The article proposes two 3D and 2D numerical FE models of frictional heating for the estimation of temperature distributions in railway tread brake in 1xBg configuration during repeated long-term braking. The results of computations were compared with the time courses of temperature measured using thermocouples throughout the duration of the tests on a full-scale dynamometer for two different brake shoe materials in combination with a steel wheel. The resulting temperature distributions calculated using the proposed models agreed well with the experimental measurements, and the maximum difference in temperature values does not exceed 20%. It has been proven that 2D FE model can be as efficient as 3D model to estimate the temperature distribution during long-term and variable braking in the considered friction node. The differences in the calculation of the temperature values using these models did not exceed 3%, and the calculation time for the 2D model, compared to the 3D model, was shorter approximately 85 times for the braking cycle lasting 5032 s, and approximately 45 times for the braking cycle lasting 3297 s. Despite the development of railway technology, tread brake, designed over 100 years ago, is still a widely used solution in railway vehicles, in particular in freight wagons and vehicles where available space is a significant limitation in the structure, e.g., in motor bogies of motive power units or in subway vehicles. One of the most important advantages of the tread brake is its simple design and high reliability. In a typical pneumatic railway brake, the force exerted on friction elements is generated by compressed air in the brake cylinder. In tread brake, the force from the brake cylinder is multiplied by brake rigging and presses the brake block (equipped with brake shoe) against the wheel running surface. The heat generated leads to rapid increase in temperature on the friction surfaces of brake components and other parts of the brake assembly.The condition of tread-braked wheel running surface is significantly influenced by the material, from which the brake shoe is made. One of the important factors that led to the development of composite brake blocks in Europe was an attempt to reduce rolling noise of wheelsets, which is closely related to roughness of their running surface ,2. The uManufacturers of railway braking systems verify friction pair selection on full-scale inertia dynamometer, i.e., such on which the friction pair is tested in its normal size. During the tests of this type, the actual operating conditions of the brake are simulated, including the routes of the proposed railway vehicles. The determined friction pair characteristics are evaluated, e.g., what is the relationship between the value of the coefficient of friction or wear and temperature, sliding velocity, pressure, or braked mass. The condition of the friction elements is also analyzed, i.e., whether signs of thermal degradation of the material or its damage are observed under given operating conditions. Dynamometer tests are also a stage of the process to receive approval granted by UIC  to friction elements , and areFull-scale railway brake dynamometers are also used to determine temperature of friction elements in the course of brake application. In the article , Kim stuAdditionally, reduced-scale dynamometers are used to study tribological phenomena related to railway braking. In the article  Tang et Due to the cost of conducting tests on dynamometer stands, and bearing in mind how important it is to determine the operating temperature and thermal loads of the friction pair for given parameters of railway vehicle operation, the object of interest of both scientific research and industry is modeling of the frictional heating process. This is evidenced by the multitude of papers published so far, the subject of which are experimental studies of temperature fields as well as analytical and numerical modeling of the frictional heating process.A two-dimensional axisymmetric FE model to determine the mean temperature on the surfaces of the brake shoe and wheel was proposed in the papers ,13. The The model presented by Vernersson in the article  was caliPetersson developed a two-dimensional model of the railway tread brake with a single brake shoe using FEM . The modIn the paper  MiloševiIn the article  SuchánekHanda et al. combined full-scale dynamometer test and FE model to investigate hollow wear of wheel running surface characteristic of tread-braked railway wheels . It was Additionally, disc brakes are the subject of scientific research concerning mathematical modeling of frictional heating. A few papers are shortly summarized below.Sayeed Ahmed and Algarni  examinedThe analytical model of a multi-disc braking system with the discs made of carbon friction composite material Termar-ADF was proposed in the article by Yevtushenko et al. . The autThe methodology for selection of materials for disc brake pads was studied using 3D numerical model of the disc brake . Six pad2 were studied in the article [Tribological characteristics  of copper-graphite composites reinforced with Cu-coated or uncoated SiO article . The meaA broader review regarding experimental research as well as analytical and numerical modeling of frictional heating in braking systems is presented in the articles ,25,26.Comprehensive analysis of braking systems which find application in railway vehicles was presented by Günay et al. . The autApart from introduction, the paper is divided into five sections. First, the experimental part of the study is discussed, including description of the full-scale dynamometer, materials used in the research, test program, and results of braking torque measurement. Then, the statement of the boundary value heat conduction problem is given and finite element models of the wheel-brake shoe system are presented. Subsequent section contains results of numerical analysis, namely calculated temperature fields, their discussion and comparison with the experimental measurements. Finally, the study is summarized, and conclusions are drawn.Experimental tests on inertia test benches , for braking systems of rail vehicles, are usually complicated, labor-intensive, and expensive. Numerical modeling has the potential to be a good alternative for dynamometer tests at the initial stage of the railway braking system design process. Therefore, the main purpose of this article is to evaluate accuracy of temperature fields estimated by numerical calculations concerning long-lasting (order of 103 s) braking process, performed for different friction materials, using 2D and 3D FE models, where variable operating conditions and frictional characteristics are accounted for.The experimental part of this work was performed on a full-scale inertia dynamometer for testing of brake friction pairs at the Railway Research Institute in Warsaw a–c. The The simplified schematic drawing of the dynamometer is presented in The tested friction pair comprised railway wheel (4) and composite brake shoe installed in the holder, part of the brake block (5). Brake block is fixed to the frame which has axis of rotation independent from the motor-shafts-flywheels-railway wheel system but coaxial to it. This way, it is possible to measure friction generated at the wheel-brake shoe interface using load cell (7) (HBM-U2A). The principle of braking torque measurement is presented in Appendix B to UIC Code 548 . Normal z-axis direction, which gives coordinates in the cylindrical system Three K-type thermocouples  were installed below wheel running surface to measure wheel temperature in the course of the test. Thermocouples were located on average 5.8 mm below the working surface every 120° along the circumference and at the distance of 110 mm, 85 mm, and 55 mm from the edge of the wheel in the Two friction pairs were tested in 1xBg configuration ,13, i.e.The brake shoes were bedded-in before the execution of the main test program by braking at 120 km/h . The bedding-in procedure was repeated until reaching a minimum of 85% contact area between the brake shoe and the wheel. The main test on a full-scale dynamometer consisted of accelerating the wheel to angular velocity corresponding with the translational velocity of a rail vehicle in real conditions, i.e., equal to 160 km/h, 120 km/h and 80 km/h  and two-dimensional, axisymmetric (denoted 2D)—In the brake shoe-wheel contact area, denoted In the case of a two-dimensional model, friction power generated in the brake shoe-wheel contact area should be averaged using coverage factor Part of the friction power density directed towards the wheel was equal to: formula :(8)γ=KwρInitially the wheel and the brake shoes were at ambient temperature Time profile of the friction power density y change , the friV(t)Aa−1 .The purpose of computer simulations of frictional heating was to develop computational models that allow determination of temperature field changes in the volume of the wheel and the brake shoe. Particularly important was the area near the contact surfaces of both objects, including the location of measuring points from the dynamometer tests. Due to the nature of frictional heating, the highest temperature gradients occur in the normal direction from the working surfaces of the contact elements to the outer cylindrical surfaces. In the case of the brake shoe (only 3D model), linear distribution of 8 finite elements in the 1/100 ratio was set in this direction. For the wheel, number of finite elements on the entire circumference of the working surface was increased (relative to the remaining area), with a view to minimizing the total number of finite elements a. AdditiTo ensure accuracy of the results, several finite element meshes were built, starting from coarse grid and increasing the total number of model elements, including elements of the wheel’s surface layer. Due to the complex shape of the wheel and partial contact on the friction surface with the brake shoe, a mesh consisting of tetrahedral, prismatic, and pyramidal elements was used.When creating the mesh, it was necessary to merge opposite nodes of the brake shoe and wheel surfaces, hence the shape of the elements from the outside of both parts is consistent. These criteria forced a specific approach to dividing the area into spatial elements. The best solution—accuracy-wise—was to use hexagonal elements characterized by regular shapes—the edges are parallel to the direction of the largest temperature gradients. In the analyzed case it was difficult due to the fact that the surface of the brake shoe contacting the wheel is separated by slots. Therefore, the assumed contact area was smaller than determined from nominal width and length of the brake shoe. The first stage in the construction of the mesh was creating of triangular surface elements, then their extrusion from the contact surface to the outer surface of the brake shoe. In this way, prismatic elements were created. In the case of the wheel, a mesh of tetrahedral elements was generated in the entire volume. In the last stage, a layer replacing tetrahedral elements with prismatic ones was created at the working surface. Due to the largest temperature changes in the contact area, variable thickness distribution of the elements in both objects was introduced. The number of boundary layers was equal to 4, the boundary layer stretching factor 1.2, the thickness adjustment factor 1.2, thickness of first layer—automatic.Preliminary calculations were carried out to verify the approach described above. It was found that further increasing the number of elements and changing their order to a higher one did not affect the temperature distribution. Finally, Lagrange second order finite elements were used to create the model’s mesh (in the case of linear elements temperatures were significantly underestimated). The model comprised 91,794 tetrahedral, 796 pyramid, 19,202 prism, 24,872 triangular, and 1526 quadrilateral elements. The total number of degrees of freedom (DOFs) was 228,138 .By contrast, the two-dimensional model b was devNumerical calculations of the space-time temperature distribution in the friction elements of railway tread brake in 1xBg configuration were carried out, using 3D and 2D models described in Initial conditions and operating parameters for the numerical simulations were adopted from the test program carried out on a full-scale dynamometer  and are Fc  and brak braking . Knowingsities q  generateThe thermophysical properties of the considered friction pair materials, which were used for calculations using 2D and 3D numerical models, are shown in he wheel  accordinAs established in The curves of experimentally measured and calculated time courses of temperature based on the proposed numerical models are shown in Temperature evolutions measured 5.8 mm (According to the test program from =83.2 °C a. The toThe next stage of the study was the sequence of three brake applications (no. 4–6) initiated, as previously, at velocities of 160 km/h, 120 km/h, and 80 km/h and mass per wheel of 2.5 t, while the contact force was increased to 30 kN . Due to ectively a.In the final stage of the test (brakings no. 7–9) mass per wheel was increased to 10 t, and contact force was reduced to 10 kN, while the order of brake applications remained unchanged. Due to the fourfold increase in mass per wheel, the time of the entire sequence significantly lengthened, as compared to the previous two braking cycles 1–3 and 4–6 and is equal to ications a.t = 0 to The first three braking sequences according to The test program presented in this article for the second friction pair, consisting of the brake shoe made of Material B and ER7 steel wheel, differs from the previous one  in the order of initial braking velocities, i.e., 80 km/h, 120 km/h, and 160 km/h . Considet1–3 = 652 s. During the
 subsequent braking sequence . The calculation times for the Material A/ER7 pair performed were equal to 1h 35 min for the 2D model and 114 h 50 min for the 3D model. However, in the case of the Material B/ER7 friction pair, calculation times were 1 h 13 min and 51 h 32 min, respectively.In the case of friction pairs of the same type as presented 1xBg brake configuration, it must be stated that the initial estimation of the time course of temperature can be carried out using a 2D model, achieving a satisfactory approximation. The temperature calculations were performed on a workstation with following parameters: CPU IntelIn order to perform a detailed analysis of the time courses of temperature  in the braking system discussed in this work, braking no. 7 for both friction pairs was considered . For Mat−1 s) occurring e.g., in motor vehicles. The long duration of the processes, in addition to the large size of the objects such as the wheel of a rail vehicle, with an outer diameter of 870 mm (assumed rolling radius was 437 mm), require a significant computing power and lead to many longer calculations. Therefore, the results obtained in this study, apart from their correctness verified by experimental research, are also intended to justify the previously formulated statement that the 2D axisymmetric model is sufficient to provide results at a similar level of accuracy. In order to perform such analysis, temperature points 1–6 are marked on the time courses of temperature obtained from calculations made with the 2D and 3D models presented in z = 91 mm due to the lower width of the area absorbing heat through conduction.The analyzed multiple braking processes are relatively long—they differ significantly from the typical cases of single braking  and the steel wheel (ER7) demonstrates the usefulness of the developed computational models. Temperature values calculated from 3D and 2D models are slightly overestimated as compared to the results of experimental measurements and the difference between these values does not exceed 20%. For this reason, it can be stated that both the 3D and 2D model may be used to successfully estimate the temperature distribution in the friction elements of 1xBg braking system, which is beneficial in the design of new friction pairs in terms of their thermophysical and tribological properties.® Xeon® E5-2698 v4 @ 2.20GHz; RAM 64 GB (DDR4)) performed with the 2D model compared to the more general 3D model is reduced by approximately 85 times for the braking cycle lasting 5032 s, and approximately 45 times for the braking cycle lasting 3297 s. Comparison of the temperature calculated using 3D and 2D models at each time step shows that the difference is not greater than 3% for the frictional heating processes and not more than 9% during the cooling steps between successive brake applications. The comparison of models presented in the article proved that 2D frictional heating model can be successfully used to estimate the temperature distributions in the discussed friction node. The computation time (workstation CPU IntelBoth proposed numerical models of frictional heating have certain limitations of applicability. In this article speed and heat flux density determined from experimentally measured braking torque were used as input values. The next stage in the future development of the presented models will be, among others, the mutual coupling of the speed and the friction coefficient through the average temperature on the contact surface of the friction node.Despite some limitations of the proposed models, they can be used not only to estimate the temperature level during repeated and long-term braking, but also, for example, to study the effect of convective heat exchange on the average wheel temperature or detection of potential wheel overheating related to extreme operating conditions.The above numerical modeling approach can also be successfully applied to a different type of railway tread brake, e.g., 2xBgu.The authors of this work did not find any studies where 3D and 2D models of railway tread brake were compared and verified with experimental data, which is also a major asset of this work.


I) with cyclopentadienyl and 2-aminothiophenolate ligands was investigated as a homogeneous catalyst for electrochemical CO2 reduction. By comparing its behavior with an analogous complex with the phenylenediamine (II), the effect of sulfur atom as a substituent has been evaluated. As a result, a positive shift of the reduction potential and the reversibility of the corresponding redox process have been observed, also suggesting a higher stability of the compound with sulfur. Under anhydrous conditions, complex I showed a higher current enhancement in the presence of CO2 (9.41) in comparison with II (4.12). Moreover, the presence of only one -NH group in I explained the difference in the observed increases on the catalytic activity toward CO2 due to the presence of water, with current enhancements of 22.73 and 24.40 for I and II, respectively. DFT calculations confirmed the effect of sulfur on the lowering of the energy of the frontier orbitals of I, highlighted by electrochemical measurements. Furthermore, the condensed Fukui function −f  values agreed very well with the current enhancement observed in the absence of water.The cobalt complex ( On the other hand, CO2 is also considered as one of the most abundant and accessible carbon sources. Indeed, under appropriate conditions, it could be used as a fossil-free building block for the preparation of more complex derivatives and intermediates ) of an Earth-abundant metal, such cobalt, bearing two “non-innocent” ligands: cyclopentadienyl (Cp) and Rn-o-phenylenediamine (RnLNN)   (I), as summarized in NS) which has one sulfur atom and a N-H group as donor units. This compound was experimentally studied by means of electrochemical techniques to establish its electrochemical behavior and its potential as an electrochemical catalyst for the CO2 reduction reaction. In addition, a computational study was performed by using the density functional theory calculations (DFT) [I were discussed in comparison to those on complex [CpCo(LNN)] .In this paper, we investigated the effect, induced by the replacement of one of the two amino groups of the phenylenediamine ligand with a sulfur atom, on the electrochemical and catalytic properties of this class of Co complexes. The replacement of a nitrogen donor with a bigger and more polarizable sulfur atom should affect the ligand’s redox-active characteristics, such as the efficiency in stabilizing charges and its capability as a supplier and/or storage of electrons ,42,43,44n of CO2 ,45,46,47n of CO2 ,49,50, cns (DFT)  and the ns (DFT) , with thI were investigated by CV techniques. The CV of I under an inert nitrogen atmosphere showed a redox couple centered at −1.36 V  were recorded, as reported in Aiming at a broader characterization of the electrochemistry of compound ox) and reduction (Ired) processes showed a linear dependence on the square root of the scan rate (ν1/2), indicating an electron transfer process involving freely diffusing redox species (ox/Ired) remained close to unity in all the investigated scan rates. Moreover, ΔE also increased linearly with the square root of the scan rate, pointing to a quasi-reversible redox process  adduct with a different electrochemical behavior, diminishing the concentration of the free complex species.The electrochemical properties of complex I. As summarized in 2, a current 7.16- and 9.41-fold higher were observed at −2.34 V and −2.52 V, respectively; these enhancements can be related to the ability of the complex to catalyze the CO2 reduction. In fact, when the CV was performed without the complex in both N2- and CO2-saturated solutions, no significant increase in current values were observed, indicating that the CO2 reduction did not occur in a substantial manner in the investigated range of the potential  as reported in 2 binding. Similar cases have been reported in relation to very fast processes such as isomerization or protonation [PF6] (Sigma-Aldrich); in these conditions, the redox couple Fc0/+ was centered at +0.45 V. The working electrode was cleaned before each measurement as follows: after extensive washing with distilled water and isopropanol, the glassy carbon electrode was polished with diamond suspensions  and a wet pad.The electrochemical properties of complex I were bubbled with N2 or CO2 for 30 min. The effect of the presence of water was measured by an incremental addition of degassed deionized H2O in an electrochemical solution by an air-tight syringe.Depending on the runs, the solutions containing complex The number of electrons involved in the reversible redox processes were calculated by using the following Equation (1):The structure of the studied compounds in both the neutral and anionic radical forms was optimized by means of DFT calculations. In detail, geometry optimization was performed by employing the B3LYP functional as implemented in the commercially available suite of programs Gaussian 16  using thf−) was calculated as:kq(N) is the charge at the atomic center k calculated on the optimized geometry of the reduced complex, and kq(N – 1) is the charge of the corresponding neutral form with the same geometry, both calculated at the CPCM(DMSO)/UB3LYP/6-311+g level. The electrophilic attack is likely to occur on the atoms with larger kf−.Graphics of molecular models were generated using ArgusLab 4.0 . Atomic 2 reduction has been evaluated.In this paper, the effect of the replacement of a NH group with a sulfur atom in cyclopentadienyl phenylenediamine cobalt complexes towards electrochemical COd orbitals, is likely to stabilize more effectively an extra charge as in the case of the monoreduced radical anion derivative formation. In the context of metal complex-mediated electroreduction of CO2, the effect of replacing two opposite nitrogen atoms with sulfur in the Ni(cyclam) complex has been highlighted. As pointed out by Gerschel et al., such a substitution leads to lower overpotentials for the reduction of CO2, of which the reduction would occur at a more positive potential, and to enhance the HER capability of the complex [II-based N2S2-type complex for reduction of CO2 to CO, reporting a higher TON value for nickel complexes in that photocatalytic setup [I, which was constant on all the investigated scan rates. These features of complex I had an effect on its catalytic properties; indeed, it presented a higher ICO2/IN2 ratio under anhydrous conditions with respect to its nitrogenated counterpart II. Moreover, the higher reversibility is also a hint of the higher stability of complex I in comparison with II. However, in the presence of water, compound I showed a slightly smaller ICO2/IN2 in comparison with II. This result can be related to the presence of only one nitrogen atom; in fact, the NH group favors catalyst−H2O interactions which play an important role in the CO2 reduction process. Moreover, the different behavior of complex I with water seemed to be confirmed by the presence of the re-oxidation process observed, when CVs were carried out under N2 in the presence of water. This fact might suggest a low affinity of I for hydrogen reduction, and therefore, it might be a hint of a high selectivity towards CO2.As expected, a more polarizable atom such as sulfur, with empty  complex . Moreoveic setup . This asI. The sulfur effect on stabilizing the extra charge has been highlighted both by the analysis of the atomic charges and by the calculated energies of the SOMO for the corresponding radical anions of complexes I and II. Interestingly, the current enhancement observed in the absence of water correlated very well with the probability of an electrophilic attack on the core atoms of the complexes, as measured by the condensed Fukui function f−.The experimental results were supported by computational investigations. DFT calculations confirmed the effect of sulfur on the lowering of the energy of the FOs and, consequently, the reduction potential of


S. aureus (diameters of the inhibition zones between 53.6 and 64.0 mm) and on E. coli (diameters of the inhibition zones between 38.3 and 64.0 mm). Our data suggest that by applying peppermint-oil-based emulsions on a cotton support, aromatherapeutic patches, bandages and dressings with antibacterial properties can be obtained.The objective of the work was to obtain materials with aromatherapeutic and antibacterial properties by applying emulsions based on peppermint essential oil (PEO) onto cotton fabric. For this purpose, some emulsions based on PEO incorporated in various matrices  were prepared. Tween 80 was used as a synthetic emulsifier. The influence of the nature of matrices and of the concentration of Tween 80 on the stability of the emulsions was evaluated by the creaming indices. The materials treated with the stable emulsions were analyzed in terms of sensory activity, of the comfort characteristics, and of the gradual release of the PEO in the artificial perspiration solution. The sum of volatile components retained by samples after exposure to air was determined by GC-MS. The results regarding antibacterial activity showed that materials treated with emulsions have a good inhibitory effect on  In recent years, essential oils have attracted both the attention of researchers as well as of consumers due to their aromatherapeutic ,2, antibEssential oils are complex mixtures of volatile compounds extracted from different parts of plants , by various methods  . The losVarious studies approaching the modification of the surfaces of textile supports in order to obtain dressings with antibacterial and anti-inflammatory activities with a wide spectrum of action have been reported, for example, by applying nanoparticles containing silver and zinc on the surface of cotton fabric , by the The introduction of essential oils used as active substances within polymeric matrices based on polyvinyl alcohol/polyvinyl pyrrolidone (PVA/PVP) offers an effective opportunity for their use in various wound dressings .Emulsions used as essential oil release systems have earned particular interest due to their properties  ,39,40,41Peppermint essential oil is also an effective natural pain reliever, an anti-inflammatory and a good antimicrobial and antioxidant agent due to its monoterpene and ketone content ,49,50,51Considering the antimicrobial and antifungal properties of peppermint essential oil, it can be used in the manufacturing of antibacterial dressings and food packaging, and for improving indoor air quality.Materials with aromatherapeutic properties are obtained by the treatment of cotton fabrics with emulsions or hydrogels containing various essential oils of rosemary ,56, thymThis work aims to obtain textile materials with aromatizing and antibacterial proper-ties by applying emulsions containing essential peppermint oil. The prepared emulsions differ from each other by their concentration of Tween 80 and by the nature of the essential oil incorporation agent. The novelty of the work consists of reducing the amount of synthetic emulsifier Tween 80 by using natural, ecological biodegradable polymers as co-emulsifiers. In addition, wax and gelatin used as incorporation agents of MEO are cheap products that are easy to procure. The release kinetics of the essential oils from the textile materials were analyzed according to the Korsmeyer—Peppas model.−1 was supplied by Fluka Chemie GmbH, Switzerland. The chitosan solution was obtained by the complete dissolving of chitosan into a 1% acetic acid solution. n-Hexane with 96% purity was purchased from Merck, SUA.Peppermint essential oil (MEO) was purchased from S.C. Fares S.A, Orăștie, Romania, Tween 80 was supplied by Merck , the vegetable glycerin (purity 99.5%) was supplied by S.C. Comecom SRL Bucharest , the beeswax was procured from a private apiary in the northern-eastern region of Romania, and the gelatin was purchased from S.C. Lesaffre Romania SRL. The chitosan, with molecular weight 100,000–300,000 g∙mol®, IKA, Taufkirchen, Germany).The emulsions were prepared as follows: (i) the beeswax was melted at 75 °C; (ii) the solutions containing distilled water, Tween 80, gelatin, glycerin, and chitosan  were impregnated with the freshly prepared emulsions using a Benz  padding foulard at a squeezing degree of 160% . After padding, each sample was (i) immediately introduced into a sealed tight plastic bag for the release study of the essential oil into an artificial perspiration solution or (ii) exposed to air in order to study the release of the volatile components.The experiments were conducted on textile supports made of 100% cotton fabric, washed and bleached having a mass of 160 g/mMicroscopic evaluation was carried out using the KRUSS optical microscope, and the microscopic images were captured for computerized analysis using a photo-digital camera .The pH values of the emulsions were measured with a WTW InoLab pH 720 pH meter .CI%) was calculated according to Equation (1) ) and is calculated as in the equation:The preparations were applied on the surface of the culture media, after it was seeded with a cellular suspension of tested microorganisms 5 × 10The comfort indices for the studied samples were determined as follows: hygroscopicity was determined according to the Standard EN ISO 12571:2000, permeability of water vapors was determined according to ISO 11092:1993 on a Permetest  apparatus, and the air permeability was determined according to SR EN ISI 9237 on the METEFEM  apparatus, using a pressure difference of a 10 mm water column.The stability of the emulsions is an important factor for their evaluation. From the presented microphotographs, we can notice that the emulsions E1, E3, and E6 show a texture with a greater number of small particles and a more uniform distribution of the particle size, which provides them with time stability. All images were taken at the same degree of magnitude (×10). Samples E1, E3 and E6 (which showed good stability) were further studied. Samples E2, E4 and E5 were not studied because they did not show good stability over time .The pH of the emulsion is an important parameter considering the destination of the treated fabrics . pH values for the treated samples are shown in The skin pH is normally acidic with pH values in the range of 4–6. Since the obtained emulsions have pH values between 5.3–5.7, it can be concluded that all these materials are suitable for topical applications.The emulsion stability was evaluated by the creaming index. The calculated values of the creaming index are shown in According to the obtained results, the best stability was exhibited by emulsions E1, E3, and E6, while emulsion E2 (which contained the least amount of emulsifier Tween 80), emulsion E4 (that did not contain gelatin) and emulsion E5 (that did not contain chitosan) exhibited lower stability. The synthetic emulsifier Tween 80 has the role of ensuring a fine dispersion of the oil particles by reducing the surface tension at the oil/water interface. Decreasing the concentration of Tween 80 (less than 1.5%) decreases the surface tension which is the thermodynamically driving force responsible for the coalescence of oil droplets. Chitosan and gelatin can be considered as amphiphilic macromolecules that play an essential role in the stabilization of emulsions. By forming complex structures between gelatin and chitosan , improved functional properties resulted compared to gelatin and chitosan used alone. This compact network of chitosan-gelatin formed around the oil droplets created protective films that hindered the collision of the droplets, preventing the phenomena of coalescence and flocculation ,65.Considering that emulsions E1, E3, and E6 were the most stable over time, the samples treated with these emulsions coded as TE1, TE3 and TE6 were the ones used in the further investigations. The untreated sample was denoted as UT.Textile materials are excellent media for transferring fragrance compounds. The samples treated with the prepared emulsions were kept at room temperature and were smelled every day. The sensorial evaluation was performed by a group of 10 subjects. From the obtained data it can be concluded that the intensity of the smell decreases over time. The wax-containing samples (TE1 and TE3) retain the odor intensity for a longer period compared to the wax-free TE6 sample.SEM images for the untreated cotton sample and the treated cotton samples are presented in 3/m2∙min and 14.11 m3/m2∙min compared to the air permeability of the untreated cotton sample which had a value of 37.16 m3/m2∙min.From the analysis of the SEM microphotographs, it can be noticed that the application of the emulsion onto the surface of the textile support caused a reduction in the spaces between the cotton fibers. This modification of the surface explains the lower air permeability of the samples treated with the emulsion, which varied between 12.72 mIn the case of the EDX analyses, for each sample three determinations were carried out . EDAX analyses of the samples TE1, TE3, and TE6 confirmed the presence of nitrogen coming from chitosan and gelatin, respectively, contained by the E1, E3, and E6 emulsions applied to the textile support: The Fourier transform infrared (FTIR) spectra of the untreated cotton sample and the cotton samples treated with the emulsions E1, E3, and E6 are shown in −1 corresponds both to the stretching vibrations of the O-H bonds within the hydroxyl groups of cellulose for the untreated sample  vibrations of C-H bonds from the CH2 groups of cellulose, chitosan, beeswax, and from the CH3 groups of gelatin and beeswax. The peaks in the range 1161 cm−1–1031 cm−1 are attributed to the stretching vibrations of the C–O bonds within the C–O–C glycoside linkages present in cellulose and chitosan. The peaks located around 700 cm−1 are attributed to the out-of-plane bending (twisting and wagging) vibrations of the C-H bonds from the CH2 groups.The strong and wide absorption band recorded at 3336 cmd sample a, and tod sample b–d. In tellulose a. In the beeswax b–d. The  beeswax b,c. The  gelatin b–d. The Essential oils are gradually adsorbed by the skin from the textile fabric by a release mechanism over time. The quantities of peppermint essential oil, which were released from the textile support after 1, 2, 3, 4, and 5 h, respectively, were calculated using the calibration curve of the peppermint essential oil solution y = 1.609·x, wherein x represents the concentration of the biologically active compounds, and y is the absorbance at 275 nm. The controlled release of the peppermint essential oil from the emulsion-treated materials allowed the biologically active compounds to act gradually over a longer period .Analyzing the obtained results, it was observed that in the case of the samples treated with the E6 emulsion, which did not contain beeswax, the essential oil was released in a shorter period. The same amount of oil was released more slowly, for a longer time, for the samples treated with the emulsions E1 and E3 that contain beeswax, gelatin, and chitosan. The slower release in time of the peppermint essential oil from these samples could be explained on the one hand by the greater affinity that the hydrophobic beeswax exhibits towards the oil particles and on the other hand by the fact that the chitosan and gelatin-containing emulsions reduce the spaces between the textile fibers, which causes a more difficult release of the essential oil.The Korsmeyer–Peppas model was used to elucidate the release kinetics of the peppermint essential oil from the textile materials treated with the prepared emulsions. The experimental data analyzed according to this model are shown in 2 which are higher than 0.962 indicate that the essential oil was released according to the Korsmeyer—Peppas kinetic model.The kinetic parameters corresponding to this kinetic model are shown in KP constant indicates a higher release rate of the essential oil from the cotton sample treated with the emulsion E6 (the sample TE6 which does not contain wax) compared to the samples treated with the other emulsions containing wax (which retains the oil particles more strongly due to its hydrophobic character).The “n” is a constant which characterizes the rate of release. The values higher than 0.5  suggest that the release of the biologically active compound is controlled from case to case (depending on the nature of the matrix) by diffusion or by swelling followed by diffusion. The highest value of the kThe solution of peppermint essential oil in 2% hexane, and the extracts in the hexane of the cotton fabric samples impregnated with emulsions and exposed to air for 0, 3 and 6 h, respectively, were analyzed by GC-MS in the method conditions. The chromatograms and the identified compounds were presented in the From the analysis of the chromatograms of the extracts in hexane of the cotton fabric samples it was confirmed that the volatile substances corresponded to those of the peppermint essential oil. The obtained chromatograms and the chemical composition of the peppermint essential oil in hexane and of the extracts in hexane of the cotton fabric samples are presented in the Analyzing the data presented in the tables from the -After 3 h of air exposure, in all 3 samples analyzed, volatile components of the essential oil of peppermint were found in the range of 90.10–92.72% compared to the initial moment;-After 6 h of air exposure, the volatile components of the remaining essential oil of peppermint are 63.12% (sample TE1), 74.08% (sample TE3) and 55.65% (sample TE6).-The highest amount of initial and residual volatile peppermint oil after 3 and 6 h, respectively, was found in sample TE3 and the lowest amount in sample TE6.-Thus, sample TE3 not only incorporates but also retains the largest amount of essential peppermint oil.-The smaller amount of mint essential oil retained by sample TE6 (which did not contain wax) compared to samples TE1 and TE3 (which contained beeswax) can be explained by the fact that wax, a hydrophobic compound, retains the essential oil more strongly in the emulsion, respectively, on the surface of the textile material.Considering the destination of cotton samples treated with peppermint-essential-oil-based emulsions, a significant role is played by the comfort indexes, i.e., hygroscopicity, vapor permeability, and air permeability. The effect of treatment with emulsions on the comfort properties of the cotton samples is presented in For each comfort index, 3 experiments were performed. Between the obtained experimental results there were no differences greater than ±1.2%. In the graphical representation of each comfort index , the aveThe composition of the emulsions applied on the cotton support significantly influences the comfort indices. Polar groups in chitosan, gelatin, glycerin, and Tween 80 cause an increase in hygroscopicity and a decrease in vapor permeability for the treated samples compared to untreated samples. The sample treated with the E6 emulsion that did not contain wax had the highest hygroscopicity and the lowest vapor permeability. All the samples treated with emulsions showed a lower air permeability compared to the untreated sample.Taking into account the large number of different classes of chemical compounds existing in the composition of essential oils, it is likely that the antimicrobial activity could not be attributed to a specific mechanism but rather to a large number of target locations in the microorganism cell. The mechanism of action of the essential oils includes the degradation of the cell wall, damaging of the cytoplasmic membrane, cytoplasm coagulation, damaging of the membrane proteins, and the increase in the membrane permeability leading to leakage of the cell content. An important characteristic of the essential oil components is their hydrophobicity, which allows them to partition in the lipids of the cell membrane and mitochondria, making them more permeable; the loss of molecules and indispensable ions leads to bacterial cell death ,66,67.S. aureus and E. coli bacteria, which are the most frequently encountered pathogenic bacteria that affect life.The antibacterial activity of peppermint oil was investigated against Escherichia coli accounts for 17.3% of clinical infections requiring hospitalization and Escherichia coli represents the second most common source of infection behind Staphylococcus aureus (18.8%). Infections caused by these bacteria are usually treated with antibiotics but, in recent years, the emergence of some Staphylococcus aureus and Escherichia coli strains that exhibit resistance against many antibiotics, has been observed worldwide. Originating from the negative impact that antibiotics can exert on health and from the increasing resistance of some bacteria towards antibiotics, there are currently ongoing questions about the use of essential oils as agents with antibacterial properties [According to the Broad Institute (2010), infections due to operties ,69,70,71Determination of the antibacterial activity for the samples treated with the stable emulsions was achieved ‘in Vitro’ by using the diffusion method in accordance with the working methodology previously described.The antibacterial activity of the samples treated with emulsions was evaluated based on the diameter of the inhibition zone, respectively of the degree of inhibition and the IC50 Index. For the calculation of the IC50 index emulsions with a composition similar to that of the E3 emulsion were used wherein only the oil concentration and the water amounts were varied. The samples treated with the emulsions in which the oil concentrations were 2% (emulsion E3A) and 6% (emulsion E3B), denoted TE3A and TE3B, respectively, were selected to investigate the effect of essential oil concentration on antibacterial activity.The obtained results are presented in E. coli and S. aureus). From the analysis of the results obtained, the following conclusions can be drawn regarding the influence of the composition of the emulsions on the antibacterial activity:The data presented show that the samples treated with the emulsions containing the peppermint essential oil exhibit an antibacterial action against both tested bacteria  The untreated cotton sample does not show antibacterial activity against the two bacteria (ii) The peppermint oil, which contains as the main components the terpene compounds menthol (62.87%), 3-p-menthene (13.16%), menthone (12.78%), and camphene (3.15%) , exhibitE. coli and 53.6 mm for S. aureus) as well as for the sample treated with the emulsion TE3 (40.6 mm for E. coli and 58.3 mm for S. aureus), that contained beeswax, were larger compared to the diameters of the inhibition zones of the sample treated with the emulsion TE6 which did not contain wax (34.6 mm for E. Coli and 50.5 mm for S. aureus). The results obtained are in accordance with the data from the scientific literature concerning the antibacterial activity that the wax manifests against the tested bacteria [(iii) The diameters of the inhibition zones both for the sample treated with the emulsion TE1  The different sensitivities of the two bacterial species to the tested oil are due to the structure of their cell wall, which is different in Gram-positive bacteria compared to Gram-negative bacteria .E. Coli bacteria and 56.27 mg oil/g material in the case of the S. aureus bacteria, respectively [(v) Applying emulsions containing increasing amounts of oil  to the cotton fabric increases its antibacterial activity against the tested bacteria, as can be seen from ectively .S. aureus and E. coli bacteria compared to the sample TE6. The advantages of using these emulsions to obtain materials with flavoring and antimicrobial properties consist of the following: (i) the use of essential oils extracted from mint, which is a perennial plant that multiplies very easily; (ii) gelatin and wax are relatively cheap and easy-to-procure products; (iii) the amount of synthetic emulsifier Tween 80 used for the preparation of emulsions can be lower.Materials with flavoring and antimicrobial properties were obtained by applying emulsions containing peppermint essential oil on cotton fabric. Several emulsion formulations containing various incorporating agents with peppermint essential oil were prepared and evaluated. The most stable emulsions were the ones that contained chitosan, gelatin, beeswax and Tween 80 (in a concentration higher than 1.50%) namely the emulsions E1, E3, and E6. Emulsions applied on cotton fabrics influence the comfort indices . The amount of oil released in the artificial perspiration solution differs depending on the composition of the emulsions. For the sample TE6 (that did not contain beeswax), the release of peppermint essential oil was accomplished in a shorter time compared to the samples TE1 and TE3 (that contained beeswax). In the case where the release was performed in air, the content of volatile components that remained on the material (after 6 h) was 63.12% for the sample TE1, 74.08% for the sample TE3 and 55.65% for the sample TE6, respectively. The samples TE1 and TE3 exhibited a higher antibacterial activity against From the results obtained, it can be concluded that using the application of emulsions containing peppermint essential oil on various textile supports, it is possible to obtain a varied range of patches and bandages with aromatherapeutic and antibacterial properties, that allow a controlled release of the essential oil.


The results show that when the nano-SiO2 dosage is 1%, the optimal compressive strength of the specimens at the curing age of 7 d can be obtained compared with cemented materials without nano-SiO2, and the compressive strength of the modified specimens raises by 84%; when the nano-SiO2 dosage is 1%, the optimal tensile strength and shear strengths of the modified specimens can be obtained at the curing age of 28 d, increasing by 82% and 142%. The results reveal that nanocomposite fibers can be used as additives to change the mechanical properties of cemented backfill materials made using coal-based solid waste. This study provides a reference for the disposal of coal-based solid waste and the enhancement of the mechanical properties of cemented backfill materials.Previous studies have shown that coal-based solid waste can be utilized in combination with cement, silica fume, and other modified materials to create a cemented backfill material. However, traditional cemented backfill materials have poor mechanical properties, which may induce the emergence of mining pressure and trigger dynamic disaster under complex mining conditions. In this study, the nanocomposite fiber was used to modify the traditional cemented backfill materials and a new cemented backfill material was developed using coal-based solid waste, nanocomposite fiber and other materials. Specifically, coal gangue, fly ash, cement, and glass fibers were used as the basic materials, different mass fractions of nano-SiO Coal constitutes a significant component of the global energy industry, with an estimated production exceeding 7 billion tons in 2018 alone . GeneralThe extensive accumulation of coal-based solid waste is a prevalent concern in coal mines around the world; therefore, the disposal of coal-based solid waste has become an important factor affecting resource development and environmental protection, and the comprehensive utilization of coal-based solid waste on a large scale is an important approach to address the issue of solid waste treatment. The utilization of coal-based solid waste was initially adopted in developed Western countries and garnered significant attention worldwide until the late 1960s. In the 1970s, the slogan of “Resource recycling” was put forward, and the United States, Germany, the Netherlands, and other countries realized a relatively high degree of utilization of coal gangue and formulated corresponding technical standards. In terms of the comprehensive use of coal gangue, an integrated treatment and utilization system has been formed in many countries for power generation, paving, the production of building materials, the production of chemical raw materials, agricultural applications, and underground filling. For example, coal gangue has been used to generate electricity in coal mine power plants and coal plants of Germany, the Netherlands, and other countries since the 1970s ,7. Coal At present, coal-based solid waste made of cemented backfill material are widely used in mining engineering. The main composition of cemented backfill materials includes solid wastes  with a mass proportion of about 70–85% as an aggregate, additives (such as cement), and water; after the preparation, cemented backfill materials are transported to the goaf to support the surrounding rock . This ba2 as an additive can effectively improve the mechanical properties and durability of ultralight cementitious composites [2 on the workability, microstructure, and compressive strength of concrete samples after early negative-temperature curing and concluded that this method can effectively improve the microscopic hydration structure and increase the compressive strength of the material. In some instances, the incorporation of chemical additives into nanofibrous materials can enhance the brightness of composites. Research has demonstrated that nano-modified suspensions containing thin hydrotalcite, graphene, and carbon nanotubes as additives can also improve concrete strength [Nanocomposite fibers are crystalline materials with high chemical activity , which cmposites , and celmposites . Chen etmposites  exploredmposites  analyzedstrength . The incstrength . Some ststrength .2 dosages and curing ages on the tensile strength, compressive strength and shear strength of the modified cemented backfill materials were analyzed. The enhancement degree of the mechanical properties of the modified cemented materials was discussed, and the optimal nano-SiO2 dosages and curing age were obtained. This study provides a theoretical basis for the preparation of cemented backfill materials made of nanocomposite fibers and coal-based solid wastes.In summary, nanocomposite fiber materials can serve as additives to enhance the properties of cemented materials , leading to significant improvements in the macromechanical and other properties of the materials. However, the majority of studies have been conducted in the field of civil engineering, and there are quite a few studies on the modification of coal-based solid waste materials using nanocomposite fibers in the field of mining. To this end, nanocomposite fibers were employed to modify coal-based solid waste cemented backfill materials, and nanocomposite fiber materials were applied in the field of backfilling mining in this study. Besides, experiments on mechanical properties of cemented backfill materials made of coal-based solid waste and nanocomposite fiber were conducted, and the effects of different nano-SiOThe equipment required for this test included an electro-hydraulic servo press, a jaw crusher, an X-ray diffractometer, a standard curing box, and a hand-held mixer. 2, and water were used to prepare the cemented backfill materials, as shown in According to the continuity of engineering practice and materials research ,41, fly Coal gangueCoal gangue is one of the main solid wastes in the mine. In this test, irregular black-grey gangue taken from a mine in Shandong Province was selected. The gangue samples were crushed to less than 20 mm by a jaw crusher, the curves of particle size grading were drawn in 2.Fly ashThe fly ash used in this test was purchased. According to Chinese standard GB1596-91 , fly ashPO42.5 silicate cement was used, and the diffraction pattern of the cement was obtained via X-ray diffraction, as shown in 3.2Glass fibers with nano-SiO2 were purchased from companies in Shanghai and Suzhou, China. 2.According to the continuity of the test , glass f2 dosages of 0%, 0.1%, 0.5%, and 1% were added to specimens, respectively. Using the electro-hydraulic servo universal testing machine (WAW-1000D), uniaxial compressive, tensile and shear tests on specimens cured for 3 d, 7 d, 14 d, and 28 d were conducted at the shear angles of 40°, 50° and 60°, and the compressive strength, tensile strength, and shear strength of the specimens were analyzed [The previous studies have shown that the best mechanical properties and conveying properties of cemented materials could be obtained when the mass proportion of gangue- and fly ash-based cementitious material was 81% , or thatanalyzed . A const2 was added for dry mixing and then tap water was added and mixed for 3–4 min. The mixing time can be extended appropriately to ensure the homogeneity of the additives. According to Standard for test method of performance on building mortar [According to the above test program, due to the limitations of the multi-functional mixer and mixing bucket, the cemented material could only be stirred in a single group and in a single-component type. Each group was prepared with 3 specimens, and the average value of the three specimens was taken as the final experimental result. Fly ash, gangue, cement, and glass fibers required for a single group were added to the mixing bucket for dry mixing. After the ingredients were stirred evenly and full contact was achieved, nano-SiOg mortar , the preTaking the specimen with a nano-dosages of 0.5% as an example, the compressive damage morphology of cemented specimens made of coal-based solid waste and nanocomposite fibers is obtained, as shown in (1)Cracks developed from the corners of the specimen at the curing age of 3 d. With the increase in load, the cracks at the corners of the specimen gradually propagated upwards until they penetrated through the entire specimen. When the cracks in the corners of the specimen developed, cracks in the middle of the specimen also appeared, while they did not pass through the whole specimen. The side of the specimen exhibited two large cracks, and a large number of fibers were observed in the cracks, which pulled each other to maintain the complete form of the specimen.(2)The specimen at the curing age of 7 d was damaged from the left side of the lower corners. With the increase in the load, the two small cracks on the left side of the specimen developed and expanded, and eventually penetrated the whole specimen. The penetrating cracks were located in the middle of the specimen, and the width of the specimen reached the maximum. As the loading time increased, small cracks were generated on the right side of the specimen, and large cracks appeared in the middle of the specimen and extended to the end of the specimen.(3)The damage location of the specimen at the curing age of 14 d was the same as that of 7 d, and the damage on the specimen started from the left side of the lower corners. At the beginning, two cracks were generated in the corners of the specimen. With the increase in load, the two cracks developed upward, and the specimen was constantly broken in the process. Due to the fiber tension, the specimen still maintained high integrity, and the two cracks in the corners eventually penetrated through the whole specimen. Small cracks were also generated on the left side of the specimen.(4)The specimen at the curing age of 28 d was damaged from the right side of the lower corners. The cracks formed on the right side and in the middle of the specimen simultaneously. With the increase in load, two cracks developed and extended 1/2 of the specimen’s length, and finally cracks formed through the middle of the specimen at an angle of 45°. There was a peeling phenomenon on the surface of the right side of the specimen, while the specimen still maintained high integrity. Due to the development of cracks on the left surface of the specimen, a large number of fragments fell off, and the evenly distributed glass fibers can be seen on the cross-section of the fallen fragments.As shown in This shows that the compressive failure morphology of specimens exhibits different forms at different curing ages. With the increasing age, the specimen changed from a small amount of debris peeling to a large amount of debris shedding, and the number of cracks also increased with the increasing curing age in the compressive test.2 dosages.2 was not significantly improved in the early stage of curing. The peak compressive stress of the specimen containing 1% nano-SiO2 was 5.78 MPa at the curing age of 14 d. At the curing age of 28 d, the overall peak stress of the specimens became larger; the compressive strength of the specimens containing 0.5% and 1% nano-SiO2 reached about 6.7 MPa, and the compressive strength of the specimens containing 1% nano-SiO2 significantly improved. With the extension of the curing period, the compressive strength of the specimens increased significantly with the increase in nano-SiO2 dosage. However, as the curing age reached 28 d, the compressive strength of the specimens no longer significantly increased with the increase in nano-SiO2 dosage. The main reason is that when a small amount of nano-SiO2 was added, nano-SiO2 could not fully participate in the reaction of volcanic ash in the early curing stage, and less of the C-H-S gel produced by the cement hydration was generated [2 was added, nano-SiO2 fully participated in the reaction of volcanic ash, and the cement hydration reaction was promoted, resulting in a small difference in compressive strength among specimens with different nano-SiO2 contents after the curing age of 28 d. This finding was consistent with the previous results in the literature [2 had a negative impact on the improvement of compressive strength.As shown in enerated , contribterature , indicat2 had a significant impact on the compressive strength of the specimen. However, the addition of more nano-SiO2 dosage was unable to significantly enhance the later strength of the nanocomposite fiber bonded specimen.Therefore, for the early strength of the specimen, an increase in the amount of nano-SiO2.2 was 0.99 MPa, 1.09 MPa, and 1.68 MPa, respectively. Compared to the specimens only reinforced with glass fiber, the compressive strength of the specimens containing 0.1% nano-SiO2 increased by 47%, while that containing 0.5% and 1% nano-SiO2 decreased by 13% and 4%, respectively. This indicates that the incorporation of a small amount of nano-SiO2 is adverse to the early compressive strength of the specimen. After 7 days of curing, the specimens containing 0.1% nano-SiO2 exhibited a maximum compressive strength, increasing to 4.38 MPa. After 14 days of curing, the compressive strength increased by 55%. After 28 days of curing, the addition of nano-SiO2 resulted in a more than 19% increase in compressive strength for the specimens. However, the compressive strength of the specimens containing 1% nano-SiO2 was actually lower than that containing 0.5% nano-SiO2. This may have been caused by the short curing age, large nano-SiO2 dosage, and incomplete reaction of nano-SiO2, which had a negative impact on the compressive strength of the specimens.When the curing age was 3 d, the compressive strength of the specimens containing 0.1%, 0.5%, and 1% nano-SiO2 was added, the peak compressive strength of the specimen corresponded to an increase in strain, while the strain of the specimen did not increase with the increase in the nano-SiO2 dosage. The maximum increase in compressive strength and strain of the specimen was 14% at the curing age of 3 d, 104% at the curing age of 7 d, 68% at the curing age of 14 d, while there was a minimum decrease of 6% at the curing age of 28 d. The results show that the compressive strength and strain of the specimen decreased after nano-SiO2 was added at the curing age of 28 d. Therefore, the addition of nano-SiO2 greatly increased the early strain of the specimen rather than the late strain, and the specimen strain was not linearly correlated with the nano-SiO2 dosage.When nano-SiO2 can improve the compressive strength of the specimens to a certain extent. As the curing age increased, and the more nano-SiO2 added, the higher the slope and faster the growth rate of the peak compressive strength curve of the specimen in the early curing stage. When the nano-SiO2 dosage was within 1%, the more nano-SiO2 that was added, the better the early compressive strength of the specimen was. However, the later strength of the specimen did not increase with the increase in the nano-SiO2 dosage. According to the fitting equations of different dosages of nano-SiO2 and glass fiber in the figure, the fitting degree R2 was above 0.9626. However, for specimens with a nano-SiO2 dosage of 0.1%, the growth of compressive strength and the curing age had a high correlation. The fitting equation curve shows the slowdown of compressive strength at varying degrees during the curing process from 14 d to 28 d. This suggests that the compressive strength slope of the specimen changed gently within a certain curing age.The compressive strength of nanocomposite fiber bonded specimens was higher than that of the control specimens at different curing ages. This indicates that the addition of nano-SiO2 increased by 47% compared to that without nano-SiO2. At the curing age of 7 d, the compressive strength of the specimen containing 1% nano-SiO2 was only 3% higher than that without nano-SiO2. This indicates that a small amount of nano-SiO2 had little effect on the early compressive strength of the specimen. After 28 days of curing, the growth of compressive strength of the specimen slowed down further. Only the specimen containing 0.1% nano-SiO2 exhibited an increase in slope after 28 days of curing, and the compressive strength of the specimen containing 0.5% nano-SiO2 was higher than that containing 1% nano-SiO2. This could be attributed to the excessive presence of nano-SiO2 particles that fail to undergo a pozzolanic reaction, thereby impeding cement hydration and hindering the enhancement of compressive strength under the nano-SiO2 dosage of 1% [At the curing age of 3 d, the compressive strength of the specimen containing 1% nano-SiO2, the strain of the specimen increased significantly at the curing age of 3 d, 7 d, and 14 d. Even after 7 days of curing, the strain of specimens containing 1% nano-SiO2 increased by 104% compared to those without nano-SiO2. At the curing age of 3 d, the strain of the specimens with different nano-SiO2 dosages increased by about 10%. At the curing age of 7 d and 14 d, the strain of the specimens with different nano-SiO2 dosages increased significantly, with an average increase of about 60% compared to that of the specimen reinforced with 0.3% glass fiber. However, at the curing age of 28 d, the strain of the specimens with different nano-SiO2 dosages decreased by 18%, 20%, and 6%, respectively. This is due to the fact that the added enhancement of nanoscale materials prevented the development of cracks within the composites, and the increase in the maintenance cycle allowed for better reactive bonding with other materials, which required more energy to initiate and extend the cracks and led to specimen failure [After the addition of nano-SiO failure .2 dosage of 0.5% as an example, the tensile failure morphology of the cemented specimens made of coal-based solid waste and nanocomposite fibers was obtained, as shown in (1)Under the action of axial pressure, two cracks were generated from the upper end of the specimen at the curing age of 3 d. With the increase in the load, the cracks extended downward. Ultimately, one crack passed through the entire specimen, while the other one extended to approximately one-fourth of the specimen’s length. The sample was not directly broken into two parts along the crack, and the sample still has a certain amount of residual tensile strength.(2)The cracks of the specimen at the curing age of 7 d developed from the bottom, and the cracks of the specimen extended upward under the action of axial force. As the cracks developed upward, the width of the cracks decreased gradually, and the cracks penetrated the whole lower part of the specimen, while these cracks were almost invisible in the upper part of the specimen. Compared with the specimen at the curing age of 3 d and 7 d, the cracks developed in different positions and extended in different directions. The crack width in the specimen at the curing age of 7 d was much smaller than that of the specimen at the curing age of 3 d.(3)The cracks of the specimen at the curing age of 14 d appeared from the bottom and extended upward. Although the cracks did not run through the specimen on the surface, the tensile strength dropped to a certain low value. After the specimen was removed from the press machine, the specimen did not break into two parts. The crack width of the specimen at the curing age of 14 d was smaller than that of the specimen at the curing ages of 3 d and 7 d.(4)The specimen at the curing age of 28 d had the same failure mode as that at the curing age of 14 d. That is, the cracks did not run through the specimen on the surface. The cracks of the specimen at the curing age of 28 d were generated from the bottom. With the increase in axial force, the cracks developed and extended upwards. During the extension of the cracks, an audible sound was produced.Taking a specimen with a nano-SiOWith the increase in the curing age, the width of the cracks of the cemented specimen modified by nanocomposite fibers decreased gradually, and there was no through crack on the surface of specimens at the curing ages of 14 d and 28 d.2 dosages.2 dosages compared to those reinforced with glass fiber only.2 was lower than that of the specimens with only glass fiber added. This can be explained as follows: due to the small amount of nano-SiO2, nano-SiO2 failed to participate in the volcanic ash reaction, resulting in lower tensile strength of the specimen. At the curing age of 28 d, the specimen containing 0.1% nano-SiO2 had the highest slope of the stress–strain curve of tensile strength and the largest increase in the tensile strength. At the curing age of 14 d, the specimen containing 0.5% nano-SiO2 had the largest increasing amplitude in tensile strength. At the curing age of 7 d, the specimen containing 1% nano-SiO2 had the largest increasing amplitude in tensile strength. The results indicate that the addition of nano-SiO2 dosage had a significant impact on the increase in tensile strength of the specimens at different curing ages.As shown in 2. However, as the nano-SiO2 dosage increased, the decreasing amplitude gradually decreased. When the nano-SiO2 dosage was 1%, the tensile strength of the specimen increased significantly, and the highest increase in the tensile strength was 82%. When the nano-SiO2 dosage was 0.1%, the tensile strength of the specimen decreased by 15%. When the curing age was 28 days and the nano-SiO2 dosage was 0.1%, a large amount of pozzolanic reaction was produced by nano-SiO2, which promoted cement hydration and led to the formation of abundant C-S-H gel [As shown in -S-H gel . As a re2 can be expressed by a quadratic polynomial. The fitting degree R2 of the two factors reaches 0.9491 or above. With the increase in curing age, the growth rate of the tensile strength of blank control specimens gradually slows down, even showing a downward trend. As the curing age increases to 28 d, the curve of tensile strength tends to flatten.The relationship between tensile strength and curing age of blank control specimens and specimens with 0%, 0.1%, and 0.5% nano-SiOTaking a specimen at the shear angle of 40° as an example, the shear failure morphology of the cemented specimens made of coal-based solid waste and nanocomposite fibers was obtained, as shown in (1)With the increase in load, cracks in the specimen at the curing age of 3 d were generated along the shear angle. When the cracks developed to the bottom of the specimen, the cracks bifurcated; one crack continued to develop along the shear angle, while the other one developed to the specimen’s corners. Through the development of cracks along the shear angle, a large number of small cracks were generated on the upper part, especially at the corners of the specimen. Finally, the specimen was penetrated by the cracks, while the integrity of the specimen was maintained.(2)The specimen at the curing age of 7 d was not damaged along the shear angle. With the increase in load, a large number of small cracks were initiated in the upper part of the specimen, and a peeling phenomenon occurred; the cracks at the specimen edge expanded with the increase in load, and ultimately, the edge of the specimen fell off.(3)The cracks in the specimen at the curing age of 14 d were developed from the position of the fixture gasket (the edge of the specimen). With the increase in load, the cracks gradually expanded and had a significant effect on the specimen. The surface of the specimen began to buckle and has a tendency to fall off; the specimen edges were gradually broken, but the edges did not fall off.(4)The penetration crack of the specimen at the curing age of 28 d did not develop along the shear angle, and the two cracks penetrated the whole specimen at a certain angle with the shear angle. During the process of crack development, a loud sound was emitted from the specimen twice in succession; at the same time, the specimen was penetrated and the upper corners of the specimen were crushed, while the integrity of the specimen was still maintained, and no fragments fell off.The shear failure morphology of cemented specimens modified by nanocomposite fibers and glass fibers was quite different. Specifically, cemented specimens modified by glass fibers were destroyed along the shear angle, while the cracks of cemented specimens modified by nanocomposite fibers had a certain angle with the shear angle, and there were a lot of small fissures generated around the main crack.2 dosages.As shown in 2 dosage. When the shear angle was 50°, the shear strength of the specimen increased with the increase in nano-SiO2 dosage. The shear strength of the specimen containing 1% nano-SiO2 at the curing age of 3 d and 7 d significantly improved; the specimen containing 0.5% nano-SiO2 at the curing age of 14 d and 28 d exhibited the fastest increase in the shear strength. When the shear angle was 60°, the small addition of nano-SiO2 in the early curing stage had little effect on the shear strength of the specimen. When the curing age reached 14 d, the shear strength of the specimen showed a trend of first increasing and then decreasing with the increase in the nano-SiO2 dosage. When the curing time was 28 d, the shear strength of the specimen increased with the increase in the nano-SiO2 dosage; the specimen containing 1% nano-SiO2 exhibited the highest shear strength slope and the fastest increase.When the shear angle was 40°, the shear strength of the specimens modified by nanocomposite fibers was greater than that of control specimens, and the shear strength of the specimens modified by nanocomposite fibers increased with the increase in the nano-SiOIt can be seen from the figure that:2 increased by 25%, 55%, and 126% compared to the specimens only reinforced with glass fiber. However, when the shear angle was 40°, 50°, or 60°, the specimens modified by nanocomposite fibers had the same increasing amplitude of shear strength, and the shear strength of the specimens increased with the increase in nano-SiO2 dosage. At the curing age of 7 d, the specimen containing 1% nano-SiO2 had the largest increasing amplitude in the shear strength, increasing by 126%, 117%, and 70% under shear angles of 40°, 50°, and 60°. Therefore, the addition of more nano-SiO2 significantly improved the early shear strength of the specimen, and as the shear angle increased, the increasing amplitude in the shear strength of the specimen also decreased.The early shear strength of the specimens modified by nanocomposite fibers significantly improved after the curing age of 7 d and 28 d. When the shear angle was 40°, the shear strength of the specimens containing 0.1%, 0.5%, and 1% nano-SiO2 increased by more than 53%. At the curing age of 28 d, the shear strength of the specimens containing 1% nano-SiO2 had the largest increase, increasing by more than 130%. However, the shear strength of the specimens containing 0.1% and 0.5% nano-SiO2 increased by more than 50% and 70%, respectively. Therefore, the addition of nano-SiO2 significantly improved the shear strength of the specimens mixed with nano-SiO2 in the later stage, and the shear strength increased with the increase in the nano-SiO2 dosage.In the later curing stage, compared with the specimens only mixed with glass fiber, the shear strength of the specimens mixed with nano-SiO2 dosage of 0.5% at different curing ages.2, the shear strength of all specimens increased, except the specimens containing 0.5% nano-SiO2 at the curing age of 3 d under a shear angle of 60°, which decreased by 46%. When the shear angle was 40°, the shear strength of specimens at curing ages of 3 d, 7 d, 14 d, and 28 d was 0.62 MPa, 1.50 MPa, 2.26 MPa, and 2.30 MPa, respectively. In this case, the shear strength of specimens increased with the increase in curing age. At the curing age of 3 d, the shear strength of the specimen was 0.62 MPa, which was 100% higher than that of the control specimen. At the curing age of 28 d, the shear strength of the specimens increased by 92% compared to those only mixed with glass fiber. When the shear angle was 50°, the specimen presented the largest stress increase at a curing age of 14 d, and the stress increase reached 103%. When the shear angle was 60°, the specimen experienced a stress increase reaching 85% at the curing age of 28 d. As shown in 2 had a smaller effect on the early strength improvement of the specimen and a greater effect on the later strength improvement of the specimen.As shown in x-axis and the curing age as the y-axis, the shear strength surface equations of (b), (c), and (d) can be obtained through surface fitting as follows:It can be seen that the shear strength of the cemented specimen modified by nanocomposite fibers decreased with the increase in shear angle and increased with the increase in curing age . When thThe sum of the squares of the residuals of each surface equation is 0.801, 0.9694, and 0.9874. The fitting equation of the largest shear strength of the cemented specimen modified by nanocomposite fibers and the curing age is obtained, and the fitting degree can be as high as 96%.(1)2 dosage at a curing age of 7 d. The specimen containing 1% nano-SiO2 has a peak compressive strength which is 84% higher than that of cemented materials only reinforced with glass fibers. When 1% nano-SiO2 is added, the tensile strength of the specimen at the curing age of 28 d is significantly improved, which is 82% higher than that of the cemented material only reinforced with glass fiber. When 1% nano-SiO2 is added, the shear strength of the specimens at the curing age of 28 d under the shear angles of 40°, 50°, and 60° reaches its peak, with a large slope and the fastest increase in shear strength. Among them, the shear strength of the cemented materials modified by nanocomposite fibers under a shear angle of 40° increases by 142% compared to those only reinforced with glass fibers.The compressive strength of cemented materials modified by nanocomposite fibers increases with the increase in nano-SiO(2)2 is added to cemented material, the relationship between the growth of compressive strength and curing ages is linearly correlated with a quadratic polynomial. The tensile strength and curing age of specimens with a nano-SiO2 dosage of 0%, 0.1%, and 0.5% are linearly correlated with quadratic polynomials, with a fitting degree R2 of 0.9999 for specimens containing 1% nano-SiO2. The shear strength, shear angle, and curing age of cemented materials modified by nanocomposite fibers exhibit a cubic polynomial relationship, with a fitting degree of 96%.When 1% nano-SiO