Steel slag inhibits the early-age hydration of cement. However, its mechanism is still unclear. In this paper, the early-age hydration kinetics and the evolution of the solid phases, aqueous species ...and microstructures in a cement-steel slag composite binder are investigated to explore how steel slag inhibits the early-age hydration of cement. Two novel phenomena are found: (1) steel slag slows the depletion of gypsum and reduces the formation of ettringite, and (2) steel slag significantly inhibits the precipitation of CH and CSH. The results show that the addition of steel slag increases the Ca concentration in the pore solution, reduces the supersaturation of the pore solution with respect to CH and inhibits the nucleation and growth of CSH. Based on the above results, the retardation mechanisms of steel slag on the initial setting of cement paste are explained.
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•50 wt% of GGBS was replaced by SS or FNS to prepare alkali-activated slag mortars.•Autogenous shrinkage of AAMs is reduced with the incorporation of SS or FNS.•Compared with PC ...mortar, GGBS/SS or GGBS/FNS mortar possesses superior performance.
With the continuous development of industry, a huge amount of industrial wastes have been produced and caused severe environmental problems. In order to reduce the issue caused by industrial waste, in this investigation, 50 wt% ground granulated blast furnace slag (GGBS) replaced by steel slag (SS) or ferronickel slag (FNS) was used to prepare alkali-activated blended slag mortar. Hydration process, strength, autogenous shrinkage, drying shrinkage, pore structure, chloride ion diffusion coefficient and water absorption of mortars were investigated and compared with the same strength level Portland cement (PC) mortar. The results show that the utilization of 50 wt% SS or FNS can prolong the setting time, increase the fluidity and porosity, but decrease the hydration heat, 7 days autogenous shrinkage, drying shrinkage and chloride ion diffusion coefficient of mortar. Compared with PC mortar of the same strength, alkali-activated GGBS-SS mortar or GGBS-FNS mortar possesses relatively lower hydration heat, porosity, water absorption capacity and chloride ion diffusion coefficient.
Fe-rich alkali activated materials (AAMs) require detailed understanding of their durability prior to their real-life application in the construction industry. Three mixes were formulated with ...fayalite slag (FS) as the main precursor. The effect of incorporation of ladle slag (LS) or blast furnace slag (BFS) on the shrinkage and exposure to physical and chemical attacks representing environmental conditions in cold and tropical regions (acidic solution at room temperature and in freeze-thaw, combined sodium sulfate and sodium chloride solution at room temperature and in freeze-thaw, freeze-thaw in water and dry-wet cycles) was investigated via visual observation, mass loss, compressive strength, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP), and scanning electron microscope coupled with energy dispersive X-ray spectroscopy (SEM-EDS). Experimental results show the considerable role of incorporated LS and BFS in modifying the gels formed and controlling material degradation of blended AAMs after exposure. In contrast, sole FS-based samples were completely degraded particularly those exposed to freeze-thaw in water, acid, and combined sodium sulfate and sodium chloride solution, indicating their vulnerability to frost and chemical attacks.
•Durability of Fe-rich alkali-activated materials (AAMs) exposed to different environmental conditions was elucidated.•Sole fayalite slag-based AAMs were completely degraded during exposure to freeze-thaw in water, acid and combined sodium sulfate and chloride•Incorporation of ladle slag (LS) or blast furnace slag (BFS) helps to control AAMs degradation during exposure to aggressive environments.•AAMs containing LS or BFS exhibited better mechanical, microstructural and durability properties after exposure.•Deterioration of AAMs was caused by water and chemical uptake in the pores.
Microstructure tailoring of metallurgical slags allows the production of alternative construction binders with customized properties. In this study, the variations of rheology and strength of ...alkali-activated basic-oxygen-furnace (BOF) slags are quantified. Two modifications of BOF slag were created adding amounts of alumina and silica at high temperature (>1250 °C). The additions, defined by thermodynamic modeling, lowered the liquidus temperature facilitating the generation of amorphous when the slag was fast cooled. The first modification (SAT1) incorporated 5 wt% silica and 11 wt% alumina, while the second (SAT2) included around 13 wt% alumina. Both modifications generated a hybrid microstructure composed of cementitious and non-cementitious crystalline phases and an amorphous fraction. During alkali activation using NaOH solutions of 0.25 M, rheological measurements on fresh paste using SAT2 registered plastic viscosity values 2.3 times higher than those of SAT1. The compressive strength after 28 days for the binder developed from SAT2 slag was 10–30% stronger than the one from SAT1. These binders showed similar crystalline reaction products but compositional differences in the amorphous gel correlated to the initial slag modification. The detected differences in the binder properties are significant enough to justify BOF-slag engineering as a way to deliver customized precursors for alkali activation.
The phase evolutions in sodium hydroxide and sodium silicate–activated slag cements upon sulfate salt attack were investigated via thermodynamic modeling. The effects of different sulfate salts ...(i.e., Na2SO4 and MgSO4) and slag compositions were studied. In thermodynamic modeling, a solid solution model, that is, MgAl–SO4–LDH_ss, was proposed to describe the sulfate‐intercalated hydrotalcite. The modeling results were presented and discussed in comparison with experimental observations. Upon sulfate salt attack, ettringite, gypsum, sulfate‐intercalated hydrotalcite, magnesium silicate hydrate, and so on were predicted to form. By quantitatively evaluating the composition change of C–(N–)A–S–H gel, solid phase expansion, and alteration in pore solution chemistry, it was found that magnesium sulfate induced severer degradation of alkali‐activated slag cements compared to sodium sulfate. Upon sulfate salt attack with a fixed sulfate concentration, the ideal outcome shows that the slag with lower Al2O3 content not only gave a larger content of C–(N–)A–S–H gel but also caused the reduced decalcification and dealumination of C–(N–)A–S–H gel and solid phase expansion.
The Special Issue presents almost 40 papers on recent research in modeling of pyrometallurgical systems, including physical models, first-principles models, detailed CFD and DEM models as well as ...statistical models or models based on machine learning. The models cover the whole production chain from raw materials processing through the reduction and conversion unit processes to ladle treatment, casting, and rolling. The papers illustrate how models can be used for shedding light on complex and inaccessible processes characterized by high temperatures and hostile environment, in order to improve process performance, product quality, or yield and to reduce the requirements of virgin raw materials and to suppress harmful emissions.
Ladle furnace slag in asphalt mixes Skaf, M.; Ortega-López, V.; Fuente-Alonso, J.A. ...
Construction & building materials,
09/2016, Volume:
122
Journal Article
Peer reviewed
Open access
•LFS works properly as filler, presenting good adhesion with the bitumen.•The LFS had superior bitumen absorption than the conventional materials.•Porous mixes with LFS provided results in line with ...those of the standard mixture.•LFS mixes presented good cohesion and excellent mechanical behavior.
Ladle Furnace Slag (LFS) may be used in substitution of fine aggregate (2–0.063mm), and filler (<0.063mm) in bituminous mixtures, considering its suitable particle size and hydraulic properties. From among the range of bituminous mixtures, this research is conducted on Porous Asphalt mixes (PA). Their high void ratio means they can absorb any eventual expansion of the LFS.
Mechanical behavior, moisture susceptibility and durability are all tested. The results report the performance of the LFS mixtures, which showed compliance with the specifications of the relevant standards and no significant differences from those made of natural aggregates and cement.
Tar management is one of the key components to achieve high energy efficiency and low operational costs connected to thermal gasification of biomass. Tars contain a significant amount of energy, and ...unconverted tars result in energy efficiency losses. Also, heavy tars can condense downstream processes, resulting in increased maintenance. Dual fluidized beds for indirect gasification operated with active bed material can be a way to better convert and control the tar generated in the process. Using an active material to transport oxygen in an indirect dual reactor gasification setup is referred to as chemical-looping gasification (CLG). A higher oxidative environment in the gas phase, in addition to possible catalytic sites, could mean lower yields in comparison to normal indirect gasification. This paper investigates the effect of using Steel converter slag (LD slag), a byproduct of steel manufacturing, as an oxygen-carrying bed material on tar species generated in a 10 kWth dual fluidized bed biomass gasifier. The results are compared to the benchmark oxygen carrier ilmenite and conventional silica sand. Three different solid biofuels were used in the reactor system: steam exploded pellets, pine forest residue and straw. Tar was absorbed from the raw syngas using a Solid Phase Adsorption (SPA) column and was analyzed using GC-FID. Bench-scale experiments were also performed to investigate benzene conversion of LD slag and ilmenite at different oxidation levels. The findings of this study suggest that oxygen carriers can be used to decrease the tars generated in a dual fluidized bed system during gasification. Phases in LD slag possess catalytic properties, resulting in a decreased ratio of heavy tar components compared to both ilmenite and sand. Temperature and fuel load showed a significant effect on the tar generation compared to the circulation and steam ratio in this reactor system. Increased temperature generated lower tar yields and lower ratios of heavy tar components for LD slag in contrast to sand.
In this study, four ecotoxicological tests on Vibrio fischeri bacteria, Sinapis alba L. (white mustard), Daphnia magna S. (daphnia's) and earthworms were performed for three types of aqueous slag ...(ladle, blast furnace and converter) leachates with two-grain sizes (<4 mm, <10 mm). Concentrations of toxic elements and concentrations of Cr(VI), Ca, Na, Al, and other ions were determined. The raw slags were analyzed using X-ray fluorescence spectroscopy (XRFS), and major substances were determined by X-ray powder diffraction (XRD). The aqueous slag leachates passed ecotoxicological tests and met the required criteria, showing no toxicity to Vibrio fischeri and complying with white mustard test criteria. According to the results of the ecotoxicity tests with daphnia, the blast furnace slag samples were not ecotoxic, while two other slag samples were found to be entirely compliant. Characterization of the slags showed that the effect of element/ion leachability and slag grain size is essential. Biplot principal component analysis (PCA) showed that grain size does not significantly affect the separation of individuals on the plane. A positive correlation on toxicity was found with pH, conductivity, calcium content, dissolved content, salinity and fluoride concentration, whereas a negative correlation was found with magnesium concentration, dissolved organic carbon and potassium concentration. The effective concentration at 50% inhibition (EC50) value for Vibrio fischeri correlated with the first dimension of bivariate assessment. In summary, it was found that the investigated slags can be effectively reused as they comply with regulations and do not endanger the environment.
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•Ecotests on mustard, daphnia, Vibrio fischeri bacteria were compared with EU norms.•The chemical composition of the leachates affects the results of ecotoxicity tests.•Toxic unit values for Vibrio fischeri bacteria were within norms and non-toxic.•Most of the effective concentration values for the daphnia test were acceptable.•Principal component analysis found grain size effect on two organisms.
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