracking was tracked. After reaching a given level of loading, the load was fixed and maintained unchanged with a spring cassette for 300 days. Deformations were measured using strain gauges and dial gauges. Deflections and relative deformations of the extreme upper and extreme lower fibers for three types of beams are determined. It has been established that stabilization of deflections in beams from steel fiber concrete occurs much earlier (100 days) than in beams made of ordinary concrete (175 days). Studies have shown that the beams of ordinary concrete in the process of long-acting load lowered the carrying capacity by 5.5%. The bearing capacity of steel concrete beams, in contrast, increased by 7.6%.

Application of the design code for steel fibre reinforced concrete into finite element software

Steel fibre reinforced concrete (SFRC) is more and more used as construction material. Well-known are applications for industrial floors. Nevertheless, this material is also widely used in structural concrete elements where it is especially effective to cover crack widths in combination with standard conventional reinforcement. Currently there is no general part in Eurocode 2 [1] for buildings regarding steel fibre concrete. There are various standards and recommendations for the calculation of the steel fibre contribution. One of the most applied publications is the German guideline DAfStb [2] which was used as a basis for the numerical analysis outlined in this paper. Thus, company SCIA N.V. together with Bekaert N.V. as producer of DRAMIX® fibres developed a special tool for designing and checking SFRC structures. This tool was built in into finite element software SCIA Engineer and based on the German guideline. To gain a fundamental understanding of the structural behaviour, we have also developed non-linear FEM models, which contain a built-in module for SFRC structures. Numerical simulation results are compared to experimental performance of SFRC slab on piles of the Nanhui project in Shanghai in terms of ultimate load and crack pattern.

Magnetic alignment of steel Fibres in self-compacting concrete

ABSTRACTThe dispersion of short or micro steel fibres in the concrete matrix generally assumes a more random orientation. In this paper, we propose an assessed technique of exploiting the electromagnetic field, supplemented with vibration, to align the steel fibres in self-compacting concrete. The low viscosity of self-compacting concrete stimulates the consideration of this mixture, and thereby, the chance for success is more likely. The alignment approach was applied to nine prisms of a size of 100 × 100 × 500 mm and provided with different percentages of microfibres. The efficiency of alignment was compared with three prisms produced with random fibres. Visual inspection was used to assess the alignment efficiency. The fibre orientation factor for the aligned fibres ranged between 0.80 and 0.95 in comparison to 0.3–0.5 for the randomly dispersed fibres. The flexural failure load for the prisms of aligned steel fibres increased by 40% compared to the prisms of randomly distributed fibres.

Effect of steel and polypropylene fibers on the quasi-static and dynamic splitting tensile properties of high-strength concrete

The influence of steel-polypropylene hybrid fibers on the tensile properties of high-strength concrete is investigated by quasi-static and dynamic Brazilian disc splitting tests. The failure modes of fiber reinforced concrete specimens and the influence of different fiber mixing ratios on the splitting tensile strength of the specimens are analyzed. The research results indicate that the plain concrete and single-doped polypropylene fiber concrete specimens show straight cracks along the loading line during the experimental process, showing the brittle failure characteristics; while the single-doped steel fiber concrete and hybrid fiber concrete specimens show more bifurcated micro-cracks along the loading line, showing the ductile failure characteristics. The splitting tensile strength of concrete specimens increases with the increase of steel fiber content, and increases first and then decreases with the increase of polypropylene fiber content. The mixed use of steel fiber and polypropylene fiber not only improves the splitting tensile strength of concrete specimens, but also reduces the risk of brittle failure of concrete. Especially when the steel fiber content is S2 (2.5%), the hybrid of steel-polypropylene fibers has a great improvement effect on the splitting properties of concrete specimen. In addition, it is found that the splitting tensile strength of fiber reinforced concrete specimens increases with the increase of force loading rate, showing the enhancing effect of loading rate. Comparing the rate-enhancing effect of specimens with different fiber content, it is found that the change of fiber content has a certain influence on the loading rate-enhancing effect of specimens.

Experimental research on impact response of novel steel fibrous concretes under falling mass impact

This paper attempts to pioneer an impact response of four types of fibrous concrete viz., Conventional Steel Fibrous Concrete (CSFC), Two Stage Fibrous Concrete (TSFC), Slurry Infiltrated Fibrous Concrete (SIFCON) and Layered Fibrous Concrete (LFC). The study of CSFC, TSFC, SIFCON and LFC subjected to falling mass impact has been stated in the literature independently. Nevertheless, the combined study of impact response of four types of fibrous concretes is a novel topic and outcome of this research has been compared with each other. The present study involves preparation of ten mixes consisted the aforementioned fibrous concrete types prepared from innovative 5D hooked end steel fibres, where fibre dosage varies between 1.0% and 10%. The impact strength of all specimens is tested using falling mass impact test according to ACI Committee 544 recommendations. The Weibull distribution method was utilized to investigate scattered experimental test results in terms of reliability function. The results revealed that the superior impact strength was observed in SIFCON followed by LFC, TSFC and CSFC specimens. Due to the effortlessness production technique and superior impact strength in novel TSFC, SIFCON and LFC are tough contenders for many pioneering applications.