CN114716198B - Built-in carbon nano tube composite sensor with concrete structure and preparation method - Google Patents

Built-in carbon nano tube composite sensor with concrete structure and preparation method Download PDF

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CN114716198B
CN114716198B CN202210386911.7A CN202210386911A CN114716198B CN 114716198 B CN114716198 B CN 114716198B CN 202210386911 A CN202210386911 A CN 202210386911A CN 114716198 B CN114716198 B CN 114716198B
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CN114716198A (en
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郭健
傅宇方
胡山
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Southwest Jiaotong University
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
    • C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L1/00—Measuring force or stress, in general
    • G01L1/20—Measuring force or stress, in general by measuring variations in ohmic resistance of solid materials or of electrically-conductive fluids; by making use of electrokinetic cells, i.e. liquid-containing cells wherein an electrical potential is produced or varied upon the application of stress
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01L—MEASURING FORCE, STRESS, TORQUE, WORK, MECHANICAL POWER, MECHANICAL EFFICIENCY, OR FLUID PRESSURE
    • G01L25/00—Testing or calibrating of apparatus for measuring force, torque, work, mechanical power, or mechanical efficiency
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/00474—Uses not provided for elsewhere in C04B2111/00
    • C04B2111/00991—Uses not provided for elsewhere in C04B2111/00 for testing
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2111/00—Mortars, concrete or artificial stone or mixtures to prepare them, characterised by specific function, property or use
    • C04B2111/90—Electrical properties
    • C04B2111/94—Electrically conducting materials
    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B2201/00—Mortars, concrete or artificial stone characterised by specific physical values
    • C04B2201/50—Mortars, concrete or artificial stone characterised by specific physical values for the mechanical strength
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A30/00—Adapting or protecting infrastructure or their operation
    • Y02A30/30—Adapting or protecting infrastructure or their operation in transportation, e.g. on roads, waterways or railways

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  • General Physics & Mathematics (AREA)
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  • Chemical Kinetics & Catalysis (AREA)
  • Inorganic Chemistry (AREA)
  • Materials Engineering (AREA)
  • Structural Engineering (AREA)
  • Organic Chemistry (AREA)
  • Investigating Or Analyzing Materials By The Use Of Electric Means (AREA)
  • Measurement Of Length, Angles, Or The Like Using Electric Or Magnetic Means (AREA)

Abstract

The invention provides a concrete structure built-in carbon nano tube composite sensor and a preparation method thereof. The built-in carbon nano tube composite sensor of the concrete structure comprises, by weight, 0.2-1 part of carbon nano tubes, 0.3-1 part of water reducer, 99-100 parts of cement, 200-300 parts of sand and 35-60 parts of deionized water, wherein the carbon nano tubes are mixed according to parts by weight. The built-in carbon nano tube composite sensor of the concrete structure has pressure-sensitive self-sensing capability, can perform special response to stamping load to be monitored due to the structural characteristics, uses the amino multi-wall carbon nano tube as a main functional component, and has the advantages that the compressive strength of the prepared sensor reaches about 35MPa, the strain factor of the sensor reaches 1600, and the amino multi-wall carbon nano tube has the advantages of enhancing the mechanical property and the electrical property of the sensor.

Description

Built-in carbon nano tube composite sensor with concrete structure and preparation method
Technical Field
The invention relates to the field of mechanical measurement, in particular to a built-in carbon nano tube composite mechanical sensor of a concrete structure.
Background
The concrete structure has various remarkable advantages, so that the concrete structure is widely applied in the civil engineering field, however, the concrete material has durability, and due to the lack of a proper monitoring means, a large number of concrete structures cannot be maintained in time, so that the concrete structure is in a damaged state, even structural damage is caused, therefore, the timely monitoring of the damage of the structure is of great importance, particularly when a ship collides with a bridge foundation or a bridge support to be subjected to heavy traffic, the traditional method generally adopts a conventional sensor embedded in the structure or adopts a surface detection technology to monitor or detect, and the traditional sensor and the testing method have the problems of high manufacturing cost, lack of targeted accurate test on the stamping load, incapacity of realizing long-term durable monitoring, insensitivity to mechanical transmission response of the concrete structure and the like.
Aiming at the problems, a concrete intelligent material sensor with a self-monitoring function is put forward to be a research focus, common concrete belongs to poor conductors of electricity, but after materials such as graphite, metal powder and carbon fiber are added, the concrete material has good conductivity, pressure sensitivity and durability, and meanwhile, the concrete intelligent material sensor can be well compatible with a concrete structure, so that the method enhances the mechanical property of the concrete material on one hand, and enables the concrete material to have the capabilities of conducting susceptibility damage assessment and health monitoring on the other hand.
The Chinese patent document CN104446176A discloses a cement-based composite material and a pressure-sensitive sensor thereof, and adopts graphene oxide and carbon fiber as functional components, so that the cement-based composite material has the advantages of high strength, good durability, fewer pore defects and good compactness, but the graphene oxide does not have conductivity in the manufacturing process, and the carbon fiber as a conductive component has general conductivity and is difficult to process properly, and finally has negative effects on the electrical and mechanical properties of the sensor.
The Chinese patent document CN111620617A discloses an ultra-high performance cement-based composite material for a sensor, the sensor and a preparation method thereof, wherein the prepared cement-based composite material sensor has good conductivity, sensitivity and mechanical property, however, the starch used in the document can influence the dispersion of an internal conductive material, the electrical property of the prepared product is inconsistent easily, and the mass production is difficult to be used in engineering practice.
The Chinese patent document CN113149526A discloses a composite cement-based material and a composite cement-based material sensor, and the content of the composite cement-based material is that a carbon fiber material doped with grafted carbon nano tubes into cement mortar has the advantages of better dispersibility and sensitive monitoring, but the embodiment 1 with the best effect in the technical scheme can obviously show that after one round of loading, the resistivity of the sensor is changed from about 72 omega ∙ cm to 70 omega ∙ cm, and the sensor is proved to be unstable in performance and can not be built in a structure for a long time for monitoring with good effect.
The nano carbon black cement-based composite material prepared by Dai Y W et al in the document Electromagnetic wave absorbing characteristics of carbon black cement-based composite can be used for manufacturing a structural health monitoring sensor, wherein the compressive strength of the corresponding nano carbon black cement-based composite material is reduced from 67MPa to 22MPa in the process that the volume doping amount of the nano carbon black is increased from 0 to 2.78%, and the increase of the content of the externally added material has obvious negative influence on the strength of the cement-based composite material.
The sensor responds to loads in all directions due to the characteristics of the sensor, so that when the sensor receives loads with complex dynamic changes, the obtained response can be highly coupled and difficult to decouple, the accuracy and the application range of the sensor are limited, and the problem to be considered is solved how to reduce the coupling influence; meanwhile, the sensor has the monitoring effect through the change of the resistance value, so that the characteristics have reasonable application scenes, and the problems make the prior art difficult to apply to engineering practice.
The prior art only provides a cement-based composite sensor, the basis of feasibility of monitoring common impact load and pressure load in actual engineering scenes is not provided, the defect that the actual application range of the sensor is limited exists, the response of the prior art sensor is not specific to the direction of the load, the direction source of the load in reality is complex and changeable, the response of the sensor is coupled and very difficult to decouple, the precision and application of the sensor have very large limitations, graphene oxide and carbon fiber are adopted as functional components in the prior art, however, graphene oxide is hardly conductive, common carbon fiber is difficult to form a reliable conductive network in the cement-based material, in addition, the carbon fiber is oxidized by nitric acid, the performance of the carbon fiber can be reduced, the prior art treatment process possibly causes the carbon fiber to have acid liquor and an oxidant which are not easy to elute, the performance of the final formed cement-based composite material sensor is negatively influenced, the content of the nano carbon black material is reduced from 0 to 2.78%, the accuracy of the sensor is greatly limited by application of the graphene oxide and the graphene oxide-based composite material, the dispersion effect of the sensor is reduced from the cement-based composite material to the dispersion strength of the dispersion material is easily influenced by the dispersion mechanism of the dispersion technology, and the dispersion technology is better than the dispersion technology, and the dispersion effect of the dispersion technology is easily influenced by the dispersion technology is reduced in the cement-based composite material, and the dispersion effect of the dispersion technology is better than the dispersion technology is formed by the dispersion of the dispersion technology is more conductive-based material; the starch has high viscosity in the mixing process, the starch also can influence the dispersion of internal conductive fibers in the cement-based composite material manufacturing process, the electrical property of the manufactured sensor is greatly changed due to the instability of the internal material property after the manufactured sensor bears a round of load, the resistivity of the sensor is changed from about 72 omega ∙ cm to 70 omega ∙ cm, the sensor performance is unstable, the service life is short, and the sensor cannot be built in the structure for monitoring for a long time.
Disclosure of Invention
(one) solving the technical problems
Aiming at the defects of the prior art, the invention provides a built-in carbon nano tube composite sensor of a concrete structure and a preparation method thereof, and solves the problems that the feasibility of the prior art applied to practical engineering is insufficient, the application range is limited, the structural strength is negatively influenced, the effect is general, the cost is high and the structure cannot be monitored for a long time.
(II) technical scheme
In order to achieve the above purpose, the invention is realized by the following technical scheme: a concrete structure built-in carbon nanotube composite sensor, comprising: a carbon nanotube; and the cement-based composite material comprises, by weight, 0.2-1 part of carbon nanotubes, 0.2-1 part of a dispersing agent, 0.3-1 part of a water reducer, 99-100 parts of cement, 200-300 parts of sand and 35-60 parts of deionized water.
Preferably, the aspect ratio of the concrete structure built-in carbon nano tube composite sensor is 1, and the aspect ratio is more than 2.
Preferably, the carbon nanotubes are aminated multi-walled carbon nanotubes.
Preferably, the pipe diameter of the amination multiwall carbon nano-tube is 3-15 nm, the pipe length is 15-30 um, and the specific surface area is 250-270 m/g.
Preferably, the dispersing agent is a carbon nanotube dispersing agent, and the mass ratio of the carbon nanotube dispersing agent to the carbon nanotube is 1:1.
Preferably, the carbon nanotube composite sensor with built-in concrete structure further comprises electrodes, wherein the electrodes are arranged at two ends of the carbon nanotube composite sensor with built-in concrete structure in a copper grid mode.
A preparation method of a concrete structure built-in carbon nano tube composite sensor comprises the following steps: s1, fully dissolving 2.5g of dispersing agent in 450ml of deionized water, slowly and uniformly stirring to enable the dispersing agent to be fully dissolved in water, weighing 2.5g of amino multi-wall carbon nano tubes, adding the dispersing agent into an aqueous solution of the dispersing agent, uniformly dispersing the carbon nano tubes in the aqueous solution by using an ultrasonic crushing device, suspending for 3s after each 3s of starting of ultrasonic treatment, wherein the total dispersing time is 10mins, and dropwise adding 0.3ml of defoaming agent to perform defoaming treatment on the carbon nano tube liquid; s2, pouring the dispersed carbon nanotube liquid into a stirring pot, pouring 1000g of Portland cement, starting the stirring pot to stir for 2 minutes, pouring 2000g of standard sand, stirring for 4 minutes, stopping stirring equipment, standing for 2 minutes, and starting the equipment to stir for 4 minutes; s3, pouring cement mortar into a 40mm multiplied by 160mm rubber sand standard mould, parallelly inserting two copper grids with the distance of 14cm and the distance of 4mm multiplied by 5mm, vibrating the whole mould for 60 times by a vibrator, curing at room temperature for 36h, and removing the mould for standard curing for 28d.
(III) beneficial effects
The invention provides a concrete structure built-in carbon nano tube composite sensor and a preparation method thereof. The beneficial effects are as follows:
1. the invention provides a built-in carbon nano tube composite sensor with a concrete structure, provides a solution and a basis for monitoring common impact load and pressure load, solves the problem of insufficient feasibility when the prior art is applied to actual engineering, has a response to load in a non-monitoring direction less than 10% of the response to load in a monitoring direction, and solves the problems of inaccurate sensor test result and limited application range caused by high response coupling due to sensitivity of the sensor to multi-directional complex load;
2. compared with the externally added material in the prior art, the aminated multiwall carbon nanotube has better enhancement effect on the mechanical property of the cement-based composite material, the compressive strength of the composite sensor manufactured by using 42.5 silicate cement in the technical scheme is about 35MPa, and is obviously higher than the compressive strength of 32.5MPa of a common 42.5 silicate cement mortar block, so that the problems that the strength of the sensor is reduced due to the externally added material and the structural strength is negatively influenced when the composite sensor is built in a structure in the prior art are avoided;
3. the invention can realize excellent effect only by externally adding special materials (0.2% -1%) with the mass smaller than two orders of magnitude of cement materials, and solves the problems of the prior art that the special materials with higher content are required to be added, the effect is general and the cost is higher;
4. compared with other materials, the aminated multiwall carbon nano tube has stronger dispersibility, is not easy to agglomerate in the cement-based material, and the characteristic ensures that the aminated multiwall carbon nano tube is uniformly dispersed in the cement-based material, so that the performance of the sensor in all aspects can keep high consistency when the sensor is manufactured in a large scale, the resistance value difference among a plurality of composite sensors manufactured by the technical scheme is very small, the maximum resistance difference among 3 groups of composite sensors is only 13 omega, and the fact that the carbon nano tube is uniformly dispersed in the sensor is proved, wherein the cement-based material manufactured by the aminated carbon nano tube has stable performance;
5. according to the technical scheme, the resistance of the composite sensor is recovered to 1589 omega from the initial value 1588 omega after loading, so that the composite sensor is stable in performance, and the problems that the resistance value of the sensor is greatly changed after unloading, the service life of the sensor is short, and the sensor cannot be built in a structure for monitoring for a long time in the prior art are solved.
Drawings
FIG. 1 is a schematic diagram of a built-in carbon nanotube composite sensor with a concrete structure according to the present invention;
FIG. 2 is a schematic diagram of a concrete structure built-in carbon nanotube composite sensor according to the present invention in a test;
FIG. 3 is a graph showing the pressure and displacement of the built-in carbon nanotube composite sensor with a concrete structure according to the present invention, which is tested by a universal tester;
FIG. 4 is a schematic view of the structure of the present invention for monitoring impact load;
fig. 5 is a schematic diagram of the structure of the present invention for monitoring the pressure change of the support.
Detailed Description
The following description of the embodiments of the present invention will be made clearly and completely with reference to the accompanying drawings, in which it is apparent that the embodiments described are only some embodiments of the present invention, but not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Some embodiments of the present invention provide a concrete structure built-in carbon nanotube composite sensor (abbreviated as composite sensor in this specification) comprising carbon nanotubes and a cement-based composite material. Wherein the cement-based composite material comprises a dispersing agent, a water reducing agent, cement, sand and deionized water. The carbon nanotubes are uniformly dispersed in the cement-based composite material. The composite sensor has pressure-sensitive sensing capability, can be built in a concrete structure for long-term service without greatly influencing the structure, and can be used for carrying out special response on the load in the direction to be monitored and also can be used for monitoring the impact load and the pressure load received by the structure in real time in a targeted manner because of the structural characteristics.
In some embodiments, the carbon nanotubes are mixed in a weight ratio of 0.2 to 1 part, and the cement-based composite material comprises 0.2 to 1 part of a dispersing agent, 0.3 to 1 part of a water reducing agent, 99 to 100 parts of cement, 200 to 300 parts of sand and 35 to 60 parts of deionized water.
In some embodiments, the carbon nano tube is 0.4 to 0.7 part by weight, and the cement-based composite material comprises 0.4 to 0.7 part by weight of dispersing agent, 0.5 to 0.8 part by weight of water reducer, 99 to 100 parts by weight of cement, 230 to 280 parts by weight of sand and 45 to 50 parts by weight of deionized water. In some embodiments, the ratio of the carbon nanotubes to the dispersant in parts by weight is 1:1.
the carbon nanotube is a one-dimensional quantum material. The carbon nano tube mainly comprises a plurality of layers to tens of layers of coaxial round tubes formed by carbon atoms which are arranged in a hexagonal mode. The distance between layers is kept to be 0.3-0.4 nm. The carbon nanotubes may be single-walled carbon nanotubes or multi-walled carbon nanotubes, depending on the number of layers of the coaxial round tube.
The radial dimension (pipe diameter) of the carbon nano-tube is nano-scale, and the axial dimension (pipe length) is micro-scale. In some embodiments, the carbon nanotubes have a tube diameter of 2-20 nm, a tube length of 10-40 um, and a specific surface area of 230-280 m/g. In some embodiments, the carbon nanotubes have a tube diameter of 3-15 nm, a tube length of 15-30 um, and a specific surface area of 250-270 m/g.
In some embodiments, the carbon nanotubes are aminated multi-wall carbon nanotubes. The aminated multi-wall carbon nanotube is prepared from multi-wall carbon nanotubes. For example, the aminated multi-wall carbon nanotube is prepared from multi-wall carbon nanotube by free radical reaction, and then Al-NiCl is adopted 2 ∙6H 2 The 0-THF system is reduced to produce the aminated multi-wall carbon nano-tube. Compared with other materials, the aminated multi-wall carbon nano tube has stronger dispersibility and is not easy to agglomerate in the cement-based material, and the characteristic ensures that the aminated multi-wall carbon nano tube is uniformly dispersed in the cement-based material, so that the performance of the sensor in all aspects can be kept highly consistent during mass production. Meanwhile, compared with the externally added material in the prior art, the aminated multiwall carbon nanotube has better enhancement effect on the mechanical property of the cement-based composite material, and the compressive strength of the composite sensor manufactured by using 42.5 silicate cement in the technical scheme is about 35MPa, which is higher than the compressive strength of 32.5MPa of a common 42.5 silicate cement mortar block, so that the problems that the sensor strength is reduced due to the externally added material in the prior art and the structural strength is negatively influenced due to the fact that the composite sensor is built in the structure are avoided.
The dispersing agent is used for dispersing the carbon nanotubes and preventing the carbon nanotubes from agglomerating and depositing. The dispersant may include, but is not limited to, carbon nanotube dispersant (TNWDIS), carbon nanotube alcohol dispersant (TNADIS), carbon nanotube ester dispersant (TNEDIS), and the like.
The water reducer is used as a concrete additive for reducing the mixing water consumption under the condition of maintaining the slump of the concrete basically unchanged. The water reducer can increase the fluidity, the dispersion effect and the like of the concrete mixture. The water reducer can be lignosulfonate, naphthalene sulfonate formaldehyde polymer and the like.
The cement may be Portland cement, alumina cement, etc. The cement may be numbered 32.5, 32.5R, 42.5R, 52.5R, etc.
The composite sensor further includes an electrode. The electrodes are arranged at two ends of the composite sensor in the form of grids formed by conductive materials. The conductive material is a conductive metal material such as copper, aluminum, silver and/or a conductive nonmetallic material such as graphite. In some embodiments, the electrodes are two copper grids, one at each end of the composite sensor. The copper grid and the cement-based composite material have good compatibility, low contact resistance and low cost and are easy to obtain.
Illustratively, as shown in fig. 1, the composite sensor has an external shape, for example, an aspect ratio of 1 and an aspect ratio of greater than 2. The copper grids are arranged in the cement-based composite material in a semi-inserted mode perpendicular to the long sides, and are arranged in parallel. The carbon nanotubes are aminated multiwall carbon nanotubes. The dispersing agent is carbon nano tube water dispersing agent. The weight ratio of the carbon nano tube to the dispersing agent is 1:1.
the original common cement-based composite material is hardly conductive, and when the conductive carbon nano tube (such as the amination multi-wall carbon nano tube) is doped, the carbon nano tube has good conductive performance due to the fact that P electrons of carbon atoms on the carbon nano tube form a large-range delocalized pi bond and the conjugation effect is obvious. The conductive carbon nanotubes are dispersed in the cement-based composite material, wherein the connected part of the carbon nanotubes form conductive channels like wires, so that electrons can pass through, and the part of the carbon nanotubes which are close to each other but not connected form conductive channels (the conductive channels of the type have a smaller effect than the conductive channels generated by directly connecting the carbon nanotubes) due to the tunneling effect, and the existence of the conductive channels enables the cement-based composite material which is hardly conductive to have stronger conductivity as a whole, thereby providing a basis for manufacturing a sensor.
Assume that the initial dimensions of the cement-based sensor are: long lengthL x Width of the steel sheetL y High and highL z At the receiving edgexAfter axial pressure in the axial direction, its geometry becomes:
Figure 961727DEST_PATH_IMAGE001
wherein, the liquid crystal display device comprises a liquid crystal display device,ε x to strain the sensor in the x-axis direction after stretching,υ xy 、υ xz the Poisson ratio of the cement-based material is generally 0.1-0.2.
As can be seen from the formulas (1) - (3), when a compressive strain is generated along the x-axis direction, only 0.1-0.2 tensile strain is generated along other directions, so that the spacing between the carbon nanotubes along the x-axis direction is obviously reduced, and the increase of the spacing between the carbon nanotubes along the y-axis direction and the z-axis direction is relatively insignificant; such a change increases the contact points between the carbon nanotubes, macroscopically showing a decrease in the resistance of the carbon nanotube sensor as a whole, and when a load F acts on the yz plane of the sensor, there is, according to the mechanics of the material:
Figure 878868DEST_PATH_IMAGE002
when the same load acts on the sensor xy-plane, there are:
Figure 658605DEST_PATH_IMAGE003
Figure 116131DEST_PATH_IMAGE004
wherein the method comprises the steps of，EIs the modulus of elasticity of the material,A 0 、A 1 the cross-sectional areas of the yz plane and the xy plane are respectively,νfor the poisson's ratio of the sensor,ε 0 、ε 1 respectively along the x-axis and along the z-axis,ε 2 is strained in the x-axis direction when a force acts on the xy-plane.
Taking poisson's ratioν0.2, sensor widthL y High heightL z The ratio is 1, when it is longL x Wide width ofL y When the ratio is more than 2, it is possible to obtainε 2 Less thanε 0 An order of magnitude.
According to the deformation characteristic of the sensor, when the aspect ratio of the sensor is 1 and the aspect ratio is larger than 2 (for example, the aspect ratio of the composite sensor can be 2.5, 3, 4, 5, 6, etc.), the sensor is sensitive to load response along the x-axis direction, and the influence of load along the y-axis direction and the z-axis direction can be almost ignored in practical engineering, which forms a theoretical basis for reducing the coupling influence of the multidirectional load in the technical scheme, and achieves the effect which cannot be achieved by the prior art. In the embodiment, the response of the composite sensor to the load in the non-monitoring direction is less than 10% of the response of the load in the monitoring direction, so that the problem that the sensor is sensitive to complex loads in multiple directions, and the sensor test result is inaccurate due to high response coupling and the application range is limited is solved.
Further embodiments of the present invention provide a method for manufacturing a composite sensor (illustratively, having a carbon nanotube content of 0.25%), the method comprising the steps of:
s1, fully dissolving 2.5g of dispersing agent in 450ml of deionized water, adding the dispersing agent into water to form a transparent colloid, slowly and uniformly stirring, fully dissolving the dispersing agent into the water, weighing 2.5g of amino multi-wall carbon nano tubes, adding the dispersing agent into the water solution of the dispersing agent, uniformly dispersing the carbon nano tubes in the water solution by using an ultrasonic crushing device, and suspending for 3s after each 3 seconds(s) of ultrasonic treatment, wherein the total dispersing time is 10 minutes (mins), and a large amount of foam influence dispersing effect can be generated due to the fact that the dispersing agent is a surfactant during the ultrasonic treatment, and 0.3ml of defoaming agent can be dripped into the carbon nano tube liquid to perform defoaming treatment;
s2, pouring the dispersed carbon nanotube liquid into a stirring pot, pouring 1000g of Portland cement, starting the stirring pot to stir for 2 minutes, pouring 2000g of standard sand, stirring for 4 minutes, stopping stirring equipment, standing for 2 minutes, and starting the equipment to stir for 4 minutes;
s3, pouring cement mortar into a 40mm multiplied by 160mm rubber sand standard mould, inserting a metal grid, wherein the metal grid used in the embodiment is a copper grid, the grid specification is 4mm multiplied by 5mm square grid, inserting two pieces into a test piece, arranging the two pieces in parallel, vibrating the whole mould for 60 times by a vibrator at a distance of 14cm, and removing the mould for standard curing for 28 days (d) after curing for 36 hours at room temperature.
The prepared composite sensor is tested, as shown in fig. 2, and the specific test process includes:
s1, attaching strain gauges on two surfaces of the cured composite sensor perpendicular to a loading direction (for example, the loading direction is a length direction) for measuring a strain value of the composite sensor in the loading process;
s2, connecting an electrode of the composite sensor with a signal acquisition instrument, a strain gauge and a strain gauge respectively by using a wire, wherein the composite sensor is made of a colloid composite material, the resistance of the composite sensor drifts due to dielectric properties, and after the connection is finished, a power supply of the signal acquisition instrument is turned on to stabilize the resistance value of the composite sensor, so that the composite sensor is polarized for 6000 seconds;
s3, placing the composite sensor in a universal testing machine for loading, wherein the loading speed is 250N/s, and the maximum loading speed is 8MPa so as to ensure that the loading is in an elastic range, and recording strain data and resistance change values in the loading process;
s4, calibrating the sensitivity of the composite sensor through the measured value of the strain gauge and the resistance change data to obtain a strain factor in the elastic range of the sensor;
s5, monotonously loading the compound sensor until a test piece is damaged, obtaining the compressive strength of the compound sensor, wherein the pressure and displacement curve of the universal testing machine is shown in figure 3, the maximum pressure is 87.9KN, the test piece starts to be damaged, the compressive strength is 35.16MPa, and the test data of the electric property, the mechanical property and the strain factor are shown in the following table:
carbon nanotube content% Rate of change of resistance Strain factor Compressive Strength after 28 days
0.25% 34% 1600 35.16MPa
From the above data, it can be seen that only 0.25% of carbon nanotubes is needed, and the mechanical properties of the composite sensor are improved compared with those of common cement mortar, and the strain factor of 1600 is achieved.
Based on the performance of the composite sensor obtained by the test, the composite sensor can be applied to detection of impact load, monitoring of support pressure change and the like.
(1) Monitoring of impact loads
As shown in fig. 4, when the structure receives an impact load in a certain direction, the composite sensors are sensitive to the load in a single direction, and only one or more composite sensors respond very strongly (determined by the size of the impact surface), and the position of the impact load can be judged according to the position and the response degree of the composite sensors, so that the impact load can be monitored in real time.
(2) Monitoring of support pressure changes
As shown in FIG. 5, the composite sensor is calibrated after being manufactured, then a plurality of composite sensors are uniformly arranged under the bridge support, and when the pressure on the support changes, the change is transmitted to the composite sensor, and as the composite sensor is only sensitive to the unidirectional load response, the pressure change of the bridge support can be monitored through the change of the position and the response of the composite sensor.
It should be noted that the application of the composite sensor is not limited to monitoring the impact load and the support pressure, for example, the stress of a building with a high-rise or complex structure can be monitored.
The composite sensor has low sensitive response to load response in the non-monitoring direction, so that anisotropic monitoring is realized. In the scheme, the response to the load in the non-monitoring direction is less than 10% of the response to the load in the monitoring direction, so that the problem that the conventional sensor is sensitive to the response of the complex load in multiple directions, and the sensor test result is inaccurate due to high coupling of the response, and the application range is limited is solved.
In the scheme, the excellent effect can be realized only by externally adding special materials (carbon nanotubes and the like) with the mass smaller than two orders of magnitude (0.2% -1%) of the cement material, and the problems that the special materials with higher content are required to be added, the effect is common and the cost is higher in the prior art are solved.
In the scheme, the aminated multi-wall carbon nano tube is used as a functional component, the compressive strength of the prepared composite sensor reaches 35.16MPa, which is higher than that of the common 42.5 cement mortar by 32.5MPa, and the strain factor of the sensor reaches 1600, so that the aminated multi-wall carbon nano tube has the advantage of simultaneously enhancing the mechanical and electrical properties of the sensor.
In addition, in the scheme, the resistance value difference among the plurality of composite sensors manufactured based on the method is very small, experimental data shows that the maximum resistance difference among the 3 groups of sensors is only 13 omega, the carbon nanotubes are uniformly dispersed in the composite sensors, according to the characteristics that the aminated multiwall carbon nanotubes are weak in hydrophobicity and difficult to agglomerate and disperse, the dispersion liquid of the carbon nanotubes is prepared by selecting a water dispersing method and an ultrasonic dispersing method, the resistance values of the manufactured groups of composite sensors are kept almost consistent, the inside dispersion of the manufactured carbon nanotube dispersion liquid is uniform, compared with the better dispersing effect in the prior art, the manufactured sensors have quicker and better response to the change of external load (can accurately respond under the frequency of a signal acquisition instrument 2 HZ), the dispersing operation process is safer and more convenient, the performance of the aminated carbon nanotubes is stable, and the sensor resistance manufactured by the carbon nanotubes has very strong reversibility, namely the sensor resistance can recover to the resistance before loading in the unloading process.
In the test of the scheme, the resistance of the composite sensor is recovered to 1589 omega from the initial value 1588 omega after loading is finished, and compared with the prior art, the weak drift and the strong reversibility enable the durability of the composite sensor to be better, and the composite sensor has more outstanding performance when being placed in a structure for long-term service.
Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims (3)

1. A concrete structure built-in carbon nanotube composite sensor, comprising:
a carbon nanotube; and
a cement-based composite material, wherein,
according to the weight portion, the carbon nano tube is 0.4 to 0.7 portion, and the cement-based composite material is composed of the following components: 0.4 to 0.7 part of dispersing agent, 0.5 to 0.8 part of water reducing agent, 99 to 100 parts of cement, 230 to 280 parts of sand and 45 to 50 parts of deionized water,
the aspect ratio of the built-in carbon nano tube composite sensor of the concrete structure is 1, the aspect ratio is 2.5, the carbon nano tube is an amino multi-wall carbon nano tube, the pipe diameter of the amino multi-wall carbon nano tube is 3-15 nm, the pipe length is 15-30 um, and the specific surface area is 250-270 m/g.
2. The concrete structure built-in carbon nanotube composite sensor of claim 1, wherein the dispersant is a carbon nanotube water dispersant.
3. The concrete-structured built-in carbon nanotube composite sensor of claim 1, further comprising:
and the electrodes are arranged at two ends of the built-in carbon nano tube composite sensor of the concrete structure in a copper grid mode.
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