Ultra-high performance concrete and method for producing the same

Abstract

The application relates to the field of concrete, and particularly discloses a kind of ultra-high performance concrete and a preparation method thereof. Each volume part of the ultra-high performance concrete comprises the following components by weight: 210-250 parts of water, 800-950 parts of cement, 150-250 parts of silica fume, 150-800 parts of quartz sand, 250-750 parts of graphite tailings, 200-300 parts of silica powder, 100-200 parts of steel fiber, and 10-100 parts of water reducing agent. The ultra-high performance concrete has good mechanical properties, electrical conductivity and self-sensing performance.

Description

Technical Field

[0001] This invention relates to the field of concrete, and more particularly to an ultra-high performance concrete and its preparation method. Background Technology

[0002] Graphite plays a key role in energy storage and high-performance materials, and its demand has been rising in recent years. However, a large amount of tailings are inevitably generated during the graphite mining process. These tailings not only occupy valuable land resources, but also easily cause water, soil and air pollution and damage the ecosystem due to poor storage management. Existing measures for the resource utilization of graphite tailings have the following disadvantages: (1) When tailings are used for backfilling or as filler in civil engineering, the particle size of graphite tailings is fine and the mechanical strength is limited. They need to be mixed with other materials and have low added value. (2) When graphite tailings are reprocessed to recover useful minerals, it is difficult to meet the requirements of simple processing technology and high recovery rate. (3) When graphite tailings are used to partially replace fine aggregates or mineral admixtures in concrete or mortar, the replacement rate is limited. Excessive graphite tailings will cause uneven gradation, resulting in the gradual loss of filling effect and adversely affecting the strength of materials. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to provide an ultra-high performance concrete that can maintain good mechanical properties under high graphite tailings content, and can also endow the ultra-high performance concrete with electrical conductivity and self-sensing properties.

[0004] Another technical problem that this invention aims to solve is to provide a method for preparing ultra-high performance concrete.

[0005] To address the aforementioned technical problems, this invention provides an ultra-high performance concrete, wherein each volume fraction of the ultra-high performance concrete comprises the following components in parts by weight: Water 210-250 parts, cement 800-950 parts, silica fume 150-250 parts, quartz sand 150-800 parts, graphite tailings 250-750 parts, silica fume 200-300 parts, steel fiber 100-200 parts, water-reducing agent 10-100 parts. It should be noted that the volume parts and weight parts in this application correspond to kg / m³. 3 This can also be a proportional scaling up or down of the correspondence, such as g / L, mg / cm³. 3 And so on, but not limited to these.

[0006] As an improvement to the above technical solution, the cement is PO42.5 grade cement or PO52.5 grade cement; and / or The silica fume contains ≥92wt% SiO2; and / or The SiO2 content in the quartz sand is ≥99wt%.

[0007] As an improvement to the above technical solution, the cement is PO52.5 grade cement; and / or The silica fume contains 92-94 wt% SiO2; and / or The SiO2 content in the quartz sand is 99~99.5wt%.

[0008] As an improvement to the above technical solution, the average particle size of the silica fume is 0.1~0.2μm; and / or The fineness of the quartz sand is 70-90 mesh; and / or The average particle size of the silicon micropowder is 8~12μm; and / or The steel fibers are 5-8 mm in length and 0.1-0.4 mm in diameter.

[0009] As an improvement to the above technical solution, the chemical composition of the graphite tailings includes: SiO250~60wt%, CaO 5~10wt%, Al2O310~20wt%, Fe2O33~10wt%, K2O 1~10wt%, MgO 3~8wt%, Na2O 0.1~1, SO30.5~2.5wt%.

[0010] As an improvement to the above technical solution, the gradation of the graphite tailings is as follows: 0.5~2wt% for mesh size greater than 16, 1~5wt% for mesh size 16~28, 20~30wt% for mesh size 28~55, 50~60wt% for mesh size 55~150, 10~15wt% for mesh size 150~200, and 1~3wt% for mesh size less than 200.

[0011] As an improvement to the above technical solution, the graphite tailings include a first graphite tailings and a second graphite tailings, wherein the maximum particle size of the first graphite tailings is ≤0.08mm and the minimum particle size of the second graphite tailings is >0.08mm. The weight ratio of the first graphite tailings to the second graphite tailings is (2~4):1.

[0012] As an improvement to the above technical solution, the first graphite tailings conforms to the following relationship:

[0013] In the formula, LOI 900 It is the loss on ignition of the first graphite tailings at 900°C in air; LOI 700 It is the loss on ignition of the first graphite tailings at 700°C in air; LOI 400This refers to the loss of the first graphite tailings on ignition at 400°C in air. Using the aforementioned first graphite tailings can effectively improve both the mechanical and electrical properties of ultra-high performance concrete, and optimize its self-sensing performance.

[0014] As an improvement to the above technical solution, the second graphite tailings conforms to the following relationship:

[0015] In the formula, It refers to the SiO2 content in the second graphite tailings. The values ​​represent the K2O content in the second graphite tailings, both in wt%. Using the aforementioned second graphite tailings can effectively improve the mechanical properties of ultra-high performance concrete.

[0016] Accordingly, the present invention also discloses a method for preparing ultra-high performance concrete, comprising: Mix 210-250 parts water, 800-900 parts cement, 150-250 parts silica fume, 500-750 parts quartz sand, 250-500 parts graphite tailings, 200-300 parts silica fume, 100-200 parts steel fiber, and 10-100 parts water-reducing agent evenly to obtain the final product.

[0017] Implementing this invention has the following beneficial effects: The ultra-high performance concrete in one embodiment of the present invention comprises the following components in parts by weight: 210-250 parts water, 800-950 parts cement, 150-250 parts silica fume, 150-800 parts quartz sand, 250-750 parts graphite tailings, 200-300 parts silica fume, 100-200 parts steel fiber, and 10-100 parts water-reducing agent. This ultra-high performance concrete possesses excellent mechanical properties, electrical conductivity, and self-sensing properties. Attached Figure Description

[0018] Figure 1 This is the equivalent circuit model diagram of Experiment Example 2 of this invention; Figure 2 This is the conventional circuit model diagram in Experimental Example 2 of this invention; Figure 3 This is a graph showing the stress-resistivity change rate of a sample made from ultra-high concrete in Example 2 under a cyclic load of 25 MPa. Figure 4 This is a strain-resistivity change rate graph of the ultra-high concrete sample prepared in Example 2 under a cyclic load of 25 MPa; Figure 5 This is a graph showing the change rate of resistivity as a function of moisture content for the specimens prepared in Examples 1, 2, 3, and Comparative Example 4 during the immersion test. Figure 6 This is a broken line curve showing the resistivity of the specimens prepared in Examples 1, 2, 3, and Comparative Example 4 in Test Example 4 as a function of temperature within the range of -20℃ to 60℃. Detailed Implementation To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain this application, and should not be construed as limiting this application. Furthermore, it should be understood that the specific embodiments described herein are merely for explaining this application and are not intended to limit this application.

[0019] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used in this specification is for the purpose of describing particular embodiments or examples only and is not intended to limit the invention. The optional range of the term "and / or" as used herein includes any one of two or more of the related listed items, as well as any and all combinations of the related listed items, including any two related listed items, any more related listed items, or a combination of all related listed items.

[0020] The following embodiments are provided for the purpose of illustrating various embodiments of the present invention and are not intended to limit the invention in any way. Those skilled in the art will understand that variations and other uses as defined in the claims are included within the spirit and scope of the invention. Unless otherwise specified, the materials, reagents, etc., used in the following embodiments are commercially available.

[0021] In this invention, the technical features described in an open-ended manner include both closed-ended technical solutions composed of the listed features and open-ended technical solutions that include the listed features.

[0022] Unless otherwise specified, the percentage contents mentioned in this invention refer to solid-liquid mixtures and solid phases. Solid-phase mixing refers to mass percentage; for liquid phases... Liquid phase mixing refers to volume percentage.

[0023] Unless otherwise specified, all percentage concentrations mentioned in this invention refer to the final concentration. The final concentration refers to the proportion of the added component in the system after the addition of that component.

[0024] Example 1 This embodiment provides an ultra-high performance concrete with the following formula: Water 211.71 parts, PO52.5 grade cement 846.85 parts, silica fume 211.69 parts, quartz sand 698.69 parts, silica powder 254.11 parts, steel fiber 156 parts, graphite tailings 232.90 parts, water-reducing agent 21.17 parts. The silica fume is Elken silica fume 920, with a SiO2 content of 93.6 wt%; the quartz sand has a particle size of 70-90 mesh and a SiO2 content of 99.5 wt%; the average particle size of the silica fume is 10 μm; the steel fiber has a length of 6 mm and a diameter of 0.2 mm; the chemical composition of the graphite tailings is: SiO2 52.18 wt%, CaO 8.89 wt%, Al2O3 16.8 wt%, Fe2O3 8.16 wt%, K2O 3.21 wt%, MgO 4.23 wt%, Na2O 0.73 wt%, SO3 1.66 wt%, and other components 3.52 wt%. The particle size distribution of the graphite tailings is as follows: greater than 16 mesh 1.5wt%, 16-28 mesh 2.8wt%, 28-55 mesh 23.70wt%, 55-150 mesh 58.50wt%, 150-200 mesh 12.50wt%, and less than 200 mesh 1wt%. The water-reducing agent used is RHEOPLUS401 manufactured by BASF AG.

[0025] Example 2 This embodiment provides an ultra-high performance concrete with the following formula: Water 211.71 parts, PO52.5 grade cement 846.85 parts, silica fume 211.69 parts, quartz sand 465.80 parts, silica powder 254.11 parts, steel fiber 156 parts, graphite tailings 465.79 parts, water-reducing agent 21.17 parts. The silica fume is Elken silica fume 920, with a SiO2 content of 93.6 wt%; the quartz sand has a particle size of 70-90 mesh and a SiO2 content of 99.5 wt%; the average particle size of the silica fume is 10 μm; the steel fiber has a length of 6 mm and a diameter of 0.2 mm; the chemical composition of the graphite tailings is: SiO2 52.18 wt%, CaO 8.89 wt%, Al2O3 16.8 wt%, Fe2O3 8.16 wt%, K2O 3.21 wt%, MgO 4.23 wt%, Na2O 0.73 wt%, SO3 1.66 wt%, and other components 3.52 wt%. The particle size distribution of the graphite tailings is as follows: greater than 16 mesh 1.5wt%, 16-28 mesh 2.8wt%, 28-55 mesh 23.70wt%, 55-150 mesh 58.50wt%, 150-200 mesh 12.50wt%, and less than 200 mesh 1wt%. The water-reducing agent used is RHEOPLUS401 manufactured by BASF AG.

[0026] Example 3 This embodiment provides an ultra-high performance concrete with the following formula: Water 211.71 parts, PO52.5 grade cement 846.85 parts, silica fume 211.69 parts, quartz sand 232.90 parts, silica fume 254.11 parts, steel fiber 156 parts, graphite tailings 698.69 parts, water-reducing agent 21.17 parts. The silica fume is Elken silica fume 920, with a SiO2 content of 93.6 wt%; the quartz sand has a particle size of 70-90 mesh and a SiO2 content of 99.5 wt%; the average particle size of the silica fume is 10 μm; the steel fiber has a length of 6 mm and a diameter of 0.2 mm; the chemical composition of the graphite tailings is: SiO2 52.18 wt%, CaO 8.89 wt%, Al2O3 16.8 wt%, Fe2O3 8.16 wt%, K2O 3.21 wt%, MgO 4.23 wt%, Na2O 0.73 wt%, SO3 1.66 wt%, and other components 3.52 wt%. The particle size distribution of the graphite tailings is as follows: greater than 16 mesh 1.5wt%, 16-28 mesh 2.8wt%, 28-55 mesh 23.70wt%, 55-150 mesh 58.50wt%, 150-200 mesh 12.50wt%, and less than 200 mesh 1wt%. The water-reducing agent used is RHEOPLUS401 manufactured by BASF AG.

[0027] Example 4 This embodiment provides an ultra-high performance concrete with the following formula: The composition includes: 211.71 parts water, 846.85 parts PO52.5 grade cement, 211.69 parts silica fume, 232.90 parts quartz sand, 254.11 parts silica fume, 156 parts steel fiber, 524.02 parts first graphite tailings, 174.67 parts second graphite tailings, and 21.17 parts water-reducing agent. The silica fume is Elken silica fume 920 with a SiO2 content of 93.6 wt%. The quartz sand has a particle size of 70-90 mesh and a SiO2 content of 99.5 wt%. The average particle size of the silica fume is 10 μm. The steel fiber has a length of 6 mm and a diameter of 0.2 mm. The maximum particle size of the first graphite tailings is ≤0.08 mm, and its chemical composition is: SiO2 46.1 wt%, CaO 9.46 wt%, Al2O3 9.51 wt%, Fe2O3 8.35 wt%, K2O 3.22 wt%, MgO... 5.05 wt%, Na₂O 0.83 wt%, SO₃ 5.65 wt%, other 11.83 wt%. LOI 900 It is 5.84 wt%, LOI 700 The LOI was 4.31 wt%. 400 The content was 1.05 wt%. The minimum particle size of the second graphite tailings was >0.08 mm, and its chemical composition was: SiO2 55.4 wt%, CaO 8.35 wt%, Al2O3 17.45 wt%, Fe2O3 7.15 wt%, K2O 4.44 wt%, MgO 2.45 wt%, Na2O 0.65 wt%, SO3 2.21 wt%, and others 1.9 wt%. The water-reducing agent was BASF AG's RHEOPLE PLUS 401.

[0028] Example 5 This embodiment provides an ultra-high performance concrete with the following formula: The composition includes: 211.71 parts water, 846.85 parts PO52.5 grade cement, 211.69 parts silica fume, 232.90 parts quartz sand, 254.11 parts silica fume, 156 parts steel fiber, 524.02 parts first graphite tailings, 174.67 parts second graphite tailings, and 21.17 parts water-reducing agent. The silica fume is Elken silica fume 920 with a SiO2 content of 93.6 wt%. The quartz sand has a particle size of 70-90 mesh and a SiO2 content of 99.5 wt%. The average particle size of the silica fume is 10 μm. The steel fiber has a length of 6 mm and a diameter of 0.2 mm. The maximum particle size of the first graphite tailings is ≤0.08 mm, and its chemical composition is: SiO2 48.3 wt%, CaO 6.38 wt%, Al2O3 12.69 wt%, Fe2O3 7.98 wt%, K2O 2.7 wt%, MgO... 4.9 wt%, Na₂O 0.58 wt%, SO₃ 8.42 wt%, other components 7.84 wt%. LOI 900It is 7.02 wt%, LOI 700 The LOI is 3.52 wt%. 400 The content was 1.43 wt%. The minimum particle size of the second graphite tailings was >0.08 mm, and its chemical composition was: SiO2 56.3 wt%, CaO 8.16 wt%, Al2O3 16.78 wt%, Fe2O3 7.56 wt%, K2O 3.85 wt%, MgO 3.15 wt%, Na2O 0.68 wt%, SO3 2.31 wt%, and other 1.21 wt%. The water-reducing agent was RHEOPLUS401 manufactured by BASF AG.

[0029] Comparative Example 1 This embodiment provides an ultra-high performance concrete with the following formula: Water 211.71 parts, PO52.5 grade cement 846.85 parts, silica fume 211.69 parts, quartz sand 931.59 parts, silica fume 254.11 parts, water-reducing agent 21.17 parts; The silica fume is Elken silica fume 920 with a SiO2 content of 93.6 wt%; the quartz sand has a particle size of 70-90 mesh and a SiO2 content of 99.5 wt%; the average particle size of the silica powder is 10 μm; and the water-reducing agent is RHEOPLUS401 produced by BASF.

[0030] Comparative Example 2 This embodiment provides an ultra-high performance concrete with the following formula: Water 211.71 parts, PO52.5 grade cement 846.85 parts, silica fume 211.69 parts, quartz sand 931.59 parts, silica fume 254.11 parts, steel fiber 156 parts, water-reducing agent 21.17 parts; The silica fume is Elken silica fume 920 with a SiO2 content of 93.6 wt%; the quartz sand has a particle size of 70-90 mesh and a SiO2 content of 99.5 wt%; the average particle size of the silica powder is 10 μm; the steel fiber has a length of 6 mm and a diameter of 0.2 mm; and the water-reducing agent is RHEOPLUS401 produced by BASF.

[0031] Comparative Example 3 This embodiment provides an ultra-high performance concrete with the following formula: Water 211.71 parts, PO52.5 grade cement 846.85 parts, silica fume 211.69 parts, quartz sand 931.59 parts, silica fume 254.11 parts, steel fiber 234 parts, water-reducing agent 21.17 parts; The silica fume is Elken silica fume 920 with a SiO2 content of 93.6 wt%; the quartz sand has a particle size of 70-90 mesh and a SiO2 content of 99.5 wt%; the average particle size of the silica powder is 10 μm; the steel fiber has a length of 6 mm and a diameter of 0.2 mm; and the water-reducing agent is RHEOPLUS401 produced by BASF.

[0032] Comparative Example 4 This embodiment provides an ultra-high performance concrete with the following formula: 211.71 parts water, 846.85 parts PO52.5 grade cement, 211.69 parts silica fume, 254.11 parts silica powder, 156 parts steel fiber, 931.59 parts graphite tailings, and 21.17 parts water-reducing agent. The silica fume used was Elken silica fume 920, with a SiO2 content of 93.6 wt%. The average particle size of the silica fume was 10 μm. The steel fibers had a length of 6 mm and a diameter of 0.2 mm. The chemical composition of the graphite tailings was: SiO2 52.18 wt%, CaO 8.89 wt%, Al2O3 16.8 wt%, Fe2O3 8.16 wt%, K2O 3.21 wt%, MgO 4.23 wt%, Na2O 0.73 wt%, SO3 1.66 wt%, and other components 3.52 wt%. The particle size distribution of the graphite tailings was: greater than 16 mesh 1.5 wt%, 16-28 mesh 2.8 wt%, 28-55 mesh 23.70 wt%, 55-150 mesh 58.50 wt%, 150-200 mesh 12.50 wt%, and less than 200 mesh 1 wt%. The water-reducing agent was BASF RHEOPLUS401.

[0033] The following experimental examples are used to evaluate the performance of the ultra-high performance concrete in this invention: Experimental Example 1: Mechanical Property Analysis of Ultra-High Performance Concrete (1) Preparation of specimens For mechanical specimen preparation, the mixed mortar was poured into steel molds coated with a release agent. The mold dimensions were 40mm×40mm×40mm and 20mm×20mm×80mm. For self-sensing specimen preparation, the uniformly mixed slurry was poured into two types of steel molds coated with release agent: a 40mm×40mm×40mm mold with a pair of stainless steel mesh electrodes inserted along its length, spaced 20mm apart and 10mm from the edge; and a 20mm×20×80mm mold with a pair of stainless steel mesh electrodes inserted along its length, spaced 40mm apart and 20mm from the edge. Three specimens were prepared for each group of mechanical and compressive self-sensing specimens. The specimens were then placed on a vibration table and vibrated for 60 seconds to eliminate air bubbles, and the surface slurry was smoothed with a trowel.

[0034] In this technical solution, all specimens are first subjected to 3 days of standard curing (including curing time), followed by 3 days of hot water curing at 90°C, and then placed in a standard curing chamber until testing. Before testing, the specimens are removed and allowed to air dry naturally at room temperature until the surface is dry. The surface of the specimens is then sanded until smooth to prevent stress concentration caused by unevenness during the test.

[0035] (2) Compressive strength test The test specimens were removed from a standard curing room at 20±1℃ and 95% humidity for testing. Three samples were tested in each group, and the average value was calculated. The specimen size for the compressive strength test was 40mm×40mm×40mm, using a 2000kN mechanical testing machine (Changchun Xinke Testing Instrument Co., Ltd.). The compression surface was the 40mm×40mm non-formed surface, and the testing rate was 0.6mm / min. Three specimens were tested in each group, and the average value was taken as the ultimate load for the compressive strength test of that group of specimens. F c If the absolute value of the difference between two of the three specimen values ​​and the average value exceeds 15% of the average value, the test group is invalid and needs to be retested. Calculate the compressive strength of the composite UHPC according to the following formula, accurate to 0.01 MPa.

[0036]

[0037] In the formula: f c Indicates compressive strength, in MPa; F c The ultimate load for the compressive strength test of the specimen is N; A The distance between the support points is in mm.

[0038] The compressive strengths of all test groups are shown in Table 1. As can be seen from the table, in Comparative Examples 1-3, when only steel fibers were added, the compressive strength of the specimens gradually increased with the increase of steel fiber volume content, indicating that the addition of steel fibers significantly enhanced the compressive performance of concrete. In Examples 1-3, when graphite tailings and steel fibers were added, the compressive strength first decreased and then slightly increased with the increase of graphite tailings content, but the overall compressive strength was relatively low. However, by adding the first and second graphite tailings and controlling their addition ratio and chemical composition (Examples 4 and 5), the compressive strength increased significantly.

[0039] Table 1 Mechanical Properties of Concrete Specimens

[0040] Experimental Example 2: Electrical Conductivity Analysis of Ultra-High Performance Concrete This technical solution establishes a reasonable electrical equivalent circuit model through electrochemical impedance spectroscopy (EIS) testing to analyze the formation mechanism of continuous conductive pathways within UHPC. To further investigate the influence of different conductive fillers on the impedance characteristics of the UHPC matrix, this application employs an electrochemical workstation for EIS testing, constructs an equivalent circuit model of the conductive pathway, fits the Nyquist plot, and performs parameter analysis, thereby clarifying the role mechanism and influence of the conductive fillers.

[0041] (1) Electrochemical impedance spectroscopy test: AC impedance testing typically involves applying a small AC signal (usually 5mV) and measuring the current and voltage responses to obtain an impedance spectrum. By fitting these data, information about the electrochemical properties of the material can be obtained, such as charge transfer impedance, electrolyte interface characteristics, and diffusion impedance. This patent uses a 20mm × 20mm × 80mm specimen for electrochemical AC impedance testing, and employs an electrochemical workstation (CHI660 electrochemical workstation, Shanghai Chenhua Instrument Co., Ltd.) for the AC impedance testing. The specific testing process is as follows: Connect the workstation's electrode interfaces to the reference electrode, auxiliary electrode, and working electrode. Follow the electrochemical workstation's instruction manual for connections, ensuring each electrode is securely connected and avoiding signal interference. Set the excitation voltage to 50mV and apply a small-amplitude sinusoidal voltage of 5mV to the electrodes, testing its response from 10... -2 Hz to 10 6 After measuring the current signal in the Hz frequency range, an AC impedance spectroscopy model of the UHPC was established, and the model was verified using Zsimpwin software. The influence of filler and dosage on the AC impedance spectrum of the UHPC was analyzed in conjunction with the conductive path model, and the conductivity mechanism of the UHPC was further analyzed.

[0042] GT-UHPC employs an equivalent circuit model based on conductive path theory. This model posits that composite materials consist of three parts: connected conductive paths, discontinuous conductive paths, and insulating paths. The equivalent circuit model is constructed as follows: Figure 1 As shown. Where: a connected conductive path is equivalent to a resistive element. R 1. It not only encompasses interconnected pores and conductive fillers such as steel fibers, but also includes conductive channels formed by the overlapping of pores and conductive fillers. R A smaller value of 1 indicates a more complete conductive network within the matrix, resulting in lower resistance along the main current path through the matrix. Discontinuous conductive paths are equivalent to series resistors. R 2 and capacitor C 2. This represents not only isolated pores but also unconnected conductive filler channels. Finally, the insulation path is equivalent to the capacitance of the entire matrix. C1. It reflects the dielectric properties brought about by the matrix composed of particles such as slurry within the matrix.

[0043] In the fields of structural health monitoring and intelligent sensing materials, the regulation mechanism of conductivity is particularly crucial. Especially after the introduction of conductive fillers, the conductive network structure and frequency response behavior of the matrix significantly affect the overall functional performance. Therefore, constructing a reasonable equivalent circuit model and extracting parameters are of great significance for revealing the conductivity mechanism and optimizing material design. To facilitate parameter calculation, further... Figure 1 The equivalent circuit in the diagram is transformed into, for example: Figure 2 The conventional circuit model shown, in which C a and C b This represents two constant phase elements (CPE). R a and R b This represents the ohmic resistance in two conductive paths.

[0044] The fitting results of the two models can be converted using the following formula:

[0045]

[0046] Considering the relaxation phenomenon commonly observed in actual tests, constant-phase elements typically do not behave as ideal capacitors. Therefore, a simplified Brug model formula is used to... C a , C b Perform equivalent capacitance ( C eff )calculate:

[0047] In the formula, Y 0 represents the CPE amplitude constant; n The dispersion coefficient (0) <n≤1); R p The polarization resistance is in parallel with the CPE, in Ω; To obtain equivalent circuit element parameters reflecting the electrochemical properties of materials and further elucidate the impedance behavior mechanism, the following approach was adopted. Figure 2The equivalent circuit model shown was fitted to the AC impedance spectrum using Zsimpwin software, and the fit was compared with the impedance diagram obtained from actual tests to verify the degree of fit. The results show that the chi-squared values ​​of the fits for each experimental group are all below 5%, indicating small iteration errors during the fitting process and good consistency in the fitting results. Based on the construction of the equivalent circuit model and the completion of parameter extraction, further research was conducted on the effect of different conductive fillers on key impedance parameters to further reveal the conductivity mechanism of GT-UHPC. R 1 and C The following is a detailed analysis of two aspects: the impact of 1, and the verification of the rationality of the established equivalent circuit model based on the frequency response experimental results in the previous section. (2) R1 and C1 of ultra-high performance concrete After obtaining the Nyquist plot by fitting it using Zsimpwin software, the chi-square value of the fitted plot is calculated to obtain the matrix impedance characteristic parameters in Table 2. R 1. C 1.

[0048] Table 2. Matrix Impedance Characteristic Parameters

[0049] Based on matrix impedance characteristic parameters of different experimental groups R 1. C 1. The results comparison shows that with the addition of graphite tailings, R 1. Significantly decreased C The conductivity gradually increases. This trend indicates that with the introduction and increase of the conductive phase in the graphite tailings, a continuous conductive pathway is gradually formed and perfected inside the UHPC, resulting in a decrease in matrix resistance, an increase in dielectric energy storage capacity, and the ability for more current to be conducted through the interconnected filler network, while also increasing the matrix capacitance. Furthermore, data from Examples 4 and 5 show that controlling the specific composition and proportion of the first and second graphite tailings can effectively improve conductivity.

[0050] Experimental Example 3: Analysis of the self-sensing compressive properties of ultra-high performance concrete The specimen size for self-sensing performance analysis (including pressure, temperature, and humidity self-sensing tests) is 40mm×40mm×40mm. Strain gauges are attached to the non-perpendicular surfaces of the specimen to measure the vertical compressive strain. To eliminate the influence of humidity on the test results, the specimens are dried in a drying oven to constant weight, and the pressure self-sensing test is performed after the specimens have cooled to room temperature.

[0051] The testing system for compressive self-sensing performance mainly includes loading equipment and data acquisition equipment. A 250kN electronic universal testing machine (Instron 5985) was used for cyclic compressive loading, and a 2000kN mechanical testing machine (Changchun Xinke Testing Instruments Co., Ltd.) was used for monotonic compressive loading. Strain and AC resistance were acquired using a static strain gauge (DH3818N-2, Jiangsu Donghua Testing Technology Co., Ltd.) and an AC meter (Agilent U1733 AC meter, Agilent Technologies). During the loading process, the stress acquisition frequency was 50Hz; the vertical compressive strain value acquisition frequency was 1Hz; and the AC meter test frequency was 10kHz, with an acquisition frequency of 1Hz.

[0052] Before loading the test, an insulating film (Teflon film) was placed between the UHPC pressure surface and the testing machine's pressure table. The specimen was then placed on the universal testing machine. The LCR meter was connected to both terminals of the specimen, and the computer-side acquisition mode was set to collect resistance information. After balancing the data acquisition instrument's channels, the loading testing machine system was turned on. The positions of the specimen and support were adjusted, and the load, displacement, and crack width were zeroed. During loading, the testing machine and the resistance acquisition system were started simultaneously to collect stress, strain, and resistance data. The loading method was as follows: 1. Cyclic loading: Apply a vertical load directly to the specimen using a testing machine, and cyclically load 7 times at a loading rate of 0.08 mm / min. The loading amplitude should be less than 1 / 3 of the ultimate stress of the test group. The ultimate load of cyclic loading is set to 40 kN, i.e. 25 MPa. 2. Monotonic load: A vertical load is applied directly to the specimen using a testing machine until failure, at a loading rate of 0.6 mm / min.

[0053] The self-sensing performance of a specimen is evaluated using three indicators: resistivity change rate, stress sensitivity, and strain sensitivity. The formula for calculating the resistivity change rate is shown below:

[0054] In the formula: FCR The rate of change of resistivity; ρ t Resistivity under pressure test, in Ω·m; ρ 0 represents the initial resistivity of the specimen, in Ω·m.

[0055] The formula for calculating stress sensitivity is as follows:

[0056] In the formula: SES Stress sensitivity, % / MPa; FCR The rate of change of resistivity; σThe value is the vertical stress in MPa at which the resistivity change rate is at its maximum during the pressure self-sensing performance test.

[0057] The formula for calculating strain sensitivity is as follows:

[0058] In the formula: SAS For strain sensitivity; FCR The rate of change of resistivity; ε This represents the vertical strain value at which the resistivity change rate is at its maximum during the pressure self-sensing performance test.

[0059] 3. Cyclic loading test results: Seven cyclic compression tests (stress limit 25MPa) were conducted within the elastic range to simulate the material's resistive response under repeated low stress conditions during service. The changes in stress, strain, and resistivity were recorded in real time during the test.

[0060] Table 3 shows the self-sensing performance evaluation indicators for each group under a cyclic load of 25 MPa. Under 25 MPa cyclic ballast, the resistivity changes of each group of specimens showed significant differences. Comparative Example 1, without any filler, and Comparative Example 2, containing only steel fibers, showed almost no compressive self-sensing ability. Comparative Example 3, with a higher steel fiber content, exhibited a certain degree of compressive self-sensing ability. Examples 1-3 and Comparative Example 4 show that the compressive self-sensing ability improves with increasing graphite tailings content. Furthermore, Examples 4 and 5 show that controlling the chemical composition and content ratio of the first and second graphite tailings can significantly optimize the self-sensing performance.

[0061] Figure 3 The figure shown is a stress-resistivity change rate relationship graph for Example 2 under a cyclic load of 25 MPa. Figure 4 The figure shows the strain-resistivity change rate relationship of Example 2 under cyclic loading of 25 MPa. As can be seen from the figure, the resistivity change of the specimen is basically linear with stress and strain, with almost no hysteresis in the loading-unloading cycle, and the repeatability of the cyclic signal is good.

[0062] Table 3 Evaluation Indicators of Self-Sensing Performance for Each Group under Cyclic Load of 25MPa

[0063] 4. Results of monotonic loading experiment: The resistance response of specimens with different graphite tailings substitution rates under monotonic loading is consistent, showing an overall three-stage evolution trend of first decreasing, then stabilizing, and then rapidly increasing.

[0064] Each specimen was subjected to uniaxial compression until failure, and the change in resistance was recorded in real time during this process. The rate of change of resistivity (FCR) and stress-strain sensitivity at failure were also recorded. The results of the self-sensing performance evaluation indicators for each group are shown in Table 4.

[0065] Table 4. Evaluation Indicators of Self-Perception Performance for Each Group at Failure Under Monotonic Load

[0066] Experimental data show that specimens with different proportions exhibit certain resistivity changes during uniaxial compression, manifested as resistivity variations with increasing stress. Comparative Examples 1 and 2 showed almost no significant self-sensing ability under pressure, with resistivity remaining relatively stable, only exhibiting abrupt resistivity changes when the specimens cracked. In Examples 1-3 and Comparative Example 4, the FCR values ​​of the self-sensing specimens significantly increased with increasing graphite tailings content, but the FCR slightly decreased to 4.32% when graphite tailings completely replaced quartz sand. This indicates that appropriate incorporation of graphite tailings helps form a more significant conductive network response, increasing FCR within a certain range, while excessively high content may lead to a decrease in FCR increase due to overly continuous conductive phases or matrix degradation.

[0067] Experimental Example 4: Analysis of the Moisture Self-Sensing Performance of Ultra-High Performance Concrete Test method: Dry the specimen at 60℃ to constant weight and record its initial dry weight. W 0), Measure and record the initial resistance value of the specimen. R 0. The test was conducted under constant temperature conditions to prevent the influence of temperature fluctuations on moisture evaporation and specimen performance. The specimens were immersed in room temperature water. The specimens were removed and measured at specified time intervals (0, 10 min, 30 min, 1 h, 2 h, 4 h, 6 h, 12 h, 24 h, 36 h, 48 h, then at 12-hour intervals until the specimen reached constant weight). At each time point, the weight of the specimen was recorded using a weighing scale, accurate to 0.01 g; the AC resistance of the specimen was measured using an AC multimeter at a frequency of 10 kHz, and the measured resistance value was recorded. R After connecting to the AC meter, a stable value is read after 10 seconds. The measurement data at each time point should be repeated at least three times to ensure the reliability and accuracy of the data.

[0068] Weight changes at each time point ΔW=WW 0 (of which) W Record the weight of the specimen at that time, and calculate the rate of change of resistivity at each time point according to the following formula. Δρ / ρ 0:

[0069] In the formula: R 0 represents the initial resistance, in Ω;R The resistance at the current time point is expressed in Ω.

[0070] The experiment ended when all specimens reached saturation. Based on the data at each time point, curves were plotted showing the change rate of resistivity versus the change in moisture content of the specimens, and the humidity self-sensing performance of each experimental group was analyzed.

[0071] Specific experimental results are as follows: Figure 5 As shown in Figure 5, it can be seen that the moisture self-sensing performance of ultra-high performance concrete is enhanced with the increase of graphite tailings replacement rate. The relative resistivity change of Comparative Example 2 with 0% graphite tailings under saturation state is illustrated. |Δρ / ρ 0 | Only about 11.6%, while the saturation of 25%, 50%, 75%, and 100% graphite tailings groups in Examples 1, 2, 3, and Comparative Example 4 was significantly higher. | Δρ / ρ 0 | The percentages increased sequentially to approximately 14.8%, 15.3%, 19.9%, and 22.8%. It is evident that the higher the graphite tailings content, the more sensitive the material's resistivity response to changes in moisture content. This is because the incorporation of graphite tailings as fine aggregate affects the pore structure and interfacial transition zone (ITZ) of the UHPC, thus influencing water permeation behavior. High graphite tailings substitution rates (75%, 100%) introduce more interconnected pores and interfacial defects, resulting in incomplete slurry encapsulation at the aggregate-matrix interface, pore aggregation, and a loose, porous structure. This allows water to easily penetrate the material's interior, manifesting as a significant decrease in resistivity with increasing humidity and a substantial increase in humidity self-sensing ability. Conversely, a suitable amount of graphite tailings (e.g., 25%) helps optimize particle size distribution, fill voids, and improve density, while reducing porosity instead of increasing it. Therefore, at low to medium substitution rates (25%, 50%), the humidity self-sensing ability only increases slightly; while when the substitution rate reaches 75% and above, ITZ defects and pore connectivity increase sharply, and the humidity self-sensing ability rises sharply accordingly, indicating that medium doping has little effect or only improves the situation, while excessively high doping leads to a surge in pore connectivity, making the material extremely sensitive to humidity.

[0072] Experimental Example 5: Temperature Self-Sensing Performance Analysis of Ultra-High Performance Concrete To eliminate the interference of moisture in the test specimens, they were dried to constant weight before the test. The specimens were then placed in water-resistant test bags according to different groups for testing. The specific operating method is as follows: The test blocks were sequentially placed in five environments: a freezer at -20°C, 0°C, room temperature at 20°C, a drying oven at 40°C, and 60°C, and placed in each environment for 3 hours to allow for sufficient heat exchange and ensure that the internal temperature of the test block was consistent with the ambient temperature before testing. To reduce the impact of heat loss on the test results, the test blocks were removed from the drying oven and their resistance was immediately measured using an LCR meter at a frequency of 10kHz. The resistance test data for each temperature was recorded. The resistivity calculation formula is shown below:

[0073] To visually compare the effects of different functional filler combinations on the temperature self-sensing performance of ultra-high performance concrete, a piecewise linear curve of the resistivity of ultra-high performance concrete as a function of temperature in the range of -20℃ to 60℃ is presented, such as... Figure 6 As shown in the figure, the resistivity of Examples 1, 2, 3, and Comparative Example 4 all exhibit a positive temperature coefficient (PTC) effect during the heating process, meaning that the resistivity increases with increasing temperature. Specifically, when the temperature rises from -20℃ to 40℃, the resistivity of each group increases: Example 1, with the lowest graphite substitution rate, shows the most significant increase (from 6.9 × 10⁻⁶). 2 Ω·m increased to 8.6 × 10 2 Ω·m, an increase of approximately 24%, while the comparative example 4, with the highest graphite substitution rate, showed the smallest increase (from 6.7 × 10⁻⁶). 2 Ω·m increased to 7.1×10 2 (Ω·m, an increase of approximately 6%). When the temperature continued to rise to 60℃, the resistivity of each group showed a slight decrease or tended to stabilize. It can be seen that reducing the graphite tailings substitution rate will enhance the temperature sensitivity of resistivity: the lower the graphite content, the greater the influence of temperature on resistivity (the more obvious the PTC effect), while high graphite content makes the resistivity change relatively slowly with temperature.

[0074] In this specification, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to specific features, structures, materials, or characteristics described in connection with the described embodiment or example, which are included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0075] Although embodiments of this application have been shown and described, those skilled in the art will understand that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of this application, the scope of which is defined by the claims and their equivalents.

Claims

1. A type of ultra-high performance concrete, characterized in that, Each volume of ultra-high performance concrete comprises the following components in parts by weight: Water 210-250 parts, cement 800-950 parts, silica fume 150-250 parts, quartz sand 150-800 parts, graphite tailings 250-750 parts, silica powder 200-300 parts, steel fiber 100-200 parts, water-reducing agent 10-100 parts.

2. The ultra-high performance concrete as described in claim 1, characterized in that, The cement is PO42.5 grade cement or PO52.5 grade cement; and / or The silica fume contains ≥92wt% SiO2; and / or The SiO2 content in the quartz sand is ≥99wt%.

3. The ultra-high performance concrete as described in claim 1, characterized in that, The cement is PO52.5 grade cement; and / or The silica fume contains 92-94 wt% SiO2; and / or The SiO2 content in the quartz sand is 99~99.5wt%.

4. The ultra-high performance concrete as described in claim 1, characterized in that, The average particle size of the silica fume is 0.1~0.2μm; and / or The fineness of the quartz sand is 70-90 mesh; and / or The average particle size of the silicon micropowder is 8~12μm; and / or The steel fibers are 5-8 mm in length and 0.1-0.4 mm in diameter.

5. The ultra-high performance concrete as described in claim 1, characterized in that, The chemical composition of the graphite tailings includes: SiO2 50~60wt%, CaO 5~10wt%, Al2O3 10~20wt%, Fe2O3 3~10wt%, K2O 1~10wt%, MgO 3~8wt%, Na2O 0.1~1, SO3 0.5~2.5wt%.

6. The ultra-high performance concrete as described in claim 1, characterized in that, The gradation of the graphite tailings is as follows: 0.5~2wt% for mesh size greater than 16, 1~5wt% for mesh size 16~28, 20~30wt% for mesh size 28~55, 50~60wt% for mesh size 55~150, 10~15wt% for mesh size 150~200, and 1~3wt% for mesh size less than 200.

7. The ultra-high performance concrete as described in claim 1, characterized in that, The graphite tailings include a first graphite tailings and a second graphite tailings, wherein the maximum particle size of the first graphite tailings is ≤0.08mm and the minimum particle size of the second graphite tailings is >0.08mm. The weight ratio of the first graphite tailings to the second graphite tailings is (2~4):

1.

8. The ultra-high performance concrete as described in claim 7, characterized in that, The first graphite tailings conform to the following relationship: In the formula, LOI 900 It is the loss of the first graphite tailings on ignition at 900°C in air; LOI 700 It is the loss of the first graphite tailings on ignition at 700°C in air. LOI 400 It is the loss of the first graphite tailings on ignition at 400°C in air.

9. The ultra-high performance concrete as described in claim 8, characterized in that, The second graphite tailings conform to the following relationship: In the formula, It refers to the SiO2 content in the second graphite tailings. This refers to the K2O content in the second graphite tailings, both in wt%.

10. A method for preparing ultra-high performance concrete, characterized in that, include: Mix 210-250 parts water, 800-900 parts cement, 150-250 parts silica fume, 500-750 parts quartz sand, 250-500 parts graphite tailings, 200-300 parts silica fume, 100-200 parts steel fiber, and 10-100 parts water-reducing agent evenly to obtain the final product.

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