CN114316645B - Cement-based conductive material for monitoring existing building strain and cement-based sensor - Google Patents
Cement-based conductive material for monitoring existing building strain and cement-based sensor Download PDFInfo
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- CN114316645B CN114316645B CN202111484425.0A CN202111484425A CN114316645B CN 114316645 B CN114316645 B CN 114316645B CN 202111484425 A CN202111484425 A CN 202111484425A CN 114316645 B CN114316645 B CN 114316645B
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Abstract
The invention discloses a cement-based conductive material for monitoring the strain of an existing building and a cement-based sensor, wherein the material comprises the following components in percentage by mass: 5-50% of water-based epoxy resin, 20-80% of cement, 1-20% of conductive filler and 10-50% of water; the cement-based conductive material is coated on the surface of the existing building structure by brushing or spraying to form a cement-based conductive material coating, and a current loop is formed by a conductive electrode arranged on the surface of the building and a connected monitoring device. When the existing building is stressed to generate strain or cracks, the strain or cracks can act on the surface coating to generate different current signals, so that real-time monitoring is realized. The monitoring coating has the advantages of high signal-to-noise ratio of detection signals, small relaxation phenomenon, stable monitoring performance, simple laying process, high bonding strength with a building matrix, capability of being laid on the surface of any special-shaped structure, good economic benefit and long-term social benefit and very wide application prospect.
Description
Technical Field
The invention belongs to the technical field of semiconductor devices, and particularly relates to a cement-based conductive material and a cement-based sensor for monitoring the strain of an existing building.
Background
The global semiconductor industry is generally subdivided into four areas: integrated circuits, optoelectronics, discrete devices, and sensors. The concrete structure health monitoring is beneficial to finding and investigating early damage of concrete, and is important for ensuring the safe service of large-scale infrastructures such as bridge and tunnel structures and the like and the pre-control of major geological disasters. In recent years, various stress and strain sensing monitoring systems based on piezoelectric, piezoresistive, magnetoresistive, optical and acoustic effects have been developed in succession, enabling the long-term monitoring of structural strains initially by embedding sensors in concrete structures. The piezoresistive sensor is not influenced by external disturbing signals such as static charges, magnetic fields and the like, and has reliable service stability. However, the structural monitoring application of the conventional metal or polymer-based sensor is restricted by short plates, such as high cost, insufficient durability and poor compatibility with concrete, and thus, the cement-based sensor is produced accordingly. The cement-based sensor is a sensor with piezoresistive effect formed by compounding a cement substrate and conductive filler, regular resistance value changes can be generated due to stress and strain in the elastic deformation stage of the sensor, and an electric signal in direct proportion to the stress or the strain can be obtained by an external measuring circuit. The cement-based sensor has the advantages of good compatibility with a concrete structure and low price, and can improve the ductility and durability of concrete. The stress-strain of the concrete can be obtained based on the piezoresistive effect of the concrete, so that the purpose of monitoring the deformation and the load of the embedded concrete structure is achieved.
However, the cement-based sensor has large rigidity, small strain range, narrow monitoring range and unstable performance (small signal-to-noise ratio and large fluctuation), and the monitoring performance of the cement-based sensor is limited and influenced by a plurality of factors such as the agglomeration effect of the conductive filler, the rheological property of slurry, the polarization effect of ions, the monitoring mode and the like. More importantly, the existing cement-based sensor monitoring technology is mainly realized by pouring or embedding a prefabricated sensor into a newly-built concrete structure, and for the existing concrete structure, especially a long-distance and large-section bridge and tunnel structure serving in severe environments such as saline-alkali erosion, dry-wet freeze thawing and the like, a complete nondestructive monitoring technology and a safety state intelligent sensing and diagnosis technology are lacked. At present, the following core problems exist around the preparation and application development of cement-based sensors: 1. the monitoring range is narrow, the crack is easy to occur, and the bonding strength is insufficient; 2. the conductive filler agglomeration causes great discreteness of sensor performance and small signal-to-noise ratio. 3. Pre-buried/damaged arrangement, difficult replacement and complex operation; finally, the bonding force of the interface between the sensor and the substrate structure is also a necessary condition for determining the long-term and stable detection of the structural health, and if the sensor and the substrate are debonded, the signal transmission is cut off, so that the monitoring is failed.
Therefore, there is a need to provide an improved solution to the above-mentioned deficiencies of the prior art.
Disclosure of Invention
The invention aims to provide a cement-based conductive material and a cement-based sensor for strain monitoring of an existing building, and aims to solve the problems that the existing cement-based sensor needs to be installed in a pre-buried mode, is difficult to replace, has low bonding strength with a base body, is narrow in detection range and cannot realize strain monitoring on the existing building.
In order to achieve the above purpose, the invention provides the following technical scheme:
a cement-based conductive material for monitoring the strain of an existing building comprises the following components in percentage by mass:
5-50% of water-based epoxy resin, 20-80% of cement, 1-20% of conductive filler and 10-50% of water.
In the cement-based conductive material for monitoring the existing building strain, the water-based epoxy resin is preferably one or a mixture of several of anionic water-based epoxy resin, cationic water-based epoxy resin and nonionic water-based epoxy resin.
The cement-based conductive material for strain monitoring of the existing building is preferably one or a mixture of more of portland cement, ordinary portland cement, portland slag cement, pozzolanic portland cement, fly ash portland cement, composite portland cement, class G oil well cement, rapid hardening portland cement, road portland cement, aluminate cement and sulphoaluminate cement.
In the cement-based conductive material for monitoring the strain of the existing building, preferably, the conductive filler is one or a mixture of more of graphite, carbon black, graphene oxide, reduced graphene oxide and carbon nanotubes.
A preparation method of a cement-based conductive material coating for strain monitoring of an existing building comprises the following steps:
step one, weighing the waterborne epoxy resin, the conductive filler and water according to the proportion, and uniformly stirring and mixing to form slurry;
adding the slurry into cement according to a ratio, and stirring until the slurry is uniform to form slurry;
and step three, blade coating or spraying the slurry on the surface of the existing building structure, and curing and hardening to form the cement-based conductive material coating.
In the above preparation method of the cement-based conductive material coating for monitoring the existing building strain, preferably, in the third step, the curing is water spraying curing or film covering curing, the curing temperature is 0-50 ℃, and the curing time is 3-7 days.
In the above method for preparing the cement-based conductive material coating for existing building strain monitoring, preferably, the thickness of the cement-based conductive material coating is 0.1 to 10mm.
The coating is prepared by adopting the preparation method of the cement-based conductive material coating for the existing building strain monitoring.
A cement-based sensor comprising a cement-based conductive material as above or a coating of a cement-based conductive material as above, the cement-based sensor further comprising a conductive electrode mounted on a surface of an existing architectural structure in the area of the coating.
In the above cement-based sensor, preferably, the conductive electrode is a metal electrode or a graphite electrode.
Has the advantages that:
the cement-based conductive material and the cement-based sensor for monitoring the existing building strain provided by the invention have the following excellent technical effects:
1) The cement-based conductive material coating has stable piezoresistive performance, low relaxation and wide strain measurement range, and can be paved by brushing;
2) The cement-based conductive material coating utilizes the amphiphilicity of the aqueous chain segment and the oily chain segment in the aqueous epoxy resin and the ion-conductive filler interface in the set cement to induce the directional arrangement of the conductive filler and the ion channel through the interpenetrating structure of the polymer network, thereby improving the conductive efficiency and the stability.
3) The toughening, extension and bonding strength of the cement-based material are improved by adding the water-based epoxy resin: the cement-based conductive material coating can not crack, warp or deform under the condition of thin-layer coating; the bonding strength of the coating and the old concrete interface can reach 2.5MPa;
4) The ultimate tensile-compressive strain of the cement stone elastic stage is obviously increased through the water-based epoxy resin, and the monitoring bandwidth and the structural strain monitoring range of the cement-based sensor are obviously increased;
5) Can realize the nondestructive monitoring to existing building structure: the sensors are laid by the building external coating scheme, and the sensors are not required to be dug, damaged and embedded in the existing building structure;
6) The nondestructive updating replacement of old and damaged structural sensors can be realized: the replacement can be completed only by removing the sensor coating of the area to be replaced, re-pasting the electrode and coating the sensor coating, and the existing building structure is not damaged;
7) The monitoring arrangement of the existing structure, the structural vertical face and the bottom face of the special-shaped surface can be realized: the conventional acoustic and optical sensors cannot be arranged on the special-shaped surface, the pouring type electrodes cannot be laid on the vertical surface and the bottom surface of the building, and the cement-based conductive material coating can realize the structural health monitoring of the special-shaped surface, the vertical surface and the bottom surface only by being sprayed on the existing building structure;
8) The continuous monitoring of the compression resistance, the tensile resistance, the bending resistance, the angle expansion, the creep, the sedimentation, the fatigue and the cracking of the existing building structure can be realized: the cement-based conductive material coating provided by the invention can be coated on various stress surfaces such as stress surfaces, beam bottom surfaces, column side surfaces, link joint interfaces and the like, and can simultaneously monitor various building service environments in real time;
9) The preparation method of the cement-based conductive material coating for monitoring the existing building strain, which is provided by the invention, has the advantages of mature scheme and simple process, maximizes the monitoring range and improves the utilization rate of precious conductive fillers, can effectively improve the durability of the existing concrete structure, and conforms to the long-term sustainable development strategy of the country.
Drawings
The accompanying drawings, which are incorporated in and constitute a part of this specification, are included to provide a further understanding of the invention, and are included to illustrate an exemplary embodiment of the invention and not to limit the invention. Wherein:
FIG. 1 is a graph showing the correlation data between the signals of a cement-based conductive material coating (sensor) and different pressures applied to a concrete test block when the cement-based conductive material coating prepared in example 1 of the present invention is coated on the pressed surface of the concrete test block;
FIG. 2 is the correlation data between the signal of the cement-based conductive material coating (sensor) and the cyclic loading pressure applied to the test block when the cement-based conductive material coating prepared in example 1 of the present invention is coated on the pressed surface of the concrete test block;
FIG. 3 is a schematic diagram of the cement-based conductive material coating prepared in example 1 of the present invention applied to the pressed surface of a concrete test block, the test block being pressed by cyclic loading until the signal of the cement-based conductive material coating (sensor) is changed, wherein the substrate is cracked at 18000 minutes of testing;
fig. 4 is a continuous detection process of signals of a cement-based coating (sensor) coated on the lower surface of a member during the bearing bending failure of the concrete beam body in embodiment 1 of the invention, wherein the signals are two strain gages with monitoring span consistent with that of the cement-based coating and used for reflecting the real strain of the lower surface of the beam body;
FIG. 5 is a continuous detection process of signals of a cement-based coating (sensor) coated on the lower surface of a member during the bearing bending failure of a concrete beam body in embodiment 2 of the invention, wherein the signals are two strain gauges with monitoring span consistent with that of the cement-based coating and used for reflecting the real strain of the lower surface of the beam body;
FIG. 6 is a continuous detection process of the invention in example 3, in which the signal of the cement-based coating (sensor) applied to the lower surface of the member increases in the deflection of the beam until cracking failure occurs during the flexural failure of the concrete beam, and the strain gauge data is two strain gauges with monitoring spans consistent with those of the cement-based coating, and is used for reflecting the real strain of the lower surface of the beam;
FIG. 7 is a continuous detection process of signals of a cement-based coating (sensor) coated on the lower surface of a member during the bearing bending failure of a concrete beam body in embodiment 4 of the invention, wherein the signals of the strain gauges are two strain gauges with monitoring span consistent with that of the cement-based coating and are used for reflecting the real strain of the lower surface of the beam body;
FIG. 8 is a diagram illustrating the signal changes of the cement-based conductive material coating (sensor) when the test block is subjected to cyclic loading until the test block is cracked and damaged, wherein the cement-based conductive material coating is coated on the compression surface of the concrete test block in comparative example 1;
FIG. 9 is a diagram of the signal change of the cement-based conductive material coating (sensor) when the test block is subjected to cyclic loading until the test block is cracked and damaged, wherein the cement-based conductive material coating is coated on the compression surface of the concrete test block in comparative example 2 of the present invention;
FIG. 10 is a graph showing the signal change of the cement-based conductive material coating (sensor) until the test block is cracked and destroyed by cyclic load pressure in comparative example 3 of the present invention in which the cement-based conductive material coating is applied to the compression surface of the concrete test block.
Detailed Description
The technical solutions in the embodiments of the present invention will be described clearly and completely below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments that can be derived by one of ordinary skill in the art from the embodiments given herein are intended to be within the scope of the present invention.
The present invention will be described in detail with reference to examples. It should be noted that the embodiments and features of the embodiments may be combined with each other without conflict.
The main core problems in the application of the conventional cement-based sensor at present are as follows:
1. causes of narrow monitoring range, easy cracking and insufficient bonding strength
Set cement is a typical brittle material with ultimate tensile strain around 100 μm, which greatly limits the monitoring range of cement-based sensors. Although it was found that the ultimate tensile strain was increased after the incorporation of the conductive fibers or powders, the key issue was in the achievement of "true" ductility in the cement matrix: on one hand, as the molecular structure of the cement hydration product-CSH is not fundamentally changed, the cement-based device prepared by the internal doped fiber/graphene/CNT and the like can only realize submicroscopic structure toughening, but can not completely solve the problems of poor ductility/easy cracking of a cement stone material; on the other hand, the adoption of the fiber modification scheme can cause the phenomenon that the sensor cracks continuously, thereby greatly reducing the monitoring capability of the real cracking condition of the structure.
2. The reason that the dispersion of the sensor performance is large and the signal-to-noise ratio is small due to the agglomeration of the conductive filler
The uniform dispersion of conductive components such as graphene, carbon nanotubes, carbon powder, metal powder, carbon fibers, metal fibers and the like in the set cement is the premise for obtaining the accurate and stable piezoresistive effect. However, the carbon-based material is easy to agglomerate and float upwards, the fiber material is easy to agglomerate, the metal material is easy to rust, and along with various factors in the preparation process of the sensor, such as stirring, a pore structure and rheological characteristics, the piezoresistive performance is affected, so that the performance of the cement-based sensor is discrete, and the signal-to-noise ratio is low.
3. For the reasons of pre-embedded/damaged arrangement, difficult replacement and complex operation
At present, cement-based sensors are generally arranged in a pre-buried mode, the bearing capacity of the existing structure can be inevitably influenced in the mode that the cement-based sensors are required to be embedded into the existing structure through an opening, the side face and the bottom face of the structure are difficult to pave, and the problem of replacement after misalignment and failure of the sensors is not considered. Meanwhile, the pre-embedded sensor has the promotion effect of stray current on steel bar corrosion in a reinforced concrete structure, and on the other hand, the steel bar has signal interference on the piezoresistive sensor.
In order to solve the above problems and problems, the present invention provides a cement-based conductive material and a cement-based sensor for strain monitoring of existing buildings, which are prepared by using water-based epoxy resin and cement concrete as main raw materials, adding conductive filler and a proper amount of water, uniformly stirring, brushing or spraying on the surface of an existing building structure, and forming a current loop through a conductive electrode arranged on the surface of the building and a connected monitoring device. When the existing building is stressed to generate strain or cracks, the strain or cracks can act on the surface coating to generate different current signals, so that the real-time health monitoring of the existing building is realized. The cement-based intelligent protective coating prepared by the invention can achieve the purpose of monitoring the deformation, load and cracking of a concrete structure by acquiring the stress-strain of the concrete in real time, has the advantages of good compatibility with the concrete structure and low price, and can also prevent harmful media such as external carbon dioxide, rainwater, salt solution and the like from corroding the concrete, thereby obviously prolonging the service life of the existing building. The monitoring coating has the advantages of high signal-to-noise ratio of detection signals, small relaxation phenomenon, stable monitoring performance, simple laying process, high bonding strength with a matrix, capability of being laid on the surface of any special-shaped structure, good economic benefit and long-term social benefit and very wide application prospect.
The cement-based conductive material coating has stable piezoresistive performance, low relaxation and wide strain measurement range, and can be paved by brushing. The piezoresistive sensor regulates and controls the dispersibility and the connectivity of the conductive filler through a network interpenetrating structure formed by the water-based epoxy resin and the cement matrix, and balances the percolation performance and the polarization phenomenon of cement-based ions. Meanwhile, the flexibility, frost resistance and bonding performance with a concrete matrix of the sensor in the elastic stage are greatly improved by using the water-based epoxy resin as a continuous space grid, and the durability of the structure, such as frost resistance, dry-wet cycle corrosion resistance and the like, is greatly improved while the stress strain and the cracking process of the structure are continuously monitored. The demand of the market on concrete structure monitoring is met.
In addition, the preparation method of the cement-based conductive material coating for monitoring the existing building strain, provided by the invention, has a simple process, can effectively improve the durability of the existing concrete structure, and conforms to the long-term sustainable development strategy of the country.
The invention provides a cement-based conductive material for monitoring the strain of an existing building, which specifically comprises the following components in percentage by mass:
5-50% (such as 5%, 10%, 20%, 30%, 40%, or 50%) of a water-borne epoxy resin, 20-80% (such as 22%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%) of cement, 1-20% (such as 2%, 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%) of a conductive filler, and 10-50% (such as 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%) of water.
In a specific embodiment of the present invention, the aqueous epoxy resin is one or a mixture of several of an anionic aqueous epoxy resin, a cationic aqueous epoxy resin, and a nonionic aqueous epoxy resin.
In the concrete embodiment of the invention, the cement is one or a mixture of more of portland cement, ordinary portland cement, portland slag cement, pozzolanic portland cement, fly ash portland cement, composite portland cement, G-grade oil well cement, rapid hardening portland cement, road portland cement, aluminate cement and sulphoaluminate cement.
In a specific embodiment of the present invention, the conductive filler is one or a mixture of several of graphite, carbon black, graphene oxide, reduced graphene oxide, and carbon nanotubes.
The invention also provides a preparation method of the cement-based conductive material coating for monitoring the strain of the existing building, which comprises the following steps:
step one, weighing water-based epoxy resin, conductive filler and water according to a ratio, and uniformly stirring and mixing to form slurry;
adding the slurry into cement according to a ratio, and stirring until the slurry is uniform to form slurry;
and step three, blade coating or spraying the slurry on the surface of the existing building structure, and curing and hardening to form the cement-based conductive material coating.
The present invention also provides a cement-based sensor comprising a cement-based conductive material as above or a coating of a cement-based conductive material as above, and a conductive electrode mounted on the existing architectural structural surface in the area of the applied coating. A current loop is formed by a conductive electrode arranged on the surface of the building and a connected monitoring device and is used for monitoring the stress-strain condition of the existing building and knowing the structural form of the concrete building structure.
In an embodiment of the present invention, the conductive electrode is a metal electrode or a graphite electrode.
In the embodiment of the present invention, in the third step, the curing is water spraying curing or film coating curing, the curing temperature is 0 to 50 ℃ (for example, 5 ℃, 10 ℃, 15 ℃, 20 ℃, 25 ℃, 30 ℃, 35 ℃, 40 ℃, 45 ℃), and the curing time is 3 to 7 days (for example, 4 days, 5 days, 6 days).
In the embodiment of the invention, the thickness of the cement-based conductive material coating is 0.1-10mm (such as 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 3.5mm, 4mm, 4.5mm, 5mm, 5.5mm, 6mm, 6.5mm, 7mm, 7.5mm, 8mm, 8.5mm, 9mm, 9.5 mm); the coating of the cement-based conductive material is easy to crack due to the excessively thin thickness, and the conductivity of the coating is unstable; the thickness of the coating layer, if too thick, makes the coating layer less likely to adhere to the surface of the building structure, easily come off and increase the cost, and thus the thickness of the coating layer of the cement-based conductive material needs to be maintained within a certain range.
Example 1
The cement-based conductive material for monitoring the strain of the existing building provided by the embodiment specifically comprises the following components in percentage by mass:
20% of anionic waterborne epoxy resin, 50% of ordinary portland cement, 10% of conductive filler (comprising 2% of carbon nano tube and 8% of graphene oxide) and 20% of water.
The preparation method of the cement-based conductive material coating comprises the following steps:
weighing the required water, the waterborne epoxy resin and the conductive filler according to the formula proportion, and stirring the mixture to be uniform to be mixed into slurry; then slowly adding the slurry into the evenly mixed cement according to the formula proportion, and stirring the mixture to form uniform slurry; and coating or spraying the slurry on the lower surface of the concrete beam body in a scraping way, curing for 3 days at the curing temperature of 25 ℃, and hardening to obtain the cement-based conductive material coating. The thickness of the cement-based conductive material coating is 5mm. The application area is provided with a conductive electrode (graphite electrode) before the coating is sprayed, the conductive electrode and a monitoring device form a current loop, and a monitoring signal (namely sensor data) of the cement-based conductive material coating is obtained.
FIG. 1 is a graph showing the correlation data between the signals of a cement-based conductive material coating (sensor) and different pressures applied to a concrete test block when the cement-based conductive material coating prepared in example 1 of the present invention is coated on the pressed surface of the concrete test block; as can be seen, the cement-based conductive material coating (sensor) signal is consistent with the pressure signal data variable when the test block is subjected to different pressures.
FIG. 2 is the correlation data between the signal of the cement-based conductive material coating (sensor) and the cyclic loading pressure applied to the test block when the cement-based conductive material coating prepared in example 1 of the present invention is coated on the pressed surface of the concrete test block; as can be seen from the figure, the signals of the cement-based conductive material coating (sensor) are consistent with the load force data variable of the test block subjected to cyclic load pressure.
FIG. 3 is a signal change of a cement-based conductive material coating (sensor) when the cement-based conductive material coating prepared in example 1 of the present invention is coated on a pressure-bearing surface of a concrete test block and the test block is subjected to cyclic loading pressure until the test block is cracked and destroyed; it can be seen that the substrate cracked at 18000 minutes of testing; the sensor signal fluctuates significantly at 18000 minutes.
The bonding strength of the coating of the cement-based conductive material prepared in the example and the concrete beam body is tested by the method according to DL/T5126-2001, test Specification for Polymer modified Cement mortar; the method for testing the freeze-thaw resistance durability of the beam concrete refers to GB/T50082-2009 Standard test methods for the long-term performance and durability of common concrete.
The bonding strength between the cement-based conductive material coating and the concrete beam body is 2.52MPa, and the surface has no cracking, no warping and no deformation; the freeze-thaw durability index of the beam concrete is improved from DF =92% to DF =97%. The bottom surface of the beam body is provided with strain gauges with the same span in a bending bearing position and a coating monitoring area in parallel, in order to guarantee monitoring accuracy and non-eccentricity, the left and the right of the coating are respectively provided with one strain gauge for monitoring stress-strain in the fracture process (namely the results of strain gauge data 1 and strain gauge data 2 in the graph 4), and if the results of the two strain gauges tend to be consistent, the beam body is stable in bending bearing and is not damaged eccentrically. The obtained stress-strain curve of the beam body in the fracture process at the bending bearing position and the monitoring signal curve of the cement-based conductive material coating are shown in fig. 4.
As can be seen from fig. 4, the monitoring signal of the cement-based conductive material coating and the monitoring signal of the beam body in the fracture process at the bending bearing position are consistent with the development trend of the real stress-strain curve of the beam body, and the monitored fracture strain is consistent with the real fracture strain.
Example 2
In this embodiment, the concrete components of the cement-based conductive material are changed, and other method steps are the same as those in embodiment 1, and are not described herein again.
The cement-based conductive material specifically comprises the following components in percentage by mass:
10 percent of cationic waterborne epoxy resin, 55 percent of slag portland cement, 5 percent of conductive filler (wherein the graphite is 3 percent, and the carbon black is 2 percent) and 30 percent of water.
The cement-based conductive material prepared in this example was subjected to performance tests according to the performance test standards as in example 1, and the performance results were as follows:
the bonding strength of the cement-based coating and the concrete beam body is 2.61MPa, the surface is free of cracking, warping and deformation, and the freeze-thaw resistance durability index of the beam body concrete is improved from DF =95% to DF =98%. The stress-strain curve of the beam body in the bending fracture process and the monitoring signal curve of the cement-based conductive material coating are shown in figure 5.
As can be seen from fig. 5, the monitoring signal of the cement-based conductive material coating and the monitoring signal of the beam body in the fracture process at the bending bearing position are consistent with the development trend of the real stress-strain curve of the beam body, and the monitored fracture strain is consistent with the real fracture strain.
Example 3
In this embodiment, the concrete components of the cement-based conductive material are changed, and other method steps are the same as those in embodiment 1, and are not described herein again.
The cement-based conductive material specifically comprises the following components in percentage by mass:
30% of nonionic water-based epoxy resin, 40% of portland slag cement, 10% of conductive filler (wherein, 5% of reduced graphene oxide and 5% of carbon nano tubes) and 20% of water.
The cement-based conductive material prepared in this example was subjected to performance tests according to the performance test standards as in example 1, and the performance results were as follows:
the bonding strength of the cement-based coating and the concrete beam body is 2.55MPa, the surface is free of cracking, warping and deformation, and the freeze-thaw resistance durability index of the beam body concrete is improved from DF =88% to DF =96%. The stress-strain curve of the beam body in the bending fracture process and the monitoring signal curve of the cement-based conductive material coating are shown in figure 6.
As can be seen from fig. 6, the monitoring signal of the cement-based conductive material coating and the monitoring signal of the beam body in the fracture process at the bending bearing position are consistent with the development trend of the real stress-strain curve of the beam body, and the monitored fracture strain is consistent with the real fracture strain.
Example 4
In the embodiment, specific components of the cement-based conductive material are changed, the slurry is coated or sprayed on the lower surface of the concrete beam body in a scraping mode and maintained for 7 days, the maintaining temperature is 15 ℃, and the thickness of the cement-based conductive material coating is 10mm. Other method steps are the same as embodiment 1, and are not described herein again.
The cement-based conductive material comprises the following components in percentage by mass:
40% of nonionic water-based epoxy resin, 50% of portland slag cement, 5% of conductive filler (2% of graphene and 3% of carbon nanotubes) and 5% of water.
The cement-based conductive material prepared in this example was subjected to performance tests according to the performance test standards as in example 1, and the performance results were as follows:
the bonding strength of the cement-based coating and the concrete beam body is 2.54MPa, the surface is free of cracking, warping and deformation, and the freeze-thaw resistance durability index of the beam body concrete is improved from DF =93% to DF =99%. The stress-strain curve of the beam body in the bending fracture process and the monitoring signal curve of the cement-based conductive material coating are shown in figure 7.
As can be seen from fig. 7, the monitoring signal of the cement-based conductive material coating and the monitoring signal of the beam body in the fracture process at the bending bearing position are consistent with the development trend of the real stress-strain curve of the beam body, and the monitored fracture strain is consistent with the real fracture strain.
Comparative example 1
In this comparative example, the concrete components of the cement-based conductive material were changed, and the other method steps were the same as in example 1 and will not be described again.
The cement-based conductive material comprises the following components in percentage by mass:
1% of nonionic water-based epoxy resin, 59% of portland slag cement, 10% of conductive filler (wherein, 5% of reduced graphene oxide and 5% of carbon nano tubes) and 30% of water.
The cement-based conductive material prepared in this example was subjected to performance tests according to the performance test standards as in example 1, and the performance results were as follows:
the bonding strength of the cement-based coating and the concrete beam body is 1.07MPa, a large number of drying shrinkage cracks exist on the surface, and the freeze-thaw resistance durability index of the beam body concrete is improved from DF =88% to DF =89%.
FIG. 8 is a signal change of the cement-based conductive material coating (sensor) when the cement-based conductive material coating prepared in comparative example 1 of the present invention is coated on the pressed surface of the concrete test block and the test block is pressed by the cyclic load until the test block is cracked and destroyed; it can be seen from the figure that the sensor signal fluctuates severely, the signal-to-noise ratio is too small, and obvious signal distortion is found in 2000 minutes, so that an effective monitoring signal cannot be obtained.
Comparative example 2
In this comparative example, the concrete components of the cement-based conductive material were changed, and the other method steps were the same as in example 1 and will not be described again.
The cement-based conductive material specifically comprises the following components in percentage by mass:
10% of anionic waterborne epoxy resin, 55% of portland slag cement, 5% of conductive carbon fiber and 30% of water.
The cement-based conductive material prepared in this example was subjected to a performance test according to the performance test standard as in comparative example 2, and the performance results were as follows:
the bonding strength of the cement-based coating and the concrete beam body is 2.51MPa, the surface is free of cracking, warping and deformation, and the freeze-thaw resistance durability index of the beam body concrete is improved from DF =88% to DF =91%.
FIG. 9 shows the signal change of the cement-based conductive material coating (sensor) when the cement-based conductive material coating prepared in comparative example 2 of the present invention is coated on the pressed surface of the concrete test block and the test block is pressed by the cyclic load until the test block is cracked and destroyed; as can be seen from the figure, the conductivity of the conductive carbon fiber is weak, and ion percolation is unstable, so that the signal fluctuation of the sensor is severe, the signal-to-noise ratio is too small, the signal is seriously distorted, and an effective monitoring signal cannot be obtained.
Comparative example 3
In this comparative example, the concrete components of the cement-based conductive material were changed, and other steps of the method were the same as those in example 1 and will not be described herein again.
The cement-based conductive material specifically comprises the following components in percentage by mass:
70% of nonionic water-based epoxy resin, 20% of portland slag cement, 1% of conductive filler (graphene 1% of the conductive filler) and 9% of water.
The cement-based conductive material prepared in this example was subjected to the performance test according to the performance test standard as in example 1, and the performance results were as follows:
the bonding strength of the cement-based coating and the concrete beam body is 2.84MPa, the surface has no cracking, no warping and no deformation, and the freeze-thaw resistance durability index of the beam body concrete is improved from DF =91% to DF =97%.
FIG. 10 is a graph showing the signal changes of the cement-based conductive material coating (sensor) when the cement-based conductive material coating prepared in comparative example 3 of the present invention is coated on the pressed surface of the concrete test block and the test block is pressed by the cyclic load until the test block is cracked and destroyed; as can be seen, the conductive performance is significantly reduced and the ion percolation is almost ineffective due to the excessively small amount of the conductive filler and the excessively large amount of the aqueous epoxy resin. The signal-to-noise ratio of the signal is too small, the background of the signal is too high, and an effective monitoring signal cannot be obtained.
In summary, the following steps: the invention provides a cement-based conductive material and a cement-based sensor for monitoring the health of an existing building. When the existing building is stressed to generate strain or cracks, the strain or cracks can act on the surface coating to generate different current signals, so that the real-time health monitoring of the existing building is realized.
The cement-based conductive material coating prepared by the invention can achieve the purpose of monitoring the deformation, load and cracking of a concrete structure by acquiring the stress-strain of the concrete in real time, has the advantages of good compatibility with the concrete structure and low price, and can also prevent harmful media such as external carbon dioxide, rainwater, salt solution and the like from corroding the concrete, thereby obviously prolonging the service life of the existing building. The monitoring coating has the advantages of high signal-to-noise ratio of detection signals, small relaxation phenomenon, stable monitoring performance, simple laying process, high bonding strength with a matrix, capability of being laid on the surface of any special-shaped structure, good economic benefit and long-term social benefit and very wide application prospect.
The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention, and various modifications and changes may be made by those skilled in the art. Any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the protection scope of the present invention.
Claims (6)
1. A cement-based conductive material for strain monitoring of existing buildings is characterized by comprising the following components in percentage by mass:
20% of anionic waterborne epoxy resin, 50% of ordinary portland cement, 2% of carbon nano tube, 8% of graphene oxide and 20% of water;
or 30% of nonionic water-based epoxy resin, 40% of slag portland cement, 5% of reduced graphene oxide, 5% of carbon nano tubes and 20% of water.
2. A method for preparing a cement-based conductive material coating for existing building strain monitoring according to claim 1, comprising the steps of:
step one, weighing water-based epoxy resin, conductive filler and water according to a ratio, and uniformly stirring and mixing to form slurry;
step two, adding the slurry into cement according to the proportion, and stirring the mixture until the mixture is uniform to form slurry;
thirdly, blade-coating or spraying the slurry on the surface of the existing building structure, and curing and hardening to form a cement-based conductive material coating;
the thickness of the cement-based conductive material coating is 0.5-10mm.
3. The method for preparing the cement-based conductive material coating for monitoring the strain of the existing building according to claim 2, wherein in the third step, the curing is water spraying curing or film covering curing, the curing temperature is 0-50 ℃, and the curing time is 3-7 days.
4. A cement-based conductive material coating for existing building strain monitoring, characterized in that the coating is prepared by the method for preparing the cement-based conductive material coating for existing building strain monitoring according to claim 2 or 3.
5. A cement-based sensor comprising the cement-based conductive material of claim 1 or the cement-based conductive material coating of claim 4, and further comprising a conductive electrode mounted on the existing architectural structure surface in the coated area.
6. The cement-based sensor of claim 5, wherein the conductive electrode is a metal electrode or a graphite electrode.
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