Recycled Steel Fibers Research Articles

Shear strengthening of RC beams with thin panels of mortar reinforced with recycled steel fibres

Abstract The use of thin cement based panels reinforced with relatively high content of Recycled Steel Fibres (RSF) for the shear strengthening of Reinforced Concrete (RC) beams is investigated in the present work. The mechanical properties of this Recycled Steel Fibre Reinforced Mortar (RSFRM) are characterised. The panels are produced by using a mixing technique similar to the one used in the slurry infiltrated fibre concrete technology. Then, their potentialities as a shear strengthening solution for RC beams deficiently reinforced in shear are investigated by performing three-point bending tests with RC beams of “I” shape cross section. The RSFRM panels are applied in the lateral faces of the beams by using the two following strategies: (1) bonded to the concrete substrate by applying exclusively epoxy adhesive; and (2) besides epoxy adhesive, mechanical fasteners are applied. The applicability of an analytical approach for estimating the contribution of RSFRM panels for the shear resistance of RC beams is assessed, and a design example is presented.

Damage propagation rate and mechanical properties of recycled steel fiber-reinforced and cement-bound granular materials used in pavement structure

Cement-bound granular mixtures (CBGMs) represent an attractive option to increase load-carrying capacity and sustainability in highway construction. However, reflection cracking of overlying pavement layers due to the low tensile strength of CBGMs represents an important obstacle limiting their use. This study is undertaken to investigate how incorporation, in CBGMs, of recycled steel fibers extracted from old tires, at different cement levels may affect their tensile properties related to pavement design. A combination of three levels of cement (3%, 5% and 7% by wt. of aggregate and fiber) and two reinforcement contents (0% and 0.5 by volume of aggregate) was investigated. To comprehensively quantify the benefits of fibers in the presence of variable cement contents, time-dependent fracture and damage propagation were examined quantitatively utilizing a combination of macro-surface cracks, fractal analysis and both image monitoring and processing techniques. The results indicated better tensile strength and toughness after cement and fiber inclusion. Furthermore, increasing the amount of cement accelerates the crack propagation and damage dispersion rate while these two parameters reduced significantly in the case of fiber-reinforced cemented aggregate. All benefits gained from fiber usage are more evident at higher cement contents.

Structural behaviour and fracture energy of recycled steel fibre self-compacting reinforced concrete beams

Mechanical strength and structural behaviour of Recycled Steel Fibre Self-Compacting Concrete (RSFSCC) were investigated using different Recycled Steel Fibre (RSF) contents (30, 45 and 60 kg/m3) incorporated in three SCC mixes. The corresponding steel fibre volume fraction can be approximated to (0.4%, 0.6% and 0.8%) of the concrete mixtures, respectively. Compressive, splitting, and flexural strengths in addition to water absorption tests were performed to investigate some hardened properties of the tested mixes. The structural behaviour was assessed by determining and calculating flexural stiffness k, flexural toughness I and residual strength factor R for reinforced concrete beams having the dimensions of 100 × 150 × 1000 mm. Fractal dimension D was calculated using Image Processing Technique for all assessed beams to study and quantify the cracks and their tortuosity. It was found that incorporating RSF improved the mechanical properties, strength and structural behaviour of SCC. However, the best strength and behaviour in addition to best cracking resistance were achieved using 60 kg/m3 RSF content. Both first crack and ultimate load capacity were increased with RSF incorporation. The flexural stiffness and toughness in addition to residual strength factor increased with incorporating RSF. In addition, fracture mechanics parameters are determined and discussed.

Development of eco-efficient and cost-effective reinforced self-consolidation concretes with hybrid industrial/recycled steel fibers

This paper presents the results of an experimental/analytical investigation on the development of eco-efficient and cost-effective self-consolidation concretes reinforced with hybrid steel industrial and recycled fibers. Particularly, eleven mixtures containing different combinations of the hybrid industrial/recycled steel fibers were cast and examined under the compressive, tensile, flexural, and the repeated drop weight impact tests. Then, the mechanical properties were correlated to the resistance to impact actions. The effects of fiber combinations on the cost and the released carbon emission into the atmosphere were studied. Finally, a simplified optimization approach was used to obtain the eco-efficiency and cost-effectiveness of the fiber-reinforced self-consolidation concrete.The results showed that the greatest impact of replacing industrial steel fibers by recycled steel fibers was observed in the residual flexural strength, in ultimate impact resistance, and in the compactness. Moreover, recycled/industrial steel fiber combinations had the greater impact on increasing the cost than the released carbon emission.

Effect of replacing the main reinforcement by steel fibers on flexural behavior of one-way concrete slabs

The main objective of the research is to study the preparation of one way slabs of ordinary concrete, and then to prepare concrete slabs by replacing the main reinforcing steel with two kinds of steel fibers (ordinary steel fibers and recycled steel fibers) by fraction volumes of 0.125, 0.250, and 0.375%. Also, study the mechanical properties of the mixtures as a ompressive strength, indirect tensile strength, and flexural strength. Concrete slabs of these mixtures have been prepared with specific geometrical dimensions700 * 300 * 70 mm, exposed to line load, to study the bending moment and maximum failure load of these slabs. A concrete mixture was produced after proportionment based on the ACI and casting six cubes tested at the ages of 7 and 28 days where the strength requirements for design were achieved. The main mixtures of research were produced, three cubes for compressive strength testing, twenty one cylinders for indirect tensile strength testing, and twenty one prisms for modulus of rupture testing. Also sixteen concrete slabs were prepared, two of them were reference slabs without reinforcing steel, the other two with main reinforcing steel only, six of them replaced by the main reinforcing steel with ordinary steel fibers, and the last six replacing the main reinforcing steel with recycled steel fibers. The results showed that both the failure load and the resultant deflection in concrete slabs decreased by (20.09%, 51.91%) for maximum load and by (35.18%, 81.48%) compared to the reference slabs when replacing the main reinforcing steel with steel fiber, also by (25.72%, 38.29%) to failure load and (38.88%, 79.63%) for the deflection compared to the reference slabs when replacing the main reinforcing steel with recycled steel fibers. The best value for maximum load and deflection could be obtained from this study was at 0.125% replacement ratio of the main reinforcing steel with recycled steel fibers, the highest value of ductility was 3.77 at the replacement ratio of 0.250% of the main reinforcing steel with the ordinary steel fibers, also the highest hardness value was 11.67 kN / mm with the replacement ratio of 0.125% of the main reinforcing steel with recycled steel fibers and increased by 61.85% than the hardness of the reference slabs.

Fiber-reinforced concrete with low content of recycled steel fiber: Shear behaviour

The sustainability of construction materials is a mandatory issue that started to be strongly felt in view of a global perspective of environmental protection. Wasted materials often may find a new lifecycle if well re-engineered, even in structural applications. In this field short steel fibers obtained from used tyres at the end of their life may find promising applications within a concrete matrix. In the present research the mechanical properties of recycled steel fiber-reinforced concrete in terms of workability, compressive and tensile strength, toughness and shear behaviour are analysed and compared with those of industrial steel fiber-reinforced concrete and ordinary Portland concrete. An experimental campaign is illustrated, and an extensive comparison in terms of shear strength has been studied considering different experimental works available in scientific literature. Moreover, a theoretical analysis aimed at evaluating and comparing the shear modulus of the analysed concrete type was carried out. The results obtained through this study show a satisfactory behaviour of the concrete reinforced with recycled steel fibers compared with industrial new steel fibers reinforced concrete, both in terms of toughness and shear behaviour.

On the mechanical response of Hybrid Fiber Reinforced Concrete with Recycled and Industrial Steel Fibers

This paper summarizes the results of an experimental research on “sustainable” cementitious composites internally reinforced with industrial and recycled steel fibers, the latter being recovered from waste tires and employed in substitution and/or addition of the industrial steel ones. Specifically, six concrete mixtures including different amount of industrial/recycled steel fibers were produced and tested both in compression and bending. The obtained results confirm the promising prospects already observed by the authors in a previous study on concrete reinforced with recycled steel fibers obtained from waste tires. Furthermore, they clearly demonstrate that industrial fibers can be replaced by an equal amount of recycled ones without a significant decay in the relevant mechanical properties, provided that the recycled fibers present adequate geometrical characteristics.

Mechanical properties of the concrete containing recycled fibers and aggregates

Mixed Recycled Aggregates (MRA) is a mixture of recycled concrete and masonry materials. These kinds of aggregates have lower strength and higher water absorption than natural aggregates. Therefore, the concrete with recycled aggregates has lower strength than the concrete with natural aggregates. Using the steel fibers recovered from waste tires in the concrete with recycled aggregates improves the mechanical properties of this concrete as well as solving the environmental problem of these waste steel wires. In this study, the effect of recycled steel fibers on the mechanical properties of normal concrete and the concrete with recycled aggregate are investigated. Additionally, the effect of fibers on the reduction of concrete pavement thickness is studied. The replacement percentage of natural coarse aggregates with these aggregates is 0, 50 and 100%, with fiber percentage being 0.5 and 1% of concrete volume. Main results indicate that by adding recycled fibers into the concrete with recycled aggregates lead to the production of structural concrete by 50% replacement of aggregates. Moreover, adding recycled fibers by 0.5 and 1% of concrete volume reduces the thickness of concrete pavement for the amount of 8 and 16%, respectively.

Improving cracking behaviour with recycled steel fibres targeting specific applications - analysis according to fib Model Code 2010

Improving cracking behaviour with recycled steel fibres targeting specific applications - analysis according to <i>fib</i> Model Code 2010

Concrete Reinforced with Recycled Steel Fibers from End of Life Tires: Mix-Design and Application

The manufacturing technology of reinforced concrete with the use of steel fibers to improve its mechanical properties is well-known and commonly used in civil engineering. Generally, steel fibers as discontinuous reinforcement of the concrete matrix are used to limit the cracking growth following the load application. Thus, the obtained concrete is characterized by an improvement of the typically brittle behavior of the ordinary matrix, mainly referring to toughness and post-cracking behavior. In this paper the results of a recent experimental campaign carried out at the University of Salento will be discussed. It was designed to study the optimization of concrete mixtures reinforced with recycled steel fibers from end of life tires (ELTs) to be used for the realization of precast panels. This experimental campaign is part of a wider research project aimed to validate the idea that the constituent elements of the ELTs, especially rubber and steel, can be effectively reused in concrete mixtures. Taking into account the high annual amount of ELTs generated around the world and their negative impact on the global environmental sustainability, the recovery of their constituent materials and their reuse as raw materials in different technologies, is certainly an excellent way for a sustainable development.

Use of silica fume and recycled steel fibers in self-compacting concrete (SCC)

This paper aims to investigate the effects of replacing cement with silica fume in the reinforced self-compacting concrete with recycled steel fiber and study its mechanical properties and impact resistance. To characterize mechanical properties and impact resistance, 144 specimens with different fiber volume fractions of 0.25%, 0.5%, and 0.75% were experimentally tested. Mechanical properties of specimens were characterized with regard of compressive, splitting tensile, and flexural strengths. Concerning the obtained large experimental database, an analytical analysis was performed by using regression analysis to investigate the correlate between the impact and mechanical properties of self-compacting concrete reinforced with recycled steel fibers. In addition, the correlation between the mechanical properties of specimens and the content of the replaced cement with silica fume was also examined.The results revealed that the combined effects of silica fume and recycled steel fiber improved the mechanical properties and impact resistance of specimens. Moreover, linear equations were also developed to correlate mechanical properties and impact resistance of specimens with a high coefficient of determination.

Experimental Study on Bond Behavior in Fiber-Reinforced Concrete with Low Content of Recycled Steel Fiber

The use of recycled steel fibers from waste tires as reinforcement in concrete matrix appears to be a promising solution, thanks to the performance of the material in terms of toughness and postcracking behavior. The main objective of this paper is to analyze the bond behavior of recycled steel fiber–reinforced concrete (RSFRC) and steel bars, and compare the results with those of industrial steel fiber–reinforced concrete (ISFRC). The paper focuses on the characterization of the mechanical properties of concrete reinforced with short steel fibers from waste tires and on the results of pull-out tests executed both on RSFRC and ISFRC. The experimental results, in terms of failure mode, maximum bond stress, and bond stress versus slip behavior are analyzed and discussed. Finally, a theoretical analysis of the bond-slip behavior was performed. The experimental results show that most of the known performance of the ISFRC can be extended to RSFRC. Referring to the bond performance, an improved behavior of RSFRC with respect to ISFRC in terms of bond-slip law was observed.

A Basic Research on Utilizing Steel Wire from Waste Tires as Recycled Steel Fiber for Construction

A Basic Research on Utilizing Steel Wire from Waste Tires as Recycled Steel Fiber for Construction

An experimental study on the post-cracking behaviour of Hybrid Industrial/Recycled Steel Fibre-Reinforced Concrete

This paper investigates the mechanical behaviour of FRC made with both Industrial and Recycled Steel Fibres recovered from waste tyres. Specimens of various mixtures, characterised by the same volume fraction of fibres, but different proportions of industrial and recycled reinforcement were tested both in compression and bending. The results highlighted a fairly negligible influence of fibres in terms of compressive strength, whereas a significant decay in the post-cracking behaviour was observed in specimens with higher fractions of recycled fibres. However, a significant enhancement in the bending response was observed with respect to the case of plain concrete, even for specimens reinforced by recycled fibres only.

Experimental and numerical characterization of the bond behavior of steel fibers recovered from waste tires embedded in cementitious matrices

This work investigates the mechanical behavior of recycled steel fibers recovered from waste tires and, then, suitable to produce eco-friendly fiber-reinforced concrete. Particularly, the results of an experimental investigation aimed at understanding the tensile response of the aforementioned steel fibers and their bond behavior when embedded in cementitious matrices are reported and discussed. Moreover, as a case study, a fracture-based plasticity formulation for simulating the overall pull-out behavior of fibers embedded in cementitious matrices is also employed. This formulation is based on assuming a discontinuous response between interface bond stresses and the corresponding relative displacements. Then, an extensive comparison between numerical predictions and the corresponding experimental results of the pullout behavior of recycled steel fibers embedded in concrete is presented for validating and calibrating the model. A satisfactory agreement was observed between the numerical and experimental results: it demonstrates the soundness of the interface formulation.

Recycled Steel Fibre Reinforced Concrete failing in bending and in shear

Recent research is showing that the addition of Recycled Steel Fibres (RSF) from wasted tyres can decrease significantly the brittle behaviour of cement based materials, by improving its toughness and post-cracking resistance. In this sense, Recycled Steel Fibre Reinforced Concrete (RSFRC) seems to have the potential to constitute a sustainable material for structural and non-structural applications. To assess this potential, experimental and numerical research was performed on the use of RSFRC in elements failing in bending and in beams failing in shear. The values of the fracture mode I parameters of the developed RSFRC were determined by performing inverse analysis with test results obtained in three point notched beam bending tests. To assess the possibility of using RSF as shear reinforcement in Reinforced Concrete (RC) beams, three point bending tests were executed with three series of RSFRC beams flexurally reinforced with a relatively high reinforcement ratio of longitudinal steel bars in order to assure shear failure for all the tested beams. By performing material nonlinear simulations with a computer program based on the finite element method (FEM), the applicability of the fracture mode I crack constitutive law derived from the inverse analysis is assessed for the prediction of the behaviour of these beams. The performance of the formulation proposed by RILEM TC 162 TDF and CEB–FIP 2010 for the prediction of the shear resistance of Fibre Reinforced Concrete elements was also evaluated.

Moisture transport and drying shrinkage properties of steel–fibre-reinforced-concrete

Abstract Drying shrinkage has a serious impact on the structural and durability performance of concrete pavements. Shrinkage strain development and distress can only be fully understood by knowing the moisture transport and free shrinkage properties of concrete. This paper uses experiments and FE inverse analysis to determine these properties for conventional concrete (CC) and RCC reinforced with recycled-steel–fibres from tyres. Moisture diffusivity versus moisture content and a relationship between free shrinkage and moisture loss are derived. These values can be used to predict shrinkage strains and stresses in road pavements and other ground restrained slabs.

Experimental Study of Strengthening and Toughening for Recycled Steel Fiber Reinforced Ultra-High Performance Concrete

This paper presents an experimental investigation on mechanical properties (including compressive strength, tensile splitting strength and fracture energy) of ultra-high performance concrete (UHPC) with recycled steel fiber, compared with none fiber and industrial steel fiber reinforced UHPC. Moreover, the microscopic observation of fracture energy was carried out. All specimens were prepared at 0.18 water /binder (W/B) ratio and the dosage of steel fiber was controlled at 60 kg/m3. The results indicate that recycled steel fiber has a significant effect on enhancing strength and toughness of UHPC. And owing to the crimped shape, higher tensile strength (1800-2000 MPa) and appropriate diameter (1 mm) of recycled steel fiber, the steel fibers of UHPRSFRC will not immediately be pulled off and necking phenomenon is distinct.

POSITIVE INTERACTION OF INDUSTRIAL AND RECYCLED STEEL FIBRES IN FIBRE REINFORCED CONCRETE

In line with current ”green” transport initiatives, Croatia plans to build over the next investment period a high speed railway line which will connect central Croatia and its capital with coastal regions of the country. According to design documents, the track system will be built using ballastless concrete solutions. In the scope of the project “Concrete track system – ECOTRACK”, researchers from the University of Zagreb - Faculty of Civil Engineering analysed a new material, i.e. the rubberized hybrid fibre reinforced concrete (RHFRC), in order to find out whether its properties are adequate for the proposed concrete track system. The RHFRC contains by-products from mechanical recycling of waste tyres (rubber and steel fibres). The study of fibre and rubber interaction and their contribution to mechanical properties of the fibre reinforced concrete is presented, as extensive research on positive interaction between industrial and recycled steel fibres has not as yet been made. The results show that the RHFRC is an innovative, sustainable and cost-effective concrete, which is fully compliant with criteria prescribed in relevant standards.

Innovative Technologies and Logistical Solutions for the Reuse of Demolished Concrete in the Construction of Cement Concrete Pavements

The paper presents the results and conclusions of investigations aiming to encourage the use of recycled materials, namely recycled aggregates (RA) and recycled steel fibers (RSF), in the construction of durable, economic and environmental friendly rigid pavements. To minimize and limit the negative effect of RA on the mechanical properties of cement concrete pavements, the research program considered both, development of technical solutions to improve the performance characteristics of RA particle, and RSF disperse reinforcement of concrete mixtures. Roller compacted concrete (RCC) cylindrical and prismatic test specimens manufactured with natural aggregates (NA) and original/performance improved RA have been subjected to flexure and compressive testes to evaluate the influence and contribution of developed technologies. Finally, guidelines and considerations for the use of RA in RCC and plain cement concrete (PCC) pavements are drawn.