Preparation method and application of high-sensitivity red-mud-based environment-friendly self-sensing concrete strain gauge

Abstract

The invention discloses a preparation method and application of a high-sensitivity red-mud-based environment-friendly self-sensing concrete strain gauge. The preparation method comprises the following steps: carrying out crushing, grinding and drying pretreatment on red mud; the preparation method comprises the following steps: putting 35 parts of water into a cement mixer, gradually adding 0.4-0.8 part of carbon fibers into the water, stirring until the carbon fibers are uniformly dispersed, adding 100 parts of a cementing material which is composed of cement and red mud, and stirring until the cementing material is uniformly dispersed; a required composite mixture is obtained; pouring the composite mixture into a mold, and embedding a plurality of copper mesh electrodes; putting the mold on an electric vibrator, and vibrating to eliminate bubbles; and demolding, and curing in a standard curing room to obtain the red-mud-based environment-friendly self-sensing concrete strain gauge. According to the invention, the red mud is used as a granular conductive material, the carbon fiber is used as a conductive network structure in a mixed form of a fibrous conductive material, the strain sensitivity is high, the stability is good, the I-shaped strain gauge can be combined with concrete more tightly, and the adaptability to the load environment is high.

Description

Technical Field

[0001] The invention relates to the technical field of structural monitoring in civil engineering, and in particular to a preparation method and application of a high-sensitivity red mud-based environmentally friendly self-sensing concrete strain gauge. Background Art

[0002] In the field of structural health monitoring, traditional concrete structure monitoring usually relies on vibrating wire sensors and optical fiber sensors, which evaluate the health of the structure by monitoring parameters such as stress, strain, and temperature of concrete. However, such sensors have the following problems in practical applications:

[0003] Durability issues: Traditional sensors have a limited service life in concrete, and are susceptible to aging due to environmental and time effects, resulting in inaccurate data or failure. Once the concrete has solidified, vibrating wire strain gauges are relatively difficult to repair or replace, and any failure may require complex processing or additional drilling operations.

[0004] Insufficient compatibility: Traditional sensors have poor compatibility when combined with the physical and chemical properties of concrete, and are difficult to fully integrate into concrete structures, affecting long-term monitoring effects.

[0005] Complex installation: The vibrating-wire strain gauge needs to be accurately embedded in the concrete during the construction process. The installation position and method will affect the measurement results. Therefore, professional technicians are required to operate during the installation to ensure its accuracy step by step.

[0006] Susceptible to damage: The sensors and connecting cables of vibrating wire strain gauges are easily damaged during construction, and special care must be taken to protect these devices.

[0007] Signal interference: In large-scale projects, cable laying may be subject to electromagnetic interference, thus affecting the accuracy of measurement.

[0008] In recent years, self-sensing cement-based composite materials have gradually become a new technology for structural health monitoring. This type of material has the ability to sense external mechanical changes and provide real-time structural health information by adding conductive materials such as carbon fiber, graphene and MXene to ordinary concrete. The core principle of self-sensing cement-based composite materials is to use the piezoresistive effect of conductive materials to produce changes in resistivity with changes in stress and strain, thereby realizing the perception of cracks, stress and damage. However, the conductivity of existing single-doped conductive materials (carbon fiber, graphene, etc.) in self-sensing concrete is relatively limited, the conductive network construction is complex, and the piezoresistive stability and sensitivity of the material need to be improved. Since the addition of a single conductive material can easily lead to an unstable conductive network, which affects the accuracy and reliability of monitoring, it is not conducive to the promotion and application of self-sensing concrete strain gauges. Conductive materials such as graphene and carbon nanotubes, which are commonly used in self-sensing concrete, are expensive, which is not conducive to the large-scale use of self-sensing concrete.

[0009] The Bayer process for preparing alumina produces a large amount of industrial waste - red mud. Every ton of aluminum produced produces 0.8 to 1.5 tons of red mud. At present, the total amount of red mud added globally each year is about 4.5 billion tons, and the resource utilization rate of red mud is relatively low, only about 10%. The conventional treatment method for Bayer red mud is landfill and damming, but it has caused serious harm to the environment. Therefore, the reuse of red mud has become a research hotspot. Summary of the invention

[0010] Purpose of the invention: The present invention aims to provide a method for preparing a highly sensitive and stable self-sensing concrete strain gauge using red mud; another purpose of the present invention is to provide an application of a sensitive red mud-based environmentally friendly self-sensing concrete strain gauge.

[0011] Technical solution: The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge of the present invention comprises the following steps:

[0012] (6) Red mud pretreatment: crushing, grinding and drying the red mud;

[0013] (7) 35 parts of water are placed in a cement mixer by weight, 0.4 to 0.8 parts of carbon fiber are gradually added to the water, and stirred until the carbon fiber is evenly dispersed, and 100 parts of a cementitious material is added, wherein the cementitious material is composed of cement and red mud, and stirred until the carbon fiber is evenly dispersed; and the desired composite mixture is obtained;

[0014] (8) pouring the composite mixture into a mold and embedding several copper mesh electrodes;

[0015] (9) Place the mold on an electric vibrator to vibrate and eliminate bubbles;

[0016] (10) Demolding and curing in a standard curing room to obtain a red mud-based environmentally friendly self-sensing concrete strain gauge.

[0017] Preferably, in step (1), after crushing, the particle size of the red mud is 0 to 15 mm.

[0018] Preferably, in step (1), after grinding, the particle size of the red mud is 0 to 0.2 mm.

[0019] Preferably, in step (1), the red mud drying temperature is 55-65° C., the drying time is 22-26 h, the moisture content of the pretreated red mud is less than 5%, and the particle size is 0-0.2 mm.

[0020] Furthermore, in step (2), when adding carbon fiber, the stirrer speed is set to 120-150 r / min, and the stirring time is 100-150 s; when adding the gelling material and stirring, the stirrer speed is set to 120-150 r / min, and the stirring time is 100-150 s.

[0021] Furthermore, in step (2), the cementitious material is composed of cement and red mud in a ratio of 60-100:0-40.

[0022] Furthermore, in step (3), the mold is an I-shaped mold, which includes a short arm and a connecting arm, the short arm is 40*20*20mm, and the connecting arm is 20*40*20mm; there are 3 copper mesh electrodes, the mesh of the copper mesh is 2mm×2mm, and the spacing between the copper mesh electrodes is 10mm.

[0023] Furthermore, in step (4), the vibration time is 5 to 10 seconds.

[0024] Preferably, in step (5), curing is performed in a standard curing room for 28 days.

[0025] The application of the red mud-based environmentally friendly self-sensing concrete strain gauge with the sensitivity of the present invention is as follows:

[0026] After the red mud-based environmentally friendly self-sensing concrete strain gauge prepared by the above preparation method is dried at room temperature for 3 days, the red mud-based environmentally friendly self-sensing concrete strain gauge is embedded or installed on the surface of the concrete structure, and the red mud-based environmentally friendly self-sensing concrete strain gauge is connected to the monitoring system through a wire to measure the concrete strain.

[0027] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The present invention selects red mud as one of the raw materials for preparing a highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge, so that the concrete strain gauge has good self-sensing behavior, which reduces the cost compared with the existing self-sensing cement-based composite materials; the present invention provides feasibility for the potential application of red mud in cement-based materials, reduces cement consumption and thus alleviates the greenhouse effect, and realizes the recycling of red mud; the present invention uses red mud as a granular conductive material and carbon fiber as a fibrous conductive material in a mixed conductive network structure, which has the characteristics of high strain sensitivity and good stability; the concrete strain gauge prepared by the present invention has extremely small sensitivity changes at different strain rates and can cope with complex load conditions; the self-sensing concrete I-shaped strain gauge prepared by the present invention can be more closely combined with concrete and has strong adaptability to load environments. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 This is a schematic diagram of the red mud treatment process;

[0029] Figure 2 It is a schematic diagram of the process of the present invention;

[0030] Figure 3 The bar graph is the resistivity of the red mud-based environmentally friendly self-sensing concrete strain gauge;

[0031] Figure 4 The bar graph is the strain sensitivity of the red mud-based environmentally friendly self-sensing concrete strain gauge;

[0032] Figure 5 This is the particle size distribution curve of red mud and cement. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings.

[0034] The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge of the present invention comprises the following steps:

[0035] (1) Red mud pretreatment: The red mud is crushed, ground and dried for pretreatment; after crushing, the particle size of the red mud is 0 to 15 mm; after grinding, the particle size of the red mud is 0 to 0.2 mm; during drying, the red mud drying temperature is 55 to 65°C, the drying time is 22 to 26 hours, and the moisture content of the pretreated red mud is less than 5%, and the particle size is 0 to 0.2 mm.

[0036] (2) 35 parts of water are placed in a cement mixer by weight, 0.4-0.8 parts of carbon fiber are gradually added into the water, and stirred until the carbon fiber is evenly dispersed, and 100 parts of cementitious material is added, wherein the cementitious material is composed of cement and red mud in a ratio of 60-100:0-40, and stirred until the carbon fiber is evenly dispersed; and the desired composite mixture is obtained.

[0037] (3) The composite mixture is poured into an I-shaped mold, which includes a short arm and a connecting arm, the short arm is 40*20*20 mm, and the connecting arm is 20*40*20 mm; and three copper mesh electrodes are embedded, the mesh of the copper mesh is 2 mm×2 mm, and the spacing between the copper mesh electrodes is 10 mm.

[0038] (4) Place the mold on an electric vibrator for 5 to 10 seconds to eliminate bubbles;

[0039] (5) Demolding and curing in a standard curing room for 28 days to obtain a red mud-based environmentally friendly self-sensing concrete strain gauge.

[0040] In step (2), preferably, when adding carbon fiber, the stirrer speed is set to 120-150 r / min, and the stirring time is 100-150 s; when adding gelling material and stirring, the stirrer speed is set to 120-150 r / min, and the stirring time is 100-150 s.

[0041] The application of the red mud-based environmentally friendly self-sensing concrete strain gauge with the sensitivity of the present invention is as follows:

[0042] After the red mud-based environmentally friendly self-sensing concrete strain gauge prepared by the above preparation method is dried at room temperature for 3 days, the red mud-based environmentally friendly self-sensing concrete strain gauge is embedded or installed on the surface of the concrete structure, and the red mud-based environmentally friendly self-sensing concrete strain gauge is connected to the monitoring system through a wire to measure the concrete strain.

[0043] The composition ratios of Comparative Examples 1-5 and Examples 1-10 are shown in Table 1.

[0044] Table 1

[0045]

[0046] The flexural strength, compressive strength, resistivity, strain sensitivity and stability of all embodiments and comparative examples were tested by mechanical property tests, resistivity tests and strain sensitivity tests.

[0047] The mechanical properties test parameters are

[0048] a. Flexural strength

[0049] Load evenly at a rate of 50 N / S until it breaks. Keep both halves of the prism in a wet state until the compression test.

[0050]

[0051] Where: R f is the flexural strength, in MPa; F fis the load applied to the middle of the prism when it breaks, in Newton N; L is the distance between the supporting cylinders, in millimeters (mm); b is the side length of the positive and negative sections of the prism, in millimeters (mm).

[0052] b. Compressive strength

[0053] After the flexural strength test, the two halves of the specimen were taken out for the compressive strength test. During the loading process, the specimen was loaded uniformly at a rate of 2400N / S until failure. The effective compressive area was 1600mm 2 .

[0054]

[0055] Where: R c is the compressive strength, in MPa; F c is the maximum load at failure, in N; A is the compressive area, in mm 2 .

[0056] The resistivity test parameters are:

[0057] The DC power supply was set to constant current mode with the current set to 0.05A.

[0058] The strain sensitivity test parameters are:

[0059] The loading rates were set to: 0.3 mm / min, 0.6 mm / min, 0.9 mm / min.

[0060] The upper load limit is 8MPa.

[0061] The DC power supply was set to constant current mode with the current set to 0.05A.

[0062] The test results of Comparative Examples 1-5 and Examples 1-10 are shown in FIG2 .

[0063] Table 2

[0064]

[0065] like Figure 3 As shown in the figure, when the fiber concentration is low (0.4%), the effect of red mud content on resistivity is more significant, and the resistivity decreases significantly with the increase of red mud concentration; however, when the fiber concentration is high (0.8%), the effect of the increase of red mud concentration on resistivity decreases. This shows that there are significant differences in the effect of red mud particles on resistivity at different fiber concentrations. When the fiber content is high, the contribution of red mud is relatively weakened. This phenomenon is of great significance for optimizing the conductive properties of self-sensing cement-based materials, and helps to reasonably adjust the ratio of red mud and fiber without significantly reducing the mechanical properties of the material to improve the self-sensing performance of the material.

[0066] This study revealed the interaction between fiber concentration and red mud particle content, and showed that by regulating the ratio of red mud to fiber, the comprehensive performance of cement-based materials can be effectively optimized, especially achieving a balance between conductivity and mechanical properties.

[0067] Depend on Figure 5 It can be seen that the specific surface area of ​​the treated red mud is 1189.6m 2 / kg, the particle size is concentrated around 20 microns, while most of the cement is around 40 microns. Good pore size distribution makes red mud easy to distribute in cement particles, making the mixture uniform.

Claims

1. A method for preparing a highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge, characterized in that: The following steps are involved: (1) Red mud pretreatment: crushing, grinding and drying the red mud; (2) 35 parts of water are placed in a cement mixer by weight, 0.4 to 0.8 parts of carbon fiber are gradually added to the water, and stirred until the carbon fiber is evenly dispersed, and 100 parts of a cementitious material is added, wherein the cementitious material is composed of cement and red mud, and stirred until the carbon fiber is evenly dispersed; and the desired composite mixture is obtained; (3) pouring the composite mixture into a mold and embedding several copper mesh electrodes; (4) Place the mold on an electric vibrator to vibrate and eliminate bubbles; (5) demolding and curing in a standard curing room to obtain a red mud-based environmentally friendly self-sensing concrete strain gauge.

2. The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge according to claim 1 is characterized in that: In step (1), after crushing, the particle size of the red mud is 0 to 15 mm.

3. The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge according to claim 2 is characterized in that: In step (1), after grinding, the particle size of the red mud is 0 to 0.2 mm.

4. The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge according to claim 3 is characterized in that: In step (1), the red mud drying temperature is 55-65° C., the drying time is 22-26 hours, and the moisture content of the pretreated red mud is less than 5%, and the particle size is 0-0.2 mm.

5. The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge according to claim 1 is characterized in that: In step (2), when adding carbon fiber, the stirrer speed is set to 120-150 r / min, and the stirring time is 100-150 s; when adding gelling material and stirring, the stirrer speed is set to 120-150 r / min, and the stirring time is 100-150 s.

6. The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge according to claim 1 is characterized in that: In step (2), the cementitious material is composed of cement and red mud in a ratio of 60-100:0-40.

7. The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge according to claim 1 is characterized in that: In step (3), the mold is an I-shaped mold, which includes a short arm and a connecting arm, the short arm is 40*20*20mm, and the connecting arm is 20*40*20mm; there are 3 copper mesh electrodes, the mesh of the copper mesh is 2mm×2mm, and the spacing between the copper mesh electrodes is 10mm.

8. The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge according to claim 1 is characterized in that: In step (4), the vibration time is 5 to 10 seconds.

9. The method for preparing the highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge according to claim 1 is characterized in that: In step (5), the product is cured in a standard curing room for 28 days.

10. An application of a highly sensitive red mud-based environmentally friendly self-sensing concrete strain gauge, characterized in that: The details are as follows: After drying the red mud-based environmentally friendly self-sensing concrete strain gauge prepared according to any one of claims 1 to 9 at room temperature for 3 days, the red mud-based environmentally friendly self-sensing concrete strain gauge is embedded or installed on the surface of the concrete structure, and the red mud-based environmentally friendly self-sensing concrete strain gauge is connected to the monitoring system through a wire to measure the concrete strain.

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