Search Results (66)

Alkali-activated building materials have attracted the interest of many researchers due to their low cost and eco-efficiency. Different binders with different chemical compositions can be used for their production, so the reaction mechanism can become complex and the results of studies can vary widely. In this work, several alkali-activated mortars based on marginal by-products as binders, such as high calcium fly ash and ladle furnace slag, are investigated. Their mechanical (flexural and compressive strength, ultrasonic pulse velocity, and modulus of elasticity) and physical (porosity, absorption, specific gravity, and pH) properties were determined. After evaluating the mechanical performance of the mortars, the optimum mixture containing fly ash, which reached 15 MPa under compression at 90 days, was selected for the production of precast compressed slabs. Steel or glass fibers were also incorporated to improve their ductility. To reduce the density of the slabs, 60% of the siliceous sand aggregate was also replaced with recycled polyethylene terephthalate (PET) plastic aggregate. The homogeneity, density, porosity, and capillary absorption of the slabs were measured, as well as their flexural strength and fracture energy. The results showed that alkali activation can be used to improve the mechanical properties of weak secondary binders such as ladle furnace slag and hydrated fly ash. The incorporation of recycled PET aggregates produced slabs that could be classified as lightweight, with similar porosity and capillary absorption values, and over 65% achieved strength compared to the normal weight slabs. Full article

This research paper provides new insights into the impact of accelerated mineralization of alkaline waste materials on the physical and mechanical behavior of low-carbon cement-based mortars. Standardized eco-cement mortars were prepared by replacing Portland cement with 7% and 20% proportions of three alkaline waste materials (white ladle furnace slag, biomass ash, and fine concrete waste fraction) that had been previously carbonated in a static reactor at predefined humidity and CO₂ concentration. The mortars’ physical (total/capillary water absorption, electrical resistivity) and mechanical properties (compressive strength up to 90 d of curing) were analyzed, and their microstructures were examined using mercury intrusion porosimetry and computed tomography. The results reveal that carbonated waste materials generate a greater heat of hydration and have a lower total and capillary water absorption capacity, while the electrical resistivity and compressive strength tests generally indicate that they behave similarly to mortars not containing carbonated minerals. Mercury intrusion porosimetry (microporosity) indicates an increase in total porosity, with no clear refinement versus non-carbonated materials, while computed tomography (macroporosity) reveals a refinement of the pore structure with a significant reduction in the number of larger pores (>0.09 mm³) and intermediate pores (0.001–0.09 mm³) when carbonated residues are incorporated that varies depending on waste material. The construction and demolition waste (CCDW-C) introduced the best physical and mechanical behavior. These studies confirm the possibility of recycling carbonated waste materials as low-carbon supplementary cementitious materials (SCMs). Full article

This paper presents the development of two solutions for sandwich panels composed of a thin-layer alkali-activated composite (AAc) layer and a thicker insulation layer, formed by extruded polystyrene foam or expanded cork agglomerate (panels named AP_XPS or AP_ICB, respectively). The AAc combined ceramic waste from clay bricks and roof tiles (75%) with ladle furnace slag (25%), activated with sodium silicate. The AAc layer was further reinforced with polyacrylonitrile (PAN) fibers (1% content). The mechanical behavior was assessed by measuring the uniaxial compressive strength of cubic AAc specimens, shear bond strength, pull-off strength between the AAc layer and the insulation material, and the flexural behavior of the sandwich panels. The thermal performance was characterized by heat flux, inner surface temperatures, the thermal transmission coefficient, thermal resistance, and thermal conductivity. Mechanical test results indicated clear differences between the two proposed solutions. Although AP_XPS panels exhibited higher tensile bond strength values, the AP_ICB panels demonstrated superior interlayer bond performance. Similar findings were observed for the shear bond strength, where the irregular surface of the ICB positively influenced the adhesion to the AAc layer. In terms of flexural behavior, after the initial peak load, the AP_XPS exhibited a deflection-hardening response, achieving greater load-bearing capacity and energy absorption capacity compared to the AP_ICB. Finally, thermal resistance values of 1.02 m² °C/W and 1.14 m² °C/W for AP_ICB and AP_XPS were estimated, respectively, showing promising results in comparison to currently available building materials. Full article

In this work, a novel method for the disposal of ladle furnace slag (LFS) and soda residue (SR) was proposed. By applying geopolymer technology, LFS and SR were used as precursors to manufacture a geopolymer with sufficient fresh and mechanical properties that can be used in construction works, such as in non-structural components like lightweight partition walls. The effects of raw material ratios and Na₂O equivalents on the fresh properties, mechanical properties, microstructure and environmental impact of LFS-SR geopolymer (LSG) were analyzed by rheology, compressive strength, XRD, TG/DTG, SEM, and calculation of embodied carbon. The results showed that the compressive strength of LSGs increased when the SR content decreased or Na₂O equivalent increased, and the maximum compressive strength could reach 12.0 MPa at 28 d. The hydration products of LSG were mainly C-(A)-S-H gel, C₃AH₆, and AFt. Notably, the C-(A)-S-H gels formed a stable cross-linked structure, and the extremely fine granular C₃AH₆ further filled the pores. Furthermore, AFt was generated from the interaction between LFS and CaSO₄ rich in SR during the hydration process. The carbon calculation results indicated that the embodied carbon of LSGs was significantly lower than that of traditional cement, and the LSG containing 20% SR and 12% Na₂O equivalent had the highest sustainability. This study proposed strategies for mitigating the environmental hazards of alkaline solid waste and improving its resource utilization, thereby promoting sustainable development in the construction industry. Full article

Electric arc furnace oxidizing slag (EAFOS) represents 80% of the electric arc furnace slag generated. Recently, EAFOS has been utilized as high value-added functional aggregate in a growing number of cases for the construction of air-cooling technology that turns EAFOS into fine aggregate-sized particles by spraying it into the air using high-pressure compressed air. Ladle furnace slag (LFS) is a product of the reduction process, accounting for approximately 20% of the steel slag enerated; however, LFS is predominantly landfilled without being utilized. This is mainly because LFS changes into sludge as it is turned into powder during water spray cooling. Therefore, in this study, spherical particles cooled at room temperature were fabricated as fine aggregates using LFS by applying atomization technology that uses high-pressure air in the molten state for the value-added utilization of LFS. Various experiments were performed to examine whether this aggregate can be used as a construction material. The experimental results showed that the air-cooled LFS (ALFS) fine aggregate generated from two different processes met the physical and chemical properties of the fine aggregate required for concrete despite its slightly lower spherical ratio compared to EAFOS aggregate. The volumetric stability experiment results also showed that ALFS fine aggregate is more stable than river sand and standard sand. In addition, the autoclave test results revealed that the mortar produced using ALFS fine aggregate was more stable for expansion than that of comparison groups. These results confirm the applicability of ALFS as an aggregate for construction. However, because the pop-out phenomenon caused by MgO was observed on the surface of some specimens, further research is required for improvement. Full article

Ladle furnace slag (LFS), a by-product of steel refining, shows a promising reuse pathway as an alternative additive or substitute for Portland cement due to its high alkalinity and similar chemical composition to clinkers. However, LFS is often stored in large, open surface areas, leading to many environmental issues. To tackle waste management challenges, LFS can be recycled as supplementary cementitious material (SCM) in many cementitious composites. However, LFS contains some mineral phases that hinder its reactivity (dicalcium silicate (γ-C₂S)) and pose long-term durability issues in the cured cemented final product (free lime (f-CaO) and free magnesia (f-MgO)). Therefore, LFS needs to be adequately treated to enhance its reactivity and ensure long-term durability in the structures of the cementitious materials. This literature review assesses possible LFS treatments to enhance its suitability for valorization. Traditional reviews are often multidisciplinary and explore all types of iron and steel slags, sometimes including the recycling of LFS in the steel industry. As the reuse of industrial by-products requires a knowledge of their characteristics, this paper focuses first on LFS characterization, then on the obstacles to its use, and finally compiles an exhaustive inventory of previously investigated treatments. The main parameters for treatment evaluation are the mineralogical composition of treated LFS and the unconfined compressive strength (UCS) of the final geo-composite in the short and long term. This review indicates that the treatment of LFS using rapid air/water quenching at the end-of-refining process is most appropriate, allowing a nearly amorphous slag to be obtained, which is therefore suitable for use as a SCM. Moreover, the open-air watering treatment leads to an optimal content of treated LFS. Recycling LFS in this manner can reduce OPC consumption, solve the problem of limited availability of blast furnace slag (GGBFS) by partially replacing this material, conserve natural resources, and reduce the carbon footprint of cementitious material operations. Full article

The reconstruction of buildings is a complex process that often requires the consideration of the construction load when selecting correct building materials. Autoclaved aerated concrete (AAC)—which has a lower bulk density (compared to traditional masonry materials)—is very beneficial in such applications. A current trend in AAC development is the utilization of secondary raw materials in high-performance AAC, characterized by higher bulk density and compressive strength than regular AAC. The increase in bulk density is achieved by increasing the content of quartz sand in the mixing water. In this study, part of the siliceous component was replaced by ladle slag, foundry sand, furnace lining, and chamotte block powder. These materials are generated as by-products in metallurgy. The substitution rates were 10% and 30%. The samples were autoclaved in a laboratory autoclave for 8 h of isothermal duration at 190 °C with a saturated water vapor pressure of 1.4 MPa. The physical–mechanical parameters were determined, and the microstructure was described by XRD and SEM analyses. The results were compared with traditional AAC, with silica sand being used as the siliceous component. The measurement results show that sand substitution by the secondary raw material is possible, and it does not have a significant impact on the properties of AAC, and in a proper dosage, it can be beneficial for AAC production. Full article

To address SDG12 (ensure sustainable consumption and production patterns), and to provide technical evidence for alternative concrete constituents to traditional natural river sand, stone fine aggregate (SFA), brick fine aggregate (BFA), ladle-refined furnace slag aggregate (LFS), recycled brick fine aggregate (RBFA), and washed waste fine aggregate (WWF), ready-mix concrete plants were investigated. Concrete and mortar specimens were made with different variables, such as replacement volume of natural sand with different alternative fine aggregates, water-to-cement ratio (W/C), and sand-to-aggregate volume ratio (s/a). The concrete and mortar specimens were tested for workability, compressive strength, tensile strength, and Young’s modulus (for concrete) at 7, 28, and 90 days. The experimental results show that the compressive strength of concrete increases when natural sand is replaced with BFA, SFA, and LFS. The optimum replacement amounts are 30%, 30%, and 20% for BFA, SFA, and LFS, respectively. For RBFA, the compressive strength of concrete is increased even at 100% replacement of natural sand by RBFA. For WWF, the compressive strength of concrete increases up to a replacement of 20%. Utilizing these alternative fine aggregates can be utilized to ensure a circular economy in construction industries and reduce the consumption of around 30% of natural river sand. Full article

Integrating industrial wastes into soils to enhance their properties is a potential solution to current waste management challenges. Since the current literature lacks systematic studies on the mechanical performance of mixtures of soil, ladle furnace slag (LFS) and fly ash (FA), this research investigated the chemical stabilization of two different soils (clayey or sandy soil) using a concomitant mix of distinct types of industrial wastes: LFS and FA. A design of experiments (DoE) methodology was employed to systematically generate distinct mixtures for each soil sample, utilizing a simplex-centroid design. The mixtures were subjected to unconfined compressive strength (UCS), California Bearing Ratio (CBR) and resilient modulus (RM) tests. The industrial by-products improved the mechanical properties of the soils, providing UCS, CBR index and RM increases up to 130.5%, 324.4% and 132.6%, respectively. Synergistic and antagonistic effects related to the combination of different wastes were discussed, based on mathematical models with coefficients of determination ranging from 0.760 to 0.998, in addition to response surfaces generated for each response variable. The desirability function was applied to identify the optimal component proportions. The best mixture proportion was 80% soil, 20% LFS and 0% FA, which improved the formation of cemented compounds that contributed to the enhanced mechanical strength. The use of industrial waste for soil stabilization has therefore proven to be technically feasible and environmentally friendly. Full article

Ladle furnace slag (LFS) is used as a supplementary cementitious material (SCM) due to its high calcium oxide (CaO) content. Its binding properties are enhanced in the presence of siliceous materials, such as metakaolin (MK), forming a ternary mixture that can directly replace ordinary Portland cement (OPC). However, despite this blend having already been evaluated in alkali-activated mixtures, knowledge about this mixture in situations of direct replacement of OPC by slag is still lacking. This study evaluates the synergistic effects of combining LFS and MK in cementitious mortars. Due to an insufficient hydration reaction observed in the short term, this study focuses on assessing the long-term performance of these mortars. Both the fresh and hardened states at 28 and 180 days are evaluated, and the resulting microstructural characteristics and constituent phases are also examined. After 180 days of curing, the mortar with MK exhibits superior binding activity compared to the results at 28 days. Although the nominal resistance does not show a clear advantage with the application of MK, a significant reduction in the porosity of the mortar is observed. Microstructural analysis indicates that the addition of MK increases the hydration compounds when mixed with LFS. Importantly, the sample containing MK and LFS showed a 42% reduction in cement consumption, highlighting the potential for resource efficiency. Thus, this study contributes to promoting a circular economy between the steelmaking and civil construction sectors. Full article

Steel slags are solid residual materials formed as by-products throughout the process of steel production within the steelmaking industry. These wastes have good physical properties such as high stiffness and friction angle for use as road fill materials or in geotechnical applications. However, the presence of heavy metals and high alkalinity levels constitute significant environmental hazards and set limitations on using slags in engineering applications. While there have been investigations into the mechanical characteristics of steel slags, research on assessing potential harm when utilizing the materials in engineering applications is rare. This study examines the mitigation methods to address the environmental problems associated with steel slags. To do this, two different steel slags with different production techniques were treated with soils of different properties such as fine and coarse sand, bentonite, kaolin, and natural clay. The pH and electrical conductivity (EC) values of pure steel slags were determined using the water leach test (WLT). Variations in pH and EC values of steel slags subjected to treatment were evaluated through both WLT and sequential water leach (SWLT) tests. As a result, the high strength, stiffness, and drainage capability of EAF and LS steel slags make these materials suitable for road filling. This is further backed by their soaked and unsoaked CBR values. During the water leach tests, notable decreases in pH were observed with a 60% natural clay (NC) solution, resulting in a decrease of 1.2 and 0.7 in EAF and LS, respectively. The addition of sand had a negligible impact on pH due to its inert characteristics. Moreover, in sequential water leach tests, the most significant decrease in pH was observed with NC (with a reduction of 2.0 points for EAF and 0.9 points for LS) through enhanced ion exchange and extended periods of dilution and buffering. Also, the use of NC resulted in substantial decreases in EC for EAF and LS, with reductions of 77% and 81%, respectively. Moreover, heavy metal concentrations in leachate waters from pure steel slags have been detected, and the effect of treatment on aluminum and iron concentrations has been determined. The results indicate that the use of natural soil significantly drops the pH and lowers the trace metal concentrations within the leachate. Full article

The continuous improvement of the steelmaking process is a critical issue for steelmakers. In the production of Ca-treated Al-killed steel, the Ca and S contents are controlled for successful inclusion modification treatment. In this study, a machine learning technique was used to build a decision tree classifier and thus identify the process variables that most influence the desired Ca and S contents at the end of ladle furnace refining. The attribute of the root node of the decision tree was correlated with process variables via the Pearson formalism. Thus, the attribute of the root node corresponded to the sulfur distribution coefficient at the end of the refining process, and its value allowed for the discrimination of satisfactory heats from unsatisfactory heats. The variables with higher correlation with the sulfur distribution coefficient were the content of sulfur in both steel and slag at the end of the refining process, as well as the Si content at that stage of the process. As secondary variables, the Si content and the basicity of the slag at the end of the refining process were correlated with the S content in the steel and slag, respectively, at that stage. The analysis showed that the conditions of steel and slag at the beginning of the refining process and the efficient S removal during the refining process are crucial for reaching desired Ca and S contents. Full article

The temperature of hot metal (HM) is crucial for the energy input and smelting in the electric arc furnace (EAF) steelmaking process with HM and scrap as the charge structure. However, due to the influence of many factors in the heat dissipation in HM transportation before the EAF steelmaking process, the temperature drop of HM before charged is usually fluctuating and uncertain. This situation is not conducive to the input energy control and energy optimization of the EAF steelmaking process. In this paper, a three-dimensional numerical model of a 90-ton hot metal ladle is established to simulate the heat transfer characteristic of HM transportation through ANSYS Fluent 2023 and verified by on-the-spot testing and sample analysis. The effects of ambient temperature, air velocity, slag thickness and furnace cover thickness on the temperature drop of HM are investigated and quantitatively analyzed in 30 numerical schemes. The results indicate that slag thickness is the most influential factor, followed by furnace cover thickness, air velocity and ambient temperature. In the case of 50 min transport time, the temperature drop of HM is 55.2, 15.06, 12.08, 10.38, 10.29 and 10.26 °C when the slag thickness is 0, 50, 100, 150, 200 and 250 mm, respectively. While HM is not covered by slag, the furnace cover can also greatly reduce the temperature drop. Based on the simulated data, a prediction model of HM temperature drop is obtained through the multi-factor coupling analysis and mathematical fitting. This study can help develop targeted insulation measures and determine the temperature of HM, which is expected to control the input energy for deep energy-saving optimization in the EAF steelmaking process. Full article

The addition of Ladle Furnace Slag (LFS) to concrete modifies its compressive strength and modulus of elasticity and consequently impacts their relationship. This research evaluated both properties at 28, 90, and 180 days in concrete mixes produced with 5%, 10%, and 20% of two LFS types, both stabilized and non-stabilized. The relationship between them was then analyzed through these experimental results by adopting a statistical approach. A three-way analysis of variance revealed that both properties were affected by LFS differently. Thus, the effect of each LFS content on both features varied depending on its composition and pre-treatment. Furthermore, the effect of the LFS content on the compressive strength was also influenced by the age of the concrete. These facets implied that when analyzing the relationship between both mechanical properties, the monotonic correlations were stronger than the linear ones, reaching values between 0.90 and 1.00. Therefore, the double reciprocal regression models were the most precise ones for expressing the modulus of elasticity as a function of compressive strength. The model accuracy was further enhanced when discriminating based on the LFS type and introducing concrete age as a predictive variable. With all these considerations, the average deviations between the estimated and experimental values of 1–3% and the maximum deviations of 4–7% were reached, as well as R² coefficients of up to 97%. These aspects are central to the further development of LFS concrete models. Full article