Concrete electromagnetic curing method

Abstract

The invention belongs to the technical field of concrete material curing, and particularly discloses a concrete electromagnetic curing method which is characterized in that steel fibers with excellent electric and magnetic conductivity are doped into concrete, and an electromagnetic induction device is utilized to apply an alternating electromagnetic field, so that the steel fibers generate induction heating, and the interior of the concrete is uniformly heated; efficient maintenance is realized; in the curing process, the internal temperature of the concrete is monitored in real time through an embedded temperature sensor, the temperature is controlled to be 40-60 DEG C, and the humidity is maintained at a proper level in a wet cloth covering mode; the problems that an existing curing method is high in energy consumption and uneven in temperature distribution are solved, the early strength of the concrete can be remarkably improved, and the method is suitable for engineering application in cold regions or special environments; the method is efficient, energy-saving and easy to operate, and has wide popularization value.

Description

Technical Field

[0001] The invention relates to the technical field of concrete curing, and in particular to a concrete electromagnetic curing method. Background Art

[0002] Concrete is the most commonly used material in construction and civil engineering, and its curing process directly affects the mechanical properties and durability of concrete. Traditional curing methods include watering curing, steam curing and greenhouse curing, which have the following shortcomings: low efficiency: traditional watering curing is significantly affected by external temperature and humidity conditions, especially in cold areas, it is difficult to ensure the early strength growth of concrete; high energy consumption: steam curing requires high-temperature heating equipment, which consumes a lot of energy and is difficult to achieve uniform heating; poor applicability: greenhouse curing is limited by the construction site and requires more construction space.

[0003] Electromagnetic curing is a new curing method that uses electric current to generate heat to accelerate the hardening of concrete. Concrete electromagnetic curing is based on the Joule-Lenz law. Concrete is used as a resistor and an alternating current is passed through it to convert electrical energy into thermal energy, so that the concrete is heated and hardened. After the power is turned on, the cement paste containing hydration products is first heated, and then the heat is transferred to the aggregate. The resistivity of concrete changes with the hardening process. The main electromagnetic curing methods include direct electric heating, indirect electric heating, and electromagnetic induction. The direct electric heating method uses concrete or steel bars as heating resistors or buries heating resistors separately, and heats the concrete with metal electrodes or steel bars as electrodes at both ends. The indirect electric heating method uses electric heating templates, pedestals and other conduction heating products. The electromagnetic induction method uses the electromagnetic induction phenomenon to induce electricity in steel molds and steel bars, heating the concrete from both inside and outside.

[0004] For electromagnetic maintenance, how to achieve uniform heating inside the concrete is crucial to improving maintenance efficiency and quality. However, since concrete is a poor conductor of heat, there is currently no effective means to solve this problem. Summary of the invention

[0005] In view of this, an object of the present invention is to provide a concrete electromagnetic curing method, which is conducive to achieving uniform heating inside the concrete, thereby improving the curing efficiency and quality.

[0006] To achieve the above object, the present invention provides a method for electromagnetic curing of concrete, wherein a set proportion of steel fibers are added to concrete and then electromagnetic curing of concrete components is performed by electromagnetic induction.

[0007] As a further improvement to the technical solution of the present invention, the method specifically comprises the following steps:

[0008] S1. Steel fiber incorporation: Incorporate steel fibers into the concrete mixture and distribute the steel fibers evenly in the concrete;

[0009] S2. Induction coil arrangement: an induction coil is arranged outside the concrete component, and the induction coil is subjected to an alternating electromagnetic field generated by an AC power source;

[0010] S3, induction heating: steel fibers generate induced current and eddy current effect in the alternating magnetic field and generate heat, thereby uniformly heating the interior of the concrete component;

[0011] S4. Temperature and humidity monitoring and control: Real-time monitoring of the temperature and humidity of concrete components during the heating process, and control of the temperature and humidity within the set range;

[0012] S5. Continuous maintenance: After electromagnetic maintenance continues for a set time, it enters the standard maintenance stage.

[0013] As a further improvement to the technical solution of the present invention, in step S1, the amount of the steel fiber added is 1%-3% of the volume of the concrete.

[0014] As a further improvement to the technical solution of the present invention, in step S1, the length of the steel fiber is 35 mm to 60 mm.

[0015] As a further improvement to the technical solution of the present invention, in step S1, the steel fiber is a corrugated fiber structure, and its surface is galvanized or coated to enhance electrical conductivity and corrosion resistance.

[0016] As a further improvement to the technical solution of the present invention, in step S1, a composite admixture is also added to the concrete. The composite admixture includes a water reducer and an early strength agent, and the amount used is 0.5%-1.5% of the mass of cement to enhance the workability and early strength of the concrete.

[0017] As a further improvement to the technical solution of the present invention, in step S4, the internal temperature of the concrete is monitored in real time by an embedded temperature sensor, and the temperature is controlled within the range of 40° C. to 60° C.

[0018] As a further improvement to the technical solution of the present invention, in step S4, the surface humidity of the concrete component is maintained by covering it with a wet cloth.

[0019] As a further improvement to the technical solution of the present invention, in step S5, the duration of electromagnetic maintenance is 2 hours to 6 hours.

[0020] As a further improvement to the technical solution of the present invention, after entering the standard curing stage, the temperature of the standard curing environment is 20°C±2°C, the relative humidity is ≥95%, and the curing time is 1 to 28 days.

[0021] Compared with the prior art, the present invention has the following beneficial technical effects:

[0022] The electromagnetic curing method for concrete provided by the present invention creatively utilizes the electrical conductivity and magnetic conductivity of steel fibers, and performs uniform internal heating and curing of concrete through electromagnetic induction heating technology, so as to enhance the early strength of concrete and improve its mechanical properties; the electromagnetic curing method for concrete based on steel fiber materials proposed by the present invention significantly improves the efficiency and quality of concrete curing by combining steel fibers and electromagnetic induction technology; experimental results show that the method has significant advantages in enhancing the early strength of concrete, improving internal temperature uniformity, and reducing energy consumption.

[0023] Advantages of additional aspects of the present invention will be given in part in the following description, and in part will become obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The accompanying drawings constituting a part of the present invention are used to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their description are used to explain the present invention but do not constitute a limitation of the present invention.

[0025] Figure 1 is a flow chart of the present invention;

[0026] Figure 2 A diagram of the physical state of the electromagnetic maintenance performed by the present invention;

[0027] Figure 3 This is a physical picture of the concrete specimen during electromagnetic curing;

[0028] Figure 4 The layout diagram of the embedded temperature sensor. DETAILED DESCRIPTION

[0029] In order to enable those skilled in the art to better understand the technical solution of the present invention, the present invention is further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0030] Embodiment 1

[0031] This embodiment provides a concrete electromagnetic curing method, which mainly includes the following contents:

[0032] First, the selection and incorporation of steel fibers: The amount of steel fibers added is the set volume of concrete, ensuring that the steel fibers are evenly distributed within the concrete.

[0033] Second, the design of the electromagnetic induction device: the induction coil is connected to an AC power source to generate an alternating magnetic field.

[0034] Third, temperature monitoring and control: The internal temperature of the concrete is monitored in real time through embedded temperature sensors, the temperature is controlled within a certain range, and the humidity is maintained at an appropriate level by covering it with a wet cloth.

[0035] Fourth, the curing process: after the initial setting of the concrete, the electromagnetic induction device is started, the electromagnetic curing lasts for a certain period of time, and then enters the standard curing stage.

[0036] Specifically, steel fibers are added to the concrete mixture so that they are evenly distributed in the concrete. The amount of steel fibers added is 1%-3% of the volume of the concrete, and the length of the steel fibers is 35 mm and 60 mm. The steel fibers are in the shape of corrugated fibers, and their surfaces are galvanized or coated to enhance electrical conductivity and corrosion resistance. The steel fiber materials added to the concrete preferably have the following performance indicators: tensile strength ≥1200 MPa, electrical conductivity ≥1.5×10 6 S / m.

[0037] Composite admixtures can also be added to concrete. Composite admixtures include water reducers and early strength agents, with the dosage being 0.5% to 1.5% of the mass of cement to enhance the workability and early strength of concrete.

[0038] An induction coil is arranged outside the concrete component, and the induction coil generates an alternating electromagnetic field of 50Hz to 1kHz through an AC power supply; the power of the induction coil can be 65W to 120W, the coil spacing can be 30mm to 50mm, and the shape of the coil can be designed to be rectangular, circular or elliptical according to the geometric characteristics of the concrete component.

[0039] The induction coil is part of the electromagnetic maintenance device, which may include an induction coil, an AC power supply, a temperature sensor and a temperature control module. The temperature control module adjusts the induction heating power through a closed-loop control system. The induction coil may adopt a multi-layer winding structure, the winding material is copper or aluminum, and the outer layer is covered with an insulating coating, and the temperature resistance is not less than 150°C. The electromagnetic induction heating device can be adjusted according to the size of the concrete component. Its induction coil is supported by a movable frame, and the frame height and width can be adjusted according to the size of the component. The induction coil can be controlled in sections, and each section independently controls the electromagnetic heating power, which can achieve zone heating and ensure uniform temperature inside large concrete components.

[0040] The steel fibers generate induced current and eddy current effect in the alternating magnetic field, causing the steel fibers to heat up, thereby uniformly heating the concrete inside.

[0041] During the heating process, the internal temperature of the concrete is monitored in real time through the embedded temperature sensor, and the temperature is controlled within the range of 40℃-60℃, and the surface humidity is maintained by covering with a wet cloth; during the electromagnetic induction heating process, the temperature sensor monitors the internal temperature of the concrete in real time, and automatically increases the induction power when the temperature is below 40℃; when the temperature exceeds 60℃, the electromagnetic heating is stopped and the natural cooling mode is turned on. Humidity control is achieved by covering the concrete surface with a wet cloth, which is replaced every 2 hours to keep the humidity of the concrete surface not less than 70%.

[0042] During the electromagnetic induction heating process, an infrared thermal imager can also be used to detect the temperature distribution on the concrete surface in real time to ensure uniformity during the curing process.

[0043] The duration of electromagnetic curing is 2h, 4h, and 6h, followed by the standard curing stage. After electromagnetic curing, the concrete enters the standard curing stage. The standard curing environment includes a temperature of 20℃±2℃ and a relative humidity ≥95%. The curing time can be 1 to 28 days (can be extended depending on the specific situation).

[0044] This method is suitable for concrete construction in cold areas. Electromagnetic curing in low temperature environment (-10℃ to 0℃) can significantly improve the early strength of concrete.

[0045] By adopting the above method, the electrical conductivity and magnetic conductivity of steel fibers are utilized, and electromagnetic induction heating technology is used to uniformly heat and cure the concrete internally, so as to enhance the early strength of the concrete and improve its mechanical properties (it can significantly enhance the compressive strength and flexural toughness of the concrete, and greatly enhance the crack resistance and carbonization resistance of the concrete).

[0046] Specifically, the use of steel fiber has the following advantages: as a metal fiber, steel fiber has the characteristic of rapid heating. During the electromagnetic induction heating process, it can quickly generate heat and accelerate the hardening process of concrete; steel fiber can realize intelligent temperature control during electromagnetic induction heating, freely switch the heating temperature according to needs, and provide more precise maintenance temperature control; when steel fiber is used as a heating material, it can be evenly distributed in the concrete, making the overall structure relatively light and thin, which is convenient for construction and maintenance; steel fiber also has good mechanical strength and can withstand bending and pulling forces in concrete, which makes the steel fiber heating element in the electromagnetic maintenance process have good durability; as a heating material, steel fiber does not generate electromagnetic radiation during the electromagnetic induction heating process, so it is harmless to the human body and has high safety; the electric heat conversion efficiency of steel fiber in electromagnetic induction heating is high, which can save electricity and has the advantages of energy saving and environmental protection; steel fiber has good resistance to sudden changes in temperature, can remain stable under drastic temperature changes, and is not easy to burst; as a heating material, steel fiber has good corrosion resistance and is suitable for use in a variety of environments.

[0047] Embodiment 2

[0048] This embodiment provides a method for electromagnetic curing of concrete, the steps of which mainly include the following steps S1 to S5.

[0049] S1. Steel fiber is selected from corrugated steel fiber with a length of 35mm, 60mm and a diameter of 0.5mm, with a tensile strength of ≥1200MPa and a conductivity of ≥1.5×10 6S / m; add steel fiber into C30 concrete mixture at 1% to 3% of concrete volume;

[0050] Use mechanical mixing equipment to evenly mix the steel fibers with the concrete mixture to ensure uniform distribution of the steel fibers within the concrete and avoid fiber agglomeration.

[0051] S2, the induction coil adopts a rectangular structure, the coil height is 300mm, the width is 400mm; the coil generates an alternating magnetic field through an AC power supply, the power is 80W, and the coil spacing is 40mm;

[0052] The induction coil is fixed to the outside of the concrete element by an adjustable frame, the height and width of which can be adjusted according to the size of the element.

[0053] S3. After the concrete is poured, the surface is covered with plastic film, placed inside the electromagnetic curing coil, and the electromagnetic induction device is started to heat the concrete internally.

[0054] S4, embedded temperature sensor monitors the internal temperature of concrete. When the temperature is lower than 40℃, the induction power is automatically increased; when the temperature exceeds 60℃, heating is stopped;

[0055] During the curing process, the surface of the specimen was covered with a wet towel, which was replaced every 2 hours to ensure that the surface was moist.

[0056] S5. The duration of electromagnetic curing is 2h. After the curing, the steel fiber concrete specimens are transferred to the standard curing environment. The temperature is controlled at 20℃±2℃ and the humidity is kept above 95%. The curing time is 3-28 days, and the compressive strength of each age is measured.

[0057] The comparison of the results of different fiber parameters under electromagnetic curing is shown in Table 1.

[0058] Table 1 Comparison of fiber length and dosage on compressive strength

[0059]

[0060] It can be seen from Table 1 that with the increase of fiber content, the compressive strength of the specimen increases first and then decreases. As the fiber length increases, the compressive strength of the specimen decreases. When the steel fiber volume content is 2% and the length is 35 mm, the compressive strength of the specimen is the largest, indicating that this fiber parameter is optimal under electromagnetic curing. Under this parameter, the 3d and 28d compressive strengths of the concrete specimens under standard curing and electromagnetic curing are 30.1 MPa and 35.3 MPa and 47.1 MPa and 61.7 MPa, respectively, which significantly improves the strength of concrete.

[0061] After the electromagnetic curing, the content of hydration products inside the concrete was analyzed by XRD. The results showed that electromagnetic curing can significantly increase the hydration rate and reduce the proportion of unhydrated particles.

[0062] Embodiment 3

[0063] This embodiment provides a method for electromagnetic curing of concrete, and its steps are substantially the same as those shown in the second embodiment, so the same contents between the two are not repeated here.

[0064] This example studies the effect of different curing times on the performance of concrete products. Electromagnetic curing is performed with electromagnetic curing times of 2 h, 4 h, and 6 h, and a parallel control test is performed with specimens cured with standard curing.

[0065] The duration of electromagnetic curing is 2h, 4h, and 6h, and the steps are the same as those in Example 2.

[0066] After the electromagnetic curing, the steel fiber concrete specimens were transferred to the standard curing environment. The temperature was controlled at 20℃±2℃, the humidity was kept above 95%, and the curing time was 1, 3, 7, and 28 days. The compressive strength at each age was measured.

[0067] The comparison of the results under different curing times is shown in Table 2.

[0068] Table 2 Comparison of compressive strength at different curing times

[0069]

[0070] It can be seen from Table 2 that as the electromagnetic curing time increases, compared with the standard curing, the early compressive strength of the specimens is greatly improved. When the electromagnetic curing time is 6h, the early strength (1d, 3d) is improved most significantly, reaching 200% and 148% of the standard curing, respectively. However, the compressive strength in the later period (28d) also increases, but the increase is small, about 135% of the standard curing.

[0071] Embodiment 4

[0072] This embodiment provides a method for electromagnetic curing of concrete, and its steps are substantially the same as those shown in the second embodiment, so the same contents between the two are not repeated here.

[0073] This example studies the effect of different curing temperatures on the performance of concrete products. Electromagnetic curing is performed at electromagnetic curing temperatures of 40° C., 50° C., and 60° C., and a parallel control test is performed on specimens cured with standard curing.

[0074] The electromagnetic curing temperatures are 40° C., 50° C. and 60° C., and the steps are the same as those in Example 2.

[0075] After the electromagnetic curing, the steel fiber concrete specimens were transferred to the standard curing environment, the temperature was controlled at 20℃±2℃, the humidity was kept above 95%, the curing time was 1, 3, 7, and 28 days, and the compressive strength at each age was measured. The comparison of the results at different curing temperatures is shown in Table 3.

[0076] Table 3 Comparison of compressive strength at different curing temperatures

[0077]

[0078] As can be seen from Table 3, with the increase of temperature, the 28d compressive strength of concrete increases, and the improvement of the early strength of the specimens is also quite obvious. The compressive strength of the specimens with an electromagnetic curing temperature of 60°C reaches the highest. At this temperature, the compressive strengths of 1d, 3d, and 7d reach 214%, 145%, and 135% of the standard curing, respectively. The increase in temperature has no inhibitory effect on the 28d compressive strength of SFRC. This is mainly because electromagnetic heating under continuous high temperature will cause the evaporation of water inside and on the surface of cement-based materials. As the temperature increases, the evaporation rate of water increases, which may cause cracking and cracking on the surface of cement-based materials, and cause stress inside cement-based materials, which may cause the development of cracks.

[0079] Finally, it should be noted that this article uses specific examples to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only to help understand the core idea of ​​the present invention. Without departing from the principles of the present invention, the present invention may also be improved and modified, and these improvements and modifications also fall within the scope of protection of the present invention.

Claims

1. A method for electromagnetic curing of concrete, characterized in that: After adding a set proportion of steel fibers into the concrete, electromagnetic curing is carried out on the concrete components through electromagnetic induction method.

2. A method for electromagnetic curing of concrete according to claim 1, characterized in that: The method specifically comprises the following steps: S1. Steel fiber incorporation: Incorporate steel fibers into the concrete mixture and distribute the steel fibers evenly in the concrete; S2. Induction coil arrangement: an induction coil is arranged outside the concrete component, and the induction coil is subjected to an alternating electromagnetic field generated by an AC power source; S3, induction heating: steel fibers generate induced current and eddy current effect in the alternating magnetic field and generate heat, thereby uniformly heating the interior of the concrete component; S4. Temperature and humidity monitoring and control: Real-time monitoring of the temperature and humidity of concrete components during the heating process, and control of the temperature and humidity within the set range; S5. Continuous maintenance: After electromagnetic maintenance continues for a set time, it enters the standard maintenance stage.

3. A method for electromagnetic curing of concrete according to claim 2, characterized in that: In step S1, the amount of the steel fiber added is 1%-3% of the volume of the concrete.

4. A method for electromagnetic curing of concrete according to claim 2, characterized in that: In step S1, the length of the steel fiber is 35 mm to 60 mm.

5. A method for electromagnetic curing of concrete according to claim 2, characterized in that: In step S1, the steel fiber is a corrugated fiber structure, and its surface is galvanized or coated to enhance electrical conductivity and corrosion resistance.

6. A method for electromagnetic curing of concrete according to claim 2, characterized in that: In step S1, a composite admixture is also added to the concrete. The composite admixture includes a water reducing agent and an early strength agent. The amount of the composite admixture is 0.5%-1.5% of the mass of cement, and is used to enhance the workability and early strength of the concrete.

7. A method for electromagnetic curing of concrete according to claim 2, characterized in that: In step S4, the internal temperature of the concrete is monitored in real time by an embedded temperature sensor, and the temperature is controlled within the range of 40°C to 60°C.

8. A method for electromagnetic curing of concrete according to claim 2, characterized in that: In step S4, the surface humidity of the concrete member is maintained by covering it with a wet cloth.

9. A method for electromagnetic curing of concrete according to claim 2, characterized in that: In step S5, the duration of electromagnetic maintenance is 2 hours to 6 hours.

10. A method for electromagnetic curing of concrete according to claim 2, characterized in that: After entering the standard curing stage, the temperature of the standard curing environment is 20℃±2℃, the relative humidity is ≥95%, and the curing time is 1 to 28 days.

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