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Waste fiber reinforced concrete is gaining recognition as a high‐performance construction material, offering notable load‐bearing capacity, corrosion resistance, and enhanced durability features. As the building and construction industry focuses on sustainable practices, fibers derived from waste materials create an opportunity to be utilized further in composite designs. This study explores the tensile, compressive, and flexural behaviors of cardboard fibers (kraft fibers) and textile polyester fibers in concrete materials. The composite microstructure is also investigated using a scanning electron microscope (SEM) to measure the bonding performance of the fibers within the cementitious matrix. Four mix designs were created using 2.5% textile fibers as a reinforcement agent and 5% silica fume modified kraft fibers (SFKFs) as a partial cement replacement. The combination of fibers achieved 44 MPa compressive strength, equaling the control. Tensile strength was enhanced by 5% when using the combination of the two fibers, achieving 3.58 MPa in comparison to 3.41 MPa. However, flexural strength was reduced among all fibrous concrete materials. SEM images distinguished the natural and synthetic characteristics associated with the two fibers within the cementitious matrix. Namely, demonstrating the chemical bonding of SFKFs in comparison with the physical bonding properties of the textile fibers. This study serves as a valuable resource for future investigations and the broader adoption of binary waste fiber composite designs in cementitious composite applications. [ABSTRACT FROM AUTHOR]

The use of ultra‐high‐performance fiber reinforced concrete (UHPFRC) to repair or rehabilitate old concrete structures has been shown to be appropriate due to its properties, such as higher compressive strength, ductility, and durability than conventional concretes. One of the studied strengthening techniques is the reinforced concrete columns jacketing by UHPFRC. Some recent research evaluated some parameters, such as the repair thickness and the volumetric ratio of stirrups. However, other important parameters, such as UHPFRC jacketing thickness in different column cross‐sections and the concrete core compressive strength, need to be addressed. In addition, the analytical models presented in the literature are restricted to only one concrete grade. The present study aims to evaluate the behavior of short reinforced concrete columns strengthened with UHPFRC subjected to centered compression. Numerical analyses of three‐dimensional models were performed using the finite element method, validated, and calibrated using experimental results. The influence of the concrete core compressive strength, the UHPFRC jacketing thickness, and the shape of the cross‐section were evaluated. Numerical simulations concluded that the lower concrete core compressive strength columns showed the best relative increase performance. Moreover, the concrete core strength was inversely proportional to the resistance capacity of the repair system. In addition, the increase in repair thickness contributes to the axial strength of the column. Furthermore, the cross‐section influences the distribution of stresses and strains, showing the best performance for circular sections. Finally, regardless of cross‐section type, the proposed equations accurately predicted the numerical results. [ABSTRACT FROM AUTHOR]

High‐performance fiber‐reinforced concrete (HPFRC) can be considered a promising material for the construction of precast concrete girders for road bridges. This paper presents conceptual considerations and numerical analysis to support this statement. The HPFRC is a compromised alternative between FRC and UHPFRC mixes. Specifically, a tailor‐made mix design of HPFRC jointly developed by ACCIONA and the authors is presented, and then compared with the other types of fiber‐reinforced concretes collected from the technical literature. In addition, some trends observed in the database are described. This material characterization is followed by a conceptual analysis of the advantages of the application of HPFRC to road bridges. Specifically, a proposed bridge for the case of a 60 m‐span box girder is analyzed. A comparison between alternatives based on the use of HPFRC and conventional reinforced concrete is discussed. The results shed light on the viability of this material for bridge application. Specifically, the main finding show potential significant material savings in structural elements of the superstructure. Finally, ongoing and future research for a wide application to the construction sector are briefly discussed. [ABSTRACT FROM AUTHOR]

In order to comprehensively examine the influence of basalt fiber on the basic mechanical properties of concrete, the axial compression, axial tension and direct shear tests were carried out on basalt fiber reinforced concrete (BFRC) with different fiber contents and fiber lengths. The failure modes and stress–strain curves under different loading modes were obtained from the test data, and the basic mechanical parameters of BFRC were extracted from the curves. Based on the results, the following conclusions were drawn. With the increase of fiber content, both the compressive strength and tensile strength showed an upward trend first followed by a downward trend. In general, the shear strength of BFRC was lower than that of ordinary reinforced concrete with no fiber (RC). All BFRC specimens had an increased peak strain and significantly improved deformability compared to RC. Based on a comprehensive analysis, the specimen with a fiber content of 0.2% and a fiber length of 6 mm (BFRC‐0.2%‐6) exhibited the best mechanical properties. In addition, mathematical regression analysis was performed on the normalized stress–strain curves of BFRC, and the influencing parameters model of basalt fiber was proposed based on the fiber content and fiber length. Moreover, scanning electron microscopy (SEM) and computed tomography were utilized to analyze the influencing mechanism of basalt fiber content and fiber length on the mechanical properties of concrete from the microcosmic and mesoscopic perspectives. [ABSTRACT FROM AUTHOR]

This study examines the use of steel fibers in enhancing the ductility of an economical ultra‐high strength concrete (UHSC). The addition of fibrous material with very small geometry in this mixture is an effective solution to improve its ductility and prevent its brittle failure which is a common characteristic of UHSC. Different mechanical properties of reinforced and unreinforced concrete (e.g., slump flow, compressive, splitting tensile strength tests, and failure modes) were taken into account to find out the efficiency of micro steel fibers. The test results showed that concrete containing 25 mm length and 0.20 mm diameter steel fibers at a volume fraction of 0.5% not only presented a reasonable improvement in ductility performance but also ensured cost‐effectiveness. The cost evaluation conducted on several existing mix designs is also introduced in this study to investigate the influence of various steel fiber contents on the total cost of concrete so that figure out the lowest budget solution. The evaluation shows the high price of fiber reinforcement in which an addition of steel fibers by 5% volume could increase 7% of the total concrete cost. [ABSTRACT FROM AUTHOR]

The disposal of waste from coal plants and waste glass (WG) is causing significant environmental problems all around the planet. Currently, the amount of discarding of these wastes is increased. One possible option is to utilize fly ash (FA) from coal plants as a partial substitute for the cement and EG as a fractional substitute for sand in concrete, respectively. Besides, fibers can improve the strength and durability of concrete; explicitly speaking, using coconut fibers (CFs) is in trend due to their highest toughness among natural fibers making it suitable material as fiber reinforcement in concrete. This research studies the concrete behavior with 15% FA as a partial substitute of cement with 2% CFs and waste beverage glass as sand at various replacement levels (14%, 15%, 16%, 17%, 18%, 19%, and 20%). Mechanical and durability characteristics of concrete were assessed, such as compression strength, water absorption, flexural strength, density, workability, and water absorption. The current study results show that adding FA, CFs, and WG improved microstructure quality at 16% replacement of sand. The study showed that the M4 mix has enhanced the properties of concrete samples as compressive and flexural strength was improved to 47.2 and 6.2 MPa and improved apparent density by 20%. Adding more WGP than the optimal proportion (16%) led to detrimental effects on void ratio, permeability, and water absorption. Therefore, 16% of sand with WG and 15% of FA with cement can be substituted with 2% CFs to develop sustainable concrete. [ABSTRACT FROM AUTHOR]

This article proposes a new constitutive model for the cyclic behavior of rubberized concrete confined with fiber‐reinforced polymer (FRP) sheets. The model is calibrated with experimental results from 18 confined rubberized concrete (CRuC) cylinders tested in cyclic compression. The cylinders had 60% total aggregate volume replacement with recycled tyre rubber. Parameters investigated include the type of confining material (Carbon or Aramid FRP) and number of layers (two, three, or four). The results indicate that using FRP confinement leads to a strong (up to 100 MPa) and highly deformable (axial strains up to 7%) rubberized concrete that can be used in structural applications. The proposed constitutive model predicts accurately the material response under cyclic loading and can thus be used for design/analysis of highly deformable components made of FRP CRuC. This article contributes toward the development of advanced constitutive models for FRP CRuC, thus promoting the wider use of recycled materials in construction industry. [ABSTRACT FROM AUTHOR]

In this paper, concretes including three different fiber types (carbon steel fiber [CSF], forta ferro fiber [FFF], and polypropylene fiber [PPF]) with different percentages by volume (0.5%, 1%, and 1.5%) and crumb rubber (CR) as a replacement of fine aggregate by volume (5%, 10%, and 15%) are mechanically investigated. Compressive strength, flexural tensile strength, pull out strength, and elevated heat resistance tests are conducted 28 days after casting on the prepared concrete specimens. For the elevated heat resistance test, samples are exposed to 200, 400, and 600°C heat for 2 h and then compressive strength test is applied. According to the test results, fiber reinforcement limits compressive strength decrease and improves flexural tensile strength properties of the rubberized concretes. The positive effect of the fiber reinforcement is also observed on the samples conducted to pull out strength and elevated temperature resistance tests. CSF and PPF reinforced rubberized concretes perform better pull‐out resistance then the FFF reinforced rubberized concretes. Elevated heat resistance test is as expected since with elevation of the temperature strength of the concrete decreases. But according to the test results of the present study, the strength decrease seems to be limited with fiber reinforcement. As a result, incorporation of the fiber and CR could help to utilize more waste tire (CR) in concrete to produce sustainable eco‐friendly concrete. [ABSTRACT FROM AUTHOR]

Investigations on steel fiber reinforced concrete (RC) beams in torsion show, that the steel fibers positively influence the torsional load‐bearing behavior. Since a systematic evaluation of the previously known test results and the derivation of a generally valid design model were lacking until recently, current codes such as Model Code 2010 do not contain any design models for the consideration of the steel fiber load‐bearing effect in the torsion design. Due to this, the existing torsion tests on steel fiber RC were summarized in a database. Furthermore, on the basis of the test results and observations, the space truss model developed by Rausch and later refined by Lampert and Thürlimann, among others, was further developed and supplemented by additional longitudinal and transverse steel fiber tension struts. This modified space truss model was validated with the database and shows good to very good predictions to the torsion test data. [ABSTRACT FROM AUTHOR]

Although steel fiber reinforced concrete is becoming increasingly popular in the construction industry, its application is currently limited to certain areas. One reason is the lack of an economical non‐destructive testing method to determine the content, distribution, and orientation of steel fibers in fresh and hardened concrete. However, these parameters are decisive for the assessment of the static performance of a building component. In this article a new test method is proposed, which is based on the electrical conductivity of concrete. Using a two‐electrode experimental set‐up, measurements of the electrical conductivity were done on hardened concrete cubes with defined fiber content and a correlation between electrical conductivity and fiber content could be identified. Within the scope of extensive test series, the fiber content and the age of specimens were varied, and several identical series were produced and observed to ensure statistically verified results. At this stage of research the test method based on electrical conductivity measurement provides reliable results on the fiber content of preconditioned concrete cubes. Based on the results a new model was developed to quantify the fiber content of the examined cubes. This model is based on the estimation of the relative conductivity, the so‐called increase of conductivity. Undesired influences caused by aging, respectively hydration in the young concrete age were eliminated, by relating the conductivity of fiber reinforced concrete to an unreinforced concrete. Further investigations with focus on the influence of concrete composition and other specimen sizes are going to be conducted as next steps for the development of an in situ test setup for the diagnosis of concrete structures. [ABSTRACT FROM AUTHOR]

When designing steel fiber‐reinforced concrete, for example, according to Model Code 2010, the residual flexural strength values must be specified as fundamental properties. It is often difficult to establish the relationship between residual flexural strength values and the required dosage of steel fibers depending on the type of steel fibers and the concrete quality. For an estimation of the presumably necessary dosage of steel fibers, various empirical approaches exist for the approximate determination of the residual flexural strength values, which, however, are based on different tests and have been almost exclusively been derived on the basis of few or "own" test results of the respective institute. For this reason, the validity of the respective approximation approach is often limited. Using the bending beam database "Steel Fibre Reinforced Concrete", selected approaches were systematically analyzed and an improved approach for determining the residual flexural strength values of steel fiber‐reinforced concrete was developed. [ABSTRACT FROM AUTHOR]

In the worst-case scenario, a projectile would penetrate the whole thickness of the "absorbing" energy shield layer, bounce off the ordinary concrete, and lose the rest of its energy while ricocheting inside the shield layer. The proposed concrete, intended as a shield layer covering structural concrete, is based on light aggregates and is modified by fiber.[[4], [6]] The created porous and weakened (in terms of compressive strength)[[7]] matrix is easily penetrated by a projectile. Anti-terrorist concrete shields absorbing projectiles with no ricochets. [Extracted from the article]

Macro‐synthetic fiber‐reinforced iron ore tailings (IOT) concrete is an environment‐friendly building material featured by recycling IOT and improving performance of IOT concrete due to fiber incorporation. In this study, the mechanical properties of macro‐synthetic fiber‐reinforced concrete incorporating IOT were investigated. Two different replacement ratios of IOT (i.e., 0% and 50%) and six types of macro‐synthetic fibers at 1.0 vol% were adopted to investigate the effects of IOT, aspect ratio, elastic modulus, and tensile strength of macro‐synthetic fibers on mechanical properties of concrete. The results indicate that the concrete with IOT for natural sand (NS) replacement in 50 wt% demonstrates no loss in compressive strength and a minor loss of 7.67% in fracture energy, but the incorporation of IOT lowers splitting tensile strength and limit of proportionality, especially the splitting tensile strength with a decrease of 18.50%. The splitting tensile strength, equivalent flexural tensile strength, residual flexural tensile strength, and fracture energy were notably improved by adding macro‐synthetic fibers. Experimental results using Tukey test and Student's t test demonstrated that the fiber aspect ratio was more effective in improving equivalent flexural tensile strength, residual flexural tensile strength, and fracture energy than the elastic modulus and tensile strength of fibers, and the residual flexural tensile strength fR,4 was enhanced by 146.34% when increasing the fiber aspect ratio from 36 to 60. [ABSTRACT FROM AUTHOR]

The concrete undergoes brittle failure, which is a disadvantage for stability and safety analysis. This drawback was compensated by addition of different types and size of fibers for improving the compressive and fracture characteristics. The incorporation of multi‐scale hybrid fibers in concrete showed enhanced performance at multi‐level than that of single type or size of fiber. This study examined the influence of basalt fiber length (12, 25, 37, and 50 mm) and content (0.15% and 0.3%) on compressive and fracture parameters of hybrid fiber reinforced concrete (HyFRC). Systematic experimentations were performed on mechanical properties which include compressive strength (f'c), toughness index (ɳ) and capability coefficient index (ξ), initial fracture toughness (KiniIC), unstable fracture toughness (KunsIC), and fracture energy (GF). The crack resistance process and fiber‐matrix interaction obtained by scanning electron microscopy analysis were also discussed. The proposed analytical models of HyFRC stress–strain equations indicated great suitability for fitting of experimental behavior with R2 ≥ 0.92. The basalt fiber with different length and contents showed a great potential in HyFRC and indicated a substantial degree of enhancement for the compressive and fracture properties, as compared to that of PC and HyFRC without basalt fiber. [ABSTRACT FROM AUTHOR]

The focus of this study is to investigate the effect of using coarse recycled concrete aggregates (RCAs) as an alternative material to natural coarse aggregate on the fresh, mechanical and durability behavior of concrete reinforced with steel fiber. Eighteen unique concrete mixes with RCA content of 0%, 50%, and 100% and steel fiber content of 0%, 1%, and 2% were prepared, and tests were performed to study slump, density, compressive and splitting tensile strengths, flexural behavior, surface hardness, surface abrasion resistance, water absorption, and sorptivity of each mix. It is shown that concrete containing RCA has a lower unit weight, compressive, splitting tensile and flexural strength, flexural toughness, surface hardness, and abrasion resistance, and a higher water absorption and sorptivity in comparison with conventional concrete. An increased compressive, splitting tensile and flexural strength, flexural toughness, surface hardness, and abrasion resistance, and a decreased water absorption and sorptivity of concrete with an increased steel fiber content from 1% to 2% is less significant compared to those from 0% to 1%. The results also show that, at RCA content of 50%, incorporating 1% steel fiber develops a concrete mix with similar or even better properties compared to unreinforced conventional concrete. At 100% RCA content, incorporating 2% steel fiber develops a concrete mix with similar properties to unreinforced conventional concrete having water to cement ratio of 0.3, but inferior properties to unreinforced conventional concrete having water to cement ratio of 0.5. These findings indicate that recycled aggregate concrete with similar or even better properties compared to concrete with natural aggregate can be developed through properly designing mixes, providing a great avenue toward the production of green construction material for structural applications. [ABSTRACT FROM AUTHOR]

The natural fibers are evolving in the construction industry in many forms due to its dominant characteristics since decades. This paper delivers a review of the behavior of basalt fiber reinforced concrete under static and dynamic loading conditions. The main aim of the paper is to signify the influence of basalt fibers in concrete as chopped fibers, minibars, rebars, and meshes by showcasing the physical and mechanical properties of the concrete. The proposed review paper furnishes a summary of obtainable evidence about the incorporation of basalt fibers in concrete under various loading conditions. The effect of size and volume fraction of the fibers in concrete subjected to static loading and dynamic loading is discussed and reviewed. Additionally, the optimum length, diameter, and aspect ratio of the fibers with its volume fraction depending on the constituents in concrete is exhibited. Basalt fibers, can operate as an exceptional reinforcing material which can replace the conventional reinforcement with appropriate implementation. Highlights: Application of basalt fibers in concrete based on different loading conditions has been reviewed.Properties and applications of basalt fibers in various forms were assessed.Static and dynamic behavior of basalt fiber reinforced concrete has been summarized based on the studied literature.Addition of suitable forms and size of basalt fibers in concrete were examined.Parameters such as volume fraction, aspect ratio of basalt fibers has been highlighted. [ABSTRACT FROM AUTHOR]

The redistribution of moment within a statically indeterminate reinforced concrete beam at the ultimate limit state occurs through variations in the flexural rigidities and through the formation of hinges. The phenomena of moment redistribution (MR) is used to increase the efficiency of reinforced concrete design by allowing moments to be transferred away from critical cross sections thereby resulting in lower design moments. To allow for this effect in design, two main approaches are adopted. The first is to perform an elastic analysis and then to adjust the resulting distribution of moment using a codified MR factor. The second is to apply a plastic analysis allowing for the formation of hinges, and to calculate the rotational requirements at the hinges from first principles. This paper uses fundamental plastic analyses to derive closed‐form expressions for the hinge rotational requirements for full MR (that required to achieve the theoretical maximum applied load within the beam based on the moment capacity of sections within the beam). These closed‐form solutions are then used to quantify the maximum load on a beam when the rotational capacities at a hinge are less than the rotational requirements for full MR (partial MR). Closed‐form solutions are then used to derive MR factors which do not require semimechanical calibration. [ABSTRACT FROM AUTHOR]

The energy balance method has been widely used in the extant literature to derive the ultimate axial strain of conventional confined concrete columns. However, researchers noted that this method yields unrealistic results compared to experimental data when it is applied to fiber‐reinforced polymer (FRP) confined concrete columns. Therefore, it is deemed that the existing ultimate strain model based on the energy method cannot be directly applied to FRP‐repaired concrete. With this model shortcoming in mind and through a theoretical analysis with proper calibration, the current study extended the energy balance approach to develop a generalized model to determine the ultimate strain of FRP repaired concrete columns. This proposed new model can be used to predict the ultimate strain of repaired columns under both concentric and eccentric loadings. Because this model is established in a unified form without any restrictions to the cross‐sectional geometry, it is applicable to different shapes of repaired columns. On the other hand, although the energy balance method is unconservative for heavily damaged concrete, it exhibits a better performance with respect to the existing models when compared with the test result. [ABSTRACT FROM AUTHOR]

This paper presents a simple yet accurate technique for determining the strength of steel fiber reinforced concrete beams loaded in pure torsion. The results of the model are compared with 21 beams found in the literature as well as two new beams tested by the authors and reported herein. The model considers the beneficial effect of the fibers in resisting tension after the concrete matrix has cracked, and it is implemented into the widely accepted space truss analogy for reinforced concrete members subjected to pure torsion. The proposed model provides good correlations to the collected test data with a test to predicted ratio of 1.10 and COV of 0.19. A simplified method of the aforementioned model, suitable for design, is also presented and is shown to provide good predictions to the test data. [ABSTRACT FROM AUTHOR]

A new and appealing mean of improving the cracking behaviour of RC elements is the combined use of rebars and fibres. Previous research has shown that steel fibres recycled from end-of-life tyres are effective for this purpose. This paper presents and discusses practical applications that would benefit from the use of this technique. Firstly, two previously published examples of crack width calculation according to fib Model Code 2010 are expanded to the case under study. These practical applications show how a fibre-reinforced concrete ( FRC) with a rather poor post-peak behaviour can exhibit large improvements in cracking behaviour while being economically attractive, too. The case of jointless structures is then considered, and the improvements in terms of maximum achievable length are presented and discussed. Finally, an analysis regarding the effectiveness of this solution as a function of the reinforcement ratio is discussed for both tension and bending. The main objective of this paper is to encourage the use of recycled steel fibres as an effective and sustainable mean of dealing with cracking behaviour for specific applications. [ABSTRACT FROM AUTHOR]

The post-heating bond behaviour between fibre reinforced lightweight aggregate concrete (LWAC) and 20 mm-diameter steel bars was experimentally investigated using a modified type of pullout specimen. These were cast using volcanic tuff aggregate concrete with and without hooked steel, brass-coated steel, and a mixture of both types of fibres at a volumetric fraction of 2%, before being water cured for 28 days and subjected to high temperatures, ranging from 300 to 700°C. Standard cubes were also cast, cured and heat-treated under similar conditions before being tested to evaluate compressive and splitting strengths. Duplicate specimens, from various mixtures, were cured in water for a similar period and used as controls. The post-heating cracking pattern and extent were evaluated, and residual strengths and bond behaviour determined and described before and after heating then cooling. The results showed marked reductions in residual bond, compressive and splitting strengths of plain and fibre reinforced LWAC being exposed to high temperatures. Pullout specimens prepared with fibres attained higher residual bond strength and bond ductility after exposure to high temperatures than those of plain ones. The contribution of hooked steel fibres (at volumetric fractions of 1 or 2%) to salvaging bond was over the entire temperature spectrum, while that of brass-coated steel fibres was limited to the lower range of that spectrum (from 300 to 500°C). The findings of the present study confirmed the benefit of using lightweight aggregate in reinforced concrete structures as it contributes to maintaining higher post-heating residual bond strength than that of conventional concrete. [ABSTRACT FROM AUTHOR]

The article offers information on Task Group 8.8 in fédération internationale du béton (fib) Commission 8. It aims to produce a state-of-the-art report and a suggestion on the structural design with flowable concretes. The Task Group 8.8 consists of two Working Parties (WP), WP1 (plain concrete) and WP2 (fibre reinforced concrete).