Fiber-reinforced Concrete Mixtures Research Articles

Optimization of Foams-Polypropylene Fiber-Reinforced Concrete Mixtures Dedicated for 3D Printing.

The continued global urbanization of the world is driving the development of the construction industry. In order to protect the environment, intensive research has been carried out in recent years on the development of sustainable materials and ecological construction methods. Scientific research often focuses on developing building materials that are renewable, energy-efficient, and have minimal impact on the environment throughout their life cycle. Therefore, this article presents research results aimed at developing a concrete mixture using cement with reduced CO2 emissions. In the context of increasing ecological awareness and in line with European Union policy, the development of a mixture based on environmentally friendly cement is of key importance for the future development of the construction industry. The article compares the physical properties of two mixtures, their foaming possibilities, and the influence of the added polypropylene (PP) fibers on the strength properties of the produced composites. It was found that bending strength and compressive strength were highest in the material with silica fume and aluminum powder at 5.36 MPa and 28.76 MPa, respectively. Microscopic analysis revealed significant pore structure differences, with aluminum foamed samples having regular pores and hydrogen peroxide foamed samples having irregular pores. Optimizing aluminum powder and water content improved the materials' strength, crucial for maintaining usability and achieving effective 3D printing. The obtained results are important in the development of research focused on the optimization of 3D printing technology using concrete.

About Dynamics of Improving the Foam Concrete Technological and Operational Properties upon Disperse Reinforcement with Polypropylene Fibers

Introduction. The efficiency of the foam concrete products manufacture and application in construction is briefly overviewed. The reasons constraining the nomenclature of the manufactured products are listed. The information about evolvement of the foam concrete disperse fiber-reinforcement technology is provided. The need for scientific research aimed at studying the dynamics of the foam concrete technological and operational properties upon disperse reinforcement with polypropylene fibers is formulated.Materials and Methods. The composition and properties of the materials used for manufacturing the foam concrete mixtures are listed. The methods used for assessing the technological and mechanical properties of the materials under study are indicated.Results. The results of the experimental assessment of the polypropylene fiber length and amount influence on the dynamics of the plastic strengthening growth of the equally dense foam and fiber-reinforced concrete mixtures are presented. The scope of the polypropylene fiber influence on the dynamics of the studied mixtures plastic strengthening is analysed. The scientific substantiation of the reasons accelerating the mass transfer processes during the disperse reinforcement of mixtures with fibers is given. The results of the bending tensile strength tests of the large-size D600 concrete specimens are presented.Discussion and Conclusion. The efficient positive influence of the polypropylene fiber, in correlation with its length, on the following foam concrete properties has been distinguished:speed of phase transfer;ultimate extensibility;elasticity and strength modulus of D600 concrete.

Rocket blast resistance of the fully demountable high performance FRC tongue and groove blocks

AbstractWithin the scope of this study, the design and testing of a fully demountable high‐performance fiber‐reinforced concrete (FRC) barriers with high resistance to sudden dynamic explosion and impact loadings is investigated. In order to solve such an engineering problem, a special FRC “tongue and groove” blocks are designed in a way that could be constructed by two persons to form barriers of various shapes and sizes by combining them easily. The structures produced with these blocks were produced using a hybrid, special FRC mixture in order to resist various bullets, rocket launchers, and explosion effects to protect the person behind them. Within the scope of this study, the resistance of five different special FRC mixtures with different properties against sudden dynamic blasting effects was determined by comparing and interpreting the acceleration‐time and strain‐time measurements taken from the wall directly. The results obtained from the dynamic blasting tests carried out in the field were compared with the results of the numerical analysis performed using the Ls‐Dyna finite element software. As a result of the study, the barrier structure produced with special FRC, in which hybrid nylon and steel fibers are used as reinforcement, exhibited the most successful results for absorbing the energy caused by the rocket blast loadings.

Implementation of two-stage mixing approach to improve the performance of fiber reinforced concrete for sustainable construction

Concrete has a significant impact on the environment, and the use of fibers in concrete is a way to mitigate its environmental impact. In this study, two-stage mixing approach (TSMA), typically utilized to enhance the quality of the interfacial transition zone (ITZ) of recycled aggregate concrete mixtures, was employed to enhance the performance fiber reinforced concrete (FRC) mixtures by improving the fiber–matrix ITZ. To investigate the effectiveness, FRC mixtures were prepared using standard (ordinary) and modified (TSMA) mixing approaches. Subsequently, their mechanical properties were measured, and microstructural analyses were conducted to examine fiber–matrix ITZ. In the end, a case study for a concrete pavement was carried out to examine the effect of improved performance on the cost and environmental impact of FRC. Based on the results, up to a 30.6% increase in FRC residual flexural strength ratio was obtained for modified mixing method, without considerable change in strength and stiffness. Microstructural analyses were found to support the ITZ improvement provided by the employed mixing methodology. Furthermore, material-related cost and environmental impact values were found to decrease up to 6% based on the case study conducted. As a result, the implementation of TSMA for FRC was found to be a promising technique to enhance FRC performance and suggestions were provided for the future studies to further improve the obtained benefits.

Numerically optimized post‐cracking branch of the constitutive tensile model for fiber‐reinforced concrete with natural and recycled aggregates

AbstractThis paper investigates the post‐cracking behavior of glass fiber‐reinforced recycled concrete (FR‐RAC). This was done on eight fiber‐reinforced concrete (FRC) mixtures, with three types of recycled aggregates (RAs), while the used fibers were the CEM‐FIL Minibars™ with a fiber content of 0.50 and 0.75 V%. Based on those investigated mixtures, it was found that the proposed constitutive tensile model of the fib Model Code 2010 and the model of di Prisco overestimate the measured load–CMOD curves. Therefore, the post‐cracking branch of the constitutive tensile model was numerically optimized. This was done by optimizing the ka and kc value in the simplified model (Equations 16 and 17), proposed by Vandevyvere and based on the model of di Prisco. The ka value relates to the tensile strength at serviceability limit state, while the factor kc relates to the tensile strength at ultimate limit state (ULS). The numerically optimized ka and kc value, abbreviated by and , indicates a lower value and a higher value than the model of di Prisco et al. In addition, the extensive test data in this study show an increased post‐cracking behavior for the 0.75 V% mixtures with RAs. However, the and values are 0.325 and 0.710 for NAC‐0.75 V%, and only slightly different and values are obtained for the FR‐RAC mixtures. Therefore, one unified constitutive tensile model is proposed for all FRC mixtures. In addition, the numerically optimized model indicates a lower neutral axis location as well as a higher maximum tensile strain () and compressive strain () for the recycled concrete mixtures. The value at CMOD3 is 0.074‰ for NAC‐0.75 V%, while the nRAC‐0.75 V% mixture indicates a value of 0.100‰. This explains the improved fiber activation of the fiber‐reinforced recycled concrete mixtures (with 0.75 V% glass fibers).

A Review Study of the Mechanical Characteristics of Nano Concrete Reinforced with Hybrid Fiber

Due to poor strength and hardness, low tensile strength, and inadequate cracking resistance, conventional concrete has recently posed a significant barrier to the modernization of the structural sector. To solve these issues, researchers investigated and found ways of implementing nanotechnology in concrete production. Nano concrete can be produced by incorporating nanomaterials in the concrete mix. This concrete type can also be reinforced by incorporating hybrid fibers and nanofibers. This review paper conducted an in-depth study on two types of nanomaterials that could be used in the production of nano concrete. Additionally, hybrid fibers were used to strengthen nano concrete. The objective of this paper was to identify some nanomaterials used in the production of nano concrete. Even though this unique hybrid material has been the subject of several investigations, there have only been a few reviews on its production procedures, effectiveness, and performance of this type of concrete. To identify these nanomaterials, their potential, and their properties, a review method was used to study previous works of some researchers and scientists on related and similar works. Some properties of these nanomaterials were discussed in this paper. Summarizing and concluding the research works of previous authors and this current study, it was found that nano concrete has better properties compared to normal conventional concrete. However, there are some limitations associated with the uses and applications of these nanomaterials in concrete for mass production. By tracking the beginning and spread of cracks, it was discovered that mixing various fiber types into a concrete mix enhances the cementitious matrix's strength qualities. The mechanical and toughness characteristics of fiber-reinforced concrete mixtures may be significantly improved by incorporating composites hybrid fiber composites that utilize the synergistic impact of nano- and micro-additives.

Программа и результаты экспериментальных исследований характеристик фибробетона, изготовленного по механической технологии создания агрегированного ориентированного фибрового армирования

Statement of the problem. The pace of development of modern construction creates the need to develop new technologies that make it possible to impart special properties to classical building materials, allowing them to expand the range of their application. The developed technology of mechanical distribution and orientation along the fiber fibers acting in the structure of tensile stresses in the body of linear fiber-reinforced concrete and fiber-reinforced concrete elements can provide more efficient use of fiber-dispersed reinforcement by including more fibers in the work of the section. It is necessary to develop a program of experimental studies of the strength and deformation properties of fiber-reinforced concrete in order to test the technology of laying fiber-reinforced concrete mixture developed by the authors.
 Results. A program of experimental studies of the strength and deformation characteristics of fiber-reinforced concrete, manufactured using the mechanical technology for creating aggregated oriented fiber reinforcement, is presented. The results of experiments carried out in accordance with the developed program are also presented.
 Conclusions. The presented program of experimental studies of the characteristics of fiber-reinforced concrete, made according to the technology developed by the authors for the mechanical creation of aggregated oriented fiber reinforcement, became the basis for experimental studies, the purpose of which was to test the technology developed by the authors for the mechanical laying of a fiber-reinforced concrete mixture with a uniform distribution of fiber fibers in a concrete matrix, as well as obtaining new data on the mechanical and deformative properties of such fiber-reinforced concrete.

Development of Concrete Mixture for Spun-Cast Full-Scale Precast Concrete Pipes Incorporating Bundled Steel and Polypropylene Fibers.

Spin casting is the oldest method of manufacturing precast concrete pipes among all existing methods. While improved concrete mixtures incorporating fibers for other methods of concrete pipe manufacturing, such as the vibration method and roller compaction method, have been developed, no such concrete mixture has yet been developed for spun-cast concrete pipes. This study was designed to explore the possibility of incorporating locally manufactured steel fibers and commercially available polypropylene fibers to develop an improved concrete mixture for use in the manufacturing of full-scale spun-cast concrete pipes. The used steel fibers were of two types, i.e., straight and bundled steel fibers, manufactured by cutting locally available long straight and bundled steel wires, respectively. Various dosages of steel fibers (i.e., 20, 30, 40, and 50 kg/m3) and polypropylene fibers (i.e., 5, 10, 15, and 20 kg/m3) were used in mono and hybrid (steel and polypropylene) forms. The properties in the fresh state and mechanical properties of the test mixtures were investigated. Full-scale spun-cast concrete pipes having a 450 mm internal diameter were manufactured and tested using the three-edge bearing test. The compressive strength of the mixtures was largely insensitive to the dosage of the fibers. The splitting tensile strength of all fiber-reinforced concrete mixtures was higher than that of the reference mixture without fibers, with a 24% increase recorded for the concrete mixture incorporating 50 kg/m3 of bundled steel fibers relative to the reference mixture with no fibers. The flexural performance of the fiber-reinforced concrete mixtures was superior to that of the reference mixture without fibers in terms of flexural strength, toughness, residual strength, and crack control, with up to 28% higher flexural strength relative to the reference mixture without fibers. The three-edge bearing tests on full-scale spun-cast pipes incorporating steel fibers showed that the use of fibers is a promising alternative to the traditional steel cage in spun-cast concrete pipes.

Efficient reception of introducing basalt fiber in cement matrix of fiber concrete

The article is devoted to solving the problem of the distribution of basalt fiber in the environment of the filled cement paste and the total volume of basalt fiber-reinforced concrete, which is one of the most important in the preparation of basalt fiber-reinforced concrete. This article presents the results of experimental studies to establish the most effective technological method of introducing basalt fiber into the cement matrix of the composite from the point of view of increasing the strength characteristics of fiber-reinforced concrete. In the experimental studies performed, standardized methods for the study of cement paste and stone were used. As a result of the research, graphical dependences of the strength and water demand of a dispersed-reinforced cement stone on introducing basalt fiber into the composite and the quantitative content of basalt fiber in the composite were obtained. The analysis of the obtained results made it possible to establish that of the various methods for introducing basalt fiber into the cement matrix of basalt fiber-reinforced concrete, the most effective in terms of increasing the strength of the composite material, provided that the water demand of the fiber-reinforced concrete mixture remains unchanged, is preliminary dry mixing of cement with basalt fiber in a spring mill. The most favorable environment for the mechanical activation of basalt fiber in a spring mill has also been established, which makes it possible to achieve high rates in terms of the preservation of basalt fiber during joint grinding. The scientific novelty of the performed research lies in the fact that the issue of studying the distribution of basalt fiber was first studied at the level of the microstructure of basalt fiber-reinforced concrete.

Mechanical properties of hybrid fiber‐reinforced concretes made with low dosages of synthetic fibers

AbstractRecent advances made in concrete fibers have made them one of the concrete's recommended ingredients, mainly to eliminate the drawbacks associated with the weakness of cementitious materials, such as concrete, in tension. The addition of fibers, however, introduces extra cost and labor requirements, while selecting an appropriate choice and dosage of fibers has still remained a standing question. To address the outlined issues, the current study investigates the development of fiber‐reinforced concrete (FRC) mixtures with a focus on achieving superior mechanical properties with a low dosage of synthetic fibers. For this purpose, three choices of macrofibers were examined. The investigations spanned four dosages of each macrofiber mixed with three dosages of a microfiber included to ensure adequate resistance to early‐age, shrinkage‐induced strains. The experiments conducted on the developed hybrid FRC mixtures systematically measured workability, as well as compressive, splitting tensile, and flexural strength properties. The test results were then paired with the micro‐scale monitoring of the bond between individual macrofibers and the concrete matrix through scanning electron microscope images. The outcome shed light on how each of the macrofibers of choice contributed to improving the FRC's mechanical properties. This paved the way to benefit from a minimum dosage of them to achieve the expected structural response, while avoiding crack formation and propagation in various applications.

Effect of fiber ratio on the impact behavior of polypropylene fiber reinforced samples

This study investigated the effect of fiber ratio on the impact behavior of polypropylene fiber reinforced concrete cube and beam samples. Plain concrete mixtures for control samples and polypropylene fiber-reinforced concrete mixtures with fiber ratios of %0.22, %0.44, and %0.66 by volume were prepared. An instrumented drop-weight impact system was used for the dynamic tests. Static compression tests, three-point bending tests, and impact tests were performed on beam samples (with the dimension of 100×100×500 mm). Static compression and impact tests were performed on cube samples (with the size of 100 mm). It was observed that the fracture properties of polypropylene fiber reinforced concrete for both cube and beam samples were better than the control samples under impact. The crack width in the beams under the impact decreased with the increase in polypropylene fiber ratio. The cube and beam concrete samples reinforced with polypropylene fibers absorbed the impact energy better than the control samples.

Experimental evaluation of multi-functional effects of fibers on mechanical and performance properties of Roller-compacted concrete pavements (RCCP)

The weak performance of asphalt pavements in different climatic conditions, quick decay of pavement, and lack of necessary durability have caused engineers and constructors to try to find Roller Compacted Concrete Pavement (RCCP) for use in various conditions and applications with outstanding properties such as higher durability, and lower maintenance costs. This paper aimed to investigate the mechanical and durability of RCCP by considering different types and amounts of fibers. Cylindrical specimens (with two diameters of 100 and 150 mm) and bending beams with four different fiber types (steel, Kortta Emboss, Kortta Twist, and Sinusoidal plastic) and different percentages were used and subjected to various tests. The compaction time (VB or Vebe) test on fresh concrete, the compressive strength, elastic modulus, the flexural strength, the Brazilian tensile strength, impact resistance, electrical resistance, and skid resistance tests on hardened concrete were conducted. A total of 17 fiber-reinforced concrete mixtures in addition to plain specimen were considered. The test results indicated that compressive, flexural, and tensile strengths of the specimen containing steel fibers were improved up to 27, 83, and 25%, respectively. Moreover, the flexural and tensile strengths of specimens containing Kortta Emboss fibers were improved up to 80 and 19%, respectively. The impact resistance of specimens containing steel and Kortta Emboss fibers were significantly improved up to 270 and 290%. Based on evaluating the results obtained from all tests, Kortta Emboss fiber was proposed as the best option among the studied fibers to improve the properties and functions of RCCP.

Vibroextrusion flow of concrete mixtures in a right four-corner pyramidal channel

The purpose of the research was to obtain calculation formulas for describing the flow of concrete mixtures and determining their viscosity directly in the process of vibroextrusion in regular quadrangular pyramidal channels.
 In solving the flow problems, it was taken into account that concrete mixtures are non-Newtonian systems in the conditions of a vibration field, and hydrodynamic theories were used to calculate the processes and rheological characteristics.
 Since the calculation formulas for describing the flow of fluids in a regular quadrangular pyramidal channel are absent and the channel has a square cross section, an analytical dependence was used to characterize the process, which describes the flow of a Newtonian fluid in a rectangular channel of constant cross section. The authors proposed for use simplified formulas for determining the maximum flow rate and flow rate of a Newtonian fluid in a channel of rectangular cross-section.
 The degree of decrease in the flow velocity and the flow rates of a Newtonian fluid in a channel of rectangular cross-section in comparison with the flow between flat parallel plates are analyzed.
 To describe the flow of concrete mixtures in regular quadrangular pyramidal channels, the proposed coefficients for reducing the speed and flow rate, as well as the existing formulas for the flow between flat symmetric stationary walls, which converge, were used.
 The possibility of using the obtained formula for the flow rate in a regular quadrangular pyramidal channel for calculating the viscosity of a concrete mixture during vibration extrusion is shown. To simplify the experimental procedure, a new formula for calculating the viscosity based on the expiration time for a certain amount of concrete mixture has been proposed.
 The formulas obtained are convenient for further mathematical processing and have no restrictions in their application. The proposed method for determining the viscosity expands the possibilities of studying the rheological properties of concrete mixtures in the vibroextrusion of fiber-reinforced concrete mixtures.

Characterizing fiber reinforced concrete incorporating zeolite and metakaolin as natural pozzolans

Supplementary cementitious materials (SCMs), including industrial by-products or natural pozzolans are widely used as a partial replacement of ordinary Portland cement (OPC) in eco-friendly concrete, to reduce the carbon footprint and enhance mechanical and durability properties. Although many experiments have been conducted to study the effect of SCMs in concrete, the research on the effect of natural pozzolans on fiber reinforced concrete (FRC) is limited. This study investigates the effect of different amounts of metakaolin and zeolite pozzolans on the mechanical properties and durability of concrete containing polypropylene fibers. A total of 99 specimens were made in 11 experimental groups and the parameters of compressive strength, tensile strength, water absorption, porosity and density of concrete specimens were evaluated. In addition, concrete specimens were tested for ultrasonic pulse velocity (UPV) and atomic force microscopy (AFM) to further study the effect of natural pozzolans on the microstructure of concrete. The performance of FRC with natural pozzolans was compared to that of reference concrete and fiber reinforced concrete without SCMs. The results indicated that the polypropylene (PP) fibers were more effective in enhancing mechanical properties of concrete in the zeolite mixtures, so that the compressive strength and tensile strength compared to reference concrete increased by 44 and 22%, respectively, while the water absorption and porosity decreased by 48 and 45%, respectively. This is attributed to the higher viscosity of the zeolite-mixtures that allowed for a better dispersion of fibers in the mixture as well as the improved bond strength between fibers and paste due to the high pozzolanic activity of zeolite. The AFM analysis, UPV, density, and permeable voids test results revealed that the FRC mixtures incorporating natural zeolite had the most dense microstructure and the least porosity and defects among all examined FRC mixtures even compared to the mixtures that incorporated metakaolin with the same cement replacement level.

Flexural Tensile Strength of Concrete with Synthetic Fibers.

Fiber reinforcement is currently most often used in floors, railway sleepers, prefabricated structural elements such as slabs, beams and tanks, and in small architecture elements. Designing elements or structures made of fiber-reinforced concrete requires knowledge of its basic mechanical parameters. In the case of concretes with metallic fibers, the literature can find many tests and standard guidelines regarding compressive, flexural, tensile strength and fracture energy. The properties of concretes with non-metallic fibers are slightly less recognized, especially concretes with new types of polymer fibers. Additionally, the lack of standardized methods of testing concrete with polymer fibers make their application much more difficult. In the article, the possibility of using the EN 14651 standard to assess the flexural tensile strength of concrete with the addition of 2.0 and 3.0 kg/m3 of synthetic fibers with different geometry and form was presented. There was a 5.5–13.5% increase in the flexural tensile strength depending on the mixture type. Moreover, in the case of fiber-reinforced concretes, the ductility was enhanced and the samples were characterized by significant residual flexural tensile strengths. Additionally, from the workability tests it was concluded that after the incorporation of fibers, the consistency class decreased by one, two or three. Nevertheless, the compressive strengths of concrete with and without fibers were very similar to each other, and varied from 58.05 to 61.31 MPa. Moreover, it was concluded that results obtained from three-point bending tests significantly differed from empirical formulas for the calculation of the flexural tensile strength of fiber-reinforced concretes with dispersed steel fibers present in the literature. As a result, the new formula determined by the authors was proposed for concrete with polymer fibers with a nominal fiber content ≤1.0% and slenderness of up to 200. It must be mentioned that the formula gave a very good agreement with studies presented in different literature positions. In addition, an attempt was made to evaluate the strengths of tested mixes in accordance with the Model Code 2010. However, it occurred that the proposed fiber-reinforced concrete mixtures would not be able to replace traditional reinforcement in a form of steel bars. Furthermore, in uniaxial tensile tests, it was not possible to determine the σ–w graphs, and received results for maximum tensile strength did not show the clear influence of fibers incorporation on concrete. Then, the fracture energy enhancement (from about 16 to 22 times) and dependencies: crack mouth opening displacement–deflection; crack mouth opening displacement–crack tip opening displacement; and crack tip opening displacement–deflection were analyzed. Finally, the results from flexural tensile tests were compared with measurements of the surface displacement field obtained through the Digital Image Correlation technique. It was concluded that this technique can be successfully used to determine the crack mouth and crack tip opening displacements with very high accuracy.

Meta-Analysis of Steel Fiber-Reinforced Concrete Mixtures Leads to Practical Mix Design Methodology.

The analysis of hundreds of SFRC mixtures compiled from papers published over the last 20 years is reported. This paper is focused on the relationships between the size and dosage of steel fibers and the relative amounts of the constituents of SFRC mixtures. Multiple linear regression is applied to the statistical modeling of such relationships, leading to four equations that show considerable accuracy and robustness in estimating SFRC mixture proportions as a function of fiber content and dimensions, maximum aggregate size, and water-to-cement ratio. The main trends described by these equations are discussed in detail. The importance of the interactions between aggregates, supplementary cementitious materials, and fibers in proportioning SFRC mixtures, as well as implications for workability and stability, are emphasized. The simplicity of these data-driven equations makes them a valuable tool to guide the proportioning of SFRC mixtures. Their predictive performance when used together as a data-driven mix design methodology is confirmed using a validation dataset.

Crack Width Estimation Using Measurements of Central Deflection in ASTM C1609/C1609M

Abstract The ASTM C1609/C1609M beam test, Standard Test Method for Flexural Performance of Fiber-Reinforced Concrete (Using Beam with Third-Point Loading), has been used for assessing the flexural performance of fiber-reinforced concrete (FRC) for many years. The procedure involves the application of third-point loading to a relatively short, simply supported beam that consequently cracks and experiences extension and pull-out of fibers across the crack. The flexural performance of FRC tested in this way is normally expressed as a function of vertical deflection at the center of the beam. This is limiting because central deflection is specific to this test and is difficult to relate to structural applications. However, the two halves of the cracked beam experience essentially rigid-body rotation about the crack, raising the possibility that the maximum crack width can be calculated as a function of central deflection. Crack width is a more useful assessment parameter because it can be related to many structural applications. In the current investigation, seven FRC mixtures were produced and tested in accordance with ASTM C1609/C1609M, with both central deflection and crack width measured in all tests. The maximum crack width was then calculated as a function of central deflection and compared with the measured values. The results indicate that crack width can be calculated with sufficient accuracy using only the central deflection and crack offset from the center, thereby permitting flexural performance to be expressed as a function of crack width without any change to the current test procedure. The coefficient of variation in postcrack flexural strength was found to be slightly smaller for the same set of specimens when expressed as a function of maximum crack width rather than central deflection.

Development of effective fiber-reinforced concrete compositions used in transportation structures

The possibility of producing fiber-reinforced concrete with high deformation properties by regulating the microstructure and using it in the design of transport structures was considered. It was found that to create high-performance transport structures, it is necessary to modify fiber mixtures with complex additives, i. e. increase the strength of fiber-reinforced concrete at the micro-level. To obtain a denser structure of the concrete matrix, complex additives were used – ultrafine additive (silica fume) and Master Air 200 B air-entraining additive. It was experimentally proved that using such additives reduces the water-cement ratio and further strengthens the concrete matrix structure. The design of the unloading structure on the railway line constructed from the Karadag station (Republic of Azerbaijan) to the SOCAR oil and gas processing and petrochemical complex using fiber-reinforced concrete modified with complex additives was made. The results of designing the fiber-reinforced concrete unloading structure were analyzed and the results of designing the fiber-reinforced concrete unloading structure and the regular concrete unloading structure were compared. As a result of the comparison, it was found that using fiber-reinforced concrete decreases the cross-section diameter of the effective reinforcement of the slab – the cross-section diameter of the effective reinforcement of the pavement slab decreases from Æ2×32 mm to Æ32 mm in the upper and Æ25 mm in the lower row, respectively. Crack resistance is also increased compared to regular concrete. Thus, in order to create structures with high transport and operational parameters, it is necessary to modify fiber-reinforced concrete mixtures with complex additives

RETRACTED: Abrasion and skid resistance of concrete containing waste polypropylene fibers and palm oil fuel ash as pavement material

During the entire service life of pavement, the exposed surface must have an adequate level of roughness, so as to expedite the friction amongst vehicle wheels and the surface of the pavement. Therefore, the abrasion and skid resistance should be considered when measuring the wear, sliding, and skidding levels of a pavement surface. It is well-known that the lower the skid resistance value, the higher the percentage of traffic accidents (particularly under wet conditions). Therefore, this study aimed to enhance the abrasion and skid resistance of concrete as a pavement material by reinforcement with polypropylene (PP) fibers. The influences of waste PP fibers and palm oil fuel ash (POFA) on the tensile and compressive strengths, modulus of elasticity, abrasion resistance (tested using a Bohme surface abrasion machine), and skid resistance (tested using a British pendulum skid resistance tester) of the concrete were investigated. Overall, 12 mixes were cast, including six concrete mixtures comprising 0%, 0.25%, 0.5%, 0.75%, 1%, and 1.25% PP fibers with 100% ordinary Portland cement (OPC). Another six concrete mixtures were prepared with the same fiber dosages, but with 20% POFA as a cement replacement. The experimental results revealed that using PP fibers at concentrations up to 1.25% reduced the compressive strength of concrete mixtures by approximately 17%. However, the addition of PP fibers significantly enhanced the tensile strength (by 30%), along with the abrasion and skid resistance of all of the fiber-reinforced concrete mixtures. It was found that the 1.25% PP fiber mix had the highest abrasion and skid resistance, i.e., approximately 25% higher than that of a control mix. In addition, the POFA mixes performed better than the OPC mixes, owing to the high pozzolanic activity and the formation of additional hydration products.

Technologies for creating directional orientation of fiber reinforcement in concrete

Information on the analysis of methods for creating directional orientation of steel fiber rodding of reinforced concrete structures is presented. The design of a mobile experimental setup for the manufacture of fiber-concrete and fiber-reinforced concrete linear elements with a directional orientation of steel fibers by mechanical means has been developed. The test results of the pilot plant are presented. The required dimensions of the bunker for the fiber-reinforced concrete mixture, the type of the leveling element and the method of increasing the fiber-reinforced concrete mobility during casing using a pilot unit have been determined. The creation of a directed orientation of fiber threads in fiber-reinforced concrete makes it possible to make the most of this material‘s advantages. Despite a sufficient number of theoretically possible ways to create a directional orientation of fibers in a concrete mixture, not all of them can be applied in real construction conditions. Also, a number of methods introduce additional difficulties into the concreting process, which can adversely affect the construction processes duration. The use of a mechanical method for creating a directional orientation of steel fiber reinforcement in concrete made it possible to obtain the desired result on a mixture already containing fiber threads, without the need for their separate laying. The optimal design of the mechanical element leveling and the features of the process of leveling steel fibers in concrete have been established.