Transforming industrial byproduct to eco-friendly functional material: Ground-granulated blast furnace slag reinforced paper for renewable energy storage.

This study pioneered an eco-friendly approach for reutilizing Ground-granulated blast furnace slag (GGBFS) in paper production. This investigation is the first study focusing on the usage of paper production that presents both a new usage area of GGBFS and also a new sight. So, it can contribute to save the trees. Also, GGBFS gains economical value in paper production. 15-25 % integrated slag led to markedly enhanced brightness, density and smoothness accompanied by only minor mechanical strength decreases versus pure pulp. Significantly, the electrical analysis revealed a higher conductivity at higher frequency region reaching almost S value near to 1 which might be a good choice for electromagnetic shielding, thus; higher conductivity with increasing slag contents from pure paper's 10-11 S/cm up to 10-6 S/cm for 25 % addition which confirms the modified paper's usefulness as conductive slag agent. Although the higher addition of GGBFS has led to rising in relaxation time basically from 1.77e-4 to 2.95e-3 and based on Debye relaxation, the rising time in relaxation which was observed after the addition of GGBFS reveals better polarizability values 0.29-0.35 compared to control sample 0.26 by which both longer relaxation time and higher polarizability contribute to the ability of energy storage of modified papers. The conductive characteristics and improved qualities demonstrate these recyclable slag-modified papers present unique opportunities for emerging flexible, eco-friendly electronics, capacitors, electromagnetic shielding, and renewable energy storage applications. Overall, novel integration and characterization of slag waste for enhanced sustainable paper products pioneers an unexplored territory.

Effect of Calcium on the Setting Time and Mechanical Property of a Red Mud-Blast Furnace Slag-Based Geopolymer.

This study aims to compare the effects of three calcium compounds on the workability, setting time and mechanical properties of red mud (RM)-blast furnace slag (BFS)-based geopolymers. The crystalline phase, hydration process and microstructure of RM-BFS-based geopolymers were characterized by X-ray diffraction (XRD), heat evolution, X-ray photoelectron spectroscopy (XPS), and scanning electron microscope (SEM) tests. The results showed that an appropriate amount of calcium compounds can improve the flowability and compressive strength of the geopolymers, but the excessiveness causes a decrease in strength due to rapid hardening. Other than calcium carbonate, both calcium oxide and calcium chloride played important roles in accelerating the setting times of RM-BFS-based geopolymers. The acceleration in the setting times of geopolymers could be attributed to the calcium hydroxide produced by the dissolution of the calcium compounds, which also provides nucleation sites for the geopolymerization reaction. This study gives new insights into the effect of calcium on the setting times and mechanical properties of geopolymers in the geopolymerization process.

Research on Alkali-Activated Slag Stabilization of Dredged Silt Based on a Response Surface Method.

To improve the resource utilization of dredged silt and industrial waste, this study explores the efficacy of using ground granulated blast furnace slag (GGBS), active calcium oxide (CaO), and sodium silicate (Na2O·nSiO2) as alkali activators for silt stabilization. Through a combination of addition tests, response surface method experiments, and microscopic analyses, we identified key factors influencing the unconfined compressive strength (UCS) of stabilized silt, optimized material ratios, and elucidated stabilization mechanisms. The results revealed the following: (1) CaO exhibited the most pronounced stabilization effect, succeeded by Na2O·nSiO2, whereas GGBS alone displayed marginal efficacy. CaO-stabilized silt demonstrated rapid strength augmentation within the initial 7 d, while Na2O·nSiO2-stabilized silt demonstrated a more gradual strength enhancement over time, attributable to the delayed hydration of GGBS in non-alkaline conditions, with strength increments noticeably during later curing phases. (2) Response surface analysis demonstrated substantial interactions among GGBS-CaO and GGBS-Na2O·nSiO2, with the optimal dosages identified as 11.5% for GGBS, 4.1% for CaO, and 5.9% for Na2O·nSiO2. (3) X-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses clarified that the hydration reactions within the GGBS-Na2O·nSiO2 composite cementitious system synergistically enhanced one another, with hydration products wrapping, filling, and binding the silt particles, thereby rendering the microstructure denser and more stable. Based on these experimental outcomes, we propose a microstructural mechanism model for the stabilization of dredged silt employing GGBS-CaO-Na2O·nSiO2.

Combustion visualization analysis of alternative fuels in the pulverized coal injection raceway through laminar flow reactor.

Currently, the steelmaking process uses a pulverized coal injection (PCI) system that serves as the heat source and reductant for ironmaking (blast furnace and FINEX) where system uses expensive high-grade coal and high operating costs. Hydrogen steelmaking is currently being developed to achieve carbon-free operation. To achieve a soft-landing during this phase of rapid change, the use of biomass and inexpensive, thermal coal, and coke dust is necessary. Research on their combustion characteristics is necessary to apply these alternative fuels to PCI. Therefore, this study analyzed the combustion characteristics of ignition delay, devolatilization, and char combustion using a laminar flow reactor visualization equipment that simulates blast furnace (BF) and FINEX PCI tuyere, using flame image data processing. The ignition time were generally longer in BF than in FINEX, and the char combustion length and time also showed the same trend due to the high oxygen rate which indicate under 2 ms on ignition delay, under 16 ms on char combustion. Also, the volatile cloud was qualitatively shown in the image to be highest in thermal coal and biomass with high volatile matter. Based on the correlation and theoretical calculation with proximate analysis and the results, ignition delay time had a combined effect of volatile matter and moisture except coke dust, and char combustion time affected unburned carbon. The combustion chemical characteristics were discussed with chemical percolation devolatilization (CPD) model parameter. Through SEM image and BET analysis, the surface area has been increased more than 10 times after combustion. Consequently, the biomass and high moisture thermal coal could cofired within 10 % and coke dust could be cofired within 9 %, respectively.

Elemental Design of Alkali-Activated Materials with Solid Wastes Using Machine Learning.

Understanding the strength development of alkali-activated materials (AAMs) with fly ash (FA) and granulated blast furnace slag (GBFS) is crucial for designing high-performance AAMs. This study investigates the strength development mechanism of AAMs using machine learning. A total of 616 uniaxial compressive strength (UCS) data points from FA-GBFS-based AAM mixtures were collected from published literature to train four tree-based machine learning models. Among these models, Gradient Boosting Regression (GBR) demonstrated the highest prediction accuracy, with a correlation coefficient (R-value) of 0.970 and a root mean square error (RMSE) of 4.110 MPa on the test dataset. The SHapley Additive exPlanations (SHAP) analysis revealed that water content is the most influential variable in strength development, followed by curing periods. The study recommends a calcium-to-silicon ratio of around 1.3, a sodium-to-aluminum ratio slightly below 1, and a silicon-to-aluminum ratio slightly above 3 for optimal AAM performance. The proposed design model was validated through laboratory experiments with FA-GBFS-based AAM mixtures, confirming the model's reliability. This research provides novel insights into the strength development mechanism of AAMs and offers a practical guide for elemental design, potentially leading to more sustainable construction materials.

Improving landfill liner performance with bentonite-slag blend permeated with ammonia for a Municipal solid waste landfill.

Leachate emanating from landfills contains ammonia which may cause serious health effects on living things. An effectively designed clay barrier should not allow the contaminant to infiltrate the soil and groundwater systems. The utilization of certain industrial by-products in engineered landfill barriers, not only reduces the need for conventional liner materials but also helps in sustainable waste management. This study investigated the hydraulic conductivity, unconfined compressive strength, compaction, and adsorption characteristics of lithomargic clay blended with an optimum percentage of bentonite (10%) and granulated blast furnace slag (15%) permeated with ammonia. The results revealed that increasing the content of granulated blast furnace slag decreased the maximum dry density while increasing the optimum moisture content. In comparison to lithomargic clay, the hydraulic conductivity of the amended soil liner permeated with ammonia decreased from a value of 3 × 10-8 m/s to 5 × 10-10 m/s. The unconfined compressive strength of the amended soil specimens showed an increasing trend with curing times (i.e., 0, 14, 28, and 56 days). The batch adsorption results revealed that Freundlich and Langmuir's isotherm fits the equilibrium adsorption data and the adsorption of ammonia on clay liner follows non-linear behaviour. Overall, the experimental results implied that lithomargic clay blended with 10% bentonite and 15% granulated blast furnace slag can be used as an impermeable soil reactive barrier in engineered landfills.

Fabrication and characterization of ceramic tubular composite membranes using slag waste materials for oily wastewater treatment.

In this study, low-cost tubular ceramic membranes were fabricated by using waste slag and natural raw materials in order to decrease the manufacturing carbon footprints. The effects of incorporation of phosphorus slag (PS) and blast furnace slag (BFS) in the mullite-zeolite membrane body were investigated. The structural characteristics of the fabricated membranes were evaluated using X-ray diffraction (XRD), field emission-scanning electron microscopy (FESEM), atomic force microscopy (AFM), contact angle, porosity and average pore size analyses. Thermal and mechanical stability were studied by thermogravimetric analysis (TGA) and three-point bending test, respectively. The oily wastewater treatment tests revealed that an increase in the slag percentage from 0 to 30% leads to enhancing the permeate flux from 99 l m-2 h-1 to 349 l m-2 h-1 for PS-based tubular membrane and to 244 l m-2 h-1 for BFS-based tubular membrane under 1 bar applied. The chemical oxygen demand (COD) removal percentage of all membranes was reported almost 99% for oily wastewater feed with a COD concentration of 612 mg l-1. In addition, the investigation of membrane fouling mechanisms was carried out using Hermia models indicating that the best correlation with the experimental data is observed for the complete pore blocking model. This study presents experimental foundations aimed at enhancing the performance of affordable slag-based membranes, thus fostering their applicability in engineering contexts.

Kinetics study on the low-temperature soda roasting of boron-rich blast furnace slag.

The method of preparing borax by low-temperature soda roasting and water leaching of boron-rich blast furnace slag (BRBFS) is a novel method for extracting boron from BRBFS. In order to further improve the water leaching rate of boron, this article mainly studied the low-temperature soda roasting kinetics of BRBFS. The effects of roasting temperature and Na2CO3 addition on the water leaching rate of boron were investigated. The results demonstrate that when the amount of Na2CO3 added is four times of the theoretical amount, the kinetics of NaBO2 formation can be described by the Nucleation (Avrami) model in the temperature range of 600-700 °C. The corresponding apparent activation energy is 54.45 kJ/mol, and the apparent frequency factor is 215.16 h-1. It was found that at a roasting temperature of 700 °C,when the amount of sodium carbonate added is twice, three times, and four times of the theoretical amount, the kinetics of NaBO2 formation matches with 3-D Diffusion (Jander) model, Nucleation and Growth (Avrami-Erofeev) model, and Nucleation (Avrami) model, respectively. With an increase in the amount of Na2CO3 added, the rate-controlling step for the formation of NaBO2 transitions from being diffusion-controlled to nucleation-controlled.

Study on the Compressive Strength and Reaction Mechanism of Alkali-Activated Geopolymer Materials Using Coal Gangue and Ground Granulated Blast Furnace Slag.

By reutilizing industrial byproducts, inorganic cementitious alkali-activated materials (AAMs) contribute to reduced energy consumption and carbon dioxide (CO2) emissions. In this study, coal gangue (CG) blended with ground granulated blast furnace slag (GGBFS) was used to prepare AAMs. The research focused on analyzing the effects of the GGBFS content and alkali activator (i.e., Na2O mass ratio and alkali modulus [SiO2/Na2O]) on the mechanical properties and microstructures of the AAMs. Through a series of spectroscopic and microscopic tests, the results showed that the GGBFS content had a significant influence on AAM compressive strength and paste fluidity; the optimal replacement of CG by GGBFS was 40-50%, and the optimal Na2O mass ratio and alkali modulus were 7% and 1.3, respectively. AAMs with a 50% GGBFS content exhibited a compact microstructure with a 28 d compressive strength of 54.59 MPa. Increasing the Na2O mass ratio from 6% to 8% promoted the hardening process and facilitated the formation of AAM gels; however, a 9% Na2O mass ratio inhibited the condensation of SiO4 and AlO4 ions, which decreased the compressive strength. Increasing the alkali modulus facilitated geopolymerization, which increased the compressive strength. Microscopic analysis showed that pore size and volume increased due to lower Na2O concentrations or alkali modulus. The results provide an experimental and theoretical basis for the large-scale utilization of AAMs in construction.

Impact of Ground Granulated Blast Furnace Slag on Calcium Leaching of Low-Heat Portland Cement Paste.

Low-heat Portland cement and ground granulated blast furnace slag are widely used for the preparation of hydraulic concrete. Nevertheless, the effect and mechanism of corrosion on low-heat Portland cement paste mixed with ground granulated blast furnace slag need to be further explored. This paper investigated the impact of ground granulated blast furnace slag on the calcium leaching of low-heat Portland cement paste by evaluating its mass loss, porosity, leaching depth, compressive strength, and Vickers hardness, and comparing it with the leaching performance of ordinary Portland cement paste. Furthermore, the phase composition and morphology of low-heat Portland cement paste containing ground granulated blast furnace slag were analyzed by X-ray diffraction, mercury intrusion porosimetry, and scanning electron microscopy. The results indicate that, after 180 days of soaking in ammonium chloride solution, the mass loss rate, growth rate of porosity, leaching depth, and compressive strength loss rate of low-heat Portland cement paste were 8.0%, 43.6%, 9.1 mm, and 27.7%, respectively, while those of ordinary Portland cement paste were 7.4%, 37.8%, 8.4 mm, and 30.1%, indicating that low-heat Portland cement paste is slightly more damaging than ordinary Portland cement. The addition of ground granulated blast furnace slag could significantly improve the leaching resistance of low-heat Portland cement. For instance, after adding 20% ground granulated blast furnace slag, the above test values were 2.4%, 28.5%, 5.6 mm, and 20.8%, respectively. The reason for this is that ground granulated blast furnace slag has the potential to reduce the porosity of low-heat Portland cement paste, and it can also undergo the secondary hydration reaction with its hydration product Ca(OH)2 to enhance the paste structure. Considering the cost performance, the suitable dosage of low-heat Portland cement paste for satisfactory leaching resistance is about 20%.

Comparison between the Baltic Sea and Irish Sea level of Cs-137 contamination on benthic, demersal and pelagic fish species.

The Irish Sea and the Baltic Sea are nowadays still the two most Cs-137 contaminated Seas worldwide. However, the origins of this contaminations are completely different. While the Baltic Sea was unintentionally contaminated due to global fallout after the accident in the Chernobyl nuclear powerplant in 1986, the Irish sea was intentionally used for low level liquid radioactive waste discharges from the Sellafield nuclear reprocessing facility (called Windscale until 1981) between the 1950s and 1990s. Nowadays, more than 30 years later, it is still possible to detect these contaminations in fish, water and sediments of both seas. Since fish are an important part of the human diet, monitoring Cs-137 levels in fish is essential for assessing the potential radiation exposure to humans. In 2019 and 2020 two surveys were dedicated to study the current levels of radioactive contamination in fish species from both Seas. During both surveys, fish samples were collected and analysed by gamma spectrometry later on. The results show that the average Cs-137 activity in benthic, demersal and pelagic fish species from the Baltic Sea are 2.7, 4.6 and 4.2, respectively, times higher than the corresponding values of the Irish Sea. Based on this and two other comparisons, it is concluded that the Baltic Sea is the most contaminated with Cs-137.

Influence of the chemical composition of leachates on the results of ecotoxicity tests for different slag types.

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.

Low-cost optimization of industrial textile landfill sludge re-dewatering using ferrous sulfate and blast furnace slag.

This study was based on an industrial sludge landfill with a scale of 1 million cubic meters, which had been filled for more than 10 years. It focused on the secondary dewatering of industrial textile landfill sludge (LS) with a total organic carbon (TOC) content greater than 50% and a volatile suspended solids to suspended solids (VSS/SS) ratio of 0.59. A response surface methodology (RSM) model was established using the coagulant ferrous sulfate (FeSO4) and conditioning agents such as hydrated magnesium oxide (MgO), blast furnace slag (BFS), and calcium oxide (CaO). By solving the RSM equations for the respective indicators, the optimal dosages of FeSO4, MgO, and BFS were determined to be 90 mg/g of dry sludge (DS), and for CaO 174.85 mg/g DS. Further examinations of the dewatering performance, apparent properties, extracellular polymeric substances (EPS) components, rheological characteristics, moisture distribution, and pollutant content variation led to the development of a green waste-based dewatering agent composed of FeSO4 and BFS. In small-scale diaphragm plate and frame filter press tests, the optimal water content (WC) was 69.11%. In the final production-scale experiments, it was 65.72%, with the actual application cost being only 13.07 $/ton DS. Additionally, when FeSO4 and BFS were used together, the combined action of Fe and Si could significantly reduce the biotoxicity of heavy metals (HMs), cut down 75.2% of the LS's TOC, and effectively reduced the leaching of organic substances from the leachate, which was beneficial for subsequent disposal. In conclusion, the combined use of FeSO4 and BFS for the secondary dewatering of industrial textile LS was economically efficient, effective in dewatering, and had significant harm reduction effects, making it a worthwhile for waste treatment.

Selection of an alternate cementitious mortar using ceramic tile dust waste: a hybrid MCDM approach.

Selection of a suitable alternative material from a pool of alternatives with many conflicting criteria becomes a Multi-Criteria Decision Making (MCDM) problem. In the present study, ternary blended mortars were prepared using ceramic tile dust waste (CTD), fly ash (FA), and ground granulated blast furnace slag (GGBFS) as binder components. Crusher dust (CD) was used as a fine aggregate component. Binder to aggregate ratios of 1:3 and 1:1 were prepared considering suitable flow. A total of 16 mortar mixes were cast. These mortars were tested for various conflicting criteria compressive strength, flexural strength, porosity, water absorption, bulk density, thermal conductivity, specific heat, thermal diffusivity, and thermal effusivity whose weightages obtained were 29.09%, 20.08%, 12.77%, 10.60%, 8.74%, 6.74%, 5.54%, 4.47%, and 1.97%, respectively, as per AHP analysis. Later, considering these different criteria and alternate mortars, it was observed that a 1:1 mortar with 20% CTD, 30% FA, and 50% GGBFS (RC20F30G50) is found to be the suitable mortar with the highest relative closeness coefficient of 0.861 and the highest net outranking flow of 0.316 with respect to MCDM techniques: technique for order of preference by similarity to ideal solution (TOPSIS) and preference ranking organization method for enrichment of evaluations (PROMETHEE-II), respectively. The ranking of the mortar in both methods complies with the relative weightages of the criteria and the performance of the mortars with respect to the above criteria.

Effect of Solution-to-Binder Ratio and Molarity on Volume Changes in Slag Binder Activated by Sodium Hydroxide at Early Age.

This research investigates the impact of solution concentration and solution-to-binder ratio (S/B) on the volume changes in alkali-activated slags with sodium hydroxide at 20 °C. Autogenous and thermal strains are monitored with a customized testing device in which thermal variations are controlled. Consequently, both the autogenous strain and coefficient of thermal expansion (CTE) are determined. Heat flow and internal relative humidity (IRH) are also monitored in parallel, making this research a multifaceted study. The magnitudes of autogenous strain and CTE are higher than those of ordinary Portland cement paste. Decreasing the solution concentration or S/B generally decreases the autogenous strain (swelling and shrinkage) and the CTE. The shrinkage amounted to 87 to 1981 µm/m, while the swelling reached between 27 and 295 µm/m and was only present in half of the compositions. The amplitude of the CTE, which increases up to 55 µm/m/°C for some compositions while the CTE of OPC remains between 20 and 25 µm/m/°C, can be explained by the high CTE of the solution in comparison with water. The IRH of paste cannot explain the autogenous strain's development alone. Increasing S/B eliminates the self-desiccation-related decrease.

Design and properties of ternary alkali-activated binder based on blast furnace slag, recycled powder and waste glass powder.

Ternary alkali-activated binder was prepared by blast furnace slag (GGBS), recycled powder (RP) and waste glass powder (WGP) using simplex centroid design method. By measuring the fluidity, setting time, drying shrinkage and mechanical property of specimen, the complementary effect of GGBS, RP and WGP was discussed. The reaction mechanism and microstructure were explored by X-ray diffraction and scanning electron microscopy. The results reveal that the addition of RP could significantly reduce the fluidity and setting time of paste, while WGP can obviously improve the rheological property and play a retarding role. The workability of paste can be effectively regulated by mixing RP and WGP together. Whether added alone or in combination, RP and WGP can effectively improve the shrinkage performance. In the ternary system, GGBS can be rapidly activated and form a skeleton structure. The fine RP particles can play a good role in filling the structure, and the pozzolanic reaction of WGP gradually occurs, which makes the microstructure more compact. The incorporation of GGBS, RP and WGP can promote the growth of hydration products, improve the density of microstructure, and form a certain complementary effect.

Synergistic Leaching of Titanium, Aluminum, and Magnesium Components during Dilute Acid Pressure Treatment of High-Titanium Blast Furnace Slag.

This study focuses on an improved leaching process through the combination of pressurized conditions and direct filtration of acid leaching slurry, which is conductive to improving the filterability of acid leaching systems and the extraction rates of Ti, Al, and Mg components. The effects of sulfuric acid concentration, reaction temperature, particle size of materials, acid-slag ratio, and reaction time on the leaching efficiency were systematically investigated. The results showed that pressurization significantly enhances the filtration efficiency of the reaction slurry. Under the same filtration time, the filtration efficiency increased from 46% under ordinary pressure to 78% under pressurized conditions. Moreover, under the optimal reaction conditions, the extraction rates of Ti, Al, and Mg components were more than 88.21%, 97.8%, and 96.31%, respectively. Additionally, XRD and FTIR showed that titanium oxide sulfate hydrate crystals were produced in the acid-leached residues when the reaction temperature exceeded 190 °C, thereby reducing the extraction rate of Ti component. And the XRD pattern shows that when the reaction temperature is maintained at 190 °C and the reaction time is extended to 150 min, titanium oxide sulfate hydrate crystals will be formed to reduce the extraction rate of the Ti component. In summary, this study not only provides important theoretical support for the resource utilization of high-titanium blast furnace slag but also offers a feasible solution for efficient extraction and convenient filtration, thus holding significant academic and practical implications.

Sub-Aperture Synthetic Aperture Radar Imaging of Fixed-Platform Beam-Steering Radar for Blast Furnace Burden Surface Detection.

Due to the scheme of fixed-platform beam-steering radar and the space of the blast furnace being subjected to harsh environmental influences, the traditional detection methods of burden surface are limited by geometric distortion, noncoherent clutter, and noise interference, which leads to an increase in the image entropy value and the equivalent number of views, makes the density distribution of burden surface show a diffuse state, and greatly affects the stability and accuracy. In this paper, a new fixed-platform beam-steering radar synthetic aperture radar imaging method (FPBS-SAR) is proposed in the sensory domain of the blast furnace environment. From the perspective of fixed-platform beam-steering radar motion characteristics, the target range-azimuth coupled distance history model under the sub-aperture is established, the azimuthal Doppler variation characteristics of the fixed-platform beam-steering process are analyzed, and the compensation function of the transform domain for geometric disturbance correction is proposed. For noncoherent noise suppression in blast furnaces, the trimmed geometric mean-order-likelihood CFAR method is proposed to take into account the information of burden surface and clutter suppression. To verify the method, point target simulation and imaging for the industrial field measurement data are carried out. The results indicate that geometric distortion is well eliminated, the image entropy value and the equivalent number of views have decreased, and noncoherent noise in blast furnaces is suppressed.

Link between the Reactivity of Slag and the Strength Development of Calcium Aluminate Cement.

The problem of loss of strength caused by the conversion reaction with calcium aluminate cements (CAC) is well known. It has been shown that the addition of ground granulated blast furnace slag (GGBS) to CAC inhibits the conversion process. Different slags can have a different chemical and mineralogical composition depending on their origin and production process, which can significantly influence their reactivity. This work investigated the extent to which the R3 test, developed for Portland cement and based on isothermal calorimetry and/or bound water, was used to predict the reactivity of ground granulated blast furnace slag in a CAC. Mortars and cement pastes with a 30% replacement of slag were tested to evaluate their compressive strength and microstructure. The results show that slags with higher reactivity due to their hydraulic properties lead to a lower compressive strength loss within the first 6 h, a higher strength loss after 24 h due to stratlingite formation and a lower strength loss after 28 days due to pozzolanic reaction and stratlingite formation. The results also confirm that the R3 test was used as a rapid method to predict the effects of slag on the compressive strength of CAC.

Properties of Cemented Filling Materials Prepared from Phosphogypsum-Steel Slag-Blast-Furnace Slag and Its Environmental Effect.

Phosphogypsum (PG) occupies a large amount of land due to its large annual production and low utilization rate, and at the same time causes serious environmental problems due to toxic impurities. PG is used for mine backfill, and industrial solid waste is a curing agent for PG, which can save the filling cost and reduce environmental pollution. In this paper, PG was used as a raw material, combined with steel slag (SS) and ground granulated blast-furnace slag (GGBS) under the action of an alkali-activated agent (NaOH) to prepare all-solid waste phosphogypsum-based backfill material (PBM). The effect of the GGBS to SS ratio on the compressive strength and toxic leaching of PBM was investigated. The chemical composition of the raw materials was obtained by XRF analysis, and the mineral composition and morphology of PBM and its stabilization/curing mechanism against heavy metals were analyzed using XRD and SEM-EDS. The results showed that the best performance of PBM was achieved when the contents of PG, GGBS, and SS were 80%, 13%, and 7%, the liquid-to-solid ratio was 0.4, and the mass concentration of NaOH was 4%, with a strength of 2.8 MPa at 28 days. The leaching concentration of fluorine at 7 days met the standard of groundwater class IV (2 mg/L), and the leaching concentration of phosphorus was detected to be less than 0.001 mg/L, and the leaching concentration of heavy metals met the environmental standard at 14 d. The hydration concentration in PBM met the environmental standard. The hydration products in PBM are mainly ettringite and C-(A)-S-H gel, which can effectively stabilize the heavy metals in PG through chemical precipitation, physical adsorption, and encapsulation.