A new original copper nanocomposite based on poly-N-vinylimidazole was synthesized and characterized by a complex of modern physicochemical and biological methods. The low cytotoxicity of the copper nanocomposite in relation to the cultured hepatocyte cells was found. The possibility to involve the copper from the nanocomposite in the functioning of the copper-dependent enzyme systems was evaluated during the incubation of the hepatocyte culture with this nanocomposite introduced to the nutrient medium. The synthesized new water-soluble copper-containing nanocomposite is promising for biotechnological and biomedical research as a new non-toxic hydrophilic preparation that is allowed to regulate the work of key enzymes involved in energy metabolism and antioxidant protection as well as potentially serving as an additional source of copper. It is known that an adult consumes an average of 0.6 to 2 mg of copper per day with a total absorption of the element in the intestine at 20–50% (mostly in Cu2+ state), and the safe daily intake of this microelement for an adult is 10–12 mg [2+ and Cu+ state. The excess of the trace element is transported back to the liver. Normally, the liver of an adult contains from 18 to 55 µg of copper per gram of dry weight, and, along with the brain and kidneys, is regarded as the organs containing the greatest amount of this element [Copper is one of the main trace elements necessary for the normal development of mammals. In natural systems, it can exist in both an oxidized Cu+ or redu10–12 mg ,4. The d element ,4,5. In Due to the ability to exist in different redox states, copper ions can act as catalytic cofactors for various enzymes involved in such fundamental processes as oxidative phosphorylation, antioxidant protection, the formation of connective tissue, blood coagulation, iron transport, synthesis of neurotransmitters, and others . In partDespite the importance of copper for the cell energy metabolism and antioxidant protection, excess amounts of metal ions are extremely toxic since they can serve as a source of reactive oxygen and nitrogen species , the generation of which leads to the development of oxidative stress accompanied by membrane lipid peroxidation, damage to proteins and nucleic acids, and finally results in cell death by apoptotic or necrotic pathways ,10. In tIt is known from medical practice that pathologies resulting from the accumulation in the body of excess copper amounts transcending the buffer capacity of cells are usually associated with disorders in liver functioning. This organ is considered to play the role of a Cu depot in the organism and, accordingly, carry the main toxic load when an unregulated increase in this element level occurs in the body ,14,15,16The dual significance of copper for human health induces the search for new low-toxic copper-containing compounds suitable for use in various fields of medicine and biotechnology. In this regard, the particular attention of researchers is attracted by such a rapidly developing area as the chemistry of nanocomposites containing copper in the form of nanosized particles. The application fields of such nanocomposites having a wide range of unique properties are quite diverse and include effective biomedical materials, inexpensive catalytic systems, optical nanosensors, and ecological biosorbents developing. Nevertheless, the usage of new copper-containing nanocomposites as an alternative to organic copper compounds in pharmacology and medicine is most promising . Thus, iAt the same time, the toxicity of CuNPs against normal cells and vital human organs can cause undesired adverse effects. The data on the cytotoxicity of CuNPs differ to a significant extent and, apparently, depend on both the biological object under study and the nature of the analyzed nanocomposites. For example, for different cell lines, it was noted that IC50 ranged from 54.34 µg/mL  to 1000 Another important aspect that affects both the properties of CuNPs and the characteristics of the nanocomposite in whole is the choice of the matrix. During the formation of CuNPs, problems caused by the copper activity associated with aggregation and oxidation arise. A topical area of research is the targeted synthesis of nanoparticles of a certain size with a narrowly dispersed distribution and high stability of chemical and biological properties for a long time. Natural and synthetic polymers are promising for this purpose. An important role of polymers in the formation of metal nanoparticles lies in their ability to screen the resulting nanoparticles in the nanoscale state, prevent their aggregation, and ensure long-term stability of their properties. The effective uses of polymers as matrices stabilizing copper and copper oxide nanoparticles such as cellulose ,36,37,38In this work, we report on the synthesis of water-soluble PVI and its successful use in the formation of CuNPs. All the necessary modern research methods were used to study the structure and physicochemical properties of the polymer and the nanocomposite based on it. Particular attention is paid to the discussion of the nanocomposite biological activity as well as the research of its safety and the degree of toxicity. Using a primary culture of hepatocytes, the effect of a nanocomposite with CuNPs was compared with the one of organic salt of this metal regarding the CcO and glutathione synthetase activity in cells, as well as to the activity in the medium of enzymes reflecting destructive processes and used as markers of cytolysis.3COO)2∙H2O) and ascorbic acid (C6H8O6) from Sigma-Aldrich  were applied as a metallic precursor of CuNPs and the reducing agent, respectively, without further purification. Deionized water (H2O) was used to prepare solutions. Ethanol (C2H5OH) and acetone ((CH3)2CO) were distilled and purified according to the known procedures. Argon with a purity of 99.999 was utilized in all reactions.N-vinylimidazole from Sigma-Aldrich  was used as monomer for the synthesis of polymers. α,α′-Azobisisobutyronitrile (AIBN) from Merck KGaA  was utilized as a radical polymerization initiator. Copper acetate monohydrate , collagenase, Hanks’ Balanced Salt (HBSS) were obtained from Sigma-Aldrich Co., . Williams’ Medium E, Dexamethasone and Cell Maintenance Coctail-B were acquired from Gibco . Anti-OxPhos Complex IV subunit I monoclonal antibody (Cat. ND 0589), Alexa fluor 568 goat anti-mouse IgG (H + L) (Cat. NA-11031), Alexa fluor 488 goat anti-rabbit IgG (H + L) (Cat. NA-11034), Hoechst (Cat. NH-3570) were purchased from Invitrogen , Anti-Glutathione Synthetase antibody (Cat. ab133592) were acquired from Abcam . Cell filter and 24-well plates were obtained from Corning . We used heparin , Telazol , Chloroform , set of reagents for determining the activity of ALT (Cat. B-8079) and AST-UV-Novo liquid form (Cat. B-8081) , Alkaline phosphatase Kit, IFCC Modified Method .2O5 at 50 °C until constant weight. The polymer was then dissolved in water, purified by dialysis for 48 h through a 5 kDa cellulose membrane  and freeze dried. As a result, the PVI polymer was obtained with a yield of 97% in the form of a white powder readily soluble in water, DMSO, DMF and DMAA.Poly-N-vinylimidazole (PVI) was synthesized by the method of free radical polymerization of N-vinylimidazole (VI) using AIBN as an initiator. The reaction was carried out in an ethanol solution and argon atmosphere at a temperature of 70 °C. VI  and AIBN  were dissolved in 2 mL of ethanol and placed in a glass ampoule. The ampoule with the reaction mixture was filled with argon, sealed and kept in a thermostat at 70 °C for 24 h. The product formed at the end of the polymerization in the form of a transparent glassy block was dissolved in ethanol and precipitated with acetone. The polymer was filtered off and dried in vacuum over P2) under the action of an ascorbic acid agent in an aqueous solution of PVI polymer and argon atmosphere. PVI  and CuAc2  were dissolved in 20 mL of water and stirred vigorously for 40 min at room temperature. Then the mixture was heated to 80 °C and an aqueous solution containing 0.37 g, 2.1 mmol of ascorbic acid was added dropwise over 5 min, and the reaction mixture was stirred continuously for 2 h at 80 °C. The resulting suspension was precipitated with acetone and filtered to isolate the nanocomposite. The nanocomposite was then purified by dialysis against water through a cellulose membrane  and freeze dried. As a result, a nanocomposite with CuNPs in a PVI matrix was obtained in the form of a dark brown powder readily soluble in water, DMSO, DMF, and DMAA. The copper content in the nanocomposite is 1.0%.The synthesis of CuNPs nanocomposite (NC(Cu-PVI)) was carried out by the method of chemical reduction of copper ions from copper acetate monohydrate  in the range of 300–900 nm. The molecular weight of the polymer was determined using Shimadzu LC-20 Prominence system  fitted with a differential refractive index detector Shimadzu RID-20A and column Agilent PolyPore 7.5 mm × 300 mm (PL1113-6500) . A solution of N,N-dimethylformamide was used as eluent at a flow rate of 1 mL/min. Samples were dissolved at 50 °C for 24 h with stirring. Calibration was performed using a series of Polystyrene High EasiVials polystyrene standards (PL2010-0201) consisting of 12 samples with molecular weights ranging from 162 to 6,570,000 g/mol. The copper content in the synthesized nanocomposite was determined on a Shimadzu AA-6200 instrument . The morphology of the nanocomposite and the sizes of CuNPs were determined using a Leo 906E transmission electron microscope . The zeta potential and hydrodynamic radius of nanoparticles were determined using a ZetaPALS-Zeta Potential Analyser . The measurements were carried out in thermostated cuvettes at a temperature of 25 °C and a scattered light registration angle of 90 °C. Thermooxidative destruction of the polymer and nanocomposite was studied by thermogravimetric analysis and differential scanning calorimetry using an STA 449 Jupiter derivatograph . The measurements were carried out in the temperature range of 25–700 °C at a heating rate of 10 °C/min in air. The samples weight was 5 mg.The structure and properties of the synthesized PVI polymer and a CuNPs nanocomposite were studied using all the necessary modern methods: FTIR, UV, and NMR spectroscopy, gel permeation chromatography, elemental and atomic absorption analysis, electron microscopy, dynamic light scattering, and thermogravimetry. FTIR spectra were recorded on a Vertex 70 spectrometer  in the range of 550–4000 cmAn acute experiment was carried out to isolate the primary culture of hepatocytes of Wistar rats weighing 200 g. The animal experiment was carried out in accordance with the rules of humane treatment of animals. The study was approved by the Ethics Committee of the Irkutsk Scientific Center of Surgery and Traumatology. All surgical manipulations were performed under aseptic conditions. Anesthesia 0.7 mL of a 5% solution of telazol in phosphate-buffered saline (PBS) intramuscularly and chloroform inhalation were used until the loss of locomotor activity but with maintenance of the cardiac muscle contractive activity.g for 5 min at T = 4 °C. Cells were resuspended in William’s E nutrient medium with 10% FBS and Primary Hepatocyte Maintenance Supplements composed of Dexamethasone and Cocktail solution containing GlutaMAX™, HEPES, penicillin-streptomycin, insulin, transferrin, selenium complex, BSA and linoleic acid added to the medium according to the manufacturer’s instructions. The hepatocyte culture was incubated in the 24-well plates at 37 °C, 90% humidity, and 5% CO2 in Biostation CT .The primary culture of hepatocytes was obtained by perfusion through the portal vein of a solution containing 500 units of heparin in 1 mL of 0.9% NaCl and then a solution of Krebs–Ringer buffer with EDTA without calcium  . After 6 and 24 h, the nutrient medium was taken to determine the alanine transaminase (ALT), aspartate transaminase (AST), and alkaline phosphatase (ALP) activity.Two hours after hepatocyte isolation, the nutrient medium was replaced and a solution of NC(Cu-PVI) or of CuAcBiochemical studies of the culture medium after hepatocyte incubation with the test substances were carried out on a Mindray BS-380 biochemical analyzer . The activity of ALT, AST was investigated by the kinetic method using the set of reagents for determining the activity of ALT- and AST-UV-Novo liquid form. Alkaline phosphatase was investigated using the Alkaline phosphatase Kit, IFCC Modified Method.Cells for immunofluorescence studies were fixed with 70% ethanol for 2 h and stained with antibodies to CcO  and Anti-Glutathione Synthetase antibody (GS) in a dilution of 1:200. Alexa fluor 568 goat anti-mouse IgG (H + L) or Alexa fluor 488 goat anti-rabbit IgG (H + L) in a dilution of 1:300 was used as secondary antibody. Nuclei were stained with Hoechst, 1:300 ,56. The Statistical analysis was carried out in the programming environment R. Single-factor analysis of variance was performed using Kruskal–Wallis test. Post hoc analysis was carried out with applying the Tukey test. Mann–Whitney–Wilcoxon test was used for pairwise comparison.Polymerization of VI in the presence of the AIBN initiator in an ethanol solution and argon atmosphere proceeds according to the free radical mechanism .The resulting polymer is a white powder readily soluble in water, DMSO, DMF, and DMAA. For further study of the polymer, a fraction with Mn, Mw and Mw/Mn being 15.635, 20.623 kDa and 1.32, respectively, was isolated by fractional precipitation from an ethanol solution using acetone and hexane as precipitants.−1; CH groups of the azole ring: 1110 and 1089 cm−1; and bending vibrations of the heterocycle: 916, 822 cm−1 , 2.95–3.14 ppm. , 6.65–6.69 ppm. . PVI is characterized by high resistance to thermal oxidative degradation since the thermal decomposition of the polymer begins above 380 °C.The FTIR spectra of the polymer contains absorption bands of stretching vibrations of the imidazole fragment: 2933 (C–H), 1501, 1600 (C=N), 1417 (C–N), 1285 (C–H) cm822 cm−1 . The ban2 and is accompanied by an increase in the viscosity of the solution and the formation of a yellow suspension. With the subsequent portion-wise addition of ascorbic acid to the reaction mixture, copper ions were gradually reduced to zero valence, and the mixture became dark brown. The resulting CuNPs were stabilized in the nanoscale state and retained a uniform distribution over the volume. Ascorbic acid has a significant advantage over sodium borohydride and hydrazine, which are widely used for copper reduction since it is an environmentally friendly and natural antioxidant. The reaction was carried out in an argon atmosphere to prevent possible oxidation of the resulting nanoparticles. The obtained nanocomposites with CuNPs were isolated and purified by dialysis for 48 h followed by freeze drying.The synthesized PVI is of great importance in the formation of a CuNPs nanocomposite. Active functional imidazole groups in the polymer structure participate in coordination interaction with copper ions ensuring their uniform distribution in the polymer matrix. This occurs at the first stage of the process with stirring of aqueous solutions of PVI and CuAc−1) of the absorption band of the C=N bond of the imidazole fragment at 1501 cm−1 is observed. This change confirms the coordination interaction of copper with the pyridine nitrogen atom , which is 1.46 times smaller than that of PVI  . This isAccording to the data of thermogravimetric analysis, the CuNPs nanocomposite shows lower stability to thermal oxidative degradation in comparison with PVI. The onset of thermal decomposition of the nanocomposite is 360 °C, which is 20 °C lower than the thermal stability of PVI. This is probably due to the catalytic properties of metal nanoparticles, which are manifested in a decrease in the activation energy of thermal destruction and oxidation of the polymer matrix.The obtained nanocomposites are characterized by high stability of the nanoscale state of nanoparticles, which is ensured by the high stabilizing ability of PVI. Even with long-term storage of aqueous solutions of the nanocomposite (more than 3 months), the nanoparticles did not agglomerate, and all the chemical and thermal properties were retained.In this study, the choice of a cell culture to estimate the cytotoxicity of a copper-containing nanocomposite was dictated by several reasons. First, hepatocyte cultures are widely used in the screening of pharmaceuticals including for ADME/Tox testing . This is attributed to the ability of liver cells to metabolize endogenous and xenobiotic compounds through the formation of water-soluble components ,64. Conv2, after 6 h of incubation, the formation of cell conglomerates was visualized (We found that after incubation for 6 h with NC(Cu-PVI), the cultured cells looked intact, and no visible changes in their morphology were found C. Howevesualized E, and thsualized F. Similasualized A,B. Howesualized D. The daThe study of the ALT and AST activity has recently been used, not only in clinical practice to diagnose diseases associated with impaired liver function, but also to research the toxicity of various drugs to 2D and 3D hepatocyte cultures ,66,67,682 did not significantly differ from the enzyme activity in the control specimens , the ALT activity in the samples exposed to the NC(Cu-PVI) and CuAcpecimens A,B. Nevepecimens C, and alt higher A–C.2, while incubation with the NC(Cu-PVI) did not lead to a significant increase in enzyme activity  or CuAcIn many studies carried out on hepatocyte cultures, an increase in the activity of both aminotransferases in the medium was observed under the influence of various compounds ,66. Howe2 for 24 h in our study may be associated with the effect of the metal ions on the hepatocyte mitochondria, which results in structural and functional disorders of organelles as well as the development of destructive processes leading to cell death. In the work carried out on a 3D culture of hepatocytes, it was also shown that the release of AST into the culture medium is especially high when cells are exposed to preparations, the toxic effect of which is related with mitochondrial dysfunction [2.Moreover, it is considered that minor damage to hepatocytes leads to the predominant release of enzymes of the cytoplasmic fraction, while severe necrotic lesions are accompanied by the exit of cytosolic and mitochondrial enzymes into the extracellular space . In thisfunction . At the function ,74. In afunction  may expl2.Despite the fact that ALP is not an enzyme localized exclusively in the liver, the determination of its activity is widely used in clinical diagnostics to make or confirm diagnoses associated with pathological processes leading to the degradation of hepatocytes. Based on this, in our study, the determination of this enzyme activity in the culture medium was used as one of the criteria indicating cell damage under the action of a NC(Cu-PVI) and CuAc2 to the culture medium  had an inhibitory effect. Although copper atoms fixed in the structure of the nanocomposite are not only able to interact with ALP affecting enzyme activity, they also exceed free copper ions in the intensity and duration of ALP inactivation. This may indicate that the synthesized matrix does not prevent the interaction of the metal ions inserted in its structure with enzymes nor does it reduce their bioavailability.In this study, the decrease in the activity of ALP in the medium may be associated not with the reduce in the destruction rate in the culture of hepatocytes but with the direct interaction of copper atoms with the analyzed enzyme leading to the suppression of its activity. For example, it was previously shown that copper can displace zinc atoms playing the role of a cofactors in the ALP catalytic centers. This leads to the loss of its functionality and a decrease in the activity recorded by standard methods . Substit2, cells were stained by the immunofluorescence method using antibodies to subunit I of mitochondrial cytochrome c oxidase (CcO).In this study, to assess the effect of the NC(Cu-PVI) on the oxidative phosphorylation intensity of cultivated hepatocytes in comparison with CuAc2 and the NC(Cu-PVI), a significant increase in the amount of the visualized enzyme in hepatocytes was observed  being the glutathione synthesis second enzyme responsible for the addition of glycine to γ-glutamylcysteine .2 becomes significantly higher than in the case of introducing a nanocomposite into the medium  interacting with metal-responsive elements (MRE) in gene promoters . OtherwiNew water-soluble stable nanocomposites with CuNPs were synthesized based on poly-N-vinylimidazole. The high efficiency of the polymer was found to stabilize CuNPs in a nanosized narrowly dispersed state and ensures the stability of the chemical and thermal properties of the nanocomposite for a long time.Our investigation showed that the obtained nanocomposite exhibits low toxicity toward cultured rat hepatocytes. It was demonstrated both by cell morphology assay and the ALT and AST activity analysis in culture media. In particular, this nanocomposite was found to be of low toxicity for hepatocyte mitochondria, considering the main intracellular target for the toxic effect of copper ions in excessive amounts. At the same time, it was shown that the chosen matrix does not prevent copper included in the nanocomposite structure to interact with various enzymes, modulating their activity. In this work, it was found that the action of the nanocomposite on cells leads to an increase in the amount of CcO, one of the key enzymes of oxidative phosphorylation. In addition, glutathione synthetase, the second enzyme for the synthesis of glutathione, is involved in chelating the predominant amount of incoming copper in mammalian cells. The opposite effect was observed when analyzing the activity of alkaline phosphatase. In this study, the described effects can be caused by the direct interaction of the nanocomposite with the enzyme, which leads to an increase in the activity of copper-containing CcO or to a more intense and prolonged decrease in the ALP activity associated with the replacement of zinc ions by copper ions in the enzyme active center. At the same time, the effect of the nanocomposite can be explained by its participation in the regulation of the CcO or GS gene expression or, in the case of the latter, by other mechanisms triggered by depleting the glutathione pool. Thus, the synthesized water-soluble copper-containing nanocomposite is promising for biotechnological and biomedical research as a new non-toxic hydrophilic preparation, allowing to regulate the work of key enzymes involved in energy metabolism and antioxidant protection, and it may serve as an additional source of copper.


The results concern the test carried out on the pneumatic actuator operational test stand, which is the actual pneumatic system with electromagnetic control. The cylinders of actuators are made of Ø 40 mm aluminum tube of EN-AW-6063 aluminum alloy which is used in the manufacture of commercial air cylinder actuators. The inner surfaces of the cylinder surfaces were covered with an Al2O3/WS2 oxide layer obtained by anodic oxidation in a three-component electrolyte and in the same electrolyte with the addition of tungsten disulfide 2H-WS2. The layers of Al2O3 and Al2O3/WS2 obtained on the inner surface of the pneumatic actuators were combined with a piston ring made of polytetrafluoroethylene with carbon (T5W) material and piston seals made of polyurethane (PU). The cooperation occurred in the conditions of technically dry friction. After the test was carried out, the scanning electron microscopy with energy dispersive spectroscopy (SEM/EDS) analysis of the surface of the cylinder bearing surfaces and piston seals of the pneumatic cylinders was performed. The analysis revealed the formation of a sliding film on the cylinder surface modified with tungsten disulfide, as well as on the surface of wiper seals. Based on the SEM/EDSM tests, it was also found that the modification of the Al2O3 layer with tungsten disulfide contributed to the formation of a sliding film with the presence of WS2 lubricant, which translated into smooth cylinder operation during 180 h of actuator operation. The cylinder with the unmodified layer showed irregular operation after approximately 70 h thereof.The article presents the results of an aluminum oxide layer doped with monolayer 2H tungsten disulphide (Al In. In−3 m 2O3 layer and C2—cylinder with the Al2O3/WS2 layer.For the sake of clarity, the article uses the following nomenclature: C1– cylinder with the AlThe test stand consisted of two actuators, the cylinders of which were the test material described above, prepared by electro-oxidation. The laboratory stand for operational testing of pneumatic actuators  is an acA Gentilin Compact-air 280 lubricant-free compressor  was used to generate the compressed air. During the tests, the actuators were fed with compressed air at a pressure of 0.5 MPa. The pressure measurements in the actuator chambers were made using Aplisens AS pressure transducers . In order to measure the temperature in the area of the friction zone, blind holes were made in the actuator cylinders, drilled to a depth equal to the thickness of the cylinder wall. The holes were halfway along the length of the cylinders. K-type thermocouples  were used to measure the temperature. They were placed permanently in the prepared holes. One of the thermocouples for measuring the ambient temperature was placed near the actuators. Both the pressure in the actuator chambers and the temperature were measured using an analogue-to-digital Spider8 transducer. During the measurement of the pressure in the actuator chambers, sampling at 200 Hz was used, and when measuring the temperature, sampling at 1 Hz was used. The acquisition of measurement data was carried out using the Catman 4.5 program. The operational tests were performed during 180 h. The initial speed of both actuators was approximately 0.4 km/h. All seals slidingly cooperating with oxide layers, both before and after the test, were weighed on a WPA 60 scale. After completion of the bench tests, the actuators were disassembled, the cylinders were cut and subjected to further tests. The study of the structure and morphology of the surface of the layers was carried out with the Hitachi S-4700 scanning electron microscope with the EDS Noran Vantage system at a magnification of 35-25000x. For proper observation, the oxide layers were sputtered with carbon using a turbomolecular carbon sputtering machine. The carbon layer enables the bouncing electrons to be discharged and carried away during the research. Surface geometrical structure (SGP) tests were carried out in order to determine the roughness parameters and the geometrical structure of the surface before and after the operational test. Measurements were made by systematic scanning using a Form TalySurf Series 2 50i contact profilographometer. Basic stereometric parameters from the amplitude group and the Abbott–Firestone curve were determined.2 was noticed. The speed of the piston rod of this actuator decreased with the test time, which was due to the increasing friction in this actuator. 2 addition to the layer structure resulted in an increase in the working time of the piston by approx. 27%.In the first hours of testing, both actuators powered by air with the same pressure operated evenly. After approximately 80 h of the test, a reduction in the speed of the actuator piston rod with the cylinder surface without modification of WS2O3 layer, which the greater resistance to movement than in the case of cylinder C1, generating a higher temperature. The reduction of the temperature difference between the cylinders C1 and C2, in the further part of the tests  and surface slope (kurtosis), respectively, and are sensitive to large individual extremes. Negative values of the skewness coefficient Ssk = −0.5 and Ssk = −0.15 were obtained for the smooth surfaces of C1 and C2 cylinders, respectively, before tribological cooperation. After tribological cooperation, this parameter changed and was, respectively, for C1: Ssk = −0.78 and for C2: Ssk = 1.02. The negative skewness of the examined layers indicates the surface of the layers of a plateau character, which is well visible in the isometric Sku = 4.38 µm and Sku = 2.8 µm for C1 and C2 before the test and Sku = 7.16 µm and Sku = 6.12 µm for C1 and C2 after the tribological test. The increase in the Sku parameter measured for the surface after the tribological test proves that the tribological cooperation of both the C1 and C2 cylinder smooth surfaces resulted in an increase in the occurrence of high and sharp peaks, which is particularly visible in The amplitude parameters of the tested surfaces are summarized in Sp and Sv or Sp and Sz gives information about the shape of the profile and allows to conclude on the abrasion resistance of the tested surface. Prior to the test, the C1 cylinder smoothing was characterized by a void coefficient Sp/Sz << 0.5  and skewness (Ssk) parameter, a slightly higher void filling parameter (Sv/Sz) and a higher parameter of the average absolute values of the heights of the five highest peaks and five lowest pits within the sampling area (Sz), compared with the bore surface of the C1 cylinder. The properties of the surface of the C2 cylinder bearing surface observed in the isometric image  and can be a measure of the effective roughness depth after the initial run-in period. The Spk parameter determines the resistance of the surface to abrasion, and its low values prove its high resistance. According to the obtained result, the C1 cylinder showed higher abrasion resistance after the test. This is most likely due to the fact that a sliding film had formed on the surface of the cylinder C2, which made the piston seals slide better during operation of the cylinders. Simultaneously the abrasion resistance thereof was lower. The Svk parameter, in turn, is a measure of the lubricant retention capacity of the sliding surfaces. This parameter was higher after friction for the C1 cylinder bearing surface. We explain this behavior as follows: the low value of the Svk parameter for the C1 cylinder after oxidation is related to the plato-type surface, on which, as a result of cooperation with the wiper seal, deeper grooves were formed, which, however, were not filled with a sliding film, as in the case of the modified layer WS2 on the cylinder C2 surface.2O3 layers with tungsten disulfide 2H-WS2 in order to increase the service life of pneumatic cylinders with oxide finish, supplied with air not lubricated with oil mist. Modification of the Al2O3 layer with tungsten disulfide contributed to the formation of a sliding film on the C2 cylinder surface and wiper seals cooperating with it, which translated into uniform piston operation during 180 h of cylinder operation. The cylinder with the unmodified layer showed irregular operation after about 70 h. Increased resistance to piston movement caused by the lack of lubrication in the C1 cylinder, contributed to excessive wear of the wiper seals and the piston guide ring as a result of tribological cooperation. The greater resistance to motion was also the reason for the higher temperature in the friction zone of this actuator. The better sliding properties of the C2 cylinder smoothing surface result from the presence of the 2H-WS2 tungsten disulfide dispersion on the surface of the layer produced by anodizing aluminum alloy in an electrolyte with the addition of this solid lubricant. The presence of WS2 on the surface of the oxide layer facilitates the overlapping of the sliding film on the cooperating elements and allows the nature of the operation of the sliding pair to be changed. Despite the higher values of the surface roughness parameters shown for the C2 cylinder bearing surface, the geometric structure of the surface of the WS2 modified layer remains favorable for tribological applications in oil-free kinematic systems.The research results and their analysis presented in the article confirm the sense of modifying the Al


To accelerate the resource utilization of coal gangue and meet the strategic requirements of carbon neutralization, alkali-activated, slag-cemented coal gangue is applied in the preparation of solid waste-based road stabilization materials. Here, the cementation characteristics and microstructure characteristics of alkali-activated, slag-cemented coal gangue road stabilization materials are studied using the alkali equivalent and coal gangue aggregate ratio as experimental variables. The results show that with the increase in alkali equivalent from 1% to 7%, the unconfined compressive strength of the alkali-activated coal gangue road stabilization material initially increases and then decreases, with 3% being the optimal group in terms of stabilization, the aggregate ratio of coal gangue increases from 70% to 85%, and the 7-day unconfined compressive strength of the stabilized material decreases approximately linearly from 8.16 to 1.68 MPa. At the same time, the porosity gradually increases but still meets the requirements of the specification. With the increase in hydration time, a large number of hydration products are formed in the alkali slag cementation system, and they are closely attached to the surface of and interweave with the coal gangue to fill the pores, resulting in the alkali slag slurry and coal gangue being brought closer together. Given its huge output and low degree of resource utilization, coal gangue is the main source of industrial solid waste in China, and it has a significant impact on the ecological environment and on mine safety ,2. At prOne of the main ways to utilize coal gangue is as a road stabilization material, and this has attracted the attention of many scholars. Xuchao et al.  highlighWith the strategic goal of carbon neutrality, the use of alkali-activated slag as cementing material for the production of a solid-waste coal gangue road stabilization layer is proposed in this paper, which could make full use of its energy savings, environmental protection, fast hardening, early strength, excellent corrosion resistance, fire resistance, and durability ,32,33. BThe chemical composition of coal gangue from Zhangji Mine in Huainan is shown in Coal gangue samples were screened according to the corresponding steps in the JTG3430 regulation [2O, wt.%) on the mechanical properties and microstructure of the specimens, the specimens with an aggregate rate of 80% and an alkali equivalent rate of 3% were taken as the reference group. The serial numbers of groups with other aggregate rates and alkali equivalents are G70N5, G75N5, G80N5, G85N5, G80N1, G80N3, and G80N7, as shown in In order to clarify the effects of aggregate rate and alkali equivalent  using a FlexSEM1000  with an acceleration voltage of 15 kV.n is the porosity; Q1 is the dry weight; Q2 is the hanging weight; Q3 is the saturated weight; ρ1 is the true density; and ρb is the apparent density.The porosity, true density, and apparent density of the test blocks were tested according to ASTM C20 . The thrThe stress–strain curves of whole-solid-waste coal gangue road stabilization materials of different ages are shown in The compressive strength of the specimens, as assessed at days 7 and 28, first increases and then decreases with the increase in the alkali equivalent. The strength of G80N1 is 0, indicating that the gangue cannot be cemented with a low-alkali equivalent, and little gel formation is observed. When the alkali equivalent exceeds 3%, the strength of the specimens begins to decline, indicating that the high alkali equivalent would not be conducive to the improvement in strength, and the best alkali equivalent in terms of strength is 3%.With the analysis of compressive strength, it is determined that the solid-waste coal gangue road stabilization material has superior strength under the conditions of 70% gangue aggregate ratio and 3% alkali equivalent.Porosity and density are two important test indexes to determine the performance of a specimen. Porosity refers to the percentage of the pore volume in the bulk material and the total volume of the material in the natural state, which directly reflects the compactness of the material. The high porosity of a material indicates its small degree of compactness. The results for the porosity and density of the test blocks are shown in It can be noted that the porosity and density values of the specimens are in accordance with the increase in aggregate rate. The unit of the coal gangue mixed with sodium hydroxide decreases with the increase in aggregate rate, leading to lower coal gangue hydration efficiency and a lower quantity of generated gel. Moreover, the larger amount of porosity also decreases the compressive strength. This is consistent with the conclusions from the compressive strength test, as previously discussed.In the case of different alkaline equivalents, the porosity slightly increases with the increase in the alkaline equivalent, and the porosity is minimal when the alkali equivalent is 3%. This indicates that an excessively high alkaline equivalent does not effectively reduce the porosity [In order to analyze the microstructure of whole-solid-waste coal gangue road stabilization materials, typical test blocks of G70N5 at days 7 and 28 were taken as the study samples, as shown in It can be seen that C–(A)–S–H gel and a small amount of ettringite are generated by the reaction between the activator and the slag. However, due to the short hydration time, the interface between the coal gangue and alkali excitation material is relatively loose, and the porosity is large. As the hydration time increases, as shown in As the alkali equivalent increases from 1% to 7%, the unconfined compressive strength of the alkali-activated gangue road stabilization materials at first increases and then decreases, and 3% is the optimal group (4.69 MPa on day 7 and 5.88 MPa on day 28);When the gangue aggregate rate increases from 70% to 85%, the NaOH of the unit gangue mixture decreases with the increase in the gangue aggregate rate, the hydration reaction rate slows down, and the cementite content decreases. Hence, the higher the porosity of the mixture, the lower the compressive strength of the mixture;It is feasible to use alkali-activated slag as a cementing material to prepare a whole-solid-waste coal gangue road stabilization material that can meet standard requirements. This material has the characteristics of fast hardening, early strength, and, compared with the ordinary crushed stone stabilized base, costs can be saved by 39.2%.This paper studies the preparation of solid-waste coal gangue road stabilization materials using alkali-activated slag as the cementing material, and the relationship between different aggregate rates and alkali equivalents, and the mechanical properties and microstructure of the stabilized materials are analyzed. The following conclusions are drawn:The research results of this paper are applicable to new roads and can provide a theoretical reference and technical basis for the large-scale resource utilization of coal gangue.


The metro engineering is in an environment rich in stray current and groundwater, which will accelerate concrete corrosion. In this study, the corrosion of cement-based materials, under stray current, consisting of direct current, was investigated, and the effects of stray current magnitude, water-binder ratio, fly ash, and silica fume on its corrosion were analyzed. The results show that, as the energisation duration of the stray current increases, the mass of the cathode side leachables increases, and the compressive strength of the cement-based materials decreases overall; at 120 d of stray current, the water-binder ratio of 0.50 shows the least reduction in strength, compared to the others; the mass of cathode side leachables decrease significantly with the increase in fly ash content; when fly ash content is 15%, the mass of cathode side leachables is the least, and the decrease in the compressive strength at 120 d of stray current is the smallest. At 10% silica fume content, the mass of the cathode side leachables is the least, and the decrease in the compressive strength of the cement-based materials at 120 d of stray current is the smallest. In general, the corrosion resistance is relatively good at 15% fly ash content and 10% silica fume content under stray current. The metros in Chinese cities such as Beijing, Shanghai, and Guangzhou all use direct current electric traction. At the beginning of the metro’s operation, the insulation between the running rail and track bed is good, so there is less stray current leakage from the running rail to the surrounding medium . HoweverAs the vast majority of the metro is located underground, concrete in metro engineering is inevitably exposed to groundwater. Long-term immersion in water with low hardness will cause a decrease in the concentration of liquid-phase lime in cement-based materials, dissolution of solid-phase lime, and decalcification transformation or decomposition of cement hydration products, resulting in increased porosity, reduced strength and durability of the slurry, and corrosion of the cement-based materials . The surIn recent years, the research on stray current has mostly focused on the destruction of steel in concrete exposed to stray current ,6,7,8,9.Additionally, chloride ions, mainly from the concrete material itself and its surroundings, are also a major cause of steel corrosion . Under tHowever, concrete itself is a channel for stray current. The chemical reactions in the pore structure and solid phase part of concrete are inevitably accelerated when stray current passes through, which ultimately affects the microstructure and durability of concrete. The study on the effects of stray current on cement-based materials is, therefore, of guiding significance for metro projects.In this study, from the perspectives of stray current magnitude, water-binder ratio, mineral admixture, etc., the dissolution of calcium ions in cement-based materials and changes in compressive strength are studied, the corrosion law of cement-based materials under stray current is analyzed, and the effects of the simultaneous presence of stray current and corrosion on rail engineering are investigated.Reference cement, produced by China United Cement Corporation, Beijing, China, was used for the test. The specifications are listed in 2/g, water demand ratio of 92.8%, and water content of 0.72%, was used in this paper. The analysis results of its chemical composition by X-ray fluorescence spectrometer  are listed in The Class I fly ash, produced by Dalian Huaneng Power Plant, Dalian, China, with a fineness  of 3%, specific surface area of 30,741.49 cm2/kg. The chemical composition of silica fume is shown in The silica fume used here was produced by ElkemMaterialsLtd. Shanghai, China, with the average particle size of 7.76μm and specific surface area of 16,000 mChina ISO standard sand, produced by ISO Standard Sand Co., Ltd., Xiamen, China, was used here. The sliced paraffin used was a white solid block produced by Sinopharm Chemical Reagent Co., Ltd., Shanghai, China, with a melting point range of 60.0–62.0 °C. Its technical conditions are in accordance with the standard Q/CYDZ 2258–2008.In this paper, the effects of corrosion on specimens were investigated for different stray currents, water-binder ratios, fly ash dosing, and silica fume dosing: (1) the voltages of the stray current were 20, 40, and 60 V, respectively; (2) the water-binder ratios were 0.40, 0.50, and 0.60, respectively; (3) the dosing of fly ash and silica fume was 5%, 10%, and 15% . The specific ratios are listed in The mixtures, mixed according to the ratios, were placed in moulds for one day and then demoulded and placed in a standard curing room for 28 days. Afterward, the specimens were subjected to the stray current and related tests. The specimen size was 40 mm × 40 mm × 40 mm.After curing, the specimens (3 per group) were placed in an acrylic box , and the sides of the adjacent specimens were bonded with neutral glass adhesive. The bottom of the specimens were also coated with glass adhesive to fix them in the center of the bottom of the box, and then paraffin wax was used to cover the neutral glass adhesive and seal any gaps that may exist. The stray current test process is shown in In this test, a stainless steel mesh was used as the electrode, the height of which was slightly higher than the inner height of the acrylic box (40 mm). The voltage of the two electrodes was measured daily with a multimeter. When the voltage was significantly lower than the test voltage, the electrodes needed to be replaced. In particular, the replacement cycle of cathode electrode should not exceed 14 days.+ at the anode, making the anode solution acidic. Damage to cement-based materials by the acidic solution could affect the determination of the corrosion of cement-based materials under stray current. To neutralise the H+, a 5% NaOH solution , with the same mass fraction as the cathode side, of deionized water was placed in the electrolytic cell on the anode side. Both the 5% NaOH solution on the anode side and deionized water on the cathode side were changed every 7 days.In the study on the corrosion of cement-based materials under stray current, the electrolysis of water by stray current normally generated H2+ concentration was measured by inductively coupled plasma atomic emission spectrometry  on a weekly basis. The effects of stray current magnitude, water-binder ratio, fly ash, and silica fume dosing on the corrosion of cement-based materials under stray current were analyzed by the above tests.During the corrosion process, cathode side leachables were analyzed using an X-ray diffractometer , step length: 0.02°, single step residence time: 0.1 s), and the compressive strength of the specimens was tested, according to the standard GB/T17671-1999 by microcomputer controlled pressure testing machine . The cathode side solution was sampled before each change of the solution of the stray current device and Ca3 is the strongest, indicating that the majority of the white leachables are CaCO3. Additionally, the calcium in the specimen dissolves from the cathode side, under the action of the electric field, and the aqueous solution on the cathode side becomes alkaline, under the action of electrolytic water. Ca2+ combines with the OH- in the alkaline solution to form Ca(OH)2 with a relatively low solubility, which crystallized into solid Ca(OH)2 after reaching a certain concentration. The solid Ca(OH)2 tends to form CaCO3 with CO2 in the air; part of the CaCO3 is solidified on the cathode side of the specimen and part is retained in the cathode side solution. Therefore, when stray current is applied, white leachables can be observed on the cathode side of the specimen, and the cathode side solution also becomes cloudy with the white precipitate (CaCO3).When stray current is applied, white leachables on the cathode side of the specimen increase. The XRD analysis see  shows thThe reaction occurs on the cathode side of the stray current device, as shown in Equation (1):The reaction occurs on the anode side of the stray current device, as shown in Equation (2):2 and O2 are generated on the cathode and anode sides, respectively, meaning that bubbles are generated on the two sides of the specimen. During each cycle (7 days), the frequency and number of bubbles generated and intensity of stray current are much greater on the first two days, after the solution change is completed, compared to that on the last five days, and there is white precipitation in the electrolyte solution on both sides of the specimen. It is indicated that the passing of stray current results in the formation of CaCO3 on the cathode side and increasing resistance of the electrolyte solution. With a constant voltage intensity, an increase in resistance results in a decrease in the intensity of stray current flowing through the specimen, and then weakens the electrolytic water reaction that occurs in the electrolyte solution on both sides of the specimen.According to Equations (1) and (2), H3 dissolves on the cathode side increased by approximately 72% at 120 d of stray current, compared to that at 90 d.- of the anode will not lose electrons, and the solution on the anode side cannot gradually change from alkaline to neutral. When the specimen is at the early stage, the strong alkaline environment may erode the specimen.The compressive strength of the specimens at 7, 14, 30, 60, 90, and 120 d of stray currents is shown in 2+ to the electrode direction. This will accelerate the dissolution of Ca(OH)2, or even C–S–H gel, and decrease the compressive strength of the material. Under the combined action of the two factors, the overall compressive strength of cement-based materials fluctuates and decreases with the increase of corrosion age, and tends to be stable when the age reaches 90 d.When the stray current voltage is 20 and 40 V, the cement-based material is in the environment of the coupling of stray current and corrosion. There are two factors affecting the compressive strength of cement-based materials, namely the hydration degree of cement-based materials, with the increase of age and corrosion. With the increase of hydration degree, more dense gel phases will be generated, which will enhance the compressive strength of cement-based materials. The existence of stray current will accelerate the movement of CaAt 120 d of stray current, the compressive strength of the specimens at voltages of 20, 40, and 60 V decreases by 1.4%, 3.7%, and 26.8%, respectively, compared to that in the pre-test period. It can be concluded that, when the voltage is 60 V, the corrosion of cement-based materials is the most serious, and the compressive strength decreases by 13.7%, compared to that of the specimen corroded with 0 V.2+ concentration in the cathode side solution is found at the voltage of 60 V, followed by the second highest Ca2+ concentration at 40 V, and the lowest Ca2+ concentration at 20 V; within 7 d to 14 d, the Ca2+ concentration at the voltage of 60 V decreases, while the Ca2+ concentration at voltages of 20 and 40 V increases; after 14 days, the Ca2+ concentration stabilizes at 2.2–3.2 mg/L every week. The possible reason is that, in order to maintain the internal charge balance of cement-based materials, there is a Ca2+ concentration threshold in the specimen. After approaching the threshold, the dissolution of Ca2+ slows down, so the Ca2+ concentration in the solution tends to be stable at 14 d. Under the voltage of 20 and 40 V, the concentration of Ca2+ in the solution increases continuously under the action of stray current during the age of 14 days, while, under the voltage of 60 V, the stray current accelerates the dissolution in the first 7 days, which makes the concentration of calcium ion in the solution higher. Within 7–14 days, the specimen can not continue to provide higher Ca2+ content, resulting in the decrease of calcium ion concentration.As shown in 2+ increases significantly, which may be because the Ca2+ supplied by C–H crystal inside the specimen is consumed. In order to maintain the internal charge balance of the specimen, the C–S–H gel is decomposed successively, and abundant Ca2+ in the specimen leads to the peak of Ca2+ dissolution and increase of calcium concentration in the solution.After 49 d, the concentration of CaUnder the action of stray current (40 V), the influence of different water-binder ratios  on cathode side leachables is shown in 3) is the most. The mass of the cathode side leachables with water-binder ratios of 0.50 and 0.60 is 17.46% and 34.52% lower, respectively, compared to those with a water-binder ratio of 0.40. In general, the corrosion resistance is the best when the water-binder ratio is 0.60. This may be because the larger the water binder ratio, the smaller the amount of cementitious material and less calcium content per unit volume. Therefore, the less cathode side leachables (CaCO3).When the water-binder ratio is 0.40, there are very few leachables on the cathode side of the specimen during the first 60 d of stray current; at 90 d, the cathode side leachables increase significantly, and the cumulative mass increases by about 65.0 times, compared to that of 60 d; at 120 d, the leachables  on the corrosion of cement-based materials under stray current (40 V) at a water-binder ratio of 0.50 is shown in The variation of the compressive strength of cement-based materials with different fly ash content is shown in 2+ concentration in the cathode side solution fluctuates with increasing stray current duration. The Ca2+ concentration in the cathode side solution of the specimen without fly ash is stable at 2.10 mg/L–2.45 mg/L, during 14 to 28 d of stray current. The Ca2+ concentration in the cathode side solution of the specimens increases during the first 14 d of stray current, when the fly ash is mixed at 5%, 15%, and 20%, indicating that the corrosion of the specimens increases under stray current; within 14 d to 28 d, the Ca2+ concentration in the cathode side solution of the specimens with 5%, 15%, and 20% fly ash content decreases overall, indicating that the corrosion reaction is weakened. When the content of fly ash is 10%, the Ca2+ concentration in the solution is generally low after 7 days of stray current; compared with other fly ash contents at 28 d of stray currents, the Ca2+ concentration is the lowest when the fly ash content is 10%. In general, after 21 d of stray current, the Ca2+ concentration of the specimen without fly ash increases, while the Ca2+ concentration of the specimens with fly ash decreases overall, and all are lower than those without fly ash.As can be seen from The effect of different silica fume content  on the corrosion of cement-based materials under stray current (40 V) at a water-binder ratio of 0.50 is shown in According to 2+ concentration is close to the threshold. The directional migration rate of Ca2+ under the action of current slows down. At this time, the hydration degree of cement-based materials increases, and more dense gel phases can resist the stray current corrosion. In the third stage, the compressive strength decreases significantly. It is considered that there are two reasons: the first is that, under the continuous action of stray current, the OH- in 5% NaOH solution is consumed, and the solution changes to acid, which produces a certain acid corrosion on cement-based materials, resulting in the decrease of strength. The second is that C–S–H hydrated gel, generated from the hydration of silica fume and C–H crystal, will decompose to maintain the internal charge balance of the specimen when the calcium concentration is low, resulting in structural damage and strength degradation.The erosion of the stray current is strong in the first 15 days. A large number of C–H crystals are contained in the cement-based material and not consumed. Under the action of directional current, calcium ions move to the cathode. The strength growth provided by cement hydration and silica fume is not enough to support the erosion damage under stray current, so the strength of the first stage is reduced. In the second stage, compressive strength shows an upward trend because the accelerated dissolution of stray current has stabilized, and the internal CaAfter stray current is applied for 120 d, the compressive strength of the specimen increases by 1.6%, with a silica fume content of 10%, while that of the specimens with silica fume contents of 5% and 15% decrease by 7.0% and 5.1%, respectively, compared with that of the specimen without silica fume; the compressive strength of the specimens with 5%, 10%, and 15% silica fume content decrease by 32.1%, 24.9%, and 30.8%, respectively, compared with the initial strength of the specimen with each content before the stray current test. Therefore, in terms of compressive strength, the specimen with 10% silica fume content possesses the best anti-corrosion effect under stray current.2+ concentration in the cathode side solution of the specimen generally increases during the first 14 days of stray current. At 7 d of stray current, the Ca2+ concentration in the cathode side solution of the specimen with 15% silica fume content is the highest of 2.93 mg/L, and that with 5% silica fume content is the lowest of 1.06 mg/L; at 28 d, the Ca2+ concentration in the cathode side solution of the specimen with 5% silica fume content is the highest of 3.04 mg/L, and that with 20% silica fume content is the lowest of 1.27 mg/L.It can be seen from (1)As the stray current energisation duration increases, the mass of cathode side leachables increase and compressive strength of cement-based materials decreases overall. The mass of cathode side leachables varies with voltage as 20 < 60 < 40 V. When the voltage is 60 V, the compressive strength of cement-based materials decreases the most, which is 13.7% lower than that of specimens corroded under 0 V.(2)3) of the specimen with a water-binder ratio of 0.40 is the highest, and that with a water-binder ratio of 0.60 is the lowest, which is 34.52% lower than that of 0.40. Additionally, the Ca2+ concentration in the cathodic side solution of the cement-based materials with a water-binder ratio of 0.60 is generally the lowest, in comparison.At 120 d of stray current, the strength of the specimen with a water-binder ratio of 0.50 decreases the least, by only 3.7%; the mass of cathode side leachables (CaCO(3)2+ concentrations of the fly ash-doped, cement-based materials are all lower than that of the un-doped materials, and the lowest concentration is found at 10% fly ash content.The mass of cathode side leachables decrease significantly with the increase in fly ash content. When the content of fly ash is 15%, the mass is the lowest. In stray current environments, the compressive strength of the fly ash-doped, cement-based materials decreases more than that of the un-doped materials. At 120 d of stray current, the cement-base materials with 15% fly ash content show the smallest reduction in strength. At 28 d of stray current, the Ca(4)2+ concentration in the cathode side solution of cement-based materials with 20% silica fume content is the lowest.When the content of silica fume is 10%, the mass of cathode side leachables of the cement-based materials is the least. At 120 d of stray current, the compressive strength of the cement-based materials with 10% silica fume content shows the least decrease, 24.9%, compared with the initial strength before the test. Therefore, in terms of the cathode side leachables and compressive strength, the specimen with 10% silica fume content possesses the best anti-corrosion effect under stray current. At 28 d of stray current, the CaIn this study, the corrosion of cement-based materials under the action of stray current is investigated, and the effects of different stray current magnitudes, water-binder ratios, fly ash admixtures, and silica fume admixtures on the corrosion of cement-based materials are analyzed. The main conclusions are as follows:In the actual subway engineering, the composition of the stray current (the respective proportion of DC and AC), direction, and periodicity are uncertain. On the basis of this study, future research can focus on effects of these practical factors.


Compared with the sand treated by EICP, the strength and stiffness of the sand reinforced by the fiber combined with EICP were greatly improved, and the ductility was also improved to a certain extent. However, the increase of CCC was extremely weak, and the inhomogeneity of CaCO3 distribution was enlarged; the influence of fiber length on the UCS and CCC of the treated sand was greater than that of the fiber content. The improvement of EICP-solidified sand by PVA fiber was mainly due to the formation of a “fiber–CaCO3–sand” spatial structure system through fiber bridging, not the increase of CCC.Enzyme-induced calcium carbonate precipitation (EICP) technology can improve the strength of treated soil. But it also leads to remarkable brittleness of the soil. This study used polyvinyl alcohol (PVA) fiber combined with EICP to solidify sand. Through the unconfined compressive strength (UCS) test, the effect of PVA fiber incorporation on the mechanical properties of EICP-solidified sand was investigated; the distribution of CaCO Both  culture ,5,6. Pre culture ,8 have s culture  used a f culture  found th culture  reinforc culture ,13,14. HIn order to study the effect of EICP and fiber-reinforced technology on soil treatment, polyvinyl alcohol (PVA) fibers at contents of 0.2, 0.4, and 0.6% by weight and at lengths of 3, 6, 9, and 12 mm were used together with EICP to treat Chinese standard sand. The influence of fiber on the mechanical properties and ductility of EICP-treated sand were investigated using the UCS and calcium carbonate content (CCC) tests. The microstructure of solidified soil samples was observed via microscope and scanning electron microscopy (SEM) to explore the action mechanism of the combination of fiber and EICP for soil improvement.Cu is greater than 5, and the curvature coefficient Cc is between 1 and 3, indicating that the sand has good grain gradation.Considering that PVA fiber has fine resistance to acid, alkali, salt, wear, sunlight, and corrosion, the test used high-strength and high elastic modulus PVA fiber ,16. The 2–urea mixture  [The EICP treatment solution consisted of 100 g/L soybean urease and CaCl= 1.0 M) ,18. The = 1.0 M)  was as fThe mold used was a cylindrical acrylic pipe with an inner diameter of 39.1 mm and a height of 100 mm, which consisted of the splicing of two half molds. A permeable stone with a thickness of 10 mm was placed at the lower end of the mold. The prepared sand sample was a cylinder 39.1 mm in diameter and 80 mm in height. A layer of PVC film was used to separate the mold from the sand column, which was convenient for demolding after molding.2–urea mixture was injected into the soil sample in the same way, and the mixture was left to stand for 24 h, which was recorded as a cycle. (4) After seven cycles, the soil sample was solidified. The sand treatment process by EICP and the prepared soil samples are shown in The soil samples were prepared as follows: (1) 161.53 g  of standard sand and a certain amount of fiber were weighed. The two were mixed evenly, divided into three equal parts, and poured into the mold successively. After each pouring, they were compacted to a predetermined height. (2) Fifty milliliters of soybean urease solution was injected from the top of the soil sample at a rate of 2 mL/min using a peristaltic pump. The mixture rested for 5 h to ensure that the urease was fully diffused in the soil sample and adsorbed on the surface of the sand particles. (3) Fifty milliliters of the CaClThe PVA fibers at dosages of 0.2, 0.4, and 0.6% by sand weight were used for tests, whose lengths at each dosage were 3, 6, 9, and 12 mm, respectively. The traditional EICP-solidified sand was taken as a control group. After obtaining the optimal length and dosage of PVA fiber through the UCS and CCC tests, the sand strengthening mechanism by fiber-reinforced EICP technology was analyzed from a microscopic perspective using a USB handheld microscope and SEM. The specific test scheme is shown in The top and bottom surfaces of the prepared soil samples were polished with sandpaper. After the samples were dried, the UCS tests were conducted at a uniform loading rate of 0.5 mm/min with an automatic pressure testing machine, and the maximum axial stress of the sample was taken as UCS.M1) was weighed. Afterward, the material was soaked in HCl (2 M) until there were no bubbles. The material was dried, and its mass (M2) was weighed again. The difference in material mass before and after acid pickling was the mass of CaCO3 precipitated during EICP (Mc). The CCC in different parts of the soil column iC  was defined as the percentage of Mc to M1 (Equation (1)), and the spatial difference coefficient of the CCC (Cv) was defined as the ratio of the standard deviation of CCC (Cs) to the average value of CCC (Av) (Equation (2)). Both Cs and Cv were used to measure the dispersion of CCC in different parts of the fiber-reinforced EICP-solidified sand samples.After performing the UCS tests, approximately 30 g of material was collected from the top (t), middle (m), and bottom (b) parts of the damaged sample and crushed. The accurate mass of each piece of material . The fiber had weak force transfer performance and poor reinforcement effect in soil. However, fibers that are excessively long are prone to bend, which inhibits the force transfer of fiber and affects the overall mechanical performance of the soil sample, resulting in loss of strength. A certain length of fiber can effectively fill the gaps between sand particles and play an anchoring role between CaCOr fibers  and thusAccording to σr, peak strength strain εf, initial elastic modulus E, and secant modulus E50 obtained from σr after failure increased gradually from zero. Except for sample U-12-0.6, εf increased with the increase of fiber length and content, and under the same fiber content; basically, the larger the fiber length, the greater the εf [εf, which was 276.5% higher than that of treated via traditional EICP. It shows that the fiber does improve the toughness of the treated sand. For fibers with a length in the range of 3 to 9 mm, the greater the content and length of fiber, the better the soil toughness. E and E50 were about 1.2 to 3.9 times of that of EICP-treated soil after fiber was incorporated. The variation of E and E50 with the length and content of the fiber was basically consistent with the variation of strength [The parameters of residual stress r the εf . The samstrength . Under t3 in EICP and increased its production. Zheng et al. [g et al.  found thαc, αs) of sand samples strengthened with fiber-reinforced EICP compared with samples only treated with EICP, and the changes of CCC  and UCS  with another factor under the condition of same fiber length or content. The addition of fiber could increase the UCS of EICP-treated sand by up to 84%, but the highest increase of CCC was only 36%. The sample U-12-0.6 had the highest CCC, but its UCS was relatively low; while the sand sample U-9-0.4 had the highest UCS, but its CCC was only at the average level of CCC of each sample with fiber additions.βcc and βsc was smaller than that of βcl and βsl, so the influence of fiber content on CCC and UCS was less than that of fiber length.Results show that the increase of CCC is only one reason for the improvement of UCS of fiber-treated sand, and the level of CCC is not the key factor and sufficient condition to determine the UCS of fiber-reinforced EICP-treated sand ,29,30,313 distribution in the top, middle, and bottom parts of a fiber-reinforced EICP-treated sand column, the proportion of CaCO3 was defined as the ratio of CCC in different parts of the sand column iC  to the sum of CCC in the three parts. The proportion of CaCO3 in the top, middle, and bottom parts of the sample under different treatment methods is shown in Cs and Cv with the length and content of the added fiber. With the continuous dripping of CaCl2–urea mixture, CaCO3 crystals first precipitated at the top part of the sample, and the sand particles were cemented by the crystals, resulting in the decrease of porosity and permeability of the samples, which hindered the flow of the mixture from up to down to a certain extent, and more treatment solution remained at the top part of the sand column. The distribution rule of CaCO3 was top > middle > bottom, which is in accordance with Darcy’s law.To analyze the uniformity of CaCO3 in the top part of the samples continued to increase, the proportion of CaCO3 in the middle part changed slightly, and the proportion of CaCO3 in the bottom part continued to decrease  between the fiber and the sand grain were enhanced.3 to form a whole through bridging action, but also act as “tie bars” to transfer stress and limit soil deformation, which effectively slowed down the development of tension cracks and improved its ductility. When the fiber length and content were excessively large, fiber clusters would appear, forming the weak area of soil reinforcement, resulting in the strength reduction.When the solidified sand was subjected to external load, the fibers scattered in the sand could not only connect the evenly distributed and non-uniformly distributed parts of CaCO3 is scattered on the surface of sand particles, partially clustered in layers. When the soil was subjected to an external load, the CaCO3 surface layer with high friction strength covering the surface of sand particles would have a certain restriction on the displacement of sand particles. For some areas with large sand grain gaps, the injected CaCl2–urea mixture flowed to this region preferentially and stayed in this region for a longer time than other regions, so the induced reaction in this area was more sufficient and intense [3 crystals formed a cementation layer , thus weakening the mechanical properties of the treated sand. Therefore, future studies can investigate the engineering properties of EICP-solidified sand with different lengths of fiber mixing. The adoption of better grouting technologies can lead to further improvement of the uniformity, strength, and toughness of fiber-stabilized sand.4. Incorporating fibers reduces the uniformity of EICP-solidified sand. In severe cases, the failure will develop along the path of minimum structural resistance (the least CaCO


Blast furnace ferronickel slag (BFFS) is generated in the production of ferronickel alloys and is used as cement replacement in concrete or mortar. The effectivity in reducing cement consumption and improving performance are limited. By referring to the paste replacement method, this work used BFFS to replace an equal volume of the white Portland cement paste to obtain greater performance enhancement. BFFS was used with five levels of replacement  and four water-to-cement ratios  were designed. Fluidity, mechanical strength, hydration products, and pore structure of every mixture were measured. The results showed that the workability of the mortars decreased due to the reduced volume of water, but the 28-day compressive strength of the mortars increased, and the cement content of the mortars was also reduced by 33 wt %. The X-ray diffraction (XRD) patterns revealed that there existed a carboaluminate phase, and the presence of the ettringite was stabilized, indicating that the accumulating amount of the hydration products of the mortar increased. Furthermore, the BFFS could consume the portlandite and free water to form a higher amount of chemically bound water due to its pozzolanic activity. A high degree of hydration and a large volume of the hydration products refined the porosity of the hardened mortars, which explained the enhancement of the strength of the mortars. Compared to the cement replacement method, the paste replacement method was more effective in preparing eco-friendly mortar or concrete by recycling BFFS for reducing the cement content of the mortar while improving its strength. In Chnd Al2O3 . Actuallnd Al2O3 ,9,10, asnd Al2O3 , as a sund Al2O3 , and as nd Al2O3 ,14, but Some major bridges such as landmark cable-stayed bridges and suspension bridges are expected to have white and clean bridge towers constructed chiefly of white Portland cement (WPC). On the other hand, there are strict requirements for the selection of raw materials , the calIn recent years, Li et al. ,24,25 deTo increase the addition of BFFS and reduce the consumption of WPC, the present work compared the paste replacement method with the cement replacement method through producing a series of mortar mixes with various amounts of BFFS and different water-to-cement ratios and analyzing the strength, workability, and microstructure of the resultant mortars. Moreover, we evaluated the effectiveness of the two replacement methods in the reduction of cement consumption, the improvement in the strength of the mortar, the densification of the mortar microstructure, and waste utilization.2/kg, was used to produce the WPC mortar. According to 2 (18.77%), and Al2O3 (3.98%). The results of the Rietveld refinement of X-ray diffraction (XRD) show that tricalcium silicate (C3S), dicalcium silicate (C2S), tricalcium aluminate (C3A), and tetra-calcium aluminoferrite (C4AF) respectively constitute 53.29%, 29.92%, 3.76%, and 0.38% of cement, while the cement contains 8.8% calcite. The moisture content, water absorption, specific gravity, and maximum particle size of the natural sand selected as the fine aggregate were measured to be 0.13%, 0.91%, 2.665, and 1.18 mm, respectively. CEM I 52.5R white Portland cement, produced in Tunisia, with a loss on ignition of 2.1%, a specific gravity of 3.077, and a specific surface area of 334 m2 (26.85%), and Al2O3 (20.92%). Moreover, the specific gravity, maximum particle size, and specific surface area of the BFFS were measured to be 2.855, 0.15 mm, and 384 m2/kg, respectively.Obtained from Fujian province in China, the original BFFS with an angular appearance  investigA polycarboxylate-based superplasticizer (SP), purchased from Subote New Materials Ltd., Nanjing, China, in the form of a white powder was used in the mixing process of the mortars to achieve the constant workability. Generally, a mortar mix with a lower water-to-powder ratio  needs a higher dosage of the superplasticizer to disperse the powder particles.In the paste replacement method, 20 mortar mixes with various volumes of the BFFS as a replacement for the mortar paste and a series of water-to-cement ratios (W/C) were designed and investigated. Firstly, the water-to-cement ratios were designed as 0.40, 0.45, 0.50, and 0.55 by mass. It should be noted that the W/C remained constant although the BFFS was incorporated into the mortar mixes to reduce the WPC content of the mortar. The total volume of the paste of all the mortar mixes, that is, the total volume of water, the WPC, and the BFFS as a percentage of the mortar volume, was maintained at 60%, and the volume of the fine aggregate was set at 40%, as listed in In addition, the experiments were designed to compare the difference between utilizing the BFFS as a replacement for the cement and using it as a replacement for the paste as described above by preparing another eight mortar samples. Similarly, in the cement replacement method, the total volume of the paste of each mix proportion was set at 60%, and the percentage of the fine aggregate remained unchanged at 40%. The volume of the BFFS varied from 0% to 20% with increments of 5%, while the corresponding volume of the cement paste decreased from 60% to 40% with decrements of 5%. It should be emphasized that the incorporation of the BFFS as a replacement for the cement did not change the volume of water but decreased the volume of the WPC, indicating that the actual W/C changed. Moreover, only the water-to-cement ratios of 0.40 and 0.55 were taken into account in this investigation. As presented in The particle size distributions (PSD) of the powder materials (the WPC and the BFFS) and the fine aggregate were measured by a laser particle size analyzer and a mechanical sieving machine, respectively. Similar to the slump flow test of concrete , this stAccording to Chinese standard JGJ/T 70-2009 , three pTo characterize the microstructure of the paste containing different volumes of the BFFS, the samples listed in The mineral composition of the raw materials and the hardened pastes was measured at the tested curing periods by the X-ray diffraction measurement (D/MAX-IIIB) using a CuKα source operated at 40 mA and 40 kV, at a 2θ angle ranging from 5° to 70°, and at a scan rate of 5°/min. 2 to measure the amount of portlandite (CH) and chemically bound water. The thermogravimetric analysis (TGA)  of the paste specimens of about 15 mg was conducted in a temperature range of 30 to 1000 °C at a heating rate of 10 °C/min under a 30 mL/min constant flow of NApproximately 1 g pieces from the inner part of the different hardened pastes were used to characterize the pore structure of the mortars by means of mercury intrusion porosimetry (MIP)  in a high-pressure mode from 140 kPa to 230 MPa and at a contact angle of 140° between the paste and the mercury.The particle size distributions of the WPC, the BFFS, and the fine aggregate measured by the laser particle size analyzer are shown in 2O4) and norsethite (BaMg(CO3)2), indicating that although the MgO content of the BFFS reached as high as 9.2% (see 2O4) and norsethite (BaMg(CO3)2). Moreover, since most of the BFFS is produced by water quenching, its mineral components are dominated by an amorphous phase and exhibit certain pozzolanic activity. Previous investigations [From the XRD pattern presented in 9.2% see , it did igations ,33 also The data in the sixth column of As shown in The third to sixth columns of Another noteworthy phenomenon was that at a given W/C, the variation in the compressive strength of the PRB mortar specimens was different from that of the CRB mortar specimens. However, at the same W/C, when the BFFS was added as a substitute for the cement, raising the volume of the BFFS from 0% to 20% reduced the 3-day flexural strength of the mortar. Similarly, when the BFFS was added as a substitute for the paste, increasing the volume of the BFFS from 0% to 20% improved the 28-day flexural strength and compressive strength; nevertheless, when the BFFS was added as a substitute for the cement, increasing the volume of the BFFS from 0% to 20% reduced the 28-day flexural strength of the mortar and increased the compressive strength of the mortar. The other mortar samples with different water-to-cement ratios also showed a similar variation in the flexural strength and compressive strength after a curing period of 3 or 28 days.To further analyze the effectiveness of the two strategies for applying the BFFS to the mortar, that is, the paste replacement method and the cement replacement method, in the enhancement of the strength of the mortar, the percentage of the change in the flexural strength and the compressive strength of the mortars cured for 3 and 28 days as a function of the volume of the incorporated BFFS are presented in The 28-day hydration products of the mortar samples at different water-to-cement ratios and various volumes of the BFFS were characterized by the XRD as shown in 2 to Al2O3, the hydration process appeared to be more inclined to form the hemicarboaluminate after 28 days of hydration. This phenomenon was also observed in other investigations [2O3 to prepare mortar and found the existence of the monocarboaluminate after 3 and 240 days of hydration, but the diffraction peaks of it were indistinguishable due to the limited amorphous Al content of the ferronickel slag. Kim et al. [2O3 as a replacement for the cement and discovered a high amount of hydrotalcite (Mg6Al2(CO3)(OH)16·4H2O) by the XRD measurement.igations ,36. A sim et al.  utilized4AH13, C3AH6 (hydrogarnet), and strätlingite because the BFFS was an alumina-rich pozzolanic material and could react with the portlandite. Strätlingite as a type of a monosulfate (Ms) phase is a typical product with a hexagonal structure and crystal composition of C2ASH8 in the cementitious pastes with aluminate-rich pozzolanic materials; it has also been reported that it coexists with the sulfate phase, ettringite, and carboaluminate. However, the peak of strätlingite, usually appearing at a 2θ angle of 7.2°, is absent in In addition to the carboaluminate phase, the hydration process of the paste containing the BFFS could consume the portlandite to form secondary hydration products, such as calcium  silicate hydrate (C-(A)-S-H) gels, C32− dissolved from the calcite could restrain the transformation of the ettringite into the Ms; thus, it indirectly stabilized the existence of the ettringite although the gypsum as the source of sulfate was depleted [Meanwhile, the diffraction peak of the ettringite in depleted . This chdepleted .Compared to the PRB samples, the samples prepared by replacing the cement with the BFFS experienced the formation of the carboaluminate phase, but the dominant phase was the monocarboaluminate rather than the hemicarboaluminate. Similar to 2. The range of the temperature of these three major peaks may be different from what is reported in other works [In this section, the results of the thermal analysis of the mortar were discussed mainly through examining the thermogravimetric analysis (TGA) curves. As shown in er works ,41 due t32−. Moreover, the consumption of the portlandite owing to the addition of the BFFS was observed as a gradually decreasing peak in a temperature range of 400–525 °C; correspondingly, the peaks of the C-S-H and the ettringite were enhanced, but the peak of the decarbonation weakened due to the higher degree of hydration.Further, the thermodynamic stability of the Ms was slightly higher than that of the Hc–Mc since its decomposition peak was higher than that of the carboaluminate phase. This difference mainly originated from the fact that the temperature of the dehydration of the octahedral layer of the Ms was slightly higher than that of the Hc–Mc . When thThe amounts of the portlandite and bound water of the pastes with different volumes of the BFFS and various water-to-cement ratios are shown in At a fixed W/C of 0.40, the portlandite content per 100 g of the cement decreased as the volume of the BFFS increased, and the percentage of its reduction rose at a higher replacement level of the BFFS. This change in the portlandite content could be explained by the pozzolanic reaction of the BFFS and the formation of the Hc and the Mc. It should be noted that, in the paste replacement method, the dilution effect does not exist since the water-to-cement ratio by mass remains unchanged when the BFFS is added. Thus, in the case of the addition of the BFFS, the normalized amount of the bound water increased correspondingly. In addition to the pozzolanic activity of the BFFS, the nucleation effect of the finer particles of the BFFS was possibly another main factor which could enhance the hydration process of the clinker with enough free water during a hydration period of 28 days to form a higher amount of the hydration products; however, the dilution effect should not be taken into account.In the case of adding 20 vol% of the BFFS, the amounts of the portlandite and bound water of the paste with a high W/C (such as 0.55) were higher than those of the paste with a low W/C (such as 0.40), indicating that the degree of the hydration of sample PRB-0.55-20 was higher, and more hydration products were formed due to the higher amount of the free water. According to the differential thermal analysis (DTA) curves in Adding the BFFS to only replace an equal amount of the cement produced the dilution effect, a higher amount of the anhydrous clinker participated in the hydration reaction. Therefore, the portlandite content of sample CRB-0.55-20 in The results of the mercury intrusion porosimetry in terms of the pore size distribution and porosity of the pastes at a curing period of 28 days are shown in r), this investigation divided the pores of the hydrated pastes into very harmful pores (r > 200 nm), harmful pores (50 nm < r < 200 nm), less harmful pores (20 nm < r < 50 nm), and harmless pores (r < 20 nm). At a fixed W/C, the addition of the BFFS could clearly reduce the porosity from 16.25% to 9.4%, while the total volume fraction of the harmless pores and the less harmful pores increased from 35% to 93%, and they then became the dominant type of the pores. When 20 vol% of the BFFS was added to the paste at a W/C of 0.55, although the total amount of the pores with a radius smaller than 50 nm was 87%, the porosity was further reduced down to 8.9%, and the volume fraction of the harmless pores increased up to 55%. The volume fractions of the harmless pores and the less harmful pores of sample CRB-0.55-20 were 31% and 21%, respectively, which indicated a potential refinement occurring in this paste due to the pozzolanic reaction of the BFFS. From an objective perspective, the efficiency of reducing the WPC consumption could not be evaluated exclusively by considering the WPC content per unit volume of the mortar. In fact, the changing pattern in the strength of the mortar should also be taken into account. When the strength of the mortar or concrete is enhanced, the construction can be designed with smaller sectional dimensions and thus less consumption of mortar or concrete, so the cement content of the mortar and energy consumption can be reduced simultaneously. Inversely, when the strength of the mortar or concrete is decreased, the construction should be designed with larger sectional dimensions and thus higher consumption of mortar or concrete, so the total cement consumption and the carbon footprint increase simultaneously. Herein, the following analysis focuses on the 3-day and 28-day flexural strength and compressive strength of the mortar mixes. As shown in To compare the changing patterns in the strength of the PRB mortars with those in the strength of the CRB mortars, −3/MPa for the 28-day compressive strength curves and 25.9 ± 0.4 kg·m−3/MPa for the 28-day flexural strength curves. With respect to the 3-day strength of the mortar, the monotonous trend in the convergence of the curves was more obvious in the C/CS curves in −3/MPa (a 54.7% reduction).In addition, the present work defined two new parameters, namely the ratio of the cement content to the compressive strength (C/CS) and the ratio of the cement content to the flexural strength (C/FS), to further evaluate the synchronous changes of the flexural strength and compressive strength at different curing periods and various amounts of the WPC. According to the results of the 3-day and 28-day strength of the mortar mixes with various volumes of the BFFS, the C/CS and C/FS are plotted against the volume of the BFFS for the paste replacement method in On the other hand, as depicted in On the basis of the above analysis, the roles of the BFFS as a replacement for the paste in the workability and strength of the mortar mixes can be summarized as follows:As demonstrated in the above microstructure analysis, the BFFS had pozzolanic activity and could act as a supplementary cementing material in the mortar mixes, which enhanced the strength of the mortar by refining its porosity. Previous works ,43 have In addition, the fine BFFS particles could also provide nucleation sites for the precipitation of the C-S-H gel and thus could improve the hydration process of the WPC, thereby further enhancing the strength of the mortar. This nucleation phenomenon practically existed in the two different methods of recycling BFFS, but the negative impact of the additional increase in the actual W/C of the CRB samples neutralized the favorable nucleation effect of the BFFS, thereby decreasing the strength of the mortar.As shown in To produce more eco-friendly mortar or concrete by recycling blast furnace ferronickel slag and reducing the consumption of white Portland cement, various mortar mixes with different volumes of the BFFS incorporated as a replacement either for the paste or for the cement at a series of initial water-to-cement ratios were produced for the examination of the workability of the paste and the 28-day strength of the mortar; the particle size distribution of the BFFS and the microstructure of the mortar were also analyzed. From the findings of this work, the following conclusions can be drawn:2, MgO, CaO, and Fe2O3, and its particle size distribution was continuously graded with an angular appearance.The BFFS chiefly consisted of SiOThere was no dilution effect in the pastes produced by the paste replacement method due to the unchanged W/C. A higher dosage of the superplasticizer was also required to obtain the expected workability, which indicated the reduction in the workability of the mortars owing to the decreased water-to-powder ratio by weight.When the volume of the BFFS increased from 0% to 20%, the 28-day compressive strength and flexural strength of the mortar enlarged, and the 3-day strength of the mortar remarkably improved in the paste replacement method.The calcite of the white Portland cement reacted with the amorphous alumina of the BFFS to form the carboaluminate phase which increased the volume fraction of the hydration products and stabilized the presence of the ettringite. The XRD results proved that, at a low volume of the BFFS, monocarboaluminate was the dominant carboaluminate phase, but it was transformed into hemicarboaluminate gradually as the volume of the BFFS increased. The absence of the strätlingite was also confirmed by the XRD patterns due to the existence of the portlandite at a curing period of 28 days. The TGA results revealed that the addition of the BFFS as a replacement for the paste could consume more portlandite to produce the hydration products and form a higher amount of chemically bound water, while the pastes prepared by the cement replacement method contained high amounts of the portlandite and chemically bound water due to the dilution effect.The analysis of the pore structure of the mortar indicated that the paste replacement method could lead to a significant porosity refinement, and the pozzolanic activity of the BFFS could refine the pore structure of the mortar; nonetheless, there was still a great number of large pores in the pastes prepared by the cement replacement method.When the volume of the BFFS increased from 0% to 20%, the paste replacement method could reduce the consumption of the white Portland cement by as high as 33% and could enhance the strength of the mortars; the ratio of the cement content to the strength of the mortar also declined by at least 50%. Furthermore, the pastes were converted from a cement-based material to a BFFS-based material since the mass percentage of the BFFS in the powder material was higher than 50%. Nevertheless, in the cement replacement method, the reduction in the white Portland cement was not significant, and it was reduced by 20% at most; in addition, the strength of the mortar could only remain unchanged as the volume of the BFFS increased up to 20%.Compared to the cement replacement method, the paste replacement method was more effective in recycling blast furnace ferronickel slag for reducing the consumption of white Portland cement and improving the general properties of cement mortar. Therefore, it is worth further investigating this method to realize its potential adequately.