Recycled Steel Fibers Research Articles

Flexural Behavior of BFRP Bar–Recycled Tire Steel Fiber-Reinforced Concrete Beams

This research advocates for the use of basalt fiber-reinforced polymer (BFRP) bars and recycled tire steel fibers to reinforce concrete beams. Six concrete beams were constructed using different volume contents of recycled tire steel fibers (0, 0.5%, 1.0%, 1.5%) and BFRP reinforcement ratios (0.48%, 0.75%, 1.08%). Mechanical properties tests were conducted to investigate the flexural characteristics and failure modes of beams utilizing the non-contact full-field strain displacement measuring technology–digital image (3D-DIC) technology. The recycled tire steel fiber (RTSF) improves flexural performance, which contributes to inhibiting crack propagation, reducing flexural deformation, and improving the first cracking and ultimate loading capacities. Under the same reinforcement ratio, in comparison to ordinary BFRP beams, the cracking load of BFRP-RTSF beams increased by 17.73%, 23.76%, and 42.94%, respectively, and the ultimate bearing capacity increased by 4.03%, 5.85%, and 13.21%, respectively. In addition, a modified calculation model of bearing capacity considering RTSF tensile strength is proposed. The predicted values of BFRP-RTSF beams match well with the experimental values.

Experimental and theoretical investigation on axial tensile behavior of ultra-high performance concrete (UHPC) with recycled steel fibers from waste tires

Experimental and theoretical investigation on axial tensile behavior of ultra-high performance concrete (UHPC) with recycled steel fibers from waste tires

Mechanical properties of recycled aggregate concrete reinforced with conventional and recycled steel fibers and exposed to high temperatures

The widespread use of concrete has significantly impacted the environment, resulting in substantial greenhouse gas emissions and strain on natural resources. This study investigated the mechanical properties of concrete made with recycled aggregate, conventional steel fibers and recycled steel fibers subjected to high temperatures. This is a crucial consideration in practical applications, such as structures exposed to fires or high temperature environments, and it is an integral part of assessing the durability and safety of alternative construction materials. The following variables were studied: three percentages of recycled aggregate substitution (0, 50 and 100 %), three quantities of conventional and recycled fibers (0, 40 and 80 kg/m3), four temperature steps (20, 200, 400 and 600 °C). The recycled steel fibers came from used tires. The studied variables were the consistency, the hardened density, the compressive strength, the dynamic and static elasticity modulus, the thermal conductivity, the flexural strength and the stress-strain behavior. Besides, scanning electron microscopy photographs were taken to analyze in detail the concrete structure. The main result obtained is that concrete with all recycled aggregate and recycled fibers underwent, in general, the same mechanical properties as a conventional concrete (without fibers and without recycled aggregate) for any temperature step.

Istraživanje utjecaja zelenih hibridnih vlakana na žilavost i mehanička svojstva betona od pijeska željezne jalovine

To improve the brittleness and susceptibility to cracking of iron tailings sand concrete, fibre blending was employed to toughen and resist cracking in the material. In this study, two inexpensive and environmentally friendly fibre materials were used: recycled tire steel fibre (RTSF) and coconut fibre (CF). The two fibre materials were blended and the resulting mixture was subjected to a series of performance tests, including compressive, tensile, flexural, impact, and bending tests. The effects of the fibre doping method and amount on the toughness and mechanical properties of iron tailings sand concrete were investigated in terms of the law of effect of the blended fibre admixture on the toughness and mechanical properties of iron tailings sand concrete. The results show that adding two types of fibres can effectively improve the toughness and mechanical properties of the specimen, and the hybrid fibre has a more obvious effect. Compared with the blank control group (Non), the compressive strength, splitting tensile strength, bending strength, impact strength, and bending peak load of the concrete with 0.75 % RTSF and 0.2 % CF increased by 20.8 %, 42.9 %, 40.4 %, 92.4 %, and 37.5 %, respectively. Combined with the theory and fracture surface morphology analysis, it was shown that recycled tire steel fibres play a major role in cracking resistance, while coconut fibres play a toughening role.

Surrogated modelling for structural reliability and safety assessments of high-strength concrete beams with industrial and recycled steel fibers

As a secondary material recycled from tyres, Recycled Steel Fibre Reinforced Concrete (RSF) aims to replace industrial steel fibres (ISF) to improve concrete matrix‘s severability, fracture toughness, and residual tensile stress. Despite the increasing attention on the mechanical properties of this material, RSF concrete’s influence on structural component strength is still neglected due to a lack of sufficient and reliable experimental data. This study looks into existing Crack mouth opening displacement (CMOD) experiment results of both types of steel fibre reinforced concrete beams together with nonlinear finite element model (FEM) simulations using the RILEM TC 162-TDF crack damage model(CDP) proposed for ISF in ABAQUS. Meanwhile, an additional parameter analysis of the experimental data related to shear capacity also examines the shear span ratio, fibre content, and fibre type of the two types of fibre reinforced concrete beams. Moreover, Kriging surrogate models (KSM) and Sobol global sensitivity analysis have been conducted. For the reference concrete beams with a fibre content of 0.4 %, the prediction accuracy ratios of ultimate strength, corresponding displacement, and stiffness between the FEM and the experiment results are 98 %, 88 %, and 100 %, respectively. This paper has been proved that the CMOD-based CDP model effectively elucidates the shear contribution of different steel fibres, which can be used in structural analysis of ISF or RSF concrete for structure components. Utilizing FEMs, a series of modified flexural strength prediction formulas based on TR63 standards are proposed to enhance structural applications with ISF and RSF. Moreover, the prediction ability of the proposed formulas is validated using the results of 183 real flexural capacity experiments of ISF reinforced concrete beams, achieving an improved R² value of 0.97.

Flexural properties of fiber-reinforced concrete using hybrid recycled steel fibers and manufactured steel fibers

This study investigates the flexural properties of fiber-reinforced concrete (FRC) using a hybrid mix of recycled steel fibers (RSF) from waste tires and manufactured steel fibers (MSF). The aim of this study is to demonstrate hybrid steel fiber reinforcement as a more environmentally sustainable alternative to traditional single-fiber systems, by assessing whether hybrid reinforcement can achieve or surpass the performance of conventional single-manufactured steel fiber reinforcement. Using a novel four-stage methodology, this paper presents a comprehensive and detailed evaluation of mechanical and ductility performance through three-point bending tests, digital image correlation (DIC), CT-scans, and scanning electron microscopy (SEM). The results from flexural stress-deflection curves were used to evaluate the flexural strength and toughness. This was followed by an in-depth eight-stage DIC analysis and Surface Damage Index (SDI) curves throughout the test. CT-scan images were used to quantify the proportion of fibers classified as pulled-out, ruptured, or bridging the crack, while SEM analyzed the efficiency of fiber reinforcement through microstructural evaluations, further validating the findings of this study. Results show that hybrid reinforcement significantly enhances both toughness and ductility while reducing surface damage. MSFs in the hybrid system improve post-peak ductility and energy absorption by bridging large cracks, while RSFs prevent micro-cracks, increasing pre-peak rigidity. CT-scan analysis reveals that the inclusion of RSFs reduces pulled-out MSFs by 26 %, further boosting flexural performance. SEM confirms the superior bond of MSFs with the concrete matrix in hybrid samples. Additionally, higher fiber content in FRC enhances toughness and ductility while reducing surface damage. This research advances our understanding of hybrid fiber-reinforced concrete and promotes more sustainable construction practices through the use of recycled steel fibers. By leveraging the combination of new methodologies, the study effectively targets gaps in the current research landscape, offering a comprehensive approach to improving performance and sustainability in construction materials.

Experimental study on mechanical properties and toughness of recycled steel fiber rubber concrete

Adding rubber particles to concrete can improve its brittleness, but it also significantly reduces its compressive strength. In order to maintain the compressive strength of concrete unchanged and enhance its tensile strength and toughness, waste steel fibers are added to rubber concrete (RC). This not only achieves the reuse of solid waste materials, but also achieves the goal of high-performance concrete. By adding different amounts of scrap steel fibers to three different strength grades of rubber concrete, scrap steel fiber rubber concrete (SSFRC) is formed. Compression strength, tensile strength, and flexural strength tests were conducted on SSFRC with different mix ratios. The toughness of SSFRC was evaluated by introducing the tensile compression ratio, flexural compression ratio, and toughness index. The microscopic characteristics of SSFRC were observed using scanning electron microscopy (SEM), and the strengthening and toughening mechanism of waste steel fibers on RC was analyzed. The results show that: adding rubber decreases the mechanical properties of concrete with various matrix strengths; adding steel fiber admixture causes a trend in the mechanical strengths of SSFRC with various matrix strengths to increase and then decrease; getting the greatest compressive strength at 1 % and the peak tensile and flexural strengths at 1.5 %; Steel fibers and rubber particles can cooperate at a specific admixture amount to increase the toughness of RC. The local hydration of the scrap steel fibers may have taken place, according to the microscopic morphology of the Transition zone at the interface between the matrix and the scrap steel fiber. In conclusion, the best mechanical strength enhancement effect and the best toughness of SSFRC are achieved at 10 % of rubber and 1.5 % of scrap steel fiber.

Challenges of a Circular Economy: The Example of Raw Recycled Tyre Steel Fibres Added to Concrete.

This research was conducted to analyse the possibility of using raw, untreated recycled tyre fibres as an effective concrete reinforcement according to circular economy principles. The aim of the article was also to develop a method for dispensing tire fibres on a real scale. Additional treatment and homogenisation of recycled steel fibres entail higher energy consumption, emissions of greenhouse gases, and increased costs. However, obtaining durable and safe concrete effectively reinforced with steel fibres is critical. Finding a balance between environmental friendliness and product durability is a circular economic challenge. Reference concrete with commercial steel fibres (15 kg/m3) and two concretes containing various quantities of non-treated, raw tyre recycled fibres (25 kg/m3 and 45 kg/m3) were industrially produced. Tests were carried out on the properties of the concrete mixture and hardened concrete, such as compressive strength, flexural strength, splitting strength, modulus of elasticity, residual flexural tensile strength, and fibre distribution in concrete. Tests revealed that increasing the amount of raw tyre fibres disturbs the structure and causes air entrainment and the formation of fibre clusters. Smaller quantities of raw tyre fibres turn out an effective concrete reinforcement. The use of non-treated tyre fibres as concrete reinforcement is possible but requires more stringent control of the concrete parameters. Implementation tests on an industrial scale are a novelty in this study, presenting an analysis of the possible dispensing of tyre fibres in a ready-mixed concrete production plant and testing the characteristics of manufactured concrete.

Production of rubberized concrete utilizing reclaimed asphalt pavement aggregates and recycled tire steel fibers

The integration of waste tire elements into concrete, specifically granular rubber and discrete steel fibers, signifies a substantial advance in the pursuit of sustainable alternatives for rigid concrete pavements. This incorporation not only improves the ductility of rigid concrete pavements, but also augments their energy absorption capabilities. Similarly, replacing natural aggregates in concrete with reclaimed asphalt pavement (RAP) aggregates makes a large contribution to the reduction of negative environmental impacts, while conserving natural resources from depletion. This investigation explores the potential application of recycled rubber particles from waste tires (WTRR) and RAP aggregates as partial substitutes for natural fine aggregates, and evaluates their impact on the performance of rigid concrete pavements. Eight mixes were cast, each with two variables: (i) fine aggregate type (fine rubber (FRu) aggregates, fine asphalt (FAs) aggregates, and combinations of both types of aggregate) replacing 50 % of the natural fine aggregate; and (ii) waste tire recycled steel fibers (WTRSF) content (0 and 40 kg/m3). The axial compressive stress–strain, flexural load–deflection, and direct shear strength behaviors, together with the dry unit weight and volume of permeable voids for all concrete mixes were investigated and compared. The results show that, although the flexural and shear strengths decrease with the inclusion of FRu and/or FAs, the use of WTRSF noticeably mitigates the losses in strength that arise from the use of WTRR and/or RAP aggregates alone. The inclusion of WTRSF enhances the strain capacity of the concrete and allows the development of adequate post-peak energy absorption capacity in flexural and shear loading. Additionally, the dry unit weight of the proposed composites decreased by as much as 8 %, and their volume of permeable voids lies within the limits of high-durability concrete mixes (9–12 %). Hence, the proposed sustainable concrete composites are promising composites for rigid concrete pavement construction.

Enhancing the pull-out behavior of ribbed steel bars in CNT-modified UHPFRC using recycled steel fibers from waste tires: a multiscale finite element study

In the current investigation, the effect of recycled steel fibers recovered from waste tires on the pull-out response of ribbed steel bars from carbon nanotube (CNT)-modified ultrahigh performance fiber reinforced concrete (UHPFRC) was considered using the multiscale finite element method (MSFEM). The MSFEM is based on three phases to simulate CNT-modified UHPC, recycled steel fibers (RSFs), and ribbed steel bars. For the first time, a bar ribbed has been simulated to make more realistic assumptions, and RSFs have been distributed in the form of curved cylinders of different lengths and with a random distribution within a concrete matrix. The interaction of the steel bar and the RSFs with the concrete is applied by the cohesive zone model (CZM). After confirming the simulation outcomes with the experimental results, the steel bar pull-out response is investigated using load-slip curves. The impact of the CNT content, RSFs and their aspect ratio on the bond strength of steel bars and CNT-modified UHPFRC was assessed. The results show that using RSFs with a lower aspect ratio (steel microfibers) significantly improves the pull-out characteristics of steel bars from concrete. Accordingly, the proposed MSFEM is considered for simulating the effects of different parameters on the pull-out response of ribbed steel bars from concrete without causing complex, time-consuming, or costly experiments. The results indicated that waste fiber or RSF can be used as a toughening component in CNT-modified ultrahigh-performance concrete and as a replacement for industrial steel fibers.

The recycling potential of fibre reinforced concrete with 4D Dramix® fibres: Experimental analysis and model verification

This experimental study aims to advance sustainable construction practices by exploring the recycling potential of steel fibre reinforced concrete with 4D Dramix® fibres from the company Bekaert. In this research steel fibres from reinforced concrete specimens with varying fibre quantities of two 4D Dramix® fibre types, more precisely, the 55/50 BG and 65/50 BG fibres are recycled. A jaw crusher at the recycling company AC Materials (Flanders, Belgium) and an impact crusher at the research and development company CTP (Wallonia, Belgium) are employed to optimize the quantity and quality of the recycled fibres. Subsequently, the recycled steel fibres are reintegrated into fresh concrete mixes. The recycling process of the fibres results in a general decrease of the residual tensile strength capacity for the concrete mixtures with recycled fibres (RSFRC) compared to those with new fibres (NSFRC), and the deviation increases with increasing crack mouth opening displacement (CMOD). It was found that fibres recovered by the impact crushing process are (generally) shorter than those obtained from the jaw crusher, which results in a fibre reinforced concrete (FRC) with a somewhat lower post-cracking tensile strength. Nevertheless, most recycled fibres retain 75 % of their original capacity, considering the mean residual tensile strength of the FRC mixtures. Consequently, current findings show promising results for the recycling potential of steel fibres and the residual strength behaviour of RSFRC compared to NSFRC. Additionally, this study highlights the potential for an improved constitutive tensile model for FRC mixtures, where the design parameters ka and kc can be estimated based on the fR3k/fR1k-ratio.

Experimental Study on Axial Compressive Performance of Recycled Steel Fiber Reinforced Concrete Short Columns with Steel Pipes

Experimental Study on Axial Compressive Performance of Recycled Steel Fiber Reinforced Concrete Short Columns with Steel Pipes

Influence of Recycled Coarse Aggregate and Steel Fiber on the Workability and Strength of Self-Compacting Concrete

Abstract Waste materials pose a significant threat to both the environment and human health. On a global scale, the quantity of recyclable material is steadily growing, and its proper disposal is a significant focus of modern study. Concrete debris is a recyclable material that poses challenges for reutilization. Concrete waste refers to the fragments or remains of ready-mix concrete plants and the debris from destroyed structures, including historic buildings and those affected by earthquakes. The objective of this study is to reuse and utilize coarse aggregate formerly used in concrete constructions to create self-compacting concrete (SCC). The purpose is to assess the performance of this recycled aggregate in both its fresh and hardened states. Natural coarse aggregate (NCA) was switched out for recycled coarse aggregate (RCA) at 0, 50, and 100% volume ratios. In contrast, concrete was mixed with steel fibers (SF) at volume percentages of 0 and 0.44. Workability tests, including V-funnel, slump flow, and L-box tests, were conducted to assess the consistency of the mixes in their fresh condition. Additionally, the tensile and compressive strength of the concrete specimens were measured to evaluate their strength in the hardened state. Overall, the experimental findings showed that the fresh qualities of almost all SCC mixes fell within the required range, as outlined in the EFNARC standards. While the steel fiber harmed the fresh characteristics, it resulted in a proportionate enhancement in tensile strength. The findings indicated that including recycled aggregates into the concrete mixture enhanced its strength. The results showed that adding (0.44%) of steel fibers to concrete reduced the decline in compressive strength when the coarse aggregate was replaced entirely with recycled aggregate. In contrast, an equivalent proportion of fibers resulted in a significant improvement in tensile strength, rising from 26% to 54%, when using recycled coarse aggregate as the replacement of natural coarse aggregate. Thus, it can be concluded that using recycled aggregates and steel fibers in concrete production results in a higher quality product than regular concrete. Removing concrete waste has other benefits, such as enhanced financial return and preservation of the environment.

Experimental investigation on mechanical properties of fiber recycled concrete filled-square steel tube columns under pure flexural based on acoustic emission technique

Currently, global countries are actively focusing on carbon emission reduction. Utilizing recycled aggregate concrete (RAC) is expected to realize global carbon neutrality objectives. However, due to its inherent mechanical limitations, its application in structural contexts is restricted. This study aimed to enhance the mechanical attributes of RAC and expand its utility beyond low-strength applications. By employing recycled aggregates, steel fibers, and ordinary Portland cement, a novel eco-friendly composite filler was developed for steel- tube filling. A comprehensive study on 16 concrete mix ratios and 23 steel-tube recycled concrete columns was conducted. The parameters included the recycled aggregate volume, steel fiber content, and steel pipe thickness. The results revealed that reasonable mix design enabled RAC to exhibit flexural performance similar to that of conventional steel-tube concrete. Moreover, while increasing the recycled aggregate content deteriorated the overall mechanical properties, incorporating steel fibers extended the elastic stage and enhanced the flexural characteristics. Optimal results were achieved with 1.2 % steel fiber addition and 75 % recycled aggregate. The comparison between the derived equation and the experimental data demonstrated a high level of agreement, confirming the accuracy of the equation. Furthermore, acoustic emission technology was employed in this experiment to monitor the failure progression of steel tube recycled concrete columns subjected to a pure bending load. The findings revealed a triphasic failure process: elastic, elastic-plastic, and strengthening stages. The analysis demonstrated a consistent correlation between acoustic emission parameters and waveform characteristics with the failure process of the specimen. Empirical evidence demonstrated the efficacy of acoustic emission technology in effectively monitoring the damage severity and failure chronology in recycled concrete steel pipe columns during bending.

Fracture behavior of environmentally friendly high-strength concrete using recycled rubber powder and steel fibers: Experiment and modeling

Ultra-high-performance concrete (UHPC) is becoming increasingly popular for its exceptional mechanical properties but suffers from high cost and limited ductility. To overcome these limitations, this study explores the development of cost-effective and ductile Environmentally friendly High-strength Concrete (E-HSC) by incorporating recycled steel fiber (RSF) and rubber powder into UHPC. Fracture properties and crack propagation behavior were examined through three-point bending fracture tests on notched beams with varying rubber powder (0 %, 5 %, 20 %, 35 % and 50 %) and recycled steel fiber (1 %, 2 % and 3 %) content. Digital Image Correlation method was Used to Measure Crack mouth opening displacement and Fracture process zone in the Fracture Process of E-HSC of the E-HSC were analyzed using the digital image correlation method. Results revealed that E-HSC with 5 % rubber powder exhibited superior fracture energy and double-K fracture toughness. The use of rubber powder and RSF enhances the ductility of concrete, with the characteristic length consistently increasing as the content of rubber powder and RSF increases. Additionally, a softening constitutive model was proposed to evaluate the fracture performance of E-HSC based on rubber powder and recycled steel fiber content. This research provides experimental data and theoretical insights for developing resilient E-HSC suitable for applications in significant structures.

Flexural behavior of BFRP bar–hybrid steel fiber reinforced UHPC beams

Ultra-high-performance concrete (UHPC) has the potential to overcome the durability limitations of conventional concrete. Basalt Fiber Reinforced Polymer (BFRP) bars can mitigate the corrosion effects of steel bars and fully exploit the properties of UHPC. Industrial Steel Fibers (ISF) are a widely used component in the preparation of UHPC. To reduce environmental pollution and costs, this study proposes using recycled tire steel fibers (RTSF) instead of ISF in the production of UHPC. RTSF will be combined with BFRP bars to prepare hybrid steel fiber UHPC beams. The study investigates the effects of RTSF substitution for ISF and BFRP reinforcement ratio on the flexural performance of UHPC beams. The study indicates that the beam's bending failure modes include concrete crushing, equilibrium, and BFRP bar tensile failure. The replacement rate of RTSF has a dual effect on the flexural performance. As the RTSF replacement rate increases from 0 % to 100 %, the cracking load and ultimate capacity of the beams decrease by 2.86 % and 10.38 %, respectively, while the mid-span deflection of the beam increases by 7.94 mm when it reaches failure. When the replacement rate of RTSF is 60 %, the beams exhibit optimal bending performance, and their ultimate capacity can be increased by 2.95 % compared to the capacity when the replacement rate is 0 %. The failure mode of the beams is significantly influenced by the reinforcement ratio of the BFRP bars. Increasing the BFRP reinforcement ratio from 1.12 % to 7.12 % resulted in a 65.8 % decrease in maximum crack width and a 57.6 % decrease in mid-span deflection, while the ultimate load is increased by 78.6 %. The proposed theoretical calculation formula can effectively predict the flexural capacity of BFRP bar hybrid steel fiber UHPC beams, providing a theoretical basis for the application of FRP reinforced hybrid steel fiber UHPC beams.

Experimental Study of Mechanical Properties and Theoretical Models for Recycled Fine and Coarse Aggregate Concrete with Steel Fibers.

With diminishing natural aggregate resources and increasing environmental protection efforts, the use of recycled fine aggregate is a more sustainable approach, although challenges persist in achieving comparable mechanical properties. Exploration into the incorporation of steel fibers with recycled aggregate has led to the development of steel-fiber-reinforced recycled aggregate concrete. This study investigates the shrinkage performance and compressive constitutive relationship of steel fiber recycled concrete with different steel fibers and recycled aggregate dosages. Initially, based on different replacement rates of recycled coarse aggregate and different volume contents of steel fiber, experimental results demonstrate that as the replacement rate of recycled coarse aggregate increases, shrinkage also increases, while the addition of steel fiber can mitigate this effect. An empirical shrinkage model for steel fiber recycled concrete under natural curing conditions is also proposed. Subsequently, based on the uniaxial compression test, findings indicate that with an increasing replacement rate of recycled fine aggregate, the peak stress and elastic modulus of concrete decrease, accompanied by an increase in peak strain, and the addition of steel fiber limits concrete crack development and enhances its brittleness while the peak stress and strain of recycled fine aggregate concrete are enhanced. However, the steel fiber volume percentage has a negligible effect on the elastic modulus. A constitutive relationship for concrete considering the effects of recycled fine aggregate and steel fiber is also proposed. This finding provides foundational support for the influence patterns of steel fiber dosage and recycled aggregate ratio on the mechanical properties of steel fiber recycled concrete.

Promoting Sustainable Green Infrastructure: Experimental and Numerical Investigation of Concrete Reinforced with Recycled Steel Fibers

Promoting Sustainable Green Infrastructure: Experimental and Numerical Investigation of Concrete Reinforced with Recycled Steel Fibers

Experimental study of the influence of the incorporation of combined recycled steel and polypropylene fibers on the compressive behavior of self-compacting cementitious composites

Experimental study of the influence of the incorporation of combined recycled steel and polypropylene fibers on the compressive behavior of self-compacting cementitious composites

A Comparative Evaluation of Modification Methods for Improving the Mechanical Properties of Recycled Aggregate-Recycled Steel Fiber Concrete

A Comparative Evaluation of Modification Methods for Improving the Mechanical Properties of Recycled Aggregate-Recycled Steel Fiber Concrete