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The paper presents a synthesis of an extensive experimental campaign on linear and two‐dimensional steel fiber reinforced concrete (SFRC) structural elements carried out to check the ductility requirements aimed at guaranteeing limit analysis approaches for the computation of ultimate load‐bearing capacity of SFRC structures; special attention is devoted to the role of the degree of redundancy of the structure. In particular, full‐scale shallow beams and slabs reinforced with steel fibers (with or without conventional longitudinal reinforcement) were tested in two different laboratories: the Politecnico di Milano (PoliMI) and the University of Brescia (UniBS). In this experimental campaign, two different fiber contents and fiber types were considered. The experimental investigation, carried out within the activities to support Annex L of Eurocode 2, was fundamental also for developing the design rules included in the fib Model Code 2020 and allowed to formulate conclusions regarding optimization of the mix design, ductility, and design prediction at the ultimate capacity. [ABSTRACT FROM AUTHOR]

The study of damage processes in concrete and their effects on the residual properties represents a key point related to the service life of reinforced concrete (RC) structures. The use of steel fibers in RC beams mainly improves the cracking control and the shear bearing capacity. Considering the shear behavior, the presence of fibers not only leads to partial or total substitution of secondary reinforcement, but they can also result in a modification of the failure behavior from a shear failure (brittle) to a bending (ductile) one. The contribution of fibers on flexural and shear behavior of sound and damaged RC beams was investigated using alkali‐silica reaction as a damaging tool. First, the evolution of deformations and cracks were measured on creep tests of RC beams with and without fibers and reactive aggregates. Second, the flexural and shear behavior of damaged and undamaged beams incorporating steel fibers were compared. Results showed that alkali‐silica reaction damage can provoke a reduction of RC beam ductility, while the flexural strength is preserved. Regarding shear, it was observed that even in damaged concrete, fibers were able to control the crack propagation and increase the bearing capacity. [ABSTRACT FROM AUTHOR]

The use of fibers in Reinforced Concrete (RC) elements changes their cracking pattern, leading to narrower and more closely spaced cracks. In addition, the presence of fibers can improve the steel‐to‐concrete bond behavior reducing the steel‐to‐concrete interface damage after cracking. Cracks and steel‐to‐concrete interface damage work like paths, for aggressive agents, to reach the rebar in cracking elements, reducing the initiation period of the corrosion process, and favoring the corrosion at the intersection between cracks and reinforcement. In this context, this article discusses an experimental program on tension ties mechanically cracked and exposed to a chloride‐rich environment with the purpose to check and eventually adequate the typical electrochemical measurements, used in the case of RC elements, for Steel Fiber Reinforced Concrete (SFRC). Adjustments related to degradation morphology and interference of steel fibers are proposed and used on Fiber Reinforced Concrete (FRC) elements for monitoring the influence of cracks and fibers on corrosion propagation. Finally, these proposed modifications were checked and validated against the results obtained by monitoring SFRC beams in the cracked stage. [ABSTRACT FROM AUTHOR]

The use of bundled bars in highly loaded concrete members instead of individual bars can reduce or even avoid reinforcement congestion, allowing easier placing and compaction of concrete, since bundles (with two or more side‐by‐side bars) are less obstructive to fresh‐concrete flow. However, there is still a lack in knowledge of the fundamental phenomena related to the bond behavior of bars in bundles. Therefore, design code rules for anchorages and splices differ significantly among International Standards (Eurocode 2, fib Model Code 2010, and ACI 318–19). The present paper reports the results of more than 100 pullout tests with short embedded length with the aim of comparing the local bond behavior of bundles with that of corresponding notional individual bars. Among the three criteria usually introduced to compare bundled and individual bars, based on the concepts of "equivalent sectional area," and "minimum or maximum sectional perimeter," the first and the second are introduced in this paper. Experimental results show that both criteria are suitable methods for evaluating the bearing capacity of bundled bar anchorages, even if equivalent area criterion seems to be slightly more conservative. The experimental results provide also information on the bursting forces generated by the wedge action of the ribs which clearly increases with bar diameter. Finally, experimental results are compared with design rules for anchorage strength of bundled bars as prescribed by fib‐Model Code 2010. [ABSTRACT FROM AUTHOR]

After several decades of research studies, design rules for fiber reinforced concrete (FRC) are now available for several structural elements. Starting from standard tests, it is possible to determine design parameters and constitutive laws to perform simplified sectional verifications and/or numerical analyses. However, one of the main issues still open is represented by the fiber orientation in the real structure that could be different from the one present in standard tests. For this reason, building codes take into account orientation factors to modify the standard material properties. The present paper aims to shed some new lights on the effects of the orientation of steel and macro‐synthetic fibers on the local variability of FRC residual strength properties in slabs made with two concretes: Vibrated (slump of 80 ± 20 mm, V‐FRC) and self‐compacting concrete (slump flow diameter of 700 ± 50 mm, SC‐FRC). In V‐FRC slabs, the orientation of polymer fibers was more influenced by pouring and compaction process compared to steel ones. In SC‐FRC slabs, the flow and wall effects resulted more significant when long steel fibers were used. The post‐cracking performances locally determined in different points of slabs were compared against the ones obtained on standard beams as well. Finally, the global response of these slabs was numerically studied by considering two different support configurations: simply‐supported slabs and slabs on grade. [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]

The use of fibers can improve the behavior at serviceability limit states (crack and deflection control) and ultimate limit states (bearing capacity) of reinforced concrete (RC) elements under flexure. Fibers reinforcement provides a postcracking resistance, leading RC element to have a more diffused crack patterns characterized by narrower and more closely spaced cracks. Some doubts are instead related to RC element ductility, which can be affected by crack localization after rebar yielding. However, most of experiments present in literature relate only to elements in steel fiber reinforced concrete with significant residual strengths (fR,1 and fR,3 greater than 3.5–4.0 MPa). This paper aims to evaluate the influence of different fiber type (steel, glass, or polymer macrofibers) on the cracking and strength capacity of RC beams under flexure by using a broad range of Fiber Reinforced Concrete (FRC) toughness (1.6 ≤ fR,1 ≤ 5.1 MPa and 0.8 ≤ fR,3 ≤ 4.5 MPa). Twenty‐one small scale RC beams with a typical value of longitudinal reinforcement ratio (0.87%) were tested under flexure. Crack and deflection control, as well as bearing capacity and crack localization were evaluated as a function of FRC toughness. Finally, results were compared against mean crack spacing and strength capacity predictions of fib Model Code 2010. [ABSTRACT FROM AUTHOR]

Different tests are proposed by international standards for the evaluation of the mechanical properties of fiber reinforced concrete (FRC); among them, either beams or round determinate panels are generally used. However, different tests are accepted by design codes if reliable correlation factors between standard parameters are provided (fib Model Code 2010). Within this context, a broad experimental program on both beams and round determinate panels was carried out in order to provide a critical discussion on material characterization and to evaluate possible correlation factors. Beam tests according to European (EN 14651), American (ASTM 1609), and Japanese (JCI‐SF4) standard, as well as small round panels and large round panels (according to ASTM 1550) were studied within an experimental program comprising 189 beams and 90 round panels. Unlike previous researches, mainly focused on steel fibers, two types of macro‐synthetic fibers were considered. Based on these experimental results, a comparison between test methods is presented, along with correlation approaches are proposed and critically discussed. [ABSTRACT FROM AUTHOR]

It is well-known that the shear strength of reinforced concrete elements without web reinforcement is affected by different factors. Among them, tensile strength of concrete, longitudinal reinforcement ratio, shear span-depth ratio, size effect, axial force, and maximum aggregate size seem to be the most important. Concerning other parameters—for example, the width-to-effective depth ratio (b/d) —there is still disagreement within the research community about its possible influence on shear bearing capacity. In this context, the present research evaluates the influence of both the b/d and bar spacing-to-effective depth ratio (s/d) on the shear strength by means of an experimental program on 17 full-scale specimens characterized by b/d ranging from 0.5 to 3.5 and an s/d from 0.24 to 0.71. Results showed that, for b/d > 1, an increase in the b/d determines a non-negligible increment in the shear strength, whereas the s/d (in the considered range) does not affect the shear bearing capacity. [ABSTRACT FROM AUTHOR]

The local splitting behaviour in Fibre Reinforced Concrete (FRC) elements under a high concentrated load is gaining a growing interest, especially with reference to precast tunnel segments. In fact, during the lining construction process, high concentrated thrust jack forces are introduced in the segments leading to both high compressive stresses under the thrust shoes that can provoke a concrete crushing and tensile transversal stresses that can cause cracks and, eventually, a splitting failure. In order to investigate the main involved mechanisms during either splitting or crushing failure, a simplified analytical study is firstly presented on the two load configurations generally adopted in practice, namely the Line Load (LL) and the Point Load (PL). Based on this analytical study, experimental tests on Steel Fibre Reinforced Concrete (SFRC) specimens subjected to a LL configuration have been carried out. Two different steel fibre types have been studied. Experimental results indicate that the use of a low amount of fibres significantly enhances both the splitting bearing capacity and the ductility. Fibres allow a stable propagation of the splitting crack both in terms of crack opening and development, as a result of a transverse stress redistribution that continuously provide equilibrium with the external applied load. [ABSTRACT FROM AUTHOR]

During tunnel boring machine (TBM) operations, thrust jacks apply high concentrated forces to the last assembled tunnel ring. These loads generate in the precast segments a disturbed region under the thrust jacks, in which significant tensile stresses (defined as splitting or bursting stresses) occur perpendicular to the load direction. In addition, due to the compatibility requirement, the combined effect of TBM high concentrated loads may determine high tensile stresses in the area between loads, which lead to cracks defined as spalling cracks. Therefore, rebars or fibre reinforcement are required in these areas. Traditionally, steel fibres were used as fibre reinforcement, although now some types of structural macro-synthetic fibres are used that impart significant toughness and ductility to concrete. In the present study, eight plane specimens were tested under two loads applied on a small area to evaluate the effect of this loading configuration and the contribution of polypropylene (PP) fibre reinforcement in controlling both spalling and splitting phenomena. The results show that failure is mainly governed by splitting phenomena, and that PP fibres could be efficiently used in precast tunnel segments as both equilibrium (splitting) and compatibility (spalling) reinforcement. [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]

The quest to replace toxic chemicals in the nearest future is revolutionizing the corrosion inhibitor research world by turning its attention to plant biomaterials. Herein, we report the corrosion inhibiting potential of butanolic extract of date palm leaves (BUT) on the corrosion of API 5L X60 carbon steel in 15 wt.% HCl solution. The mass loss, electrochemical impedance spectroscopy (EIS), potentiodynamic polarization (PDP), linear polarization (LPR), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDAX), and atomic force microscopy (AFM) techniques were employed in the investigation. We also report the effect of intensifier additives, namely formic acid (FA), potassium iodide (KI), and zinc nitrate (Zn(NO3)2) as well as temperature on the corrosion inhibiting performance of BUT. BUT exhibits inhibiting ability but the extent of inhibition is dependent on concentration, temperature, and intensifiers' concentration. At 25 °C, 200 mg/L BUT and 700 mg/L BUT protected the carbon steel surface by 50% and 88%, respectively. The addition of 3 mM FA and 5 mM KI to 200 mg/L upgraded the extract performance to 97% and 95%, respectively. Zn(NO3)2 performs poorly as an intensifier for BUT under acidizing conditions. The adsorption of BUT + FA and BUT + KI is synergistic in nature whereas that of BUT + Zn(NO3)2 drifts towards antagonistic behavior according to the calculated synergism parameter. Increase in the system temperature resulted in a slight decline in the inhibition efficiency of BUT + FA and BUT + KI but with efficiency of above 85% achieved at 60 °C. The SEM and AFM results corroborate results from the electrochemical techniques. [ABSTRACT FROM AUTHOR]

In the two last decades, world production of pig iron and steel has undergone a significant increase. In 2018, 1252.87 and 1806.46 million tons of pig iron and steel, respectively, were produced as compared to the 575.78 and 809.94 million tons of 2000. Consequently, the amount of the different types of slags deriving from these production processes has also increased considerably. In relation to the principles of sustainability and circular economy, the available literature suggests several possible reuses for these slags (bituminous conglomerates, hydraulic engineering, metallurgy, fertilizers, etc.). This paper aims to provide an overview of the iron and steel slags production and their reuse in concrete (for example as replacement of cement, fine or coarse aggregates). The characteristics of slags are analyzed in terms of chemical, physical, and mechanical properties. Mechanical and durability tests (both from material and structures point of view) carried out in the different studies and research are shown as well. Particular attention was devoted to electric arc furnace slags (EAF) since they are the most produced in Italy. Based on this deep literature review, the gaps that still require further studies have been identified and discussed. [ABSTRACT FROM AUTHOR]

Fiber addition has become one of the most prevalent methods for enhancing the tensile behavior of concrete. Fibers reduce cracking phenomena and improve the energy absorption capacity of the structure. On the other hand, the introduction of fibers can introduce a negative impact on concrete workability, whose loss is influenced by different parameters (among which are fiber content and fiber type). In this context, an exploratory study on the influence of steel (high stiffness) and macro-synthetic (low stiffness) fibers on the fresh properties of concrete was carried out, considering workability and air content, as well as resultant mechanical performance. Four fiber types at two volume fractions (0.5% and 1.0%) were studied in two base concretes with different water-to-cement ratios (0.45 and 0.50) by using the slump test, DIN flow table test and air content meter. An additional parameter for the DIN flow table test is proposed herein to quantify the potential preferential flow direction caused by fiber orientation and entanglement. Air meter results showed that the fibers caused only a slight increase in concrete air content; this agreed well with the results of mechanical testing, which showed no apparent effect on measured compressive strength. In addition, it was captured that, for a given fiber volume fraction, steel fibers more adversely affected Fiber Reinforced Concrete (FRC) workability as compared to polypropylene ones, while the opposite result was obtained considering FRC toughness. [ABSTRACT FROM AUTHOR]

• A morphological and mechanical characterization of corroded rebars. • A chloride content analysis in cracked specimens exposed to chloride-rich environment. • Perpendicular to crack wall, positive influence of fibres on the reduction of chloride content. In Reinforced Concrete (RC) structures exposed to chloride-rich environments, reinforcement corrosion might be already initiated (especially at crack location). A deep knowledge on the correlation between the mechanical properties of corroded bars and corrosive attack morphology, useful for the evaluation of the residual bearing capacity of structure, is still lacking. In this paper, morphological and mechanical characterization of steel reinforcement embedded in RC specimens (with and without fibers) both in cracked stage and subjected to cyclic exposure to a 5 % NaCl solution for 280 days was carried out. Although a chloride content higher than the critical chloride threshold was also measured in correspondence of uncracked concrete, corrosive attacks were observed only in correspondence of cracks. Pits were mostly characterized by a shallow morphology, which led to a rebar diameter loss ranging between 1 and 10 %. Furthermore, the results showed that both yielding and ultimate load of corroded rebars can be predicted by combining circular residual cross-section and mechanical properties of uncorroded rebars. [ABSTRACT FROM AUTHOR]