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Fibers are mixed within reinforced high‐strength recycled aggregate concrete (RHRAC) beams to improve their flexural performance. This study experimentally and analytically investigates the effect of using RAC combined with polyvinyl alcohol fiber (PVAF) and steel fiber (SF) on the flexural performance of RHRAC beams. A total of 11 RHRAC beams (150 × 300 × 2600 mm3) are manufactured and subject to four‐point flexural testing. The parameters of the concrete are investigated, including the volume content of the PVAF and SF. The experimental results show that SF increases the flexural strength of RHRAC beams more than PVAF does. Conversely, the effect of PVAF on deformability is more significant than that of SF. In addition, the positive influences of hybrid fiber (PVAF and SF) on the crack load, flexural capacity, and deformation capacity are superior to those of single‐mixed PVAF or SF. Three different specifications are used to calculate the flexural capacity of the test beams, among which, JGJ/T465‐2019 is the most reliable. [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 this work, the theoretical model for predicting the flexural behavior of steel‐reinforced basalt fiber‐reinforced concrete (RBFRC) beams was developed and the results were experimentally validated. The experimental results presented two failure modes of the RBFRC beams including flexural failure and flexural‐shear failure. The load‐carrying capacity, deformation ability, and crack resistance of RBFRC beams failing in flexure can be significantly enhanced with the addition of chopped basalt fiber. To verify the theoretical model, the predicted results were compared with the experimental results of RBFRC beams, and the relative error between the two methods is very small. Based on the theoretical method, a parametric study was conducted to identify the influence of several crucial materials and structural parameters on the flexural behavior of RBFRC beams. [ABSTRACT FROM AUTHOR]

There are only a few studies related to the effect of the hybrid fiber reinforcement on the flexural behavior of full‐scale beam specimens having lap‐spliced length. Thus, this study will ensure important experimental data about the effect of macro steel fibers blended with micro steel fibers on lap‐spliced length. The aim of this study was to investigate the influence of hybrid steel fiber reinforcement on the flexural behavior of full‐scale reinforced concrete beams having different lap‐spliced bars. A sum of three traditional concrete mixtures including a total of 1% fiber by volume fraction was adopted: control mixture without steel fiber, only macro steel fiber and hybrid steel fiber reinforced mixtures. For this purpose, 18 full‐scale beams (200 × 300 × 2000 mm) having three different lap‐spliced length (15, 25, and 35Ø) as tension steel bars were produced and tested under four‐point bending to examine flexural behavior, mode of failure, ductility, and energy absorption capacity properties. In conclusion, the hybrid fiber reinforcement caused the highest increase in the load carrying capacity of the beam specimens. Besides, the hybrid fiber reinforced beam specimens exhibited excellent ductility and energy absorption capacity compared to single fiber reinforced beam specimens. On the other hand, it can be addressed that the hybrid fiber reinforced structural elements had a vital important to compensate the application errors and carelessness in steel bar workmanship, inadequate the lap‐spliced length as per the codes. It can be emphasized that the lap‐spliced length as per the building codes can be reduced in 40% by containing hybrid steel fiber (0.8% macro‐0.2% micro) reinforced concrete without a reduction in load carrying capacity, ductility, and energy absorption capacity compared to control beam specimens without fiber. [ABSTRACT FROM AUTHOR]

A 3‐stage model is used to evaluate the results of an experimental campaign, previously carried out with the aim of studying the deflection of reinforced concrete structures made with reinforced concrete (RC) and fiber‐reinforced concrete (R/FRC). In particular, 12 four‐point bending tests were performed on beams, whose cross‐sections were obtained by combining four effective ratios of the tensile reinforcement (i.e., 0.73%, 1.7%, 3%, and 6.3%), two concrete covers (i.e., 32 mm and 82 mm), and three amounts of steel fibers (0, 0.5%, and 1.0% in volume) recycled from end‐of‐life tyres. In reinforced beams with low reinforcement ratios, there is a reduction in deflections and the load at yielding of steel increases with the content of fibers. On the contrary, the mechanical behavior of R/FRC and RC beams does not substantially differ in presence of a high effective reinforcement ratio. These experimental observations are in accordance with the results of the three‐stage model, introduced herein to predict the possible variation of the load‐deflection curves. For a given deflection, the model provides a possible range of applied loads, whose upper bound is related to the situation of incipient cracking (i.e., the maximum tension stiffening effects), whereas the lower bound concerns a fully cracked beam (i.e., the minimum tension stiffening effects). Regardless of the content of fibers, the difference between the upper and lower bounds vanishes in highly reinforced concrete beams. [ABSTRACT FROM AUTHOR]

Depending on the ratio of fiber contribution to conventional reinforcement contribution (quantified for example, by I f i SB 0.5 sb [or I f i SB I R i 1 sb ] and SB I s i sb , respectively), the overall behavior of the member (i.e., the sum of the two contributions) may display a hardening or a softening response. Abbreviations f 0.5 residual axial tensile stress offered by fibers at a Crack Opening Displacement COD = 0.5 mm f 1.5 residual axial tensile stress offered by fibers at a COD = 1.5 mm f R 1 residual flexural tensile stress offered by fibers at a Crack Mouth Opening Displacement CMOD 1 f R 3 residual flexural tensile stress offered by fibers at CMOD 3 f u ultimate strength of reinforcing bar f y yield strength of reinforcing bar s r 0 crack spacing Ø s diameter of reinforcing bar su ultimate strain of reinforcing bar sy yield strain of reinforcing bar s longitudinal conventional steel reinforcement ratio s, min minimum reinforcement ratio of conventional steel The paper1 presents useful and valuable information on the flexural behavior of fiber reinforced concrete (FRC) beams with varying fiber types, fiber dosages and longitudinal reinforcing ratios. [Extracted from the article]

The behavior of fiber reinforced concrete (FRC) depends on the characteristics of both the concrete matrix and fibers. Previous studies have concluded that the number of hooked ends increases the contribution of steel fibers to the tensile performance of concrete. ACI 318 code, MC10 fib code and RILEM TC 162‐TDF standard permit the use of steel fiber reinforced concrete (SFRC) for example, the minimum shear reinforcement made of deformed steel bars in flexure‐controlled elements. Other investigations have demonstrated the suitable performance of SFRC in shear‐controlled members and for seismic rehabilitation applications. It has become apparent that the adequate use of SFRC depends on the knowledge and prediction capabilities of its tensile performance. The results of three‐point bending tests on SFRC beams using the test procedure established by the European standard EN‐14651 are presented and discussed herein. Tests were executed with 20 standardized beams made of concrete with a nominal compressive strength of 24 MPa and hooked end steel fibers with an aspect ratio of 65 were applied. Variables were the fiber dosage (0, 20, 40, 60 kg/m3) and the number of fiber hooked ends (1, 1.5, and 2). A numerical model aimed at estimating the residual flexural tensile strength of the SFRC is developed. The proposed model was calibrated using a database of 256 tests, 20 from this study and the remaining 236 from 15 other studies. [ABSTRACT FROM AUTHOR]

The use of fibers in reinforced concrete (RC) beams mainly improves both the bearing capacity and the cracking control. In this way, positive effects on the service life of RC structures can be expected. In this paper, the fiber influence on the flexural behavior of RC beams with different longitudinal reinforcement ratios (0.5% ≤ ρs ≤ 1.2%) is analyzed by testing small‐scale RC beams. Concretes incorporating 0, 25 and 50 kg/m3 of steel, 6 and 12 kg/m3 of glass macrofibers, and 5 and 10 kg/m3 of polymer macrofibers were studied. Crack and deflection control, as well as bearing capacity and crack localization were evaluated for a broad range of fiber‐reinforced concrete (FRC) toughness. It is verified that fibers, in the longitudinal reinforcement ratio considered, improve the bending behavior at serviceability limit state (SLS) and ultimate limit state (ULS) of RC beams, without limiting the structure ductility. It was also confirmed the philosophy of the fib Model Code 2010, such that FRC can be considered as a composite material where performance parameters govern its mechanical behavior. Finally, the several data available allowed to deeply analyze fib Model Code 2010 formulations (mean crack spacing and flexural bearing capacity) and to propose modifications where needed. [ABSTRACT FROM AUTHOR]

Fiber‐reinforced concrete exhibits a heterogeneous microstructure formed by aggregates, fibers and a matrix, where the stress from external forces can lead to cracking and fracture. This paper discusses the development of a computational measure for predicting the fiber's efficacy by means of the energy absorbed within the initiated area of the cracks. The analytical development was verified with experimental data from the literature and the results were justified with numerical simulations in the elastic regime. This development couples the localization of the stress in the crack tip with the random distribution of the cracks, which leads to the spatial strain field. Such percolation‐based quantification of the cracks in the early‐stage particularly is useful for effective utilization of fibers during the cracking progress. [ABSTRACT FROM AUTHOR]

Authors' closure on the discussion of the article: "Assessing the influence of fibers on the flexural behavior of reinforced concrete beams with different longitudinal reinforcement ratios" (discussion by Marki'c et al.) The authors would like to thank the discussers for their interest and for opening a discussion on the ductility of RC elements with fibers, which is a very important topic. This possible negative influence is related to both longitudinal reinforcement (type and ratio) and the weighted ratio between the post-cracking performances of fiber reinforced concrete (FRC) and reinforcement strength properties. [Extracted from the article]