Recycled Steel Research Articles

Influence of welding conditions and flux composition on chemistry of welds using recycled steel slag in submerged arc welding

The slag generated by steel-making plant has been employed to manufacture flux essential for submerged arc welding process. The developed flux has been used for depositing beads on plates, and the weld metal chemistry has been evaluated. The effect of welding conditions and flux composition on element transfer behavior has been investigated. The experiments were carried out as dictated by the design matrix generated using CCRD in response surface methodology. The data generated during experimentation was used to develop mathematical models. The developed models were tested for their adequacy through the ANOVA technique in design expert software. It is interesting to note that the recycled slag provided the chemistry of weld metal which is accepted as per ASME specifications. The rise in welding current increases the amount of carbon in weld metal from 0.11 to 0.14 wt.%, whereas it decreases with increasing travel speed. Manganese content decreases (1.28 wt.% to 0.795 wt.%) with increasing welding current (250 A to 650 A). The increase in welding speed from 4.44 mm/s to 8.88 mm/s results in an increment in manganese content from 0.87 wt.% to 1.21 wt.%. Since increasing travel speed decreases heat input per unit length of the weld, evaporation of manganese is suppressed. Therefore, the highest manganese content was achieved at a lower current (250 A) and higher speed (8.88 mm/s). Smooth beads with evenly distributed ripples free from surface defects like undercuts, porosity, pockmarks, etc., were achieved.

Performance Evaluation of Steel Slag on Hot Mix Asphalt Mixture

Researchers have been actively exploring alternative substances to modify asphalt mixtures and improve their qualities. While asphalt has been the traditional binder used in road construction due to its excellent adhesive and waterproofing properties. In this investigation, an assessment is conducted in a laboratory environment to evaluate the effectiveness of incorporating recycled steel slag as an addition in hot mix asphalt. The utilization of the Superpave mix design methodology was employed in this study to modify fine steel slag with a particle size of 300 m. Various percentages of steel slag modifier, namely 5%, 10%, 15%, and 20% of the total weight of the fine aggregate, were incorporated. The outcomes of this investigation revealed that the mixtures containing steel slag exhibited superior performance compared to those without any slag addition, serving as the control sample (0% (slag. The inclusion of steel slag in the asphalt mixes has demonstrated a significant enhancement in stability while concurrently reducing the levels of permanent deformation. The outcomes derived from the study indicate that asphalt mixtures containing steel slag additives at varying proportions (5%, 10%, 15%, and 20% by weight of the fine aggregates) exhibited superior performance in terms of the indirect tensile modulus test, static creep test, and dynamic creep test when compared to the control sample. Notably, the results highlight that the incorporation of 15% steel slag yielded the most favorable overall performance values among the tested asphalt mixes.

Study on seismic performance test and calculation method of recycled steel fiber reinforced concrete shear wall

SummaryRecycled steel wire is taken from used tires, and by procedures like mechanical cutting and friction treatment, it can be converted into industrial recycled steel fiber that meets precise criteria. Such green fiber may effectively limit the growth of fractures in concrete and diffuse the fracture energy of concrete when incorporated into concrete. An investigation of the effects of materials and horizontal reinforcement spacing on the seismic performance of shear wall specimens is presented in this research. The test and numerical simulation findings indicate that the RSFRC (recycled steel fiber reinforced concrete) shear wall's fracture is substantially narrower than that of a conventional shear wall and that the shear carrying capacity and deformation ductility of the shear wall have been greatly enhanced. The energy dissipation capacity of the RSFRC shear wall specimen with varying horizontal reinforcement spacing is significantly enhanced when compared to the conventional shear wall, and the ultimate displacements are reduced. RSFRC shear wall specimen has higher stiffness in the early stage, and the overall stiffness decreases slowly. With the decrease of fiber volume fraction of RSFRC shear wall in a certain range, the shear bearing capacity and stiffness of the model will decrease slightly, but the ductility will increase significantly. Compared with the RSFRC shear wall with fiber aspect ratio of 40 and 25, the bearing capacity and ductility of the two are close, but the RSFRC shear wall with low aspect ratio is slightly insufficient. When the axial compression ratio is in the range of 0.2–0.4, the horizontal shear capacity of RSFRC shear wall increases with the increase of vertical load, but the maximum horizontal displacement becomes smaller, and the model is damaged by compression. Using theoretical calculation, this work also creates the simplified calculation method and restoring force model for the bearing capacity of the diagonal section of RSFRC shear wall. The observed findings correspond well with the test hysteresis curve and may serve as a benchmark for future study. This study provides a new research direction for the seismic performance of RSFRC structures, as well as a solid theoretical foundation and promotion for future research.

Shear capacity of reinforced concrete beams with recycled steel fibers

Abstract This study investigates the effect of using recycled steel fibers (RSFs) extracted from cut tires with dimensions of 0.8 and 40 mm in diameter and length, respectively. Different percentages of fibers were used, which are 0.5, 1, 1.5, and 2%. Ten beams with dimensions of 150 mm × 240 mm and a length of 1,700 mm were tested, two of which are control beams without stirrups and using stirrups at a distance higher than the upper limit (d/2), which is a distance of 250 mm. In the case of using steel fibers without a stirrup, it is noticed that shear resistance increases gradually, but the type of failure remains shear. When using a minimum stirrup with steel fibers, the shear resistance increased significantly by 11.1, 23.7, 33.3, and 41.4%, respectively, compared to the reference beam without steel fibers so that the increased shear capacity in the presence of the minimum stirrups and optimal ratio of steel fibers of 2% reaches 122%, compared to the reference beam without stirrup and steel fibers, as well as converting the type of failure from shear failure to pure bending failure. When using a stirrup, this effect will be greater. The presence of RSF reduces deflection at cracking load, while increasing deflection at the ultimate load. Therefore, the stiffness and ductility ratio increased with the presence of steel fibers by 41.5 and 50.3%, respectively. Also, steel fibers delayed the appearance of beam cracks and reduced their widths.

Chemistry and microstructure of duplex stainless steel powders from recycled Z100 mixed with 316L steels

Recovered metallic waste can be used in additive manufacturing as a feedstock if the subsequent steps of the waste-to-product process are sufficiently mastered. In this study, impact of recycling of Z100 duplex steel mixed with 316L steel on the resulting powders microstructure and chemical composition was investigated. The utility of the original method of recycling stainless steels into a high-grade powder suitable for additive techniques has been demonstrated. By examining three gradations of powders, namely 20–50 μm, 50–100 μm and 125–250 μm, differences in selected properties in relation to the average particle size are shown. The results suggest that with increasing the particle diameter, fine-crystalline γ-austenite is favoured to precipitate at the boundaries and within the volume of the originally formed large δ-ferrite grains. It is reflected by a decrease of δ/γ fraction ratio from 0.64 in the 20–50 μm powders to 0.20 in the 125–250 μm, respectively. Obtained results indicate non-diffusional, shear or semi-shear character of δ → γ + δ phase transformation. The resulting fine-crystalline austenite is characterised by a significant dislocation density, which induces dislocation strengthening effect, responsible for an increase in Vickers hardness from 145 HV and Young's modulus from 29 GPa in the 20–50 μm group to 310 HV and 146 GPa in the 125–250 μm fraction, respectively.

Performance and life cycle of ultra-high performance concrete mixes containing oil refinery waste catalyst and steel fibre recovered from scrap tyre

An economic solution to recycle spent equilibrium catalyst (Ecat) disposed of by petrochemical manufacturers and steel fibre recovered from scrap tyre would be their use in the production of structural concrete. In this study, the performance and life cycle of ultra-high performance concrete (UHPC) mixes containing these waste materials was examined. They were made using a total binder content of 1160 kg/m3 and also contained fly ash and silica fume in addition to Ecat and cement. Their average compressive strength at the end of 28 days was found to be above 150 MPa. The replacement of cement with Ecat reduced the CO2 emission and material cost of recycled steel fibre (RSF) reinforced UHPC samples by 15% and 6%, but there is no significant change in their compressive, flexural and split tensile strengths at the end of 28 days. Only 2% of the elastic modulus of these samples increased as a result of the addition of Ecat by weight of the binder. Ecat, an aluminosilicate material, is generally classified as a pozzolanic material, but its addition together with fly ash and silica fume in the UHPC mixture did not affect the strength gain properties. Based on our experimental findings, the use of waste materials including Ecat and RSF in the preparation of precast UHPC elements for explosion and earthquake resistant structures is recommended.

Performance Evaluation of Asphalt Concrete Incorporating Steel Slag Powder as Filler under the Combined Damage of Temperature and Moisture

Recycling steel slag into asphalt concrete is an important way to save natural resources and protect the environment. The high asphalt absorption and adsorption and the sensitivity of steel slag aggregate (SSA) to the combined damage of temperature and moisture (volume expansion and poor durability under freeze-thaw cycle damage) still pose risks for the use of SSA in asphalt concrete. It is urgent to develop new utilization methods of steel slag. With this in mind, the material properties of steel slag powder (SSP) and performance characteristics of asphalt concrete incorporating SSP filler were evaluated in this research. The SSP was prepared in the laboratory by grinding steel slag with a particle size of 2.36–4.75 mm. Firstly, the material properties of SSP including the specific surface area, particle gradation, apparent density, chemical compositions, and thermal stability were analyzed. Steel slag (2.36–4.75 mm) and common limestone powder (LP) filler were used as control groups. The grindability of steel slag and the advantages of using SSP as a filler in asphalt concrete were preliminarily analyzed based on the test results of material properties. Then, the Superpave method was used to design asphalt concrete incorporating SSP and LP. Considering that steel slag is sensitive to the combined damage of temperature and moisture, the main engineering performance of asphalt concrete after the combined damage of temperature and moisture was evaluated to further reveal the feasibility of using SSP as a filler. Two combined damage modes, namely hot water damage and freeze-thaw cycle damage, were applied. Results suggest that although the steel slag is more difficult to grind compared to limestone particles, grinding steel slag into SSP has improved the uniformity of its material properties. Good uniformity of material properties, high alkalinity, and excellent thermal stability of SSP give it some advantages in its application in asphalt concrete. Although the freeze-thaw cycle damage has a slightly more significant effect on the engineering performance of asphalt concrete than hot water damage, compared to the asphalt concrete with LP filler, even after freeze-thaw cycle damage for three cycles asphalt concrete incorporating SSP still possesses comparable or better volume stability, mechanical performance, high-temperature deformation resistance, low-temperature crack resistance, fatigue crack resistance, and fatigue durability.

Influence of steel fiber types on residual mechanical properties and explosive spalling of hybrid fiber reinforced ultra-high performance concrete: Optimization and evaluations

To investigate the influence of steel fiber on improving the high-temperature resistance of hybrid fiber-reinforced ultra-high performance concrete (UHPC), four types of UHPC specimens were prepared. The residual strength and fracture energy of all UHPCs were determined after exposure to varying high temperatures, and internal temperature in the specimens were also measured. Additionally, explosive spalling tests were performed on specimens with different moisture contents. The results indicate that the residual mechanical properties of UHPC initially increase and subsequently decrease as the target temperature increases. Notable differences in thermal conductivity were observed among the tested UHPC specimens. As the moisture content of the specimens increased, the likelihood and severity of explosive spalling in the specimens increased. Corrugated high-strength steel fibers, measuring 35 mm in length and 1 mm in diameter, are highly effective at preventing explosive spalling of UHPC, and high-temperature treated recycled steel fiber from tires also exhibits better performance than other two types of steel fiber. High tensile strength of steel fiber and its distinctive corrugated appearance can be the primary contributing factors. Furthermore, two established computational models which demonstrated a significant level of congruence were employed for evaluating explosive spalling and anti-spalling properties of UHPC specimens. This suggests that cracking resistance provided by steel fiber plays an important role in preventing the explosive spalling of UHPC, emphasizing the importance of exploring specific steel fiber based on its appearance and tensile strength.

Sub-rapid solidified high copper-bearing steel with excellent resistance to hot shortness

The removal of accumulated impurity elements during scrap refining has been regarded as the bottleneck to limiting scrap usage, among which copper is the crucial tramp element in scrap steel recycling, resulting in the final product's hot shortness and surface cracking. This study proposes sub-rapid solidification-based strip casting technology to eliminate the copper impurity introduced problems. The results reveal that strip casting could improve copper behavior in the as-cast sample. More importantly, the sub-rapid solidified sample has excellent high-temperature tensile properties and resistance to hot shortness. It suggested that strip casting technology could produce copper-bearing steel, which can tackle the hot shortness problem and provide a unique idea for steelmaking with scrap as raw materials.

Induction Heating and Cooling Performance of Asphalt Mixture as Recycling Rap and Steel Slag

Recycling reclaimed asphalt pavement (RAP) for asphalt pavement construction is of interest due to its potential to mitigate environmental impact and resource consumption; however, the addition of RAP limits the induction heating behavior of asphalt mixtures, hindering the further application of RAP in sustainable and functional asphalt pavement. This study prepared recycled asphalt mixtures with high contents of steel slag aggregate and RAP, and optimized the rejuvenator dosage and composition design to investigate the induction heating rate. The effect of the steel fiber content, heating time, and heating distance on the induction capacity were verified for the recycled asphalt mixture. Moreover, the cooling curves of the recycled asphalt mixture were explored using a constant temperature chamber and infrared camera. The results showed that 6 wt% of rejuvenator in aged asphalt could evidently restore the physical properties and surface morphology, the highest heating rate of 1.204 °C/s could be reached with 2 wt% of steel fiber content, and the effective intervals of heating time and heating distance were set as 60–120 s and 10–20 mm, respectively. This study could be a significant reference in promoting solid waste recycling and sustainable asphalt pavement construction.

Scrap endowment and inequalities in global steel decarbonization

Scrap steel recycling, powered by emission-free electricity, can produce nearly zero-emission steel at a lower cost than alternative primary production. However, the feasibility of this production method depends on future scrap availability. This study highlights the unequal distribution of future scrap availability worldwide, with the Global North having abundant scrap, while the Global South faces impending scarcity unless scrap is imported. By 2050, the European Union, North America, and developed Asia and Oceania could hold stocks of end-of-life scrap that are equal to their entire steel demand, if they chose to do so. China could also have domestic end-of-life scrap equivalent to about half of its cumulative demand. Conversely, developing countries, such as India and states in Africa, are expected to have severely limited domestic end-of-life scrap, representing less than 5% of their cumulative demand without international trade. This disparity, referred to as “scrap endowment”, is a consequence of the Global North's historical carbon emissions. The scrap endowment enables the Global North to produce zero-emission steel at a relatively low cost, while the Global South grapples with limited, more costly options. These findings imply the need for equity-focused mechanisms to assist the Global South if both hemispheres are to achieve net-zero emissions by 2050, or soon thereafter.

PERFORMANCE OF STEEL FIBER EXTRACTED FROM OLD WASTE TYRES ON MECHANICAL PROPERTIES OF CONCRETE FOR RIGID PAVEMENT CONSTRUCTION

The application of Waste Recycled Steel Fibers (WRSF) extracted from waste tyres in fiber-reinforced concrete production has great benefits in civil engineering. Thus, this creates a need to study the appropriate length and dosages of recycled steel fiber in fiber-reinforced concrete. In this experimental research, the effects of varying lengths (5cm and 10 cm) and dosages (1, 1.5, 2, 2.5, and 3%) of WRSF on various mechanical properties of fiber-reinforced concrete for rigid pavement construction were studied. The aggregates were taken from a stockpile, commercially available cement Dangote Ordinary Portland Cement (OPC), and potable water. Non-probable sampling techniques were adopted to collect extracted waste steel tyres. The quality test for sand (fine) and coarse aggregate satisfies the requirements specified in the ASTM. The concrete mix design was done in two categories; the first was a control mix concrete and the second was the experimental mix concrete with the addition of steel fibers with varying lengths (5cm and 10 cm) and dosages (1, 1.5, 2, 2.5, and 3%) of WRSF in concrete (percentages were determined by density for each fiber). The mix ratio of cement: sand: aggregate (1:2:3) with a constant water-to-cement ratio of 0.53 was used throughout this investigation. The outcome showed that the fiber fraction with 1.5% and 10cm of fiber had the maximum compressive strength which was 45.59 MPa, while for the fraction with 1% and 5cm of fiber, the maximum compressive strength was 43.85 MPa. The flexural strength had a maximum value of 5.88 MPa at 3% fiber content for 5cm fiber and 5.09 MPa at 3% for 10cm of fiber. The maximum tensile strength attained was 4.74 MPa and 3.50 MPa at 3% WRSF for 5cm and 10cm of fiber, respectively. The strain value had a maximum value at 3% for both 10cm and 5cm of fiber which were 0.53 and 0.6 respectively. The concrete strength which was obtained with the addition of steel fiber showed reasonable improvement in compressive, indirect tensile, and flexural strength. However, as the percentage of WRSF increased, the workability of concrete reduced.

Triaxial behavior of concrete containing recycled fibers- an experimental study

This study aimed to investigate the behavior of recycled steel fiber-reinforced concrete (RSFRC) under true triaxial tests. Sixteen cylindrical specimens were used to assess the effect of recycled steel fibers (RSFs) on compressive and tensile strength, and modulus of elasticity, while 80 cubic specimens with RSFs of 0, 0.2, 0.4, and 0.6 kN.m-3 were used for true triaxial tests. Experiments were performed with three loading protocols based on the Lode angle. The findings suggested that the presence of RSF has a significant effect on the behavior of the specimens in the post-peak area. Moreover, the findings indicated that the higher the density of RSF, the higher the final triaxial strength in load combinations close to the tensile meridian. This effect was less pronounced when the Lode angle shifted from the tensile meridian to the compressive meridian. The coefficient kθ was proposed to modify the meridian curves and its value depended not only on the characteristics but also on the volume of the fibers but also on the Lode angle. Comparison of laboratory results with the results for the proposed coefficient kθ showed good agreement.

Flexural behavior of reinforced concrete beams strengthened using recycled industrial steel-wire mesh high-performance mortar

Industrial recycled steel wires extracted from waste tires can be combined with high-performance mortar by weaving them into a mesh to apply this type of strengthening method, which exhibits high tensile strength, high toughness, and excellent cracking resistance in building structures. This paper presents a flexural behavior study of reinforced concrete (RC) beams under different industrial recycled steel wire working conditions. We examined the resultant steel-wire mesh high-performance mortar, investigating the stiffness, ductility, and load carrying capacity of the experimental beams under different anchorage measures using different mesh types and sizes. The results showed that both the weaving of the recycled industrial steel wire into a mesh and the rebar-planting anchorage measures were effective in preventing the stripping of the strengthening layers, allowing the tensile performance of the recycled industrial steel wire to be fully utilized and the ultimate load capacity of the RC beams to be considerably increased. At the same time, the industrial recycled steel-wire mesh also played an important role in the inhibition of crack development, with the width of the cracks in the strengthening beams decreasing and an overall appearance of "fine and dense" character. As the volume of steel bars in industrial recycled steel-wire mesh increases, the ultimate bearing capacity and stiffness of the beam increased. To verify the strengthening effect of industrial recycled steel-wire mesh high-performance mortar on the beams from multiple angles, this study used finite element analysis software to conduct numerical simulation analyses on four of the experimental beams. The damage cloud charts of the specimens from the numerical simulations were compared with experimental failure phenomena, the deviations between the simulated and experimental values of the specimens being within 10%—that is, the simulation results were in good agreement with the experimental results. The use of industrial recycled steel-wire mesh high-performance mortar strengthening could be applied in actual projects, its green low-carbon credentials achieving the purpose of solid-waste utilization as well as providing strong support for China's early realization of carbon neutrality and related strategic objectives. At the same time, the recycling of waste tires could provide a new research direction.

How can C&D waste recycling do a carbon emission contribution for construction industry in Japan city?

Japan has made a legislative commitment to achieve carbon neutrality by 2050. The construction industry in Japan contributes 30% of the carbon emissions and is the key sector for achieving carbon neutrality. Building abandonment and vacancy has become an urgent problem in Japan. However, less attention has been paid to the carbon emissions of building demolition, especially the recycling of Construction and Demolition (C&D) waste. This study clarifies the flow of C&D waste and accounts for the carbon emission of C&D waste disposal by Life Cycle Assessment and IPCC method. The contribution of C&D waste recycling to carbon emission reduction under three scenarios (Baseline scenario, Large area scenario, Long lifespan scenario) is predicted by modeling the building stock flow. The results show that in Kitakyushu, a decarbonization pioneer region, the disposal of C&D waste will generate 35,896 tons of CO2 in 2019, and the recycled products could reduce emissions by 7,845 tons for the construction industry. Disposing of concrete and steel is the major source of carbon emissions of 94.1%, recycling of steel is the biggest driver of emissions reduction. Kitakyushu will soon face rapid growth in C&D waste, contributing to a 1.9–6.8% carbon reduction in the construction industry. From a material cycle perspective, a reasonable building stock and an extended building lifespan are more conducive to achieving carbon neutrality.

Research on axial compressive behavior of steel-fiber-reinforced recycled concrete-filled square steel tube slender columns

This paper presents an experimental and analytical study of the axial behavior of steel-fiber-reinforced concrete-filled square steel tube slender columns. A total of 25 axially compressive column specimens are manufactured to investigate the effects of the mass replacement percentage of recycled coarse aggregates (Rp), tube wall thickness (Ts), length-to-width ratio of columns (Lc), and steel fiber content (Vsf) on the performance of slender columns. The results show that the effects of Lc and Ts on the compressive behavior of the column specimens are significant owing to changes in the confinement effect and instability. In terms of the bearing capacity, the compressive strength increases by 12.45%–23.19% as Ts increases from 3 to 5 mm but decreases by 4.35%–10.65% as Lc increases from 6 to 12. However, the incorporation of steel fibers improves the post-peak load mechanical behavior of the slender columns by performing anchoring and bridging effects, and when Vsf reaches 1.2%, it tends to compensate for the reduction caused by changes in Lc and Ts. The synergistic action of the column specimens under axial compression is quantified based on an energy consumption indicator. In addition, predictions of the bearing capacity of the slender columns specified in the Eurocode 4, GB 50936-2014, and Han model are compared and discussed. An incremental iteration model is proposed, and the predicted values are similar to the experiment results with reasonable safety margins.

Influence of recycled large-aggregate self-compacting concrete-filled steel tube mechanical properties under pure bending load

ABSTRACT In this study, the influence of different factors on pure bending members of recycled large-aggregate self-compacting concrete-filled steel tubes (RLA-SCCFSTs) was analyzed. Seven RLA-SCCFST members and one SCCFST member were designed to study their failure under a pure bending load and the influence of the steel tube wall thickness, RLA strength, and RLA particle size. The flexural bearing capacity was calculated using various codes. Based on the test results, ABAQUS and MIDAS FEA NX finite element analysis software were used to simulate and verify the test conditions. The results showed that under a pure bending load, the failure process of the RLA-SCCFSTs was much the same as that of an ordinary concrete-filled steel tube. Moreover, changes in the influencing factors resulted in different degrees of improvement in the flexural bearing capacity of the RLA-SCCFSTs. The factors most affecting the flexural members of the RLA-SCCFSTs – from large to small – included the steel tube wall thickness, RLA strength, and RLA particle size. The finite element simulation shows that the model based on the modified constitutive relation of core concrete was in good agreement with the experimental results. Among the various calculation methods for the bearing capacity, the results using the DBJ13-51-2003 specification were in good agreement with the test results. This study provides a reference for the reuse of waste concrete.

Physicomechanical Behavior of High-Performance Concrete Reinforced with Recycled Steel Fibers from Twisted Cables in the Brittle State—Experimentation and Statistics

This research studied the effect of recycled steel fibers extracted from twisted cable waste on the fresh and hardened states of high-performance concretes. Accordingly, slump, water absorption (WA), compressive strength (CS), flexural strength (FS), and split tensile strength (STS) were measured in the laboratory using mixtures generated by the response surface methodology (RSM). The RSM-based central composite design (CCD) was used to assess the influence of water-to-binder (W/B) ratios from 0.27 to 0.31, length-to-diameter (L/d = 46 to 80) and steel fiber content (SFC) in the range of 19 to 29 kg/m3 on the behavior of high-performance fiber-reinforced concrete (HPFRC). The accuracy and validation of the generated models were evaluated by employing analysis of variance (ANOVA) and optimal parameters. The experimental findings revealed that the use of an L/d ratio of 63, a W/B ratio of approximately 0.28, and an SFC of around 22 kg/m3 resulted in high workability in terms of slump. While a notable increase in compressive strength was observed when employing an L/d ratio of approximately 70, a W/B ratio of around 0.28, and the maximum SFC of 29 kg/m3, as confirmed by scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis.

Mapping the global flows of steel scraps: an alloy elements recovery perspective

Recycling steel scraps by the use of electric arc furnace is one of the most promising approaches for the steel industry to achieve net-zero emissions. Due to the uneven distribution of global steel scraps, many countries are actively involving in the global steel scraps trade. Steel scraps contain a range of critical elements, which may be transferred across borders through international trade of steel scraps. However, existing studies have paid little attention to the global flows of steel scraps and its embodied alloy elements (AEs). This study maps the journey of global steel scraps and the embodied AEs for the period of 2000–2021 for the first time by employing trade-linked material flow analysis and social network analysis. The results indicate that the global steel scraps trade had increased during the study period, with a few core countries (such as USA, Germany, and Turkey) leading the global steel scraps network. Also, critical metals had been transferred across borders in the form of AEs through the trade of steel scraps, especially from global north countries to global south countries. The largest AE flows include Chromium (Cr), nickel (Ni), manganese (Mn) and molybdenum (Mo) flows. Other AE flows, such as cobalt (Co), vanadium (V), and niobium (Nb) flows, were less, but with high values or being regarded scarce. From a global perspective, steel scraps trade and recycling can contribute to the decarbonization efforts of the global steel industry and address resource shortages in some countries. Therefore, it is urgent to promote the overall resource efficiency of steel scraps and the embodied AEs by various efforts.

Stress strain response of pre-damaged concrete confined with recycled steel straps- A green confining material

When an engineer is determining the restoration strategy for a deteriorated concrete building, a precise design model is particularly essential. Although many design models have been proposed previously for various confining techniques, these models are not suitable for confinement using pre-tensioned recycled steel straps. This because pre-tensioned steel straps confinement has larger confining pressure at the onset of loading stage compared to other existing confining techniques. In this study, stress-strain responses of concrete repaired using pre-tensioned steel straps are assessed through experimental tests. Concrete cylinders were prepared and pre-damaged to a certain damaged degree to resemble damaged structures. They were then confined by using pre-tensioned steel straps. This acts as a repairing technique to restore the loading capacity of the damaged concrete. The experimental results showed that the confining volumetric ratio and pre-damaged degrees are two most important parameters that affects the stress-strain response. For this reason, previously developed design models are unable to capture the experimental test results in this study. Hence, confining volumetric ratio and pre-damaged degrees should be included in the development of the design model in future. In this study, a new design model is proposed by calibrating these two parameters into previous models. This proposed model is shown to be able to capture the stress-strain behaviour and is in good agreement with the experimental results. It is believed that engineers can apply this model in the design of repair works for a deteriorated concrete building.