Chemical, Mineralogical, and Morphological Properties of Steel Slag

Steel slag is a by-product of the steel industry. Understanding of the chemical, mineralogical and morphological properties of steel slag are necessary for its use in sustainable practices. This paper provides an overview of the different types of steel slag that are generated from basic-oxygen-furnace (BOF) steelmaking, electric-arc-furnace (EAF) steelmaking, and ladle furnace steel refining processes. The mineralogical and morphological properties of BOF and electric-arc-furnace- ladle (EAF(L)) slag samples generated from two steel plants in Indiana were determined through X-Ray Diffraction (XRD) analyses and Scanning Electron Microscopy (SEM) studies. The XRD patterns of both BOF and EAF(L) slag samples were very complex, with several overlapping peaks resulting from the variety of minerals present in these materials. The XRD analyses indicated the presence of free MgO and CaO in both the BOF and EAF(L) slag samples. SEM micrographs showed that the sand-size steel slag particles had subangular to angular shapes and very rough surface textures. The characteristics of the steel slag samples considered in this study are discussed in the context of a detailed review of steel slag particle properties for its potential use in geotechnical applications.

Characteristics of steel slag under different cooling conditions

In this study, the carbonation and hydration behavior of electrical arc furnace (EAF) slag and basic oxygen furnace (BOF) slag were examined. Steel slag is a latent hydraulic material. Its early strength can be activated by carbonation reaction. The carbonated steel slag can be used as a binder to replace Portland cement in the fabrication of building products. It was found that steel slag could develop a compressive strength of 20 MPa in EAF slag and 36 MPa in EAF–BOF hybrid slag after a combination of carbonation and hydration. Higher calcium silicate content and longer carbonation time could result in a higher compressive strength. The activated steel slag binders were composed of calcium carbonates intermingled with calcium silicate hydrates, forming a particle reinforced composite material. It was the calcium silicate content in raw slag, rather than the CaO content, that determined the extent of carbonation activation. Replacing Portland cement with steel slag could help preserve natural resources, reduce the embodied energy and promote carbon utilization in building products.

The use of steel slag to prepare cementitious materials has significant economic and environmental benefits. However, steel slag has shortcomings such as large fluctuation in composition, high content of free calcium oxide, and difficulty in stable control of product quality in industrial production, which seriously restricts the large-scale applications of steel slag in building materials industry. This study proposes to use electric arc furnace (EAF) slag as a component adjustment material to react with basic oxygen furnace (BOF) slag at high temperature, in order to optimize the composition and structure of BOF slag, thereby improving its cementitious activity. The results show that using EAF slag as a component adjustment material to remelt BOF slag at high temperature can improve the cementitious properties of BOF slag mortar samples at various curing ages. When the early cementitious properties are the main target, the optimal remelting conditions are: the remelting temperature is 1150 °C–1200 °C, and the dosage of EAF slag is 10%–15%.

Slag is a by-product of different metal extraction and refining processes. This paper reports the results of an experimental study on replacing part of ordinary Portland cement (OPC) with iron and steel slags. In Iranian iron and steel plants, slags are generated at three different stages of processing; Basic Oxygen Furnace (BOF), Electrical Arc Furnace (EAF) and Granulated Blast Furnace (GBF) are the slags used in this study. In this respect, some mixtures were made with 10%, 20% and 30 wt% of each slag replaced in ordinary Portland cement. For this study, the effects of slag additions in cement was determined by measuring of electrical conductivity and pH of slurry, setting time of paste and mechanical strength of mortar at various ages. According to the results, 10% EAF or BOF slag can safely replace part of OPC in mortars.

Characteristics of steel slags and their use in cement and concrete—A review

This study was conducted in order to evaluate the effects of long term ageing on toughness and resilient modulus of asphalt concrete mixtures containing Electric Arc and Basic Oxygen Furnace steel slags. After initial evaluation of the properties of steel slags using X-ray Diffraction and Scanning Electric Microscope, eleven sets of laboratory mixtures were prepared. Each set was treated replacing various portions of limestone coarse aggregates of the mixture (≥ 2.36 mm) with steel slags. The main laboratory program consisted of the determination of resilient modulus at three testing temperatures of 5, 20 and 40˚C (ASTM D4123) and indirect tensile strength of the samples at 20˚C. In order to evaluate the long term performance of mixtures containing slags, the specimens were subjected to ageing according to AASHTO PP2 standard method. Results showed that the peak tensile strength, area up to peak tensile strength and total dissipated energy density of the specimens containing Electric arc furnace slag were greater than the control mixtures. Fracture energy was almost the same for both mixes containing basic oxygen furnace slag and limestone. Results also indicated that the resilient modulus of mixtures increased along with an increase in slag contents in asphalt mixtures. The ratio of aged to unaged resilient modulus of the specimens decreased upon increasing slag contents. It was concluded that mixtures containing electric arc furnace slag exhibited less susceptibility to ageing compared with mixtures containing basic oxygen furnace slag and limestone. At 5oC, the highest ratio belonged to control mixtures, which might indicate that at lower temperatures, the susceptibility to ageing of the control mixtures were more pronounced

The aim of this study is to investigate the utilization possibilities of steel slags, basic oxygen furnace (BOF) and electric arc furnace (EAF) slags, as backfill material in coastal structures. Within the scope of the study, physical, mechanical and chemical properties of the steel slags were investigated and their potential to create environmental risks were evaluated. The results showed that soundness loss and filler content ratio were below the limit values for steel slags to be used as backfill material. It was determined that the density, porosity, water absorption and Los Angeles abrasion ratios of steel slags were generally higher than natural aggregates. In order to reach the California Bearing Ratio (CBR) limit (> 25%), the maximum particle size of the steel slag was reduced to 25 mm. In this particle size, CBR of the slag samples generally gave better results compared to the natural aggregate (38%), except for Kardemir and Asil samples. In addition, the concentration values of heavy metals (Cu, Cd, Cr, Pb, Ni, Zn, Hg and As) were below the limit values specified in the regulation. It is suggested that EAF slags should be aged for at least 6 months and BOF slags for at least 24 months in open air conditions before being used as backfill material in coastal structures after the maximum particle size is reduced to 25 mm.

Steel slag is an industrial by product of steel manufacturing processes and has been widely utilized within civil and construction materials for road materials and environmental remediation in countries like Japan, USA, and European Union nations. However, the current utilization of steel slag in Vietnam is very low mainly because of lack of quality control of slag treatment and chances for reuse of treated steel slag. This paper presents the up to date steel slag production status in Vietnam through the extensive survey and sampling at seven large steel factories. The paper also highlights the environmental and quality control issues of these steel slags to use as road construction aggregates by assessing the heavy metals concentration in the leachate. The basic oxygen furnace (BOF) and electric arc furnace (EAF) slag samples were collected to evaluate leaching properties of metals leached from the slags. The two standardized batch leaching tests of steel slag roadbed material in Japan (JIS K 0058-1) and toxicity characteristics leaching procedure (TCLP-EPA method 1311) were performed to the evaluated the hazardous metals. The results of the leaching test show that almost all of the concentration of the metals in the leached solution does not exceed the National Standard for Industrial Wastewater Discharge (QCVN 40-2011). The pH and parameters such as total chromium, nickel, copper, lead, arsenic, and manganese differ from the two test methods. The acidic conditions employed in the EPA 1311 were not representative of condition excepted during slag reuse in road constructions because in the operation condition of the road, acidic liquid is absent. The leaching test results confirmed that JIS test which uses deionized water with gentle mixing prevents the slag sample from size degradation is suitable for the environmental assessment of steel slag use for roadbed material. This research suggests that the adjustment of pH value prior to disposal or reuse as base materials and official guideline should be promulgate by the authorities to ensure the leachate meet the surface water quality standard.

Characteristics of Engineered Waste Materials Used for Road Subbase Layers

Comparative study on different steel slags as neutralising agent in bioleaching

Basic oxygen furnace (BOF) slag is a by-product of steel plants and is different from conventional natural aggregates. Studies have shown that BOF slag asphalt concrete is able to store heat. However, no quantitative research results have been presented. In this study, conventional natural aggregates and reclaimed asphalt pavement (RAP) are replaced by BOF slag in an asphalt concrete mixture. To observe the temperature variations in BOF slag asphalt concrete pavement during construction and after being opened to traffic, test roads with different levels of BOF slag and RAP were constructed in Kaohsiung City, Taiwan. The goal of this study was to provide information about the temperature differences between asphalt concrete pavement containing natural aggregates and those containing BOF slag aggregates. The results of this research indicate that for the same transportation time and distance, the temperature of asphalt concrete pavement with 40% BOF slag was approximately 7°C higher than that with 0% BOF slag. Because the internal heat energy of pavement with a large amount of BOF slag is not easily released, a longer curing time is needed after rolling compaction of the pavement, and thus, a longer time is needed before the BOF slag pavement can be opened to traffic. The temperature required to open the pavement to traffic was approximately 65°C. Furthermore, after opening the road to traffic, temperatures at depths of 3 and 5 cm in pavement with 40% BOF slag were 2 to 4°C lower than at the same depths in pavement with 0% BOF slag.

Basic oxygen furnace (BOF) slag is a main byproduct produced during the converter steelmaking process. The poor grindability of BOF slag limits its added-value application. In this paper, the grinding characteristics of unmodified and reconstructed BOF slag were compared. Additionally, the grinding property of reconstructed steel slag was also studied after SiC foaming. The results show that the solid solution of divalent metal oxides’ RO phase, considered as the hardly grinding phase, discomposes after lime-bauxite reconstruction. The characteristics of BOF slag were tested through particle size analysis, XRD, SEM and MIP. The SSA (specific suface area) and the particle diameter of unmodified BOF slag could reach 303.1 m2/kg and 51.75 µm after 10 min of grinding, but that of reconstructed BOF slag could reach 354.5 m2/kg and 18.16 µm after the same grinding time, respectively. The grinding efficiency of steel slag was obviously increased and the particle characteristics were improved after foaming modification. BOF formed as a porous structure after SiC foaming; its porosity, SSA, and particle diameter can reach 31.79%, 424.4 m2/kg, and 24.36 μm and increased by 10.31%, 19.72%, and 39.04%, compared with the reconstructed steel slag of undoped foaming agent, respectively, and the grindability was further improved. A theoretical basis for large-scale BOF slag utilization is provided.

The steel industry has grown rapidly, leading to the production of large quantities of steel slag, a by-product from processes like basic oxygen, electric arc, and ladle furnaces. Once seen as an industrial waste, steel slag is now valued in agriculture as a soil enhancer and nutrient source. This review aims to summarise key findings on how steel slag affects soil chemistry, nutrient dynamics, microbial interactions, and crop performance, while also addressing safety and practical considerations for its use in agriculture. This review highlights the benefits of using steel slag in sustainable farming, focusing on its nutrient content, environmental safety, and influence on crop productivity. It is rich in essential plant nutrients such as calcium, silicon, magnesium, and phosphorus, along with micronutrients like iron and manganese. Its alkaline nature helps to reduce soil acidity, improve nutrient availability, and support microbial activity in the soil. Steel slag is a by-product produced during steel manufacturing and is mainly generated from three types of furnaces: basic oxygen furnaces (BOF), electric arc furnaces (EAF), and induction furnaces (IF). Steel slag also has the ability to reduce the mobility of harmful metals like cadmium, arsenic, and lead, lowering the risk of heavy metal contamination in crops. Its application improves crop growth, enhances stress tolerance, and boosts yield. Steel slag with biochar in paddy fields raised soil pH by 14.2% and salinity by 98% compared to untreated soil. Field studies from Bangladesh, China, Japan, Indonesia, and Korea have shown that slag fertiliser can reduce methane emissions from rice fields by 0.6% to 56% depending on factors like soil type, slag composition, and application rate. Moreover, it helps to reduce methane and nitrous oxide emissions in flooded rice fields by altering soil microbial dynamics and redox conditions. When combined with materials like biochar, slag enhances carbon retention and microbial health, supporting long-term soil fertility. This review compiles recent research on various types of slag used in farming, emphasising their role in improving soil properties, limiting toxic metal uptake, and supporting sustainable crop production. It also addresses safety and regulatory considerations for practical use in agriculture. Research has shown that slag use can increase crop yields, improve plants’ resistance to stress and diseases, and make farming more sustainable. With proper management, steel slag can be a low-cost, eco-friendly option to improve soil quality and support sustainable agriculture.

Steel slag is a by-product of steelmaking and refining processes. In 2006, 10-15 million metric ton of steel slag was generated in the U.S. Out of the total steel slag produced in the U.S. every year, about 50-70% is used as aggregate for road and pavement construction and approximately 15-40% is stockpiled in steel plants and eventually landfilled at slag disposal sites. Since current levels of steel slag stockpiling and landfilling are not sustainable, alternative geotechnical engineering applications for steel slag are being explored to alleviate the slag disposal problem and to help save dwindling natural resources. The main objectives of this research were to determine the geotechnical engineering properties of two types of steel slag generated from different steelmaking operations and to assess their potential use in subgrade stabilization and embankment construction. Samples of fresh and aged basic-oxygen-furnace (BOF) slag and of fresh electric-arc-furnace-ladle (EAF(L)) slag were characterized through a series of laboratory tests (specific gravity, grain-size analysis, X-ray diffraction, compaction, maximum and minimum density, large-scale direct shear, consolidated drained triaxial and swelling tests). The effects of gradation on the engineering properties of both fresh and aged steel slag samples were also investigated. Various mixtures of steel slag [BOF and EAF(L)] and Class-C fly ash were also investigated. The mixtures were prepared by adding 5 and 10% Class-C fly ash (by weight) to aged BOF slag and 5, 10 and 20% Class-C fly ash (by weight) to fresh EAF(L) slag. Unconfined compression tests were performed after various curing times to evaluate the strength gain characteristics of the mixtures. Long-term swelling tests were performed for compacted mixtures of both fresh and aged BOF slag and 10% Class-C fly ash (by weight) and for compacted mixtures of fresh EAF(L) slag and 5, 10 and 20% Class-C fly ash (by weight). The effect of adding 10% ground rubber (by weight) to fresh and aged BOF slag on the long-term swelling behavior of the mixtures was also investigated. The optimum moisture content and maximum dry unit weight of BOF slag were in the ranges of 4-8% and 19.5-21.8 kN/m3, respectively. The critical-state friction angle of fresh and aged BOF slags was in the 45.3°- 48.1° range according to large-scale direct shear test results. Based on isotropically consolidated drained triaxial test (CIDTX) results, the peak friction angles of aged BOF slag (with minus 9.5 mm gradation) samples prepared at 90% relative compaction were equal