The acoustic signal in the operation of a power transformer contains a lot of transformer operation state information, which is of great significance to the detection of DC bias state. In this paper, three typical parameters used for DC bias state detection are selected by comparing the acoustic variation of a 500 kV Jingting transformer substation No. 2 transformer with that of the core model built in the laboratory; then, acoustic samples of the 162 EHV normal state transformers are collected, and the distribution regularity of three typical parameters in normal state is given. Finally, according to the distribution regularity, clear warning threshold of typical parameters are given, and the DC bias cases from the 500 kV Jingting transformer substation are used to verify the effectiveness of the threshold. With EHV transmission projects widely used, the number and voltage level of DC transmission lines are growing, and the DC magnetic bias problem caused by AC/DC hybrid transmission is becoming increasingly serious ,2,3,4. TIn recent years, the acoustics or vibrations of a transformer have been analyzed from the perspective of mechanism explanation and experimental simulation ,21,22,23In order to obtain reliable acoustic parameters of DC bias state and its definite early warning threshold, this paper first carries out the DC bias state acoustic signal collection on the 500 kV transformer (from Jingting Substation in Anhui Province) and the transformer model (built in the laboratory). Secondly, two sets of acoustic signal samples parameters are calculated and compared, and three typical parameters that are beneficial to the detection of the DC bias state are screened out. Then, the typical parameters of 162 normal state single-phase transformers in Hebei Power Grid are statistically analyzed, which provide data support for the delineation of early warning threshold and use real DC bias case to verify the effectiveness of the threshold application.Transformer vibration can be divided into core vibration and winding vibration. Compared with the core vibration component, the winding component is extremely small, so this section mainly analyzes the core vibration law.λ will first increase to the maximum value max λmax. As the magnetic field intensity H increases, at this time, the magnetization M of the ferromagnetic material is the saturation magnetic domain wall shift magnetization MWS. The magnetostriction process at this stage is determined by the magnetic field. Domain wall shift dominates. When the magnetic field intensity H further increases, the magnetization M enters the saturation zone. The magnetostriction process at this stage is dominated by the magnetic domain rotation, while the magnetostriction gradually decreases . In addition, according to the magnetostrictive experiment of soft magnetic materials [εV in the normal state is shown in (1).λ0(σ) is the magnetostriction value caused by the domain wall shift under the preload; the λmax is the maximum magnetostriction value when the saturated wall moves. Similarly, the transcendental function form of the core vibration characteristics εV in DC bias state [The magnetostriction of the core material aterials , it is kas state ,32 is shM is the power frequency signal, and the main vibration frequency of transformer core is the double frequency of power frequency signal. Moreover, M is not a perfect sine wave in the actual operation process; it contains a small amount of high-order harmonic components, so the results of the experiment usually contain a small amount of n × 100 Hz . When DC bias occurs, M can be considered as the superposition of DC component and power frequency. At this time, the main vibration frequency of transformer core has components in n × 50 Hz , and the size of each component will increase with the increase of DC component in M.From (1) and (2), it can be seen that when the transformer is in normal state, In order to explore the characteristics of DC bias acoustic signal of an actual operation transformer, this paper collected the operation acoustic signal of the 500 kV Jingting substation before and after DC bias treatment. Before the treatment of DC bias, the neutral grounding value of the No. 2 transformer in Jingting station was 21.4 A, which exceeded the expected treatment standard (18 A), and the increase of transformer vibration and noise was obvious. After the DC bias treatment, the neutral grounding value decreased to 10.7 A, although there is still a certain degree of DC bias, but it has dropped to the governance standard.In the aspect of acoustic signal acquisition, according to IEC60651 standard, the measuring frequency band of the acquisition device covers 25 Hz~16 kHz, the sampling frequency is 96 kHz, and the frequency response meets the sampling requirements. The microphone should follow the following principles: (1) avoid the end face of the cooler; (2) be arranged on the side of the long end face; (3) be located in the middle of the end face; (4) the direction of the microphone is perpendicular to the position of the non-stiffener on the surface of the transformer; (5) the horizontal distance from the transformer tank wall is 100 cm; (6) the vertical distance from the ground is 150 cm. The schematic diagram of the acoustic signal acquisition scheme for the transformer is shown in Most of the energy in the transformer acoustic signal is contributed by the core vibration. Therefore, a core model was made to simulate a transformer acoustic signal in the laboratory. The silicon steel sheet used in the model is B30P105, and its geometric dimension and signal acquisition layout are shown in The magnetic flux density at the measuring point will directly affect the vibration and voiceprint of the iron core. Therefore, before applying different excitation signals, the test pressure level is determined according to the magnetic flux density amplitude of the core pillar to ensure that the iron core works in the unsaturated region. The pressurization level and scheme of the test are shown in There are some differences in the acoustic parameters of DC bias between the real transformer and the laboratory core model. In order to find more suitable acoustic parameters for DC bias state early warning, it is necessary to compare and analyze parameters of the two groups of experiments.The acoustic frequency domain signal of the 500 kV transformer in Jingting substation under normal state and DC bias state is shown in The acoustic frequency domain signal of the core model under normal state and DC bias state is shown in (1)F1,Dominant frequency According to the variation of acoustic signal in the above experiment, four typical parameters can be extracted:(2)F2,Ratio between odd and even harmonics (3)F3,Ratio of fundamental frequency (4)F4,fX is the amplitude of frequency component at frequency f; fmax is the upper limit of statistical frequency. Because the energy of transformer acoustic signal is mainly distributed in the range of 0–2000 Hz, fmax is generally 2000 Hz. The calculation results are shown in Total harmonic distortion It can be seen from the calculation results of signal typical parameters that the actual case of the transformer parameters variation law is consistent with the core model, but there are some differences.Consistency: Compared with the transformer acoustic signal in normal state, the actual case and the laboratory core model acoustic signal have the rule of fundamental frequency proportion decreasing, total harmonic distortion increasing, and ratio between 50 Hz and 100 Hz harmonic increasing, which is consistent with the theoretical analysis conclusion in Differences: (1) Compared with the transformer in normal state, the acoustic signal dominant frequency increased in the actual case of DC bias, but is always kept at 100 Hz in the laboratory core model. This is because there are many interference factors in the operation of the transformer, the voltage contains lots of high-frequency harmonics, and the DC current is large; the results show that the high-frequency harmonics of 50 Hz in acoustic signal share the energy of the fundamental frequency. (2) From the value of the parameter, there is a big gap between parameters from the laboratory core model and parameters from the actual transformer. For example, the ratio of the fundamental 500 kV transformer is in the range of 0.01% to 0.6%; however, that which is calculated by the core model is in the range of 35% to 75%. Other parameters have similar laws.This paper holds that the difference in acoustic parameters between the core model and the real transformer is mainly caused by two reasons: (1) the DC bias current of transformer core model in the laboratory is small, so the frequency spectrum distortion of acoustic signal is weak; (2) the acoustic wave transmission medium of the real transformer is more complex, and the frequency response function of the oil and tank have an important impact on the acoustic frequency spectrum.D(f) is DC bias state frequency spectrum distortion function. H(f) is frequency response function of oil and tank. EM(f) is frequency spectrum of core model, and ER(f) is the simulated real transformer frequency spectrum.Based on the above two reasons, a frequency spectrum conversion model is proposed. The model isIn order to verify the effectiveness of the model, the acoustic signal of the core model  is calculated as a case.H(f) is extracted. After normalizing, H(f) is shown in From the investigation work of , the freD(f) can be preliminarily obtained. After averaging and normalizing the three phase transformers of data in D(f) is shown in According to the frequency spectrum of 500 kV transformer under DC bias and normal state, EM(f) is shown in ER(f) can be calculated by H(f) given in D(f) given in The core model frequency spectrum According to Therefore, the following conclusions can be drawn: (1) The reduction of ratio of fundamental frequency, the rise of total harmonic distortion, and the rise of ratio between odd and even harmonics are the necessary conditions to judge whether the transformer is in DC bias state, while the rise of dominant frequency is not a necessary condition. (2) The core model under the ideal condition and the actual case of the transformer can only compare a typical parameter variation rule, but the numerical comparison of parameters is meaningless.The above two conclusions mean that the core model in the laboratory can provide some guidance for the selection of the actual transformer acoustic diagnosis parameters, but the results in the laboratory cannot provide data support for the identification of the anomalous state of the transformer. Therefore, we need an explicit acoustic diagnosis parameter warning threshold.According to conclusions of the previous chapter, the early warning method of the DC bias state is determined as follows:F2, ratio of fundamental frequency F3, and total harmonic distortion F4, are selected for early warning.Firstly, select parameters used for acoustic signal discrimination: three necessary discrimination parameters, including ratio between odd and even harmonics Then, determine the early warning threshold for the selected parameters: there are few anomalous cases on the real transformer. Although the laboratory model can produce a large amount of anomalous state acoustic signal data, according to conclusions of the previous chapter, the parameter value is not available in the real transformer warning work. Therefore, this paper collected a large number of normal transformer acoustic signal samples and made probability distribution statistics on the parameters of normal samples. Thus, the distribution of normal state parameters is obtained.Finally, the upper or lower limit of the parameter distribution is used as the parameter early warning threshold. If the acoustic diagnostic parameters of a sample exceed the threshold, the sample is considered anomalous.In this paper, acoustic signal acquisition is carried out for 500 kV, 1000 kV transformers under the jurisdiction of State Grid Hebei Electric Power CO., LTD. Because all transformers are single-phase split transformers, and each group of transformers is relatively independent, this paper takes single-phase transformers as sample individuals for statistical analysis. The sample covers 162 transformers with 3 types of cooling methods, 10 manufacturers, and 21 stations. The sample library covers various types of transformers, which can support the reliability of acoustic signal parameter analysis results. The layout principle of microphone and acoustic signal acquisition equipment is the same as that in (1)F2:The 50 Hz odd/even frequency multiplication ratio F2 is shown. It can be seen from the figure that the F2 of transformer under normal state is mainly distributed between 0 and 0.6. According to the cumulative probability curve, 99% of the samples are below 0.9.As shown in F2 is right-skewed and presents the characteristics of lognormal distribution. F2 of the sample is lnF2 after calculating the logarithm, and lnF2 of all samples constitutes aggregate D2. Assume D2~N(2), where F2 and F2. The fitting results are F2 obeying the lognormal distribution.The parameter distribution of (2)F3:Fundamental frequency proportion F3 is shown. It can be seen from the figure that the F3 of transformer under normal state is mainly distributed between 0.025 and 0.3. According to the cumulative probability curve, 99% of the samples are above 0.025.As shown in F3 is right-skewed and presents the characteristics of lognormal distribution. F3 of the sample is lnF3 after calculating the logarithm, and lnF3 of all samples constitutes aggregate D3. Assume D3~N(2), where F3 and F3. The fitting results are F3 obeying the lognormal distribution.The parameter distribution of (3)F4:High/low-frequency ratio F4 is shown. It can be seen from the figure that the F4 of the transformer under normal state is mainly distributed between 0.1 and 0.8. According to the cumulative probability curve, 99% of the samples are below 0.14.As shown in F4 is right-skewed and presents the characteristics of lognormal distribution. F4 of the sample is lnF4 after calculating the logarithm, and lnF4 of all samples constitutes aggregate D4. Assume D4~N(2), where F4 and F4. The fitting results are F3 obeying the lognormal distribution.The parameter distribution of F2 and F4 of the acoustic signal to rise, and F3 to fall. Thus, after excluding a small number of outliers, the 99% quantile line was selected as warning threshold of F2 and F4, and the 1% quantile line was selected as warning threshold of F3.According to the rule obtained from the experiment in F2, F3, and F4 of DC bias state 500 kV transformer cases all exceed the warning threshold. The comparison results show that the early warning threshold given according to the statistics of three parameters can identify the DC bias state.In order to test the effectiveness of the warning threshold set above, in this paper, the DC bias state 500 kV transformer cases in In this paper, by comparing the acoustical parameters of the core model with the 500 kV transformer, three typical parameters were selected for DC bias state acoustic warning, and clear parameter warning thresholds were given.(1)F1 variation law of acoustic signal in the laboratory core model is different from that in the 500 kV real transformer. This is because the DC bias state of the real transformer is more serious, and the acoustic signal of the real transformer will be affected by the frequency response function of the acoustic transmission medium.The dominant frequency (2)Under ideal laboratory conditions, the core model and DC bias state acoustic signal of field transformer can only compare their acoustical parameters with state changes, but cannot compare the values with each other. Therefore, the data of the laboratory model cannot be used to delineate the parameters warning threshold.(3)F2, F3, and F4 parameters of a large number of transformer acoustic samples in the normal state has strong aggregation. The comparison results of real cases illustrate that the warning threshold given in this paper based on three-item parameter data statistics enables stable identification of DC bias state.The numerical distribution of


At present, the many domestic, large mined-out areas caused by single filling ability of the slurry flow state, thin layer flow and hardening after filling in multilayer structure generally need to finish filling for many times, because after a filling experience shows that filling body in the last solidification of flow, this leads to a lower one side of the roof, and far distance part of the filling body cannot pick up top. The determination of backfill strength is the key problem of the cemented backfill method, and it is affected by many factors. Therefore, through theoretical calculation, laboratory testing and numerical simulation methods, combined with the field filling process, this paper has verified the flow accumulation and stratification characteristics of stope layered filling slurry. When the slurry concentration is 60–73%, the slope increases exponentially from 2.5° to 8°. It is revealed that the delamination and meshing state are the key factors to determine the overall strength of large-scale stope filling through the testing of particle size distribution in interlayer and flow direction. The reduction effect of the number and Angle of structural weak surface formed by layering and filling on strength is revealed: cement–sand ratio 1:12, concentration 68%, standard curing R28 > 1.81 MPa. The strength reduction coefficient is 61.31% and 92.96% when the number of layers is 1–4. The higher the number of layers, the greater is the reduction coefficient, and when the stratification angle increases by 2, the strength of backfill decreases by 20–30%. The verification of stope filling coring shows that the in situ strength reaches 2.42 MPa, which is 0.61 MPa higher than the standard curing strength, with an increase of 33.7%. When the depth is from 1 m to 5 m, the strength increases from 2.26 MPa to 2.69 MPa, with an increase rate of 18.2%. Finally, through the research and application of the comprehensive technology of mining and filling coordination under the complex goaf group, the residual ore resources of Xianglushan tungsten mine are effectively recovered, the volume of goaf is significantly reduced, and the safety of goaf is improved. For the goaf with a large area to be filled, the following problems generally exist in the filling process: First, the paste filling flow rate that has been built in China is generally 80–100 m3/h, and the single filling capacity is 300–800 m3. When the area to be filled is larger than 300–500 m2, the height of a single filling is less than 1 m, resulting in a thin layer flow of slurry and a multilayer structure of the hardened filling body. Second, the stope generally needs several filling operations to fill, and the later filling slurry flows on the surface of the previously consolidated filling body. After the solidification of the slurry, the filling body Angle makes the interior of the stope look like an inclined plane. The higher position is close to the roof, while the lower side is far from the roof, leading to part of the filling body unable to be connected to the roof. Thirdly, the particle distribution affects the strength of backfill in the process of paste flow consolidation. Paste with high concentration and uniform properties can be regarded as non-sedimentation fluid, but it is still possible to produce particle size classification in the actual filling process [The volume of underground goaf in China is about 1.3 billion mFor these problems, scholars at home and abroad have done a deal of research in recent years. As for the influence of stratified structure on the mechanical properties and failure mode of backfill, Wang Jie et al. prepared different backfill samples under the conditions of 1:4 cement–sand ratio, 75% slurry concentration and 1, 2 and 3 backfill layers, respectively, and carried out triaxial cyclic loading and unloading tests. The results showed that with the increase of filling times, the peak strength of backfill decreases as a polynomial function, and the peak strain increases as an exponential function ,7. ThompTo sum up, for the common mined-out areas with small area, the filling method of high strength filling materials in the upper and lower parts of the mined-out areas and low strength filling materials in the middle part can be used, which can effectively reduce the cost. However, the previous filling method is not suitable for the extra-large mined-out areas, because the large-area and large-volume mined-out areas are affected by the filling speed, and they must be filled for many times before they can be completed, which results in the existence of structural planes among the filling bodies for many times, which has a significant impact on the overall strength of the filling bodies. The existing strength design standard of backfill only considers the strength of the material itself, but ignores the structural and mechanical characteristics between the backfill and surrounding rock , especiaThe whole tailings of Xianglushan Tungsten mine were used as raw materials, 42.5 R ordinary Portland cement was used as cementing agent, and the experimental water was taken from laboratory tap water. The mold adopts a high transparent acrylic tube with a height of 100 mm and an inner diameter of 50 mm. The experimental filling body is prepared as shown in Field tailings and cementing powder were used to carry out slope flow test of L-shaped flow groove with slurry of 66%, 68%, 70% and 72% concentration, as shown in The particle size distribution along the flow direction affects the local strength of backfill, and the particle size distribution along the vertical direction is the direct cause of the structural weak surface of multilayer backfill ,14,15. TAfter the completion of filling, the slurry will stop flowing, and samples will be taken at the same flow distance between the slurry surface and bottom surface along the flow distance direction with the following inlet as the starting point and 10 cm apart. The particle size of the sample was measured by laser particle size analyzer. The instrument used in the experiment was Rise-2008 laser particle size analyzer developed by Runzhi Technology Company in Jinan, China. The particle size distribution characteristics in the horizontal and vertical directions were analyzed. The sampling location is shown in The filling body test blocks with cement–sand ratio of 1:12, mass concentrations of 66%, 68% and 70%, and layers of 1, 2, 3 and 4 layers were prepared. The curing age of the specimen was 28 days, and the constant temperature and humidity curing box was adopted for curing, with the temperature of 20 ± 5 °C and relative humidity of 95% ± 5% .(1)Mixing and mixing: first mix cement, tailings and water according to the set proportion, and then put the slurry mixture under the mixer to mix evenly and reserve;(2)Mold filling: first fill the bottom slurry according to the set height, then fill the second slurry according to the set height at an interval of 24 h, then fill the third slurry at an interval of 24 h, and finally fill the fourth slurry at an interval of 24 h to 100 mm height;(3)Demolding curing: Put the filled specimen into the curing box, and take out demolding and continue curing until 28 d for reserve after curing for 3 d, as shown in The preparation of all tailings paste is shown in The rheometer test results of the whole tailings paste are shown in According to the above test results, the full tailings paste slurry with 66% concentration is used to carry out multilayer backfill test. After each layer of filling slurry is dried, the next layer of filling slurry is injected into the feeding port, and the flow distance and Angle are detected after the flow stops. See After the filling slurry enters the groove, the shear stress caused by gravity overcomes the yield stress of the slurry itself, resulting in the viscous flow of the slurry ,18. Due The slope curve was drawn, and the slope of each layer was nonlinear fitting. See In the process of slurry flow, the yield stress of slurry itself decreases with the increase of flow spacing. The mechanical cause is shear thinning of the non-Newtonian fluid, and the microstructure is attributed to particle classification and flocculant rearrangement in the flow.A total of six slopes were formed in the multilayer stacking test with 66% concentration of filling slurry, and the representative bottom layer and the sixth layer were selected to carry out the study. Samples were taken on the bottom and surface of each backfill for particle size detection. The particle size distribution data along the flow direction are shown in It can be seen from the table that the particle size distribution characteristics of each layer flow slurry are as follows: the bottom particles are thicker than the surface particles are finer, and the farther the flow distance is, the finer the particles are. The particle size difference in the vertical direction is significantly greater than that in the flow direction.(1)Along the flow directionHappened in the process of liquid filling pulp layer segregation phenomenon, as a result of the coarse particle settling velocity relative to the fine particles is bigger, this makes the most of the coarse particle main deposit in the bottom of the fine particles are mainly concentrated on the surface, as the slurry to move forward, coarse particle precipitation stabilized, and the fine particles with the slurry flow gradually far end is pushed to the model. This results in stratification and segregation. In the flow direction, the particle size becomes fine with the increase of the flow distance. When it is close to the discharge point, the content of the particle size range of 75,300 μm is about 60%, and at the far end of stopping the flow, the particle size content of this range decreases to about 11–15%.(2)Vertical directionThe bottom grain is significantly coarser in the vertical direction. After the flow of each layer stops, the particle size of the bottom surface concentrates in the range of 75–300 μm, and the content reaches more than 90%. The particle size of the surface concentrates in the range of 0.1–37 μm, and the content is generally more than 80%.Uniaxial compressive strength is one of the most important mechanical parameters of backfill ,21. In tIn China, the strength value of complete backfill is usually used as a reference for theoretical calculation of backfill strength, whether for slicing mining, sublevel mining or stage subsequent mining ,23. By aThe concept of strength reduction coefficient of backfill is introduced , which iType: By analyzing As shown in The Angle between different backfill layers was taken as the main research object to influence the strength of cemented backfill. The ratio of slurry to cement sand was set as 1:12, the four concentrations were 64%, 66%, 68% and 70%, and the Angle between the layers of cemented backfill was set as 2°, 4°, 6° and 8°. When preparing specimens with different angles between layers, the filling time interval was set as 24 h, and the design curing age was set as 28 d. The strength of the layered backfill was studied. The production of cemented backfill samples with different angles between backfill layers is shown in The strength of backfill under the influence of stacking angle is shown in As can be seen from The inclination degree of backfill has a significant impact on the strength of backfill samples ,26. FiguThe failure of the delamination backfill is mostly the failure of crushing and swelling, and the lower backfill basically maintains the intact shape, while the failure of the non-delamination backfill is more longitudinal cracking, and the residual strength is greatly reduced. After the completion of loading, different degrees of separation and dislocation occur in the specimens of the delamination filling body at different levels, and the influence of the separation and dislocation caused by the Angle factor is much greater than that caused by the amount of delamination on the delamination filling body. After the interruption of filling, a low-strength interlayer is formed between the layers, which is easy to be damaged when the loading test is carried out, thus reducing the overall bearing capacity of the filling body, and leading to different degrees of separation and dislocation of the failure specimen at different layers.The numerical simulation of uniaxial compression of cemented tailings backfill was carried out by using PFC-2D particle flow program.(1)Particle distribution simulation–4 m, which is slightly smaller than the minimum tailings particle radius. The diameter of the sample is 50 mm and the height is 100 mm.The tailing particle gradation in the model is consistent with the real tailing particle gradation and simplified. The radius of cemented particles is set as 3.0 × 10(2)Parameter calibrationThe meso-mechanical parameters of particles in different models are the same, and only the number of cemented particles is changed ,28, as s(3)Model constructionThis simulation does not consider the influence of slurry mass concentration and curing age, and smooth joint contact is adopted for the contact between different layers of the layered backfill. The mechanical parameters of the contact model are shown in (4)Analysis of crack evolution lawIn essence, the failure process of backfill is the process of its internal crack initiation, expansion and connection, so it is of great significance to study the evolution law of its internal crack. The simulation results are shown in At the initial stage of the stress-strain curve of the layered backfill body, the contact force between particles is less than the strength of the bond between particles, the bond between particles is not damaged, and no cracks occur in the layered backfill body. With the loading process, the contact force between particles increases gradually and begins to exceed the bond strength. The bond strength is destroyed, and internal cracks begin to occur, and the crack increment curve begins to fluctuate. When the load continued to be applied, more and more contact forces between particles exceeded the bonding bond strength, and more bonding bonds were destroyed. At this time, internal cracks began to increase, and the increment curve of cracks rose slowly. When the external load gradually reached 80% of uniaxial compressive strength, the cumulative crack curve showed inflection point and increased rapidly, and the increment crack curve also jumped. When the load continued to be applied, the stress-strain curve began to decline, the crack accumulation curve continued to grow at a high speed, and the crack increment curve remained stable at a high level. Because the two parameters of PFC2D software model, porosity and friction coefficient between particles, are parameters that cannot be obtained in laboratory tests, they can only be roughly judged based on the experience of repeated tests and previous research, so some unavoidable error values will appear. Comparing the model obtained by the software with the failure mode of the laboratory block in The specimen of layered backfill is mainly manifested in three failure modes: shear failure accompanied by secondary shear crack, tensile failure accompanied by secondary tensile crack, and conjugate shear failure accompanied by secondary tensile shear failure .According to the uniaxial compression results, the function is used to draw the hot spot map, search the segmentation number and segmentation radius. The logic is to traverse the points in the model and calculate the number of cracks within the search radius with this point as the center of the circle. The degree of crack concentration can be identified according to different colors in 3. It is fed continuously for 24 h. When the tailings processing capacity is 1600–2400 T/d and the bottom flow concentration is 65%, the bottom flow rate is 58.18–87.27 m3/h, and it is directly transported to the mixing drum for filling slurry preparation. The diameter of the mixing barrel is 2000 m, and the height is 2100 mm. The ultrasonic level meter is installed on the top. The level of the mixing barrel is controlled between 1.2–1.5 m through the control system. The filled slurry stirred by two stirring drums can be switched between gravity flow and pumping through the transfer valve and conveying pipe [The filling system process of Xianglushan tungsten mine includes tailings transportation, deep cone thickening, stirring preparation, paste pumping and underground filling, as shown in ing pipe ,31.3/h, outlet pressure 8 MPa.(1)3/h, maximum 110 m3/h;Flow rate of filling slurry: 80–100 m(2)Filling slurry concentration: 58–68%, maximum 72%;(3)3;Maximum filling capacity of a single system: 300–600 m(4)Cement–sand ratio: 1:12;Operation parameters of filling system:Key technology of downhole fillingPaste conveying pump two, its model is ZBJB80/8, flow 80 mThe strength of backfill in pillar mining and normal mining is 0.5–2 MPa. The filling work of underground part is mainly to transport the prepared filling slurry in the filling station to the goaf stope that needs to be filled underground, which mainly involves the laying of filling pipe network and the construction of cofferdam retaining wall of underground stope. The cofferdam retaining wall can be filled in the stope after the completion of the above work.After the filling retaining wall is erected and laid, the goaf can be filled. In order to reduce the filling pressure on the filling retaining wall and control the settlement and shrinkage of the filling body, the height of a cavity filling is 0.3–0.5 m. After initial setting, the next filling is carried out with an interval of 24 h, as shown in Filter pipes can be arranged along the height direction of the filling goaf according to the situation, and connected to the filter pipe of the filling retaining wall to realize water filtration.After the stope filling is completed, the requirements of upward filling mining will be met. After 28 days, when the strength of the filling body reaches the requirements of LHC rolling, the workers can drill and blast the roof on the filling body to realize effective mining of the roof ore.In order to ensure that the filling strength meets the mining requirements, reduce the amount of cementing material and reduce the filling cost, cementing powder is used as the cementing material, and the slurry ratio of 1:12 is adopted for filling, which is between 1.5–2 MPa to meet the mining strength requirements.Samples were taken from the filling station and the pipe entrance of underground stope to test the strength of in situ downhole curing. The production process of downhole samples is shown in Under the condition of the same ratio and concentration, downhole environmental conservation has a significant promoting effect on the strength of backfill, which increases from 1.81 MPa to 2.00 MPa, with a growth rate of 10.5%.Downhole strength improvement is influenced by many factors ,33. The The strength of in situ backfill was sampled and tested in the backfill stope. The sampling method was on-site core drilling, and uniaxial strength test was conducted after grinding. The sampling time was 28 days after filling, as shown in The results of in situ downhole sampling showed that the average filling strength was 2.42 MPa, 0.61 MPa higher than the standard curing strength, with a growth rate of 33.7%, and 0.42 MPa higher than the downhole test block curing strength, with a growth rate of 21%.The sampling intensity is greater than the target intensity, indicating that the filling process and material ratio can meet the requirements of goaf filling and residual mining, which is helpful to realize the coordination of goaf treatment and residual mining under complex conditions, and realize the safe mining of residual ore resources to the maximum while eliminating the safety hazards of goaf.When the full-tail mortar concentration is 66%, the cement–sand ratio is 1:12, the filling slurry concentration is about 68%, the collapse degree is 24.2 cm, and the standard curing R28 strength of the backfill body reaches 1.86 MPa. When the filling body concentration is 66–70% and the filling times are 1–4 times, the strength reduction coefficient is 61.31–92.96%, indicating that the compressive strength weakening effect of the filling body becomes more obvious with the increase of filling times. When the filling slurry concentration is 64%, 66%, 68% and 70%, the included Angle of multiple filling layers is set as 2°, 4°, 6° and 8°, respectively, the uniaxial strength reduction ratio of the filling body at 2° is about 89–91%, the uniaxial strength reduction ratio of the filling body at 4° is about 67–74%, and the uniaxial strength reduction ratio of the filling body at 6° is about 50–68%. At 8°, the reduction ratio of uniaxial strength of backfill is about 43% and 50%. When the delamination Angle increases by 2°, the strength reduction rate of backfill stays at 20–30% on average. The greater the delamination Angle, the greater the intensity reduction factor. The downhole test block curing results show that under the condition of the same ratio and concentration, the downhole environmental curing has a significant promoting effect on the strength of backfill, which increases from 1.81 MPa to 2.00 MPa with a growth rate of 10.5%. The results of in situ downhole sampling showed that the average filling strength was 2.42 MPa, 0.61 MPa higher than the standard curing strength, with a growth rate of 33.7%, and 0.42 MPa higher than the downhole test block curing strength, with a growth rate of 21%. When the sampling depth increases from 1 m to 5 m, the strength increases from 2.26 MPa to 2.69 MPa, with a growth rate of 18.2%. The sampling depth of backfill samples represents the increase of drainage conditions and overburden pressure and other curing conditions after pouring. The greater the depth, the greater the overburden curing stress, the longer the filtration time. However, due to the limitation of conditions, the content of this experiment does not include the SEM scanning experiment of the sample, so it is impossible to further analyze the internal micro-morphology, particle size and structural defects of the sample. When the conditions permit, the author will continue the research in this direction, scan and analyze the samples by SEM, and propose a new method to determine the strength of backfill under the multi-demand of goaf treatment based on the concept of mining and backfilling.3, and the volume of mined-out area eliminated by cemented filling is about 1.6738 million m3, and the volume of mined-out area decreases by 1.1673 million m3, with a reduction rate of 47.1%. The research results provide a theoretical basis for the strength problems of tailings solid waste resources in the filling process, solve the problems of solid waste resources filling, realize the effective disposal and utilization of tailings solid waste resources, reduce the amount of solid waste from the source, and promote green and sustainable development.After treatment, the amount of mined-out area and pillar is significantly reduced and the safety is significantly improved. From 2013 to 2020, the volume of mined-out area increased by mining in the eastern mining area is about 506,500 m


This study demonstrates the possibility of developing SCMs with iron tailings (IOTs), fly ash (FA) and ceramic powder (CP) ternary system, as well as the optimization and improvement scheme of gelation activation. The effects of activator dosage, mix ratio and substitution rate on mechanical properties of ternary SCMs system were investigated. The formation and evolution of hydration products were analyzed by differential thermogravimetric analysis (DTA) and scanning electron microscopy (SEM). The results of the study show that there is synergy in the system. The results show that there is synergy in the system and the hydration reaction is sufficient. At the substitution rate of 30%, the doping ratio of IOTs, CP and FA is 1:2:2 and the Ca(OH) According to statistics, each ton of cement produced emits about one ton of gases, and reducing the production of cement will make an important contribution to reducing emissions. For this reason, the EU government has committed to reduce 30% of the gases affecting the greenhouse effect by 2020 and 95% by 2050 [With the continuous promotion of global infrastructure construction, cement and concrete as the main building materials, its demand is increasing, and with it comes the problem of serious environmental pollution and increasing energy consumption. Therefore, the cement and concrete industry needs to adjust the development mode, change the direction of development, reduce energy consumption, reduce environmental pollution, and take the road of sustainable development . The dec by 2050 . Use the by 2050 ,8.The role of industrial waste, mining solid waste and municipal waste as mineral admixtures in cementitious materials to control energy consumption and reduce environmental pollution is becoming more and more prominent. The accumulated solid waste not only causes waste of resources, along with the waste of land resources and serious pollution of the environment, endangering the ecosystem. Mineral admixture can not only alleviate the problem of energy consumption, but can also play a positive role in protecting the environment, and is the road to sustainable development of today’s green high-performance concrete ,10,11. FIron tailings (IOTs) are mining solid wastes, and there are a large amount of IOTs produced every year in China. The accumulation of a large amount of IOTs wastes land resources and pollutes the environment. Additionally, IOTs are potential secondary resources, besides containing valuable metals, vein minerals and other materials are the main mineral composition of IOTs, and oxides of silicon, calcium and aluminum are the main chemical components. However, IOTs are inert materials that do not have high cementing activity . To effe2 secondary hydration reaction, thus generating a large number of C-S-H and C-A-H and other substances with a certain degree of cementation, and hardening to produce strength, and it has been demonstrated that CP has no significant positive effect on the early strength development of cement mortar. It mainly acts as a microfiller, resulting in a low early strength of cement mortar. However, due to the volcanic ash activity of CP [China is the largest producer of ceramics in the world and produces about 10 million tons of ceramic (CP) waste each year, which leads to a serious waste of land resources and environmental pollution. The raw materials of ceramic products are clay, quartz and feldspar, which are then fired at high temperature to form a CP after grinding . Others ty of CP , the lat2 and Al2O3 can react with Ca(OH)2 produced during the hydration of cement clinker to produce hydration products such as C-S-H and C-A-H [Fly ash (FA) is the tiny fine ash particles collected from the flue gas produced by burning coal, and is the main solid waste from coal-fired power plants. The use of FA mixed into the original concrete to replace part of the cement can optimize the performance of concrete and improve the strength of concrete, because FA can not only save the amount of raw materials, but also can play the “volcanic ash effect” and “morphological effect” and “micro-aggregate effect”. In general, FA is similar to CP in that it is less efficient in the initial stage of cementation and acts more as a microfiller, but the volcanic ash properties prove to be effective in later stages, leading to a significant increase in strength . It has nd C-A-H , which ind C-A-H  pointed IOTs, CP, and FA are three materials used as SCM and have been the subject of a lot of research, but still cannot achieve a large consumption of solid waste, and there are many problems. It has been pointed out that there is a synergy between different materials that can be used to adjust the working properties, mechanical properties and particle gradation of concrete through multiple components . This syIn this study, we study the ternary SCMs, analyze the co-hydration process of IOTs, CP, FA and cement, clarify the physical phase changes, microscopic morphological structure evolution and macroscopic mechanical property development law during the hydration process, and elucidate the effects of multi-solid waste characteristics on the hydration process and hydration mechanism of the SCM system.2 (The purity > 99%) was used as chemical activator. The IOTs in this study were obtained from Wai tou Mountain, Benxi City, Liaoning Province, China. The FA was produced in Ya tai Company, Liaoning Province, China. The CP used is provided by Chaozhou City, Guangdong Province, Xin huan Technology Co. The chemical compositions of the three types of materials are shown in The experimental materials included IOTs, CP, FA, Portland cement, standard sand, and water. Ca(OH)The microscopic characterization and the particle morphology were measured via BET and SEM see . The spePreparation of mineral admixture by compounding IOTs, CP and FA. According to the Chinese national standard GB/T12957-2005  IndustriEach material was weighed according to The net paste is mixed and prepared in accordance with the test requirements of cement and the corresponding proportion of each admixture, then take the appropriate amount of mixed materials in disposable plastic cups and other containers, water to glue ratio of 0.5, add the appropriate amount of deionized water, while stirring with a glass rod and pour into the mold, and then in the temperature of 20 ± 1 °C, relative humidity of 95 ± 1% of the constant temperature and humidity standard curing room curing time of 24 h. After that, the mold was demolded and continued to be placed in the maintenance room until the corresponding age. After reaching the specified curing time, the core of the hydrated hardened paste and the mortar were taken out after drying at 50 °C for 2 h, and then soaked in anhydrous ethanol for 3 days to terminate the hydration. The purified slurry sample after the termination of hydration was dried at 50 °C for 24 h, followed by grinding to prepare the samples for thermogravimetric analyses. After cutting and taking the block, it was ground on sandpaper, and cured with epoxy resin for 24 h. After grinding the surface, it was put into isopropanol solution for ultrasonic cleaning to prepare SEM sample.Compression tests were performed via GYE-300B universal testing machine . A loading rate of 2.4 kN/s, as stipulated by GB/T17671-1999, was conducted during the loading.1 is the compressive strength of the admixture system test sample at 7 d and 28 d. R2 is the compressive strength of the cement mortar for 7 d and 28 d.The activity index of 7 d and 28 d mortar was determined according to the national standard GB/T12957-2005. The activity index can be calculated according to the following equation:DTA-TG was conducted using TA instruments  in a nitrogen gas flow with a 70 mL/min flow rate. Each testing sample was about 15 mg. The TGA was exposed to the temperature from room temperature to 800 °C with a rate of 20 °C/min.The microstructure of the hydration products of the paste samples at 28 days was analyzed via SEM . All specimens were immersed in anhydrous ethanol for 3 days before the SEM test to prevent water and reaction, and then the samples were dried in the oven to remove anhydrous ethanol.2 and Al2O3 and Ca(OH)2 in the SCM system continuously undergo secondary hydration reactions to generate hydration products such as C-S-H, C-A-H and AFt, but due to the reduction of cement, the amount of Ca(OH)2 that can undergo secondary hydration is small and the degree of secondary hydration is low, leading to an increase in substitution rate and a decrease in both strength and activity index. After ICF-2, the decrease of compressive strength decreases, which means that the influence of the change of substitution rate on the compressive strength of the system has been weakened, and the comprehensive consideration is that the 7 d compressive strength of ICF-1 with 30% substitution rate is 24.4 MPa, the activity index is 79%, the 28 d compressive strength is 38.4 MPa, the activity index is 88.1% can meet the requirements, and the fixed substitution rate is 30% is more suitable. The fixed replacement rate is 30%.2 dosing on the compressive strength of the system at different ages of 7 d and 28 d. It can be seen the effect of Ca(OH)2 doping on the compressive strength at different ages showed different trends. At the age of 7 d, the compressive strength increased with the increase of Ca(OH)2 dosing; while at the age of 28 d, the compressive strength showed a trend of increasing and then decreasing with the increase of Ca(OH)2 dosing. The reason [2 added at the early stage of hydration reaction will release Ca2+ and OH- microsolubly, and under the action of OH- ions, the Si-O and Al-O bonds with high polymerization in the SCM system will break and form unsaturated bonds, releasing a large number of reactive ions, and the system containing SO42- can generate AFt at the early stage of hydration to guarantee the early strength, so at 7 d time, the compressive strength increases continuously with the increase of Ca(OH)2 doping. When the hydration reaction is late, the Ca(OH)2 mixed with too much is fully dissolved, and some silicate and aluminate combine with Ca2+ to form C-S-H and C-A-H, which consume part of the active products, thus reducing the system activity, and the OH- content is too high, which inhibits the hydration reaction of cement [2 doping amount of 0.6%.e reason  is that f cement , and AFt3 produced by the carbonization of CH [As can be seen in on of CH .In order to visualize the hydration process of the ternary SCM system, the CH content of each group of samples at different ages was calculated using Equations (2) and (3).CH is the relative content of calcium hydroxide in the sample (%); CHWL is the mass loss of calcium hydroxide caused by removing water through TG (%); 3CaCOWL is the mass loss of calcium carbonate caused by removing water through TG (%); CHm is the molar mass of calcium hydroxide; 2OHm is the molar mass of water; 3CaCOm is the molar mass of calcium carbonate; and 2COm is the is the molar mass of carbon dioxide. The values of CHWL and 3CaCOWL can be obtained by data processing through the TG curve. CHm = 74 g/mol; 2OHm = 18 g/mol; 3CaCOm = 100 g/mol; and 2COm = 44 g/mol. The molar masses of calcium hydroxide, water, calcium carbonate and carbon dioxide can be obtained by substituting them into Equation (2).In the formula: The calculated results are shown in 2, the hydration product of residual cement particles, and the amount of C-S-H gels increased. Additionally, due to the different fineness of IOTs, CP, and FA, these residues are compounded together to fill each other and form a good gradation, and the particle size distribution of fine particles in the whole system is more reasonable and the pore structure is fully refined, which makes the strength increase significantly. In the figure, we can see many reacted IOTs particles, in synergy with CP and FA, IOTs not only play the role of micro-aggregate filling, it also participates in a large number of hydration reactions, and the three have good synergy. There is a synergistic hydration reaction of solids in the cementitious material system, which promotes the increase of the system strength [strength .In this paper, the effects of different influencing factors of activator dosing, composition ratio and substitution rate on the mechanical properties and microstructure of the ternary SCM system of IOTs, CP and FA were investigated. Based on the above experimental results and related discussions, the main conclusions are as follows:(1)2 is 0.6%, the strength reaches 39.9 MPa and the activity index is 91.5%. It has the potential to develop SCMs that can reduce cement usage, enable resourceful use of IOTs, CP and FA, and promote energy saving and green development.At the substitution rate of 30%, the ratio of IOTs, CP and FA is 1:2:2 and Ca(OH)(2)It can be seen in both macro and micro perspectives that FA volcanicity is higher than IOTs and CP. The FA in the system participates in the volcanic ash reaction, CP provides additional nuclei to accelerate the hydration process, and IOTs play a filling effect to provide nucleation sites, and the three materials hydrate synergistically.(3)3 inhibited the growth of strength.The amount of CH added had a significant effect on the compressive strength of the slurry. Overall, 0.6% CH promoted the formation of CSH gel, while when the amount of CH was too much, cement hydration was inhibited, and CaCO(4)Ternary SCMs system has no hydraulic property, only volcanic ash property. When the replacement rate is too high, it will seriously harm the compressive strength. It is recommended that the replacement rate be less than 30%.In summary, the appropriate amount of IOTs, CPs, and FAs is expected to be a new SCM to reduce the cement dosage in terms of mechanical properties, microstructure, and co-hydration analysis. In addition, further studies on the degree of hydration of this SCM under the conditions of other activators and the mechanical properties and durability performance of concrete prepared with this SCM are necessary.


Further development and commercialization of bulk heterojunction (BHJ) solar cells require the search for novel low-cost materials. The present study addresses the relations between the asphaltenes’ chemical structure and the morphology of the poly(3-hexylthiohene) (P3HT)/asphaltene blends as potential materials for the design of BHJ solar cells. By means of all-atom molecular dynamics simulations, the formation of heterophase morphology is observed for the P3HT-based blends with carboxyl-containing asphaltenes, as well as the aggregation of the asphaltenes into highly ordered stacks. Although the π–π interactions between the polyaromatic cores of the asphaltenes in solutions are sufficient for the molecules to aggregate into ordered stacks, in a blend with a conjugated polymer, additional stabilizing factors are required, such as hydrogen bonding between carboxyl groups. It is found that the asphaltenes’ aliphatic side groups may improve significantly the miscibility between the polymer and the asphaltenes, thereby preventing the formation of heterophase morphology. The results also demonstrate that the carboxyl-containing asphaltenes/P3HT ratio should be at least 1:1, as a decrease in concentration of the asphaltenes leads to the folding of the polymer chains, lower ordering in the polymer phase and the destruction of the interpenetrating 3D structure formed by P3HT and the asphaltene phases. Overall, the results of the present study for the first time reveal the aggregation behavior of the asphaltenes of varying chemical structures in P3HT, as well the influence of their presence and concentration on the polymer phase structure and blend morphology, paving the way for future development of BHJ solar cells based on the conjugated polymer/asphaltene blends. Nowadays, there is an active search for new acceptor materials for bulk heterojunction (BHJ) solar cells, both to increase the power conversion efficiency and stability of the devices and to reduce their production costs ,2. While61-butyric acid methyl ester (PCBM) and phenyl-C71-butyric acid methyl ester (PC71BM) [Indeed, various types of organic semiconductors were utilized as acceptors in polymer solar cells. The most famous type of such molecules are fullerene-based derivatives—mainly phenyl-C(PC71BM) ,16. Howe(PC71BM) ,18. In r(PC71BM)  and ITIC(PC71BM)  families(PC71BM) . This al(PC71BM) . The inc(PC71BM) ,22,23.As we have shown previously by means of density functional theory (DFT) calculations , the cheIn that work, we chose the well-established regioregular poly(3-hexylthiophene) (P3HT) as a model donor, as P3HT is widely studied by means of computer simulations ,26,27 anThe molecular dynamics (MD) simulations of the carboxyl-containing asphaltenes/P3HT blend revealed the heterophase morphology of the studied blend, as well as the formation of extended stacks of the asphaltenes, all of the above being essential for efficient charge transfer in the active layer. We also observed a slight ordering of the P3HT backbones, possibly due to the impact of the addition of asphaltenes .However, the exact reason for such structure formation remains unclear. A possible explanation for the formation of the heterophase morphology of the blend and the ordering of P3HT chains is in the specific interactions between the aromatic backbone of the polymer and the polyaromatic core of the studied carboxyl-containing asphaltenes. The presence of aliphatic side groups or polar carboxyl groups should affect the miscibility between the components of the mixture. In turn, the formation of stacks between asphaltene molecules might be influenced by both π-π stacking between the polyaromatic cores of the asphaltenes and the hydrogen bonding between the −COOH groups of the adjacent molecules .To gain a better understanding of the factors governing the perspective morphological properties of the P3HT/carboxyl-containing asphaltene blend observed previously , in the It should be noted that there are some complexities related to the structural organization of P3HT as a standalone phase, along with the impact on the formation of heterojunctions. The structure of P3HT, its solid-state organization and its polymorphs are at the core of a long-lasting debate. It is believed that P3HT could form two polymorphs ,37,38,39It is well known that the blend composition, namely the ratio of the two components, impacts significantly on the microstructure of an active layer and, consequently, the device efficiency . TherefoAsphaltenes occur in nature as a mixture of molecules of different chemical structures. Although various complicated asphaltene architectures were used in MD simulations ,41,42, iThe MD simulations were performed using the GROMACS software package . The genWe should note that there is a rather large number of force fields developed especially to model P3HT ,56,57. HpN = 40 repeating units each  were blended with (a) 254 Asp molecules , (b) 504 Asp-Core  and (c) 368 Asp-COOH molecules . Thus, in these examined systems, the mass ratio of the components was approximately equal to 1:1. The chosen polymerization degree of P3HT corresponds to the polymer regime where P3HT properties slightly depend on the polymer molecular weight. Such polymerization degree is often used in the simulation of this polymer [Three types of systems with the same asphaltenes/P3HT mass ratio were simulated. Namely, 27 P3HT chains consisting of  polymer ,58,59,603) with periodic boundary conditions using the GROMACS gmx insert-molecules routine. Then, to achieve a condensed state, a 5 ns long compression procedure was carried out at a temperature T = 600 K and pressure P = 100 bar utilizing the Berendsen thermostat and barostat [3). Finally, the main 5 µs long simulation runs were performed at a temperature T = 600 K and pressure P = 1 bar with the Nose–Hoover thermostat and Parrinello–Rahman barostat with time constants of 1.0 and 5.0 ps, respectively [gR calculated for the polymer chains in the blends studied, the systems can be considered equilibrated after approximately 2.5 µs of simulations, as will be discussed in the Results and Discussion section below. The required equilibration time is also confirmed by the analysis of time dependencies of the number of asphaltene clusters in the considered systems . The equilibration and simulation procedures were similar to the ones described above.The formation of the heterophase structure of donor/acceptor blends, as well as the aggregation of graphene-like acceptor molecules into stacks, is necessary for the efficient operation of BHJ solar cells on their basis ,75,76. SAs can be seen from the snapshot in The reason for the uniform distribution of Asp can be explained by the presence of aromatic and aliphatic constituents in both the asphaltenes and P3HT. A comparison of mixtures comprising the Asp-Core and Asp-COOH asphaltenes shows that the formation of the separate asphaltene phase in these systems is mostly governed by the π–π-interactions between asphaltene molecules and the absence of aliphatic groups, which lowers the affinity between the polymer and asphaltenes. However, the π–π-interactions themselves are not enough for the formation of ordered stacks by asphaltene molecules, and the interactions between the polar carboxyl groups that further decrease the affinity between the components stabilize the stacks formed by asphaltene molecules and lead to the formation of interpenetrating morphology in Asp-COOH/P3HT mixtures. Thus, the chemical nature of the side groups or their absence significantly affect the homogeneity of the P3HT/asphaltene blends even in a P3HT melt.δ using the Hildebrand approach 0.5. Both of them have aromatic and aliphatic constituents, which results in close δ values, visible miscibility between the compounds and no pronounced asphaltene aggregates formed. When the aliphatic side groups of the asphaltenes are cut off, the difference with the solubility parameter of P3HT increases to Δδ = 3.2 (J/cm3)0.5. This can be explained by stronger interactions between the pure aromatic asphaltenes, which leads to the formation of asphaltene aggregates in the mixture with P3HT. Finally, the attachment of carboxyl groups to the polyaromatic core of the asphaltenes results in further increases in the δ value of asphaltenes. This means that the interaction energy between the Asp-COOH molecules is greater than that between the Asp-Core. Therefore, there should be additional interactions between Asp-COOH asphaltenes that stabilize the aggregates formed by these molecules. So, for the Asp-COOH/P3HT blends, the formation of heterophase morphology can be expected even on a macroscale. This conclusion agrees well with the observed morphological differences between the studied blends  between the asphaltenes calculated for the carbon and sulfur atoms in the polyaromatic cores of the molecules (see g(r) curves confirms that only Asp-COOH form highly ordered stacks within the aggregates, as was discussed above (see g(r) curve for these asphaltenes, the distance between the peaks is approximately equal to 0.5 nm, which means that the planes of adjacent asphaltene cores are located at the distances typical for molecules stacked due to π–π interactions. It is worth noting that classical force fields do not directly take into account the quantum effects; however, being semi-empirical, they allow one to indirectly reproduce such interactions as, for example, π-π-stacking [g(r) for Asp to unity indirectly indicates a better miscibility between this type of particles and P3HT than that between the Asp-Core and the polymer.bove see . As can stacking . While sgmx clustsize routine with the fixed cut-off distance of 0.5 nm  chosen on the basis of the calculated pair correlation functions  contribute to the electrical conductivity in an active layer of BHJ solar cells, the ability of carbon nanoparticles to induce the crystallization of the polymer is of high interest. So, we estimated the structure of the P3HT phase in the blends in order to find out whether the formation of ordered asphaltene aggregates can lead to the initial stages of P3HT ordering.According to the typical snapshots shown in gR calculated for P3HT chains in the systems with three types of the studied asphaltenes and in an unfilled P3HT sample is represented in gmx polystat routine and then averaged over 10 ns time periods. The data on the unfilled P3HT sample containing 27 molecules were taken from our previous work for comparison purposes [gR values for the unfilled P3HT lie at the upper boundary of the reported experimental data [The time dependence of the radius of gyration purposes . The simtal data ,84 obtaigR values. The most prominent difference is observed in the case of Asp-Core, in full accordance with the behavior of P3HT observed in the snapshots  are the eigenvalues of the chain inertia tensor [To characterize the shape and orientation of P3HT chains in the systems studied, the average values of the radius of gyration meter SN ,86, werea tensor . The resThe explanation for the results observed could be as follows. The Asp molecules are too miscible with P3HT. Therefore, the blends formed are rather uniform, and only slight elongation of the polymer chains is observed. However, the P3HT chains are more oriented in the blends with Asp in comparison with unfilled P3HT. At the same time, the Asp-COOH form dense aggregates, leaving too little free space for the polymer chains to elongate and form a structure where all chains are ordered in the same direction. Thus, in the Asp-COOH/P3HT blends, the order parameter is much lower than that in blends with Asp and Asp-Core, although the shape of the P3HT chain is close to cylindrical, as follows from the values of asphericity and acylindricity. In the system with the Asp-Core, phase separation occurs with the formation of a layered structure (see density profiles in As was shown in the previous paragraph, the introduction of the asphaltenes to the polymer matrix can indeed lead to the ordering of the polymer chains. However, in the system with Asp-COOH, possessing the most promising electronic properties , the tooAs can be seen from snapshots in b and an increase in acylindricity c. Thus, the interplay between the parameters b and c indicates that the polymer chains approach the coil conformation in the mixtures with a decreasing amount of asphaltenes. Moreover, the comparison of the gyration radii of the polymer chains in the unfilled sample and the studied blends suggests that, at the minimum investigated concentration of the asphaltenes, the polymer coils are even denser than in the case of the unfilled P3HT sample. Our assumption is that, at a low content of asphaltenes in the system, the polymer chains tend to wrap up around the elongated linear aggregate of the asphaltenes (snapshot is provided in The results on the size, shape and orientation of P3HT chains provided in In this work, we addressed the effect of the chemical structure of the asphaltenes on their aggregation behavior in mixtures with P3HT and on the morphology of the polymer phase, including the possibility of the formation of the interpenetrating 3D structure within the polymer and asphaltene phases at varying concentrations of carboxyl-containing asphaltenes that could be essential for the blends intended for use in BHJ solar cells.It was found that the chemical structure of asphaltenes and their interaction with P3HT polymer chains play a crucial role in the morphology of the blends studied. Asphaltenes with aliphatic side groups were almost evenly distributed in P3HT, whereas asphaltenes with aliphatic groups cut off formed a loose cluster, and two distinct non-interpenetrating phases were formed in this composite, while the carboxyl-containing asphaltenes aggregated with the formation of prominent stacked structures. A comparison of the aggregation behavior of asphaltenes revealed that the formation of stacks was due to the π–π interactions between the polyaromatic cores of the asphaltenes, additionally stabilized by hydrogen bonds.It was shown that the asphaltene phase can serve as a director defining the orientation of the polymer chains and affect the ordering of the chains due to the π–π interactions between the polyaromatic core of the asphaltenes and the aromatic polymer backbone if the interaction between the polymer chains and the asphaltene nanoparticles is unbothered by the aliphatic side groups surrounding the asphaltene core.Thus, the present work reveals the impact of the asphaltenes’ chemical composition and concentration on the structure of the asphaltenes/P3HT blends, which may contribute to the development of low-cost BHJ solar cells based on conjugated polymer/asphaltene blends. To continue our investigation further, a collaboration could be established with experimental groups, which specialize in asphaltene extraction from natural sources and modification of asphaltenes, as well as investigation of organic photovoltaic devices. We believe that our results will help with finding a proper method of asphaltene treatment and mixture composition to develop new organic solar cells with improved performance and reduced production costs.


Dear Editor,Urticaria is a common condition, determined by the activation of mast cells, presenting clinically as wheals, angioedema, or both.The prevalence of physical urticaria (PU) in adults varies from 20% to 30% among urticaria cases and 6.2% to 25.5% in children. It is estimated that PU is present in up to 5% of the general population. In 10% to 50% of patients with CU, at least one type of PU is identified (most often symptomatic dermographism and delayed pressure urticaria).It is important to recognize that associations of CIndU and CSU are often observed, whereas a patient may simultaneously have two or more forms of CIndU. Patients with CSU with a CIndU component have a worse prognosis, with longer disease duration.CIndUs can be diagnosed through clinical history, physical examination, and lesion reproduction using challenge tests.2LEN UCARE),A retrospective study was carried out by analyzing the medical records of 179 patients with a history of CU, followed at a Urticaria Center of Reference and Excellence  were from females and 26 (14%) from male patients. The mean age was 46.3 years (6–81 years), and disease duration averaged 10.2 years. Ninety-seven (54%) patients had an association between CSU and CIndU, 63 (35%) had only CSU, and 19 (11%) had only CIndU . Among tThe present data corroborate the findings of other epidemiological studies, with a higher prevalence of CU in females, age group (20‒30 years), an association between CSU and CIndU, in addition to the most frequent type of CIndU (dermographism). On the other hand, different from the findings of European studies, the authors found a longer disease duration in the studied group (10.2 years × 3-5 years).Finally, the identification and management of CIndUs in patients with CU are extremely relevant since they are associated with a worse prognosis and longer disease duration, which negatively affects patient quality of life.None declared.Ana Carolina Miranda Carvalho Ferreira Fernandes de Souza: Approval of the final version of the manuscript; design and planning of the study; collection, analysis, and interpretation of data; intellectual participation in the propaedeutic and/or therapeutic conduct of the studied cases.Sérgio D. Dortas Junior: Approval of the final version of the manuscript; design and planning of the study; collection, analysis, and interpretation of data; intellectual participation in the propaedeutic and/or therapeutic conduct of the studied cases; critical review of the literature; critical review of the manuscript; drafting and editing of the manuscript.Guilherme Gomes Azizi: Approval of the final version of the manuscript; data interpretation; intellectual participation in the propaedeutic and/or therapeutic conduct of the studied cases; critical review of the literature; critical review of the manuscript; statistical analysis.Alfeu Tavares França: Approval of the final version of the manuscript; intellectual participation in the propaedeutic and/or therapeutic conduct of the studied cases; critical review of the literature; critical review of the manuscript; effective participation in research orientation.Omar Lupi: Approval of the final version of the manuscript, critical review of the literature, critical review of the manuscript, effective participation in research orientation.Solange O R Valle: Approval of the final version of the manuscript; intellectual participation in the propaedeutic and/or therapeutic conduct of the studied cases; critical review of the literature; critical review of the manuscript; effective participation in research orientation.None declared.


Ms 6.9 earthquake in 2022 and discuss the historical seismic activities and corresponding stress adjustment processes in the research region. To analyze and study the seismogenic structure and mechanism of the earthquake, we investigated the spatial and temporal distribution characteristics of the Menyuan earthquake sequence and analyzed the InSAR coseismic deformation field. We obtained the precise locations of the main shock and aftershocks and the coseismic InSAR deformation field of the main shock. It was confirmed that the Ms 6.9 earthquake was a shallow sinistral strike-slip earthquake, which led to the sequential activation of the Tuolaishan and Lenglongling faults. The main seismogenic fault of the mainshock was the northwestern end of the Lenglongling fault, and the earthquake rupture was segmented. It can be inferred that the earthquake was a stress-adjusted event triggered in the Qilian-Haiyuan tectonic belt caused by the northeasterly push of the Qinghai-Tibet Plateau. The risk of moderate to high earthquakes in the region remains high in the future, requiring enhanced seismic observations.Precise earthquake locations and InSAR (Interferometric Synthetic Aperture Radar) deformation observation are the major methods to understand the earthquake occurrence and disaster-causing process. This paper proposes a processing framework for analyzing strong earthquake mechanisms from one-dimensional velocity inversion to precise earthquake locations combined with InSAR deformation observation, and discusses earthquake-generating fault and dynamic mechanisms of tectonic deformation. We analyzed the Menyuan  After the occurrence of strong earthquakes, precise earthquake locations and surface deformation observation are common research methods for understanding the mechanism and process of earthquake occurrence . AccuratMS 6.9 earthquake occurred in Menyuan County, Qinghai Province, China, at 01:13 on 8 January 2022; the initial location of the epicenter was 37.77° N, 101.26° E, and the focal depth was 10 km. This earthquake was the third MS > 6 event after the two earthquakes MS 6.4 in 1986 and MS 6.4 in 2016. According to a field investigation, the surface rupture length caused by this earthquake exceeded 20 km, with a maximum 2.1 m sinistral dislocation. A total of 4052 houses were damaged and nine people were injured in several counties near the epicenter, and the tunnels and facilities of the Haomen-Junmachang section of the Lanzhou-Xinjiang high-speed railway were seriously damaged. Therefore, this earthquake has aroused widespread concern in academia and the public. According to the tomographic imaging results of the upper and middle crust in the source area, the Mengyuan Ms 6.4 (2016) and Ms 6.9 (2022) earthquake occurred in the zone of dramatic changes in P- and S-wave velocities, and this region also corresponds to the transition zone of high and low values of Poisson’s ratio and saturation [Ms 5.2 aftershock that occurred on 12 January was close to the 2016 earthquake, which suggests that this seismic activity led to a full release of the energy accumulated by the Lenglongling rupture, and that a larger magnitude earthquake is unlikely to occur in the near future [According to the China Earthquake Networks Center (CENC) report, an turation ,22. In ar future . Howeverr future . Our purStrong earthquakes occur frequently in Menyuan area, and the structural characteristics are complex. It is worth noting that the 1986 Menyuan earthquake was mainly a normal fault type, while the 2016 Menyuan earthquake was a thrust type ,25,26. Bhttp://10.5.202.37:8080/JOPENSCat, (accessed on 18 January 2022)). The distribution of earthquake epicenters in Menyuan and surrounding areas is shown in Ms 6.6 mainshock occurred at the western boundary of the Lenglongling fault near the boundary with the Tuolaishan fault. Owing to the regional stress adjustment caused by the mainshock, the following two aftershocks with magnitudes greater than Ms 5.0 occurred on the eastern edge of the Tuolaishan fault and in the middle of the Lenglongling fault.We downloaded the earthquake catalog from 2009 to 2022 from the CENC  was also dominated by compressional thrust. Since the late Quaternary it has changed to be dominated by sinistral thrust. Moreover, the fault was continuously active in the Late Pleistocene and has been active in the Holocene (Q3 and Q4) [The two creasing . The 202f 1–3 km ,38. He ef 1–3 km  found th and Q4) ,41.Ms ≧ 3.0, and two aftershocks exceeded Ms 5.0, i.e., Ms 5.1 at 2:09 on 8 January and Ms 5.2 at 18:20 on 12 January 2022. To ensure the reliability of the earthquake’s epicenter, we selected the seismic events (508 times) recorded by more than four stations for analysis. First, the VELEST location method was used to relocate the downloaded seismic events and optimize the velocity model; 500 km was selected as the threshold for the epicenter distance range, and the screened results of the seismic phase travel-time are shown in According to the CENC monitoring records, from 8 to 15 January 2022, a total of 2357 active events of the Menyuan earthquake were recorded. Among them, 1648 earthquake events were recorded by a single station, and 508 earthquake events were recorded by more than four stations; 13 earthquakes had The accuracy of the seismic location mainly depends on the selection accuracy of the seismic phase arrival and the velocity model used for location inversion calculations. An accurate one-dimensional velocity model can provide more accurate source information. At the same time, the minimum one-dimensional velocity model is reliably used in seismic location, which can minimize the root mean square (RMS) of travel time residual . Velest To further improve the location accuracy of seismic events, we continued to use the double-difference location method to perform precise location processing based on the relocated earthquake catalog. The double-difference location method (HypoDD) proposed by Waldhauser and Ellsworth in 2000 has been widely used in microseismic and natural earthquake locations ,48,49. TWe selected 50 km as the upper threshold of the earthquake event pairing distance in precision location using the double-difference method. If the distance of earthquake event pairing exceeded the threshold, it was not considered. In addition, the number of earthquake events paired with the same earthquake was set to be no more than 10, and we used a total of 64,236 P-wave phases and 55,034 S-wave phases for the double-difference method for precise seismic relocation. Considering the different degrees of errors introduced in the manual selection process of the initial seismic phases, the seismic phase weight of the P wave was set to 1.0, and the seismic phase weight of the S wave was set to 0.6 in the calculation process of the precise location in this study . The preMs 0.5–6.9 earthquakes were obtained after precise seismic location using the double-difference method. The spatial location of the main earthquake (Ms 6.9) was 37.767° N, 101.276° E, and the depth was 12.3 km. Its horizontal location was at the intersection of the Lenglongling fault and Tuolaishan fault. The earthquake location results of this paper are consistent with those of other researchers [Ms 5.1 aftershock at 2:9 on 8 January was 13.3 km, which indicated that the fault slip continued to extend and develop at deeper depths after the mainshock. After relocation, the earthquake distribution was more concentrated compared with the origin catalog, and the Ms 5.2 aftershock on 12 January occurred on the Lenglongling fault. This indicates that Lenglongling fault was activated after certain stress accumulation. A comparison of the focal mechanism inversion results of major earthquakes . The corresponding spatial distribution characteristics of the aftershocks that occurred near the Lenglongling Fault (LLLF) and the Tuolaishan Fault (TLSF) also verified the inversion results of the focal mechanism of the Ms 5.1 and Ms 5.2 aftershocks.In total, acceptable location results of 384 earchers ,52,53. Tthquakes  indicateMs 5.2 aftershock on the Lenglongling fault was about 75°. Under the same tectonic stress, the two fault zones had similar fault tendencies. It is worth mentioning that the AA’ profile was about 4 km away from the surface of the Tuolaishan Fault in horizontal projection. Regardless, according to the fault dip analysis, Tuolaishan Fault may have a specific inclination in this section. Hence, the seismic activity in this section mainly occurred within the main fault of Tuolaishan.The BB’ profile near the mainshock was fitted with an 80° dip angle of the fault plane, while the fitted fault plane dip angle of the DD’ profile of the https://dwtkns.com/srtm30m/ (accessed on 18 January 2022)). After the phase unwrapping of the phase differential interference results by the branch-cut method [InSAR technology uses the reflection of microwaves emitted by a satellite on the ground to calculate the phase difference, and then performs an inverse calculation to obtain the surface micro-deformation . After tt method , an addit method . For thet method  to estimBased on this earthquake’s InSAR coseismic deformation field, the two interferograms from the ascending and descending orbits indicated relatively obvious deformation information a,b, consThere is a linear relationship between the slip (strike-slip and dip-slip components) on the fault plane and surface deformation. According to the InSAR deformation field , we furtMW 6.55–6.78, which is similar to the magnitude in The slip distribution obtained by the inversion is shown in Ms 6.9 occurred at the intersection of the Lenglongling fault and Tuolaishan fault, the Ms 5.1 aftershock that occurred on the same day was located to the west of the Tuolaishan fault, and the Ms 5.2 aftershock that occurred on 12 January was located on Lenglongling fault to the east of the main earthquake. The InSAR coseismic deformation showed a butterfly-like deformation pattern. The similar apparent deformation size and opposite amplitude polarity characteristics of the two walls of the fault also indicated that the earthquake activity was mainly strike-slip.The surrounding terrain of the Menyuan earthquake is complex, and the altitude varies greatly, which corresponds to the complex tectonic stress field in the Menyuan area and the unstable direction of block movement. The earthquake occurred at the intersection of Lenglongling fault and Tuolaishan fault, both of which have sinistral strike-slip characteristics. Our precise earthquake location results showed that the Menyuan earthquake sequence was distributed in the range of about 50 km from east to west and about 30 km from north to south. The main earthquake of MS 6.9 earthquake is Lenglongling fault. The earthquake caused the SW hanging wall of Lenglongling fault to rupture westward toward Tolaishan fault and the NE footwall to rupture northwest toward the end of Sunan-Qilian fault. The rupture length of Tuolaishan fault caused by the earthquake was about 10 km, and that of Lenglongling fault approached 20 km. The slip distribution of this earthquake on the fault plane was mainly concentrated in the depth range of 0–13 km downward along the dip, with a maximum slip of 4.5 m. After the main shock, the aftershocks moved together in Tolaishan fault and Lenglongling fault.Based on the precise location and InSAR results of the earthquake, we believe that the main seismogenic fault of the Menyuan MS 6.4 earthquakes. However, unlike the 1986 event, which was a normal fault earthquake, and the 2016 event, which was a thrust earthquake, this event was a strike-slip earthquake. These findings indicate the complexity of the seismogenic environment in this region. The present crustal motion field shows that the Qilian-Haiyuan tectonic belt where Menyuan is located is experiencing continuous and strong lateral escape, south-north crustal shortening and strong vertical uplift due to the northeasterly push of the Qinghai-Tibet block and the Alashan block in the northeast, which indicates that the dynamic background of this area is mainly crustal shortening and sinistral shearing.This earthquake was the third strongest earthquake in Menyuan after the 1986 and 2016 Ms 5.1 earthquake on the Tuolaishan fault tens of minutes after the mainshock. The occurrence of these two strong earthquakes and other aftershocks released the stress accumulation state on the western side of the Lenglongling fault zone to a certain extent, but also caused the imbalance of the stress state on the eastern and western sides of the Lenglongling fault zone, and finally contributed to the occurrence of the Ms 5.2 earthquake on 12 January. The CC’ profile in Based on this, we believe that the occurrence of this main shock was the result of a sinistral strike-slip dislocation at the intersection of the Lenglongling fault and the Tuolaishan fault when the Qinghai-Tibet block was pushed in a northeasterly direction, resulting in a critical state. The undischarged energy triggered the MS 8.0 earthquake in 1927, Minqin MS 7.0 earthquake in 1954, Menyuan MS 6.4 earthquake in 1986, Menyuan MS 6.4 earthquake in 2016 and this MS 6.9 earthquake. Among them, both the 1986 Menyuan earthquake and the 2016 Menyuan earthquake occurred at the two end of branch fault on the northern side of Lenglongling fault [The Qilian-Haiyuan tectonic belt, where Lenglongling fault is located, is an important boundary fault for adjusting tectonic stress along the northeastern margin of the Qinghai-Tibet Plateau, where there have been many strong earthquakes in the past one hundred years, including the Gulang ng fault ,59,60. Tng fault . These fIt is well known that the occurrence of moderate and strong earthquakes is caused by the overall unstable sliding of a fault, and a decoupling layer is often required to provide the overall dislocation conditions for the fault during the unstable sliding process ,63. The Ms 6.9 earthquake and its aftershock sequence, we analyzed the precise locations of the Menyuan earthquake sequence and InSAR coseismic deformation field and finally drew the following conclusions:(1)Ms 6.9 main earthquake  occurred at the intersection of the Lenglongling fault and the adjacent Tuolaishan fault, while the following two Ms 5.1 and Ms 5.2 aftershocks occurred in the Tuolaishan and Lenglongling fault zone, respectively.According to the relocations of the earthquake sequence, the (2)Ms 6.9 mainshock changed the local stress field and activated the Tuolaishan fault zone. Subsequently, many aftershocks gradually transitioned from the Tuolaishan fault to the Lenglongling fault. The Ms 5.2 aftershock on 12 January was triggered during the eastward transmission of the stress effect.The focal mechanism solution of the earthquake and the spatial geometric distribution of the aftershock sequence exhibited prominent east-west distribution characteristics. The energy released by the (3)The earthquake reflects the calibration of accumulated tectonic stresses inside the Qilian-Haiyuan tectonic belt, where the Lenglongling fault lies under the action of northeasterly compressive stress on the northeastern margin of the Qinghai-Tibet Plateau. The higher recurrence rate of moderate-to-high earthquakes in this region also indicates that the future seismic hazard remains high, and earthquake observation and early warning in this region should be strengthened.To analyze the seismogenic process and structural characteristics of the Qinghai Menyuan


Concrete presents different internal micro-structure and damage characteristics because of the different content of steel fibers and the randomness of its distribution. Therefore, the failure process of steel-fiber-reinforced concrete (SFRC) should be divided into different stages and the damage types should be classified to further clarify the strengthening mechanism of steel fibers. The role of volume fractions of steel fibers in the splitting-tensile strength of concrete was investigated by split tensile tests for concrete with four different volume fractions of steel fibers . The acoustic emission energy and horizontal displacement of concrete in the splitting-tensile process were monitored by combing digital image correlation (DIC) and acoustic emission (AE) techniques, and the microscopic failure mechanism of SFRC was analyzed emphatically. The results showed that the addition of steel fibers improved the splitting-tensile strength of concrete. With the increase of the volume fraction of steel fibers, the splitting-tensile strength of concrete increased first and then decreased, and reached the maximum value of 5.294 MPa when the content was 1.5%. It was observed that the overall failure mechanism could be divided into four stages: slow accumulation of elastic energy (I); rapid accumulation of elastic energy (II); rapid accumulation of dissipated energy (III); a slow decrease of elastic energy and a slow increase of dissipated energy (IV). Tensile failure dominated the failure process of concrete splitting-tensile resistance, while there was a part of shear failure. In recent years, SFRC has been widely used in some fields including highway bridges, hydraulic dams, ports, and marine engineering. Due to the significant brittleness and low tensile strength of ordinary concrete, adding an appropriate amount of steel fibers can effectively improve its tensile and flexural strength ,2, crackThe DIC technique has been widely used in material strain measurement and crack propagation because of its simple operation, lack of contact, and high precision . Li et aIn summary, in previous studies, DIC and AE technologies were mainly used to study the development of FPZ in the process of concrete fracture damage and to analyze the damage degree of specimens. However, the development law of cracks in concrete in the process of splitting-tensile resistance is still unclear. Moreover, due to the disordered and random distribution of steel fibers, concrete exhibits different microstructure and damage characteristics, so it is necessary to further clarify the crack resistance and strengthening mechanism of steel fibers in the process of splitting-tensile resistance. To provide the relationship between the overall splitting-tensile failure process of SFRC and the local energy dissipation and crack propagation, the splitting-tensile failure process of concrete with four different volume fractions of steel fibers  was monitored by combining the AE and DIC techniques in this study. The full-field horizontal displacement and the parameters such as AE energy were obtained, and the influence mechanism of the volume fraction of steel fibers on the splitting and tensile properties of concrete was studied.Conch brand P.O 42.5 ordinary Portland cement produced by Liquan Conch Cement Factory in Xianyang, China was used in this test. The physical and chemical properties of the cement are shown in fμ = 3.7~1.6. Coarse aggregate used in this test is 5 mm~20 mm continuously graded gravel, which meet the standard requirements of “Specification of Pebble and Crushed Stone for Building” (GB/T14685-2011).The particle size distribution graph of the aggregate as shown in According to the Chinese standard “Fly Ash Used for Cement and Concrete” (GB 1596-91), fly ash is Grade I, with an average particle size of 12.71 μm and is produced by Shaanxi Weihe Power Plant. Its chemical properties are listed in The water reducer was produced by Shaanxi Qinfen Building Materials Co., Ltd. . Its physical properties are listed in The air-entraining agent used was produced by Jiangsu Sobute New Material Co., Ltd. , and the content was 0.01%.The milled steel fiber used was 2.0~2.6 mm in width, 0.4~0.8 mm in thickness, and about 38 mm in length, and was produced by Hengshui Junye Road and Bridge Maintenance Engineering Co., Ltd. , as shown in Four different contents of steel fibers  were used in the test. The mix proportions are listed in According to the “Standard for Test Method of Performance on Ordinary Fresh Concrete” (GB/T 50080-2002), the slump and air content of the fresh concrete were measured. The test results are shown in (1)Firstly, the premixed mortar with a water-binder ratio of 0.4 was used to paint the HJS-60 double-horizontal axis concrete mixer manufactured by Cangzhou Yixuan Test Instrument Co., Ltd.  to avoid water absorption.(2)Cement, fly ash, sand, coarse aggregates, and water reducer agent were added into the mixer and mixed at a low speed of 62 rpm for 30 s. After that, steel fibers were dispersed manually into the mixer and blended at a high speed of 125 rpm for 60 s. Finally, the air-entraining agent was dissolved into water and then the liquid was added into the mixer and mixed for 120 s.(3)The fresh concrete mixture was poured into moulds. The molds were then placed on a vibrating table and vibrated for 30 s to avoid segregation of fresh concrete. The specimens were demolded 24 h after casting and then cured for 28 days in a curing box with a temperature of 20 ± 2 °C and a relative humidity of 95%.(4)After 28 days’ curing, the specimens were taken out and painted by white-black speckles. The typical specimens prepared are shown in Specimens with dimensions of 150 mm × 150 mm × 150 mm (three specimens for each mix group) were prepared for testing the splitting-tensile strength of SFRC. The SFRC specimens were prepared in the following steps:The splitting-tensile test, with reference to GB/T 50081-2019 , was carThe splitting-tensile test was performed on a MTS2000 kN universal testing machine produced by Shanghai Qingbo Test Equipment Co., Ltd.  by applying a load at a rate of 0.05 MPa/s and plotting the load-vertical displacement curve by computer, as shown in The DIC technique was to monitor the splitting-tensile process with the 2018 version of MatchID-2D non-contact, full-field strain measurement and simulation optimization analysis system developed by Match ID company. Two cameras with a resolution of 2048 × 2048 were fixed on a tripod and placed vertically 2 m away from the surface of the specimen being photographed. The crack was expected to occur in the center of the specimen, so the camera’s horizon was focused there . The camWhile starting the tester, the DIC system and AE system were triggered at the same time to dynamically track the crack opening and propagation of the specimen during the splitting and tensile process; the loading was terminated when the specimen suffered macroscopic damage, and the DIC system and the AE system were stopped at the same time.The splitting-tensile strength of concrete with four different contents of steel fibers at 28 days of age is shown in The effect of the volume fraction of steel fibers on the The effect of volume fraction of steel fibers on the W is the work done by an external force on the system, U is the initial strain energy, T is the strain energy released after cracking, and D is the increased surface energy after cracking. When all of D was used to form a new crack area At, Equation (2) was satisfied:Griffith ,34,35 deE is the elastic modulus.The energy release rate of crack propagation  and high AF values (ring count/duration), while shear cracks have high RA values and low AF values, and tension-shear cracks have low RA values and low AF values ,44. The The percentage of cracks at different stages of the whole splitting-tensile process for concrete with different volume fractions of steel fibers is shown in The full-field horizontal displacements of SFRC at different stages during the splitting-tensile process are shown in (1)The addition of steel fibers significantly improved the splitting-tensile strength of concrete. With the increase of the volume fraction of steel fibers, the splitting-tensile strength of concrete increased first and then decreased, and reached the maximum value of 5.294 MPa when the content was 1.5%.(2)AE energy can reflect the four stages of concrete fracture characteristics; the critical state of instability can be judged effectively by the sudden increase of accumulated AE energy. The splitting-tensile process of SFRC mainly included the following four stages: Stage I (0 < (3)Tensile cracks dominated the whole process of splitting and tensile failure of SFRC. The percentage of shear cracks in SFRC with volume fractions of steel fibers of 0.0% was high in stage I, 1.0%, and 1.5% was high in stage I and stage IV. However, the proportion of shear cracks in concrete with volume fractions of steel fibers of 2.0% is between 30–40% at every stage.(4)DIC is possible to measure and accurately determine parameters of crack, such as its actual length, shape, and trajectory of propagation. The combination of AE and DIC is an effective experimental research method, which has great development potential in the field of non-destructive monitoring of SFRC structures.In this study, the splitting-tensile strength of concrete with four different volume fractions of steel fibers  was tested, and the splitting-tensile failure process of concrete was monitored by combining AE and DIC techniques. The evolution law of AE energy and the variation law of full-field displacement of concrete were obtained, and the microscopic failure mechanism of SFRC under macroscopic failure and the crack resistance mechanism of steel fiber were studied. The main conclusions are as follows: