Steel Waste Research Articles

Sustained energy generation from unusable waste steel through microbial assisted fuel cell systems.

In the present study, a novel green energy generation process assisted with Microbial Fuel Cell (MFC) principle for generation of electricity from used or wasted steel is explored. Through a unique approach, unused and other steel waste are recast by simple re-melting with a flexible wide composition for generation of green energy. A microbial-assisted electron transfer derived from the degradation of the steel material is utilized for production of green energy in a microbial galvanic reactor system. A. ferrooxidans acts as biocatalysts, facilitating the oxidization of ferrous ion (Fe2+) to ferric ion (Fe3+). The reaction takes place on the biofilm matrix which results in oxidised reactive zones that endorses further degradation or dissolution of Fe anode. This consequently results in achieving the highest power density as high as 4.92±0.03mW/cm2 at a current density of 0.01±9mA/cm2. The total cost of the unusable steel anode and other accessories are roughly estimated to be 7.94 $/m2 and 178.54 $/m2 and the gain from unit power generation is estimated to be 3.79 $/W, assuming continuous operation of 4.92±0.03mW/cm2. The present study presents a potent methodology/strategy for the generation of sustainable bioenergy from low-cost, unusable steel materials, which cannot be anyway used as such in other battery systems, say iron air cells/batteries.

Appraisal of Heavy Metal Risk Hazards of Eisenia fetida-Mediated Steel Slag Vermicompost on Oryza sativa L.: Insights from Agro-Scale Inspection and Machine Learning Analytics

The steel industry drives world economic growth, yet it generates heavy metal-rich steel slag, which jeopardizes the environment. The utilization of vermi-technology is essential for the sustainable transformation of toxic steel waste slag (SW) into organic amendments, although field-scale use of vermiprocessed SW remains unexplored. To bridge the gap, this study evaluated the efficacy of vermiprocessed SW as an organic supplement for rice field cultivation, focusing on heavy metal (HM) bioavailability, human health risk, and yield in comparison to raw slag and NPK fertilizer. The results indicated a considerable decrease in the bioavailable fraction of heavy metals in T4 (1:1 SW vermicompost 50% + 50% fertilizer). In treatments, T9 (100% SW) and T10 (50% SW + 50% fertilizer) (FIAM) free ion activity modeling confirmed grain absorption of HMs, and the FIAM HQ values indicated the health risk for the direct application of steel slag waste on the field. The risk factor evaluation of HMs’ presence in treatments T9 and T10 established the possible cancer risk for living beings. Similarly, machine learning models like SOBOL sensitivity analysis and artificial neural networks revealed potential threats associated with HMs on different treatments, respectively. The correlation coefficient revealed the negative effects of bioavailable HMs on various soil microbial and enzymatic properties. Moreover, the abundant yield of rice was attributed to the combination treatment (1:1 50% + NPK 50%), which paved the way for an alternative agronomic approach based on the utilization of vermicomposted steel waste slag.

Single-machine scheduling with setup time: a case study in the cutting of large-scale structural parts

This article considers a single-machine scheduling problem with setup time to optimize the cutting schedule for structural parts within a railway equipment manufacturing enterprise. When performing parts-cutting operations for various orders, factors such as priority, the material attribute of the steel plate and part specifications need to be considered. Notably, it is beneficial to ensure continuous cutting to minimize steel waste when these parts need the same steel plates. A mixed integer programming model and a two-stage heuristic are proposed to determine the cutting sequence of the parts. The two-stage heuristic involves preprocessing and local search. Finally, the performance of the proposed approaches is assessed using real-world cutting production data. This includes scenarios with more than 10,000 parts, allowing for a thorough evaluation. The results indicate that the proposed two-stage heuristic exhibits significant efficiency and quality advantages compared to the Gurobi tm solver and local search.

Experimental Study on Mechanical Properties and Stability of Marine Dredged Mud with Improvement by Waste Steel Slag

As marine-dredged mud and waste steel slag in coastal port cities continue to soar, the traditional treatment method of land stockpiling has caused ecological problems. Thus, it is necessary to find a large-scale resource-comprehensive utilization method for dredged mud and waste steel slag. This study uses waste steel slag and composite solidifying agents (cement, lime, fly ash) to physically and chemically improve marine-dredged mud. The physical improvement effect of the particle size and dosage of waste steel slag was studied by the shear strength test under the effect of freeze–thaw cycle. Then, based on the Box–Behnken design of the response surface method, the interaction effects of the solidifying agent components on the unconfined compressive strength were studied. Then, the water stability under dry–wet cycles and a microscopic mechanism were analyzed by XRD and SEM tests. The results show that the waste steel slag with a dosage of 30% and a particle size of 1.18~2.36 mm has the best improvement. The interaction between cement and lime and lime and fly ash has a significant effect on the linear effect and surface effect of 7d unconfined compressive strength, and the strength increases first and then decreases with the increase in its dosage. For the 14d unconfined compressive strength, only the interaction between cement and lime is still significant. The unconfined compressive strength prediction model is established to optimize the mix ratio of the composite solidifying agent. In the water stability, the water stability coefficients of the 7d and 14d tests are 0.68 and 0.95, respectively, and the volume and mass loss rates are all below 1.5%, showing a good performance in dry–wet resistance and durability. Microscopic mechanism analysis shows that waste steel slag provides an ‘anchoring surface’ as a skeleton, which improves the pore structure of dredged mud, and the hydration products generated by the solidifying agent play a role in filling and cementation. The results of the study can provide an experimental and technical basis for the resource engineering of marine-dredged mud and waste steel slag, helping the construction of green low-carbon and resource-saving ports.

Design and Site Selection of Reverse Logistics Network for Iron and Steel Enterprises from the Perspective of Green Supply Chain

The iron and steel industry is not only one of the most important components of China's national economy, but also a typical resource-and-energy-intensive industry. Under the background of "Carbon Peaking and Carbon Neutrality Goals", it is of great significance for the iron and steel industry to improve the green closed-loop supply chain and develop circular economy. From the perspective of green supply chain, this paper puts forward the three-level network structure of waste steel reverse logistics based on the present situation of waste steel recycling in China, and uses k-means clustering algorithm and accurate center of gravity method to select locations for the primary and secondary nodes. The purpose of this paper is to provide a basis for iron and steel enterprises to carry out network optimization of reverse logistics.

Effect of GBFS ratio and recycled steel tire wire on the mechanical and microstructural properties of geopolymer concrete under ambient and oven curing conditions

In this study, the effects of waste steel wire ratios, granulated blast furnace slag (GBFS) ratios, and different curing methods on geopolymer concrete (GPC) were investigated. For this purpose, 12 mixtures were produced and eight of them were cured under ambient conditions and the remaining four were cured in an oven. Steel wire ratios and GBFS ratios were added to GPC as 0–1–2–3 % and 0–10–20 % by volume and weight, respectively. As a result of the mixtures, cubes, cylinders, and beams were obtained and these elements were subjected to compression, tensile, and flexural tests. As a result of the tests, the compressive strengths of the specimens were obtained as 8.5 %, 19.7 %, and 24.9 % for ambient curing and 10.4 %, 23.2 %, and 32.2 % for oven curing, respectively, as the steel wire fiber increased from 0 % to 3 %. The maximum compressive strength of the oven-cured specimen with 3 % steel wire fiber was measured as 42.56 MPa. The tensile strength of GPC also increased as the steel wire increased. The highest tensile strength was obtained with 3 % steel wire. In addition, oven curing conditions increased the tensile strength more than ambient curing. The flexural strength (FS) increased by 21.3 %, 29.4 %, and 33.8 % with increasing steel wire ratios of 1 %, 2 %, and 3 %, respectively. The FS was further increased by oven curing conditions and the maximum FS was achieved with 3 % steel wire. In ambient curing conditions, a successful geopolymerization was achieved due to the high calcium content in the samples containing 20 % GBFS. This allowed to obtain similar strengths between ambient curing and oven curing. Although the oven curing values were higher, similar results were obtained for the samples cured in an ambient containing 20 % GBFS. As a result of the study, mixtures containing 3 % steel wire and 20 % GBFS provided sufficient strength without oven curing and increased the usability of GPC under ambient conditions.

Applicability of Waste from Al Industry toward Dephosphorization of Hot Metal in Primary Steel Making

Managing industrial waste is a global challenge. Red mud is a byproduct of the aluminum industry posing serious concerns. The presence of FeO and CaO in red mud makes it a potential DeP flux. Red mud has been utilized as a DeP flux in previous studies, but these studies deal with low Si content and no P2O5 content in the red mud. However, certain steel makers have high initial Si content (0.6–0.7 wt%) in the hot metal, and with increasing demand for low P steel, new dephosphorization fluxes need to be explored. Addressing this gap, this study investigates red mud's potential as a flux for dephosphorization in hot metal with elevated Si levels. Conducting slag–metal equilibrium experiments at 1350 °C, using red mud‐based fluxes, the research achieves a 40% dephosphorization degree under optimized conditions of double deslagging and fluxing. Analysis via wet chemical methods and inductively coupled plasma mass spectrometry confirms the effectiveness of the approach. Furthermore, thermodynamic calculations highlight the influence of O2 partial pressure and Si content on dephosphorization efficacy. Through laboratory experiments and theoretical insights, this study provides a valuable roadmap for leveraging red mud as a sustainable flux in hot metal dephosphorization processes, contributing to both waste management and steel production efficiency.

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.

EXPERIMENTAL APPROACH FOR DEVELOPMENT OF SUSTAINABLE HYBRID GRADED FIBER REINFORCED CONCRETE BY CONSUMING LATHE WASTE STEEL FIBERS WITH GLASS FIBERS FOR ENHANCED MECHANICAL PROPERTIES

Local workshops generate large quantities of industrial lathe waste steel fibers, which the steel manufacturing industries find difficult to recycle because of their sharp edges. The utilization of lathe waste steel fibers as fiber reinforcement is sustainable in concrete because these fibers have the same properties as steel fibers. Furthermore, using combinations of ductile and elastic fibers improves strain capacity and resistance to pre- and post-cracking. This research employs hybrid fiber reinforcement technology, utilizing industrial lathe waste steel fibers and glass fibers in varying proportions, to bridge the micro and macro cracks in concrete specimens. This research was done to examine the physical (workability) and mechanical properties (compressive and flexural strength) of hybrid fiber-reinforced concrete. In this research different mixtures of hybrid fiber-reinforced concrete were cast and designated as M0, M1, M2, M3, M4, M5, and M6. The mixtures included lathe waste steel fibers at 0%, 0.50%, 1%, 1.5%, 2%, 2.5%, and 3%, and glass fibers at 0%, 0.15%, 0.25%, 0.45%, 0.60%, 0.75%, and 0.90%, respectively. The ASTM-standardised protocols were followed for all laboratory testing. The physical property results showed a decrease in the workability of concrete mixes as the percentage of lathe waste steel and glass fiber increased. This suggests that a higher percentage of lathe waste steel and glass fibers leads to a lower slump value. Consequently, the mechanical property results showed a gradual enhancement in the compressive and flexural strengths of hybrid fiber-reinforced concrete up to 2.5% lathe waste steel fibers and 0.75% (M5). Further incorporation causes a reduction in strength. The physical examination of fractured samples of hybrid fiber-reinforced concrete confirms that the lathe waste steel fibers yield a maximum strain before breaking down in the concrete matrix. Furthermore, lathe waste steel fibers broke rather than being pulled out, indicating a good bond with the concrete. It is recommended that up to 2.5% lathe waste steel fibers and 0.75% of glass fibers by the total weight of the concrete can be used as hybrid fiber reinforcement for optimum strength achievement.

Synthesis of novel composite material with spent coffee ground biochar and steel slag zeolite for enhanced dye and phosphate removal.

Rising concerns over water scarcity, driven by industrialization and urbanization, necessitate the need for innovative solutions for wastewater treatment. This study focuses on developing an eco-friendly and cost-effective biochar-zeolite composite (BZC) adsorbent using waste materials-spent coffee ground biochar (CGB) and steel slag zeolite (SSZ). Initially, the biochar was prepared from spent coffee ground, and zeolite was prepared from steel slag; their co-pyrolysis resulted in novel adsorbent material. Later, the physicochemical characteristics of the BZC were examined, which showed irregular structure and well-defined pores. Dye removal studies were conducted, which indicate that BZC adsorption reach equilibrium in 2h, exhibiting 95% removal efficiency compared to biochar (43.33%) and zeolite (74.58%). Moreover, the removal efficiencies of the novel BZC composite toward dyes methyl orange (MO) and crystal violet (CV) were found to be 97% and 99.53%, respectively. The kinetic studies performed with the dyes and phosphate with an adsorbent dosage of 0.5g L-1 suggest a pseudo-second-order model. Additionally, the reusability study of BZC proves to be effective through multiple adsorption and regeneration cycles. Initially, the phosphate removal remains high but eventually decreases from 92% to 70% in the third regeneration cycle, highlighting the robustness of the BZC. In conclusion, this study introduces a promising, cost-effective novel BZC adsorbent derived from waste materials as a sustainable solution for wastewater treatment. Emphasizing efficiency, reusability, and potential contributions to environmentally conscious water treatment, the findings highlight the composite's significance in addressing key challenges for the removal of toxic pollutants from the aqueous solutions. PRACTITIONER POINTS: A novel biochar-zeolite composite (BZC) material has been synthesized. Excellent removal of dyes by BZC (~95%) was achieved as compared to their counterparts The kinetic studies performed suggest a pseudo-second-order model. BZC proves to be highly effective for multiple adsorption studies. Excellent reusability showed potential as a robust adsorbent.

Steel slag aggregate property improvement in cold mixed asphalt mixtures through surface modification treatment

Expanding the resource utilization of solid waste steel slag (SS) is necessary to reduce the environmental impact of stockpiling and disposal. However, SS has the shortcomings of poor volume stability and poor water damage resistance, which limits its application in pavement engineering, especially in cold mixed asphalt mixtures. In this work, hexamethylene diisocyanate biuret (containing -NCO) and hydroxyl acrylic resin (containing -OH) were utilized as raw materials to prepare NCO-OH composite modifier (NOCM) by regulating NCO/OH (0.75, 1.00, 1.25, and 1.50) for SS surface modification. Surface morphology, adhesion properties, aggregate properties, and prepared mixture properties of SS before and after modification were investigated, respectively, and the curing mechanism of NOCM and action mechanism were analyzed. Results show that the cured NOCM forms a dense modified film on the SS surface, and the rough surface and large pores of SS were blocked, which effectively hindered the free oxides in SS from coming into contact with water. NOCM reduced the apparent relative density, water absorption, and wear loss of SS. NOCM with NCO/OH=1.25 was recommended to modify SS to obtain the most balanced properties, at which time MSS has a roughest surface to mechanically interlock with asphalt, and there are excess -NCO groups to chemically bond with polar components in asphalt. Mixtures prepared at the optimum NCO/OH had good water damage resistance, freeze-thaw cycle resistance, and volume stability. Applying NOCM-modified SS in environment-friendly cold mixed asphalt mixtures can effectively improve pavement durability and bring good environmental benefits.

On the Use of 17-4 Precipitate Hardened Stainless Steel Waste Powder for 3D Printing of Implants with Tuneable Stress Shielding Capabilities

On the Use of 17-4 Precipitate Hardened Stainless Steel Waste Powder for 3D Printing of Implants with Tuneable Stress Shielding Capabilities

Enhancing concrete properties with steel waste: a comprehensive review of GGBS, SS, and steel waste utilization

Enhancing concrete properties with steel waste: a comprehensive review of GGBS, SS, and steel waste utilization

CONVERSION OF ALUMINO-SILICEOUS REJECTS FROM POWER AND STEEL INDUSTRIES INTO BINARY GEOPOLYMER BRICK: EXPLOITING-GBFS MATERIAL SYNERGY UNDER AMBIENT CONDITIONS FOR SUPPORTING CIRCULAR ECONOMY

In recent year, advances in construction material have enabled the utilization of abundant reject material for value added purposes. The mining and metallurgical industries, particularly those with mineral rich rejects, have emerged as alternative sources of material for the construction application. The combination of granulated blast furnace slag (GBFS) from the steel industry and fly ash (FA) has been identified as one of the most suitable materials combinations for producing geopolymer blocks without the need for reinforcement or with the additives. Binary blended FA and GBFS based geopolymer bricks were cast with variable raw precursors and activator ratio using mini brick plant setup and cured at ambient temperature. The decisive parameters based on Indian standards forwhich the testing was done are compressive strength, water absorption, efflorescence and density. The compressive strength achieved for the test cubes casted for prism test was in the range of 20 - 30 MPa at ambient temperature. The bricks were found to meet the requirements established by Indian Standard 1077:1992 for producing energy-efficient masonry products. The cost and embodied energy (EE) of the developed geopolymer bricks were estimated. As being a binary blend of FA and GBFS cured at room temperature, the developed bricks could reduce the EE and carbon dioxide emission (CO2) and energy required for heat curing. The comparative analysis for the conventionally available bricks with the geo-brick showed promising results. Utilization of steel and power industry waste is a way to achieve circular economy in the waste.

To Study the Requirement of Implementation of Zero Waste Management Plan for Steel Production Plant (A Review)

Unsustained mining practices have resulted in the overuse of shared resources this year, degrading the environment extensively. Additionally, there is an increase in nursery gas emissions from the generation of vital metals due to a continually growing demand for metals, a decline in metal grades, and complex underused stockpiles. As a result, the mineral preparation and metal production industry frequently finds itself under increasing pressure to advance the overall sustainability of its operations, notably through reducing energy consumption, outflows, and waste transfer. Large volumes of wastewater are released by the steel and press industries. Typically, a quantitative approach is used to assess the wastewater's natural effects. In any event, a more notable factor in the harm to the natural environment is the water quality of released effluent. Furthermore, there is still a gap in the thorough assessment of several contaminants in wastewater in terms of both quantity and quality. This work considers the volume of wastewater and the quality of primary forms in order to characterize an add-up to natural affect score that surveys the natural impact of wastewater release. A field check and estimation of wastewater release volume and quality is carried out to secure pH, suspend solids chemical oxygen request add up to nitrogen add up to press, and hexavalent chromium in order to actualize the totally subjective and quantitative appraisal. Coordination steel plants use five basic materials (discus, water, fuel, and control) in the process of producing steel. It is important to note that steel can be generated at a coordinate office using press mineral as well as at an auxiliary office, which mostly uses recycled steel waste to make steel. The development industry and other building applications use a variety of rolled products (sheets, tin- and zinc-plated sheets, cold rolled groups, steel channels, sheet-metal segments, etc.) and made or drawn products (bars, wires) in conjunction with crude steel. Over time, the idea of a life cycle strategy for the supportability of products and services has received more and more attention.

Porous hollow microspheres based on industrial solid waste enhance biomethane recovery from corn straw

The increasing production of industrial solid waste requires better disposal solutions. Porous hollow microspheres (PHM) are small inorganic materials with high surface area and adsorption capacity, but their potential for use in anaerobic digestion (AD) has not been explored. With PHM as additive, the effects of different industrial solid wastes (waste glass, steel slag, and fly ash) with different loadings (2 %–8 %), respectively, on the AD of corn straw were investigated in this study. The results showed that PHM could supplement trace elements and promote biofilm formation, which effectively shortened the lag period (25.00–60.87 %) and increased the methane yield (4.75 %–16.28 %). The 2 % PHM loading based on steel slag gave the highest methane yield (300.16 NmL/g VSadd). Microbial and PICRUSt2 analyses indicated that PHM enriched hydrolytic and acidogenic bacteria, increased the abundance of methanogenesis-related enzyme genes. This study provides a theoretical basis for the comprehensive utilization of coupled industrial and agricultural wastes.

A sustainable recycling approach for construction: A case of remanufacturing waste rebar into steel nails

Minimizing waste in the construction industry provides economic and environmental benefits. Since steel has high embodied energy and many applications, recycling rebar waste contributes to a circular economy. This study proposes remanufacturing rebar into nails as a valuable by-product. In an experimental case-study to prove the technical feasibility of the process, short pieces of rebar waste were stripped to remove the ribs, welded into a coil, drawn to reduce the diameter, and formed into nails. The costs and technology of four alternative remanufacturing process portfolios were analyzed, giving an average profit of 576 USD/t of waste rebar. A cement consumption database was constructed based on literature data and regression analysis was applied to analyze the consumption of concrete and new rebar. The potential rebar waste was calculated assuming 3 %, 5 %, 8 %, or 10 % of the total new rebar consumption. Cement consumption data at the global and country scales were used to calculate the consumption rates of new and waste rebar to derive profit–remanufacturing potential curves. Regression analysis of these curves was performed to determine the economic sustainability degree of satisfaction (DSes). A second approach to find DSes applied regression analysis to the remanufacturing profits for the four rates of rebar waste together. The mean DSes values (0.62–0.87) and economic sustainability index (0.33) exceed the literature threshold of 0.6 and 0.26, respectively, indicating that remanufacturing rebar waste into steel nails is an economically sustainable business. The nails can be used in the construction industry to contribute to a circular economy, thereby reducing the environmental impact of steel waste and the production of new steel nails. The overall sustainability was considered by introducing Okun's Law to ensure that profitability is not achieved at the expense of development, and weighting the importance of economic sustainability based on literature averages. Rebar is used as a standard construction material globally, so these findings have broad significance. The proposed remanufacturing process is especially relevant for less-developed economies with higher rebar waste rates to stimulate small businesses and a circular construction industry.

Performance of solid particles as thermal storage media in thermal power flexibility retrofits: Effects of charging and discharging flow rates on single piece stacking bed

An innovative, efficient, and cost-effective energy storage method was introduced for retrofitting thermal power plants, which can be connected in series to scale up quickly (like a battery) and aimed to replace expensive, hazardous molten salts. Charging/discharging processes among steam and solid particles were investigated using energy storage devices with capacities in the tens of kilowatts. Results of the study confirm the excellent performance of steel waste as a thermal energy storage medium. Key findings include that the time required for complete charging decreases from 75 to 300 kg/h, taking 173, 128, 106, and 105 min, respectively. The most efficient charging occurs when the bed temperature is most inhomogeneous, taking 68, 42, 34, and 28 min for 75–300 kg/h. The highest average charging power and heat transfer coefficient are 5 kW and 210 W/(m2·K) at 300 kg/h. In addition, 145 kg/h achieves optimal speed and quantity coupling, resulting in the highest charging efficiency of approximately 84 %. Time-optimized and efficiency-optimized charging flows are given. Real-time efficiency shows that the poorest temperature uniformity corresponds to the highest charging efficiency, with 145 kg/h exhibiting the strongest thermal inertia and 75 kg/h the weakest. Higher flow rates improve internal heat transfer and reduce stratification, facilitating multiple charge-discharge cycles. At discharge rates of 50, 75, and 100 kg/h, steam production is sustained at approximately 30, 40, and 50 kg/h for 11, 7, and 7 min, respectively. Discharge efficiency increases with flow rate, rising from 30 % to 95 %. Phase transition region migrates at approximately 10∼20 mm/s across different discharge rates, with 75 kg/h showing the fastest discharge state. As the discharge rate increases, the phase transition region's total area proportion rises, reaching about 70 % at 100 kg/h. Research demonstrates the potential of this new energy storage medium for efficient and safe retrofitting of thermal power plants.

Sustainability-driven application of waste steel and tyre rubber fibres as reinforcement in concrete: An optimization study using response surface methodology

Innovative use of waste materials has proven to be effective for improving concrete’s technical properties while eliminating the threat of environmental pollution. There is paucity of research regarding the combined use of Waste Steel Fibres (WSFs) and Waste Tire Rubber Fibres (WTRFs) in concrete. Thus, this study aimed to investigate the influence of WSFs and WTRFs as reinforcement in concrete and determine their optimal fractions for enhancing the concrete strength properties using Response Surface Methodology (RSM). WSFs of 0.3-1.5% with a 0.6% increment and WTRFs of 0.3-1.5% with a 0.6% increment by concrete volume as reinforcement in concrete with water-to-cement ratio (W/C) of 0.25–0.65 with 0.2 increment were designed using the Box-Behnken Design of RSM. A total of fourteen (14) concrete mixes with a design strength of 25 N/mm2 were prepared. The fresh and hardened properties (slump, density, water absorption, 7- and 28-day compressive and split tensile strengths) of concrete were determined using standard procedures. The RSM was used to evaluate the interaction between the concrete variables and identify their optimum combination which gave the peak values of responses. Furthermore, the characteristics and sustainability of the concrete under optimum variables were compared with that of the conventional concrete. The outcomes revealed that the inclusion of WSFs and WTRFs yielded concretes with maximum slump, density, water absorption and 28-day compressive and split tensile strengths of 25 mm, 2633 kg/m3, 5%, 41 N/mm2 and 4.54 N/mm2, respectively. The optimization technique showed the optimal variables combination which yielded the peak response values of WSFs (1.40%), WTRFs (0.66%) and W/C (0.54). The nominal variance with the absolute percent error of less than (9%) between the actual experimental verified results and predicted results for all the responses validates the predictability of the model. The split tensile strength and compressive strength increased by 28.33% and 48.85%, respectively at the optimum setpoint of variable with respect to the reference concrete. In addition, the WSFs and WTRFs-reinforced concrete exhibited lower embodied CO2 emission but the embodied energy and cost are slightly higher relative to conventional concrete. Nevertheless, the embodied energy of the concrete was significantly lesser than that of concrete that used individual fibers for reinforcement. Thus, the enhancement of concrete strength properties with the prospect for sustainable fibre-reinforced concrete production through the use of waste steel and tyre rubber fibres is feasible.

Improving sustainability of precast concrete sandwich wall panels through stone waste aggregates and supplementary

Precast concrete sandwich wall panels offer advantages such as design flexibility, ease of installation, cost-effectiveness, and energy efficiency due to the incorporated insulation layer, but regular concrete production has sustainability issues. This study aims to improve the sustainability of these panels by utilizing stone waste aggregates as a replacement for natural aggregates and supplementary cementitious materials as a partial replacement for cement. The panels were made with two concrete wythes reinforced with steel fibers and joined using basalt fiber-reinforced polymer (BFRP) connectors, with high-density expanded polystyrene (EPS) insulation (30 kg/m3) in between. Self-compacting concrete mixes with varying proportions of stone waste aggregates and supplementary cementitious materials were used. Full-scale wall panels were cast and subjected to flexural tests per ASTM standards, analyzing load-displacement curves, ultimate bearing capacity, and failure modes. The incorporation of steel fibers and stone waste aggregates resulted in substantial increases in failure load and flexural strength compared to controlled concrete panels, with the stone waste steel fiber panels exhibiting significantly higher maximum cracking loads and improved energy absorption and ductility. The inclusion of these sustainable materials, along with basalt fiber connectors and grooves in the EPS layer for mechanical interlock, prevented brittle failure modes and enhanced the composite action, leading to more ductile behavior under flexural loading. Utilizing sustainable materials like stone waste aggregates (100% replacement) and supplementary cementitious materials (30% replacement) in these panels can contribute to eco-friendly and efficient construction practices while maintaining adequate structural performance, paving the way for more sustainable building systems