Slag Aggregate Research Articles

Three-dimensional Meso-scale virtual strength test of steel slag porous asphalt mixture based on PFC3D

In recent years, steel slag has gained widespread utilization in pavement construction as a green, low-carbon building material. In this study steel slag aggregate (SSA) was used as a partial replacement for basalt aggregate in porous asphalt mixture. To gain an in-depth understanding of the microscopic cracking characteristics of steel slag aggregate porous asphalt concrete (SSA-PAC), laboratory three-point bending tests and numerical simulations were conducted. Based on CT scanning images, 3D models of SSA and basalt aggregates within particle size ranges of 4.75–9.5 mm and 9.5–13.2 mm were generated. These characteristic aggregates were then randomly placed to establish a three-dimensional model using PFC3D (Particle Flow Code in 3 Dimensions). The micro-contact parameters were derived through the conversion and calibration of macro and micro-mechanical parameters. The results of the 3D virtual strength test exhibited a close resemblance to those obtained from laboratory semi-circular bending (SCB) tests. The displacement trend chart of the aggregates revealed three distinct stages: vertical displacement, vertical displacement combined with a small amount of lateral displacement, and lateral displacement. Cracking mainly occurred at the interface between the aggregates and asphalt mortar, which aligned with actual cracking scenarios. The cracking behavior of the asphalt mixture was characterized by evaluating the number of cracks, notch width, and coordination number throughout the loading process. Additionally, the influence of loading rates on cracking behavior was analyzed. The results of this study demonstrated that the established 3D model effectively revealed the cracking characteristics of SSA-PAC.

Pre-treatment of steel slag and its applicability in asphalt mixtures for sustainable pavements

The secondary utilization of steel slag is significant for land occupation reduction, natural aggregate conservation, and environmental protection. This study aims to enhance the utilization of steel slag aggregate (SSA) in pavement engineering by providing guidance on selecting efficient and rapid pre-treatment methods. It compares the macroscopic morphological characteristics of basalt, SSA, and SSA prepared using various pre-treatment methods. The chemical composition and surface micromorphology of the samples were investigated by X-ray fluorescence spectrometry and scanning electron microscopy. The effects of the pre-treatment methods on the SSA and the performance of its asphalt mixture were comparatively evaluated based on laboratory tests. The carbon dioxide equivalent (CO2e) and cost associated with steel slag asphalt mixtures were quantified in this study. The findings revealed that the high angularity and roughness of the SSA make it an ideal candidate for use in pavement layer aggregates. Pre-treatment methods such as thermal water and acetic acid soaking expedited the hydration and oxidation reactions. Furthermore, applying a silane coupling agent resulted in the forming of a polymer membrane on the SSA surface, significantly enhancing its volume stability and adhesive properties. All these methods present compelling alternatives to natural aging. Compared with the original SSA, the performance of asphalt mixtures prepared using pretreated SSA was optimized, particularly concerning the volumetric stability and moisture damage resistance. In general, although the CO2e from using SSA for pavement construction increased compared to those using other substances, the CO2e was significantly lower than those from SSA lying idle, which positively impacts the alleviation of SSA accumulation and promotes sustainable development.

A comprehensive investigation on the impacts of steel slag aggregate on characteristics of high-performance concrete incorporating industrial by-products

Steel slag (SS), an industrial by-product of the steel industry, has the potential to serve as a natural aggregate alternative in concrete production to not only mitigate the exploitation of natural resources but also minimize the environmental impact of its treatment and disposal. This study was designed to investigate comprehensively the impacts of using SS as a full replacement for coarse aggregate and of using fly ash (FA) and ground granulated blast-furnace slag (GGBFS) as partial replacements for Portland cement on the engineering properties (i.e., workability, fresh unit weight, porosity, compressive and flexural strengths, ultrasonic pulse velocity, and drying shrinkage), durability (i.e., water absorption, surface electrical resistivity, and rapid chloride ion penetration), and microstructure (i.e., scanning electron microscopy observation) of high-performance concrete (HPC). A comparative analysis of the economic and environmental benefits of SS concrete versus natural aggregate concrete was also performed. The test results revealed that SS, FA, and GGBFS all impacted the properties of HPC significantly. The HPC mixtures in which natural aggregate had been completely replaced with SS exhibited about 20.4–21.3% higher unit weight than the natural aggregate concrete. The HPC samples with added FA and GGBFS exhibited enhanced performance in terms of mechanical strength, durability, and microstructure. Moreover, total material cost, global warming potential (GWP), and ozone depletion potential (ODP) were all found to be significantly lower in the HPC samples produced using SS and either GGBFS or a combination of FA and GGBFS. As a result, after 210 days of normal curing, the 100% SS concrete containing 15% FA and 35% GGBFS as a Portland cement substitution (S100F15G35 specimen) exhibited compressive and flexural strength values of 110.3 and 11.1 MPa, which were approximately 9.0% higher than the corresponding values of the reference concrete. Also, the S100F15G35 specimen registered the respective ultrasonic pulse velocity, surface electrical resistivity, and rapid chloride ion penetration values of 5328 m/s, 113.3 kΩ.cm, and 203 Coulombs, indicating high-quality and durable concrete. Moreover, incorporating 15% FA and 35% GGBFS in SS concrete resulted in a reduction of 15.7% drying shrinkage and 24.4% total material cost, especially reduced environmental impacts with a significant reduction in GWP and ODP by 43.5% and 29.2%, respectively. These findings further demonstrate the potential of using SS in combination with FA and GGBFS to create high-quality HPC that is both more economical and significantly more sustainable than conventional HPC.

Wear resistance analysis of steel slag aggregates based on morphology characteristics

Steel slag can be utilized in the wearing course of highway asphalt pavement. However, further research is needed to explore the impact of steel slag on the wear resistance of asphalt pavement. This study aimed to evaluate the wear resistance of two steel slag samples and compare them with three stone aggregates based on morphological characteristics. The Los Angeles abrasion test was conducted at different revolution levels, and the micro-morphology characteristics of the aggregates were analyzed through image analysis using six morphology parameters. The results showed that the steel slag samples had the lowest Los Angeles abrasion rates, indicating their superior hardness and wear resistance compared to limestone and granite aggregates. The steel slag aggregates also exhibited higher values in morphological indices of arithmetic mean height Sa, peak apex density Spd, and arithmetic mean curvature of peak apex Spc, indicating a rougher surface, more contact points and more durable wear resistance. Fluctuations were observed on variation curves of the maximum height Sz, surface skewness Ssk, and surface sharpness Sku of the steel slag during the abrasion process, suggesting the presence of numerous pits and spikes that contribute to the skid resistance of the steel slag asphalt mixture. The arithmetic mean height Sa, peak density Spd, and arithmetic mean curvature of peak apex Spc showed a consistent decrease over the number of revolutions, making them reliable indices for future research on the wear resistance of steel slag asphalt mixtures. Overall, this study provides a basis for further research on investigation the correlation between the morphology changes of steel slag aggregates and the anti-skid performance of pavement wearing courses.

Research on Water Stability and Moisture Damage Mechanism of a Steel Slag Porous Asphalt Mixture

A steel slag porous asphalt (SSPA) mixture, as the surfacing layer of permeable asphalt pavements, not only ensures the pavement surface drainage and noise reduction functions, but also improves the comprehensive utilization of steel slag resources and the inherent protection of the ecological environment. However, compared with ordinary asphalt mixtures, SSPA is more susceptible to water damage, such as scouring and frost swelling caused by external rainwater intrusion, resulting in the deterioration of the pavement performance. Therefore, it is of good practical imperative to study the water stability and moisture damage mechanism of SSPAs. In this study, the water stability of SSPA, that was subjected to a series of time–temperature H2O-immersion schemes, was investigated using the pull-out and H2O-immersion Marshall tests, whilst the microscopic mechanism of moisture damage was studied using the scanning electron microscopy (SEM), Fourier infrared spectroscopy (FTIR), and X-ray diffraction (XRD) tests. The corresponding results showed that: (a) with the increase in the H2O immersion time, the water stability of SSPA first increased and then decreased; and (b) the water stability of SSPA was strong under medium-temperature H2O-immersion or short-term high-temperature H2O-immersion. SEM, on the other hand, showed that the transition zone spacing was closely related to the chemical adhesion mechanism between the asphalt and steel slag aggregate. Additionally, the FTIR analysis further showed that the steel slag asphalt mastic spectra had new absorption peaks at 3200~3750 cm−1, inherently indicating the existence of chemical bonding between the asphalt and steel slag, with the XRD results showing that CaSO4·2H2O had a beneficial effect on the water stability of SSPA.

One-part eco-friendly alkali-activated concrete – An innovative sustainable alternative

The primary objective of this study is to develop an eco-friendly one-part alkali-activated concrete (OPAAC) by incorporating a combination of fly ash (FA), ground granulated blast furnace slag (GGBS), and micro silica (MS). In this investigation, the proportion of MS is maintained at 20% of FA, while the maximum replacement of FA with GGBS is set to 60%, varying in 20% intervals (i.e., 0%, 20%, 40%, and 60%). Further, the natural aggregates (NA) are substituted with recycled coarse aggregates (RCAs), ferrochrome slag aggregates (FCSAs), or a combination of both. The influence of GGBS and alternative aggregates (RCAs, FCSAs) on the mechanical properties of OPAAC is thoroughly examined. To provide a comprehensive assessment, the properties of OPAAC are compared against Ordinary Portland Cement (OPC) concrete (CC) of equivalent grades. Additionally, microstructural and mineralogical investigations are conducted to determine the formation of distinct hydration products, utilizing scanning electron microscopy (SEM) and X-ray diffractometry (XRD) techniques. In OPAAC containing FA, the primary hydration products identified are alkaline alumino silicate hydrates (CASH and NASH). As the GGBS content increases, calcium silicate hydrate (CSH) becomes the predominant hydration product. Furthermore, in order to assess the sustainability of OPAAC, an analysis of embodied CO2 emissions is performed, and the results are compared with CC and alkali-activated concrete. Notably, OPAAC comprising 40% FA replaced with GGBS, 50% RCAs, and 50% FCSAs demonstrates the most favourable mechanical properties and exhibits lower CO2 emissions.

Physical, mechanical, chemical, and environmental characterization of stockpiled BOF slag as railway ballast material

Crushed stone from natural sources is commonly used as ballast in railways. The material is a good ballast, but its extraction is destructive. Therefore, this study characterizes basic oxygen furnace (BOF) slag as an alternative material for railway ballast in Kazakhstan with respect to physical, mechanical, chemical and environmental properties. The characterized BOF slags are of two types (top and bottom) with 10 years minimum age. Grain size distribution, specific gravity, absorption capacity, flakiness, lightweight particles, and 3D image analysis for forms and angularity were used for physical characterization. These BOF slags were found to have high specific gravity and a predominantly spherical shape, with larger particles displaying lower sphericity and greater angularity than smaller ones. The mechanical characterization of the BOF slag were carried out using various methods, including LA abrasion, Micro-Deval, aggregate crushing value, aggregate impact value, volumetric expansion, and fouling. BOF slag aggregates demonstrated exceptional strength with good resistance to fragmentation, crushing, surface abrasion, and sudden loading. The expansion rate is considerably lower than the standard limit, and the fouling rate is better than limestone and similar to granite. X-ray fluorescence (XRF), X-ray diffraction (XRD), and scanning electron microscopy (SEM) were all used for chemical characterization. Both BOF slags contain CaO and Fe2O3 with a high peak of SiO2 and portlandite, which suggests that most of the free lime has undergone hydration due to the natural aging of the BOF slag. Regarding the environmental characterization, the tests employed were organic impurity, freeze and thaw, and sodium-based soundness. No organic impurity was observed in the BOF slag, and the BOF slag demonstrated good resistance to weathering and degradation. The characteristics of the investigated BOF slag obtained from laboratory testing were analyzed to confirm its performance for implementation in railway ballast in compliance with the specific requirements, primarily the GOST standard, which is commonly employed in Russia and former Soviet republics, including Kazakhstan. As a result, both BOF slags demonstrated total compliance with the specifications, and the possibility of using stockpiled BOF slag for railway ballast material in Kazakhstan was established.

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.

Evaluation of properties of energy-efficient geopolymer cellular concrete containing basic oxygen furnace slag aggregate

In north-western Kazakhstan, there is a higher demand for energy-efficient construction materials such as cellular concrete in the construction industry due to severe weather conditions. Moreover, construction industries in Kazakhstan are looking into developing new construction materials utilizing industrial by-products. Unlike blast furnace slag (BFS), utilization of basic oxygen furnace slag (BOFS) is limited due to its chemical composition and volumetric instability mainly caused by f-CaO and f-MgO. This study developed a total of nine energy-efficient geopolymer mixtures (3-normal geopolymer mixture and 6-geopolymer cellular concrete). Mix design variables included a partial substitution of river sand (RS) with BOFS aggregate (0%, 50%, and 100%) and three different percentages of a foaming agent (0%, 25%, and 50%). The properties of geopolymer mixtures were evaluated in terms of compressive strength, hardened density, expansion behavior, and thermal conductivity. Test results presented that replacing RS with 50% BOFS aggregates decreased compressive strength, while replacing sand with 100% BOFS aggregate led to increasing the strength regardless of the geopolymer mixture type. Geopolymer cellular concrete had lower compressive strength and thermal conductivity compared to the normal geopolymer mixture due to a higher porous cellularity structure and satisfied the threshold value of expansion due to converting f-CaO and f-MgO to CaSiO3 and MgSiO3 and absorbing the expansion stress by cellular structure.

The Use of a Friction Separator to Increase the Strength and Reduce Water Absorption of the Road-construction Slag Aggregate

The purpose of the study is to assess the influence of the parameters of the working process of a laboratory friction separator on the physical and mechanical characteristics of the enriched material (slag aggregate). To achieve the purpose, the methods of laboratory experiment (enrichment on a friction separator), physical-mechanical tests of road-building materials, mathematical processing of experimental data were used. The design of a friction separator for the enrichment of the slag aggregate is considered, the principle of its operation is described. The results of an experiment to assess the effect of the enrichment of the slag aggregate on a friction separator on its strength and water absorption are presented. The authors also established the dependencies interrelating the physical-mechanical characteristics of the slag aggregate and the parameters of the friction separator operation. A quantitative assessment of reducing water absorption and increasing the strength of road-construction slag aggregate after enrichment on a friction separator was obtained

A Review on Utilization of Steel Slag in Bituminous Concrete

Abstract: The utilization of steel slag in bituminous mixes has been gaining popularity due to environmental concerns and the potential for cost savings. However, it's essential to manage steel slag properly to prevent environmental and health hazards. To control the impact of steel slag, various efforts have been undertaken. Bituminous concrete performance is influenced by factors like binder grade and the aggregate blend. While numerous studies have examined steel slag's performance in bituminous concrete, there is still a need of more research on optimal mix design. Typically, the ideal quantity of steel slag in bituminous mixes falls within the range of 10% to 15%. It's crucial to thoroughly understand the effect of steel slag on the mechanical properties of the mix, often measured using Marshall Stability Test. In India, there hasn't been extensive work on varying percentages of steel slag in bituminous concrete and its resistance against stripping, despite numerous studies on the properties of steel slag aggregates. This paper aims to consolidate the research studies on the enhancements in bituminous mix properties by partial replacement with steel slag, as well as exploring the potential benefits of incorporating steel slag in bituminous concrete mixes.

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.

Microwave self-healing characteristics of bituminous mixtures with different steel slag aggregate and waste ferrite filler

To improve crack propagation issues of bituminous mixtures in an eco-friendly way, steel slag (SS) and waste ferrite were partially substituted for aggregate and filler in the bituminous mixtures to enhance the self-healing performance (SHP) of the mixture through microwave heating (MH). Firstly, the electromagnetic parameters of ferrite filler (FF) and SS were tested by the vector network analyzer. Secondly, the thermal conductivity (TC) of ferrite filler bituminous mixtures (FFBM) and steel slag bituminous mixtures (SSBM) was tested based on the transient plane source. Subsequently, the MH surface temperature was measured on FFBM and SSBM, and the MH efficiency and uniformity were analyzed. Finally, the SHP of two types of bituminous mixtures under different conditions was analyzed. The results revealed that both FF and SS have significant magnetic loss, and the absorption performance of FF is better at the same frequency and thickness. The TC of SSBM is higher than FFBM, but due to the porous characteristics of SS, it tends to stabilize. The MH efficiency of FFBM is lower due to its volume ratio, but it has better uniformity. The self-healing rate of SSBM is higher at 40 s MH time, but FFBM can obtain a higher self-healing rate by extending the heating time. This work contributes to understand the difference between different types of suction materials self-healing of bituminous mixtures under MH.

Application of Biomineralization Technology in the Stabilization of Electric Arc Furnace Reducing Slag

The unstable substances in steel slag are the main substances that affect its stability, which limits the large-scale resource utilization of steel slag. Most of the current methods for stabilizing electric arc furnace (EAF) slag are time-consuming and cannot be completely stabilized. In view of this, this study aimed to explore the feasibility of microbial-induced calcium carbonate precipitation (MICP) technology for stabilizing EAF reducing slag, and this was to be achieved by using the reaction between carbonate ions and free calcium oxide (f-CaO) in reducing slag to form a more stable calcium carbonate to achieve the purpose of stabilization. The test results showed that, when the EAF reducing slag aggregates (ERSAs) were immersed in a Sporosarcina pasteurii bacteria solution or water, the f-CaO contained in it would react such that stabilization was achieved. The titration test results showed that the f-CaO content of the ERSAs immersed in the bacterial solution and water decreased. The expansion test results of the ERSAs that were subjected to hydration showed that the seven-day expansion of ERSAs after biomineralization could meet the Taiwan regulation requirement of an expansion rate less than 0.5%. The thermogravimetric analysis showed that both the experimental group and the control group might contain calcium carbonate compounds. The results of the X-ray diffraction analysis showed that the CaCO3 content in the ERSAs that were immersed in the bacterial solution was significantly higher than those that were immersed in water. Moreover, the compressive strength test results of concrete prepared with ERSAs showed that the compressive strength of the control group concrete began to decline after 28 days. In contrast, the experimental group concrete had a good stabilization effect, and there was no decline in compressive strength until 180 days. At 240 days, the surface cracks of the experimental group were particularly small, while the surface of the control group showed obvious cracks. These results confirmed that a mineralization reaction with S. pasteurii bacteria could be used as a stabilization technology for ERSAs.

Performance of SSC filled circular steel tube short columns under axial compression

Steel slag concrete (SSC) filled steel tube (SSC-FST), reusing the waste steel slag, is a new type of composite members, therefore shows advantages in sustainable use of resources. In order to investigate axial compressive performance of this new types of SSC-FST short columns with circular section, ten specimens with varied steel slag aggregate (SSA) replacement ratio and cross-sectional steel ratio (α) were tested. The failure patterns, load versus deformation relationship and mechanical indexes (axial capacity, elastic modulus and ductility) of the specimens were recorded and analyzed. The test results indicate that, generally, replacing natural aggregates with SSAs and improving α lead to better structural performance of circular SSC-FST short column specimens. Moreover, a refined finite element (FE) model considering the initial strain of core concrete before loading was established to simulate the performance of circular SSC-FST short columns under axial compression, and the FE model was validated through experimental results from this research and the literature. Based on the verified FE model, the mechanism of axially compressed circular SSC-FST short columns was further analyzed. Finally, simplified equations were proposed to predict the axial capacity of circular SSC-FST short columns, and generally the calculated results show good agreement with the numerical/experimental results.

Polycarboxylate superplasticizer as strengthening additive in carbonated artificial steel slag aggregate

This article presents an investigation on the application of polycarboxylate superplasticizer (PCE) to improve the mechanical properties of carbonated artificial steel slag aggregate (CSSA). It is observed that dispersion effect of PCE on steel slag particles significantly improves the degree of compaction of CSSA before carbonation and the PCE molecules slows down the evaporation of water leading to the higher residue water–solid ratio (w/s) of CSSA after carbonation, which are beneficial for the improvement of CO2 uptake and mechanical properties of CSSA. Moreover, the cross-linked PCE molecules by calcium ions from steel slag hinders the early carbonation reaction of steel slag which is conducive to the CO2 diffusion from outside to inside of CSSA thus results in a more homogenous structure of CSSA. Additionally, reconstituted PCE molecules promotes the leaching of calcium ions leading to an increase of CO2 uptake of CSSA at the long-term (24 h) duration of carbonation. At optimum of 1% PCE, the compressive strength of CSSA reaches a maximum value of 164 MPa, which is 141% higher than that of CSSA without PCE.

Determination of the Basic Geotechnical Parameters of Blast-Furnace Slag from the Kremnica Region.

A decisive aspect of site evaluation for construction is the presence of anthropogenic materials occurring in the geological environment. The geotechnical properties of blast-furnace slag were investigated as a potential substitute for aggregates in the construction industry. The basic geotechnical parameters of the slag were determined, which are critical for evaluating its stability, environmental impact, and usability in geotechnical construction. The research focused on monitoring the physical and mechanical properties of the two samples, and also included mineralogical analysis. The obtained results demonstrated that the slag belongs to the category of poorly graded gravel, G2/GP, and gravel with an admixture of fine-grained soil, G3/G-F. In addition, other important parameters, such as the water disintegration of the slag aggregate, the minimum and maximum bulk densities, the California bearing ratio (CBR), the oedometric modulus (Eoed), and shear tests (the angle of internal friction φ and cohesion c), were determined. The results from this paper provide important information for the proper management of blast-furnace slag so to minimize its environmental impact and achieve sustainability in the mining industry. At the same time, it enables a better understanding of the use of slag as a substitute for aggregates in geotechnical tasks. Despite its local importance in relation to the investigated case, the presented study has significant educational and scientific value for the construction sector, where it is necessary to evaluate anthropogenic activities and materials.

Potential Role of GGBS and ACBFS Blast Furnace Slag at 90 Days for Application in Rigid Concrete Pavements.

Incorporating blast furnace slag into the composition of paving concrete can be one of the cost-effective ways to completely eliminate by-products from the pig iron production process (approximately 70% granulated slag and 30% air-cooled slag). The possibility to reintroduce blast furnace slag back into the life cycle will provide significant support to current environmental concerns and the clearance of tailings landfills. Especially in recent years, granulated and ground blast furnace slag (GGBS) as a substitute for cement and air-cooled blast furnace slag (ACBFS) aggregates as a substitute for natural aggregates in the composition of concretes have been studied by many researchers. But concrete compositions with large amounts of incorporated blast furnace slag affect the mechanical and durability properties through the interaction between the slag, cement and water depending on the curing times. This study focuses on identifying the optimal proportions of GGBS as a supplementary cementitious material (SCM) and ACBFS aggregates as a substitute to natural sand such that the performance at 90 days of curing the concrete is similar to that of the control concrete. In addition, to minimize the costs associated with grinding GGBS, the hydration activity index (HAI) of the GGBS, the surface morphology, and the mineral components were analyzed via X-ray diffraction, scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), and nuclear magnetic resonance relaxometry (NMR). The flexural strength, the basic mechanical property of road concretes, increased from 28 to 90 days by 20.72% and 20.26% for the slag concrete but by 18.58% for the reference concrete. The composite with 15% GGBS and 25% ACBFS achieved results similar to the reference concrete at 90 days; therefore, they are considered optimal percentages to replace cement and natural sand in ecological pavement concretes. The HAI of the slag powder with a specific surface area equivalent to that of Portland cement fell into strength class 80 at the age of 28 days, but at the age of 90 days, the strength class was 100. The results of this research present three important benefits: the first is the protection of the environment through the recycling of two steel industry wastes that complies with European circular economy regulations, and the second is linked to the consequent savings in the disposal costs associated with wastefully occupied warehouses and the savings in slag grinding.

Microstructure, mechanical property and slag corrosion resistance of (Al,Cr)2O3-Mg(Al,Cr)2O4-Ca(Al,Cr)12O19 composite refractory using alumina-chromia slag

Alumina-chromia/aluminum-chromium/(AC) slag, is basically treated as hazardous solid waste. The present work reports the preparation of (Al,Cr)2O3-Mg(Al,Cr)2O4-Ca(Al,Cr)12O19 composite refractory which is directly applicable to AC slag using reactive MgO as binder. Microstructure, mechanical properties and slag corrosion resistance to CaO-Al2O3-Fe2O3-SiO2-based slag of the prepared composite refractory were investigated. The results indicated that the obtained composites using AC slag aggregates exhibit superior corrosion resistance against the CaO-Al2O3-Fe2O3-SiO2-based slag compared with those with both AC slag aggregates and powders. Composites prepared using AC slag aggregates bonded with 5 wt% reactive MgO exhibited sufficient mechanical properties. This makes AC slag aggregates a possible candidate to prepare (Al,Cr)2O3-Mg(Al,Cr)2O4- Ca(Al,Cr)12O19 composite refractory used in iron- and steel-making process.

Application of Steel Slag as an Aggregate in Concrete Production: A Review.

Steel slag is a solid waste produced in crude steel smelting, and a typical management option is stockpiling in slag disposal yards. Over the years, the massive production of steel slags and the continuous use of residue yards have led to vast occupation of land resources and caused severe environmental concerns. Steel slag particles can potentially be used as aggregates in concrete production. However, the volume stability of steel slag is poor, and the direct use of untreated steel slag aggregate (SSA) may cause cracking and spalling of concrete. The present research summarizes, analyzes, and compares the chemical, physical, and mechanical properties of steel slags. The mechanism and treatment methods of volume expansion are introduced, and the advantages, disadvantages, and applicable targets of these methods are discussed. Then, the latest research progress of steel slag aggregate concrete (SSAC) is reviewed. Using SSA leads to an increase in the density of concrete and a decrease in workability, but the mechanical properties and durability of SSAC are superior to natural aggregate concrete (NAC). Finally, future research in this field is proposed to motivate further studies and guide decision-making.