A method and system for temperature control calibration of electric bellows grouting agent

Abstract

The present application provides a method and system for curing temperature control calibration of an electric heating bellows grouting agent. Compared with the existing technology, the method determines the appropriate heating wire specification parameters, curing strategy and input voltage through model specimens and finite element modeling analysis, and then applies the same curing method to the construction of prestressed pipes in prestressed concrete bridges. The system for curing temperature control calibration of an electric heating bellows grouting agent includes a heating module, a temperature detection module, a temperature control module and a power supply module. Compared with the existing technology, the dynamic and precise temperature control of the heating module and the temperature control module ensures that the slurry of the prestressed pipes of bridges in cold areas is fully hydrated during the solidification process, improves the reliability of grouting quality, effectively prevents the slurry from freezing and expanding in low-temperature environments, and avoids structural cracking problems caused by frost heave.

Description

Technical Field

[0001] The present application relates to the technical field of prestressed concrete bridge and prestressed pipe construction, and specifically to a method and system for curing temperature control of an electric heating bellows grouting agent. Background Art

[0002] In existing prestressed concrete bridge construction, low-temperature grouting techniques primarily rely on three methods: First, the use of low-temperature grouting agents. Commonly used low-temperature grouting agents, such as sulfoaluminate cement, can only be used above -10°C. Second, while passive insulation measures (such as covering with insulation materials and constructing temporary greenhouses) can slow heat loss, their effectiveness decreases dramatically in extremely low temperatures. Furthermore, they struggle to dynamically respond to external temperature fluctuations and ensure the grout remains within its active temperature range. Third, active heating techniques (such as electric blanket curing and steam heating) often suffer from low temperature control accuracy and uneven temperature distribution when the ambient temperature is too low, which can easily lead to thermal stress cracking in the concrete. Furthermore, the lack of systematic calibration tailored to the beam structure and environmental parameters results in a disconnect between heating strategies and actual operating conditions. Furthermore, traditional heating devices are difficult to deploy in the construction of high-altitude, long-span prestressed beams. Installation complexity and high energy consumption further limit their applicability.

[0003] While recent research has attempted to improve energy efficiency by introducing carbon fiber materials as heating elements, their application has largely been limited to building heating, and an integrated temperature control solution for prestressed pipe grouting has yet to be developed. Furthermore, existing technologies lack quantitative research on the coupling relationship between the active temperature threshold of grouting agents and structural thermal stress, making it difficult to ensure grout curing quality while avoiding structural damage.

[0004] Therefore, it is urgent to develop a grouting agent curing temperature control calibration method and system that has precise temperature control and is highly compatible with prestressed pipes. By modeling and analyzing the coupling relationship between the active temperature threshold of the grouting agent and the thermal stress of the structure, the technical bottleneck of bridge construction in high-altitude cold areas can be broken through, and the problem of the heating strategy in the existing technology being out of touch with the actual working conditions can be solved, resulting in insufficient hydration of the slurry and easy induction of thermal stress cracks in the concrete can be solved. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, the present application provides a method and system for curing temperature control of electric bellows grouting agent, which can insulate and control the temperature of the entire solidification process of prestressed pipe slurry of bridges in cold areas, ensure sufficient hydration of the slurry, improve the reliability of grouting quality, and avoid the problem of symbiotic cracking of the structure due to frost heave of the slurry.

[0006] The technical solutions provided in this application are as follows:

[0007] The present application provides a method for calibrating the curing temperature of an electric bellows grouting agent, comprising the following steps:

[0008] S1. Determine the specifications of the heating wire of the electric heating bellows, such as material, surface material, winding spacing, etc.

[0009] Specifically, the heating wire can be a heating wire made of carbon fiber material. The surface, specifications and winding spacing of the heating wire are determined. The specification of the heating wire 12 bundle is n K, 1K means that 1000 carbon fiber filaments form a bundle, and the winding method is single spiral.

[0010] S2. Prepare a model specimen according to the prestressed beam of an actual bridge, integrate the model specimen with the electric heating bellows grouting agent curing temperature control calibration system, and connect a heating module and a temperature detection module to the model specimen.

[0011] Specifically, the method for preparing the model specimen is to cut a section of the prestressed beam of the actual bridge to manufacture the model specimen, and connect the heating module and the temperature detection module into the model specimen. The temperature control module can adjust the temperature of the heating module according to the temperature detection results.

[0012] S3. Use finite element modeling to perform structural analysis on the model specimen. During the modeling process, the external ambient temperature T is loaded. The internal temperature t after heating by the heating module is analyzed through modeling calculation. The temperature difference between the inside and outside of the model specimen (Tt) is analyzed. The stress conditions inside the model specimen at different external temperatures and heating module temperatures are analyzed to determine the upper limit of the thermostat calibration temperature. Then, the lowest curing temperature at which the grouting agent inside the model specimen is completely hydrated is taken as the lower limit of the thermostat calibration temperature.

[0013] Specifically, the upper temperature limit in S3 is the value at which the maximum principal tensile stress on the beam surface reaches the concrete tensile strength, and is determined by calculating whether the maximum principal tensile stress on the beam surface reaches the standard value of concrete tensile strength using a finite element model.

[0014] S4. Determine multiple fixed temperatures between the upper and lower temperature limits determined in S3, divide the ambient temperature into multiple temperature ranges based on the fixed temperatures, determine a different maintenance strategy for each temperature range, and determine one of the maintenance strategies based on the experimental environment.

[0015] Specifically, different maintenance strategies use different grouting agents. Two fixed temperatures i℃ and j℃ are determined according to the ambient temperature from high to low, and the ambient temperature is divided into three temperature ranges: high temperature (higher than i℃), medium temperature (j℃-i℃), and low temperature (lower than j℃). In terms of maintenance strategy, ordinary grouting agent is used in the high temperature range, ordinary grouting agent plus electric heating bellows heating temperature control system is used in the medium temperature range, or low-temperature grouting agent is used, ordinary grouting agent plus electric heating bellows heating temperature control system is used in the low temperature range, or low-temperature grouting agent plus electric heating bellows heating temperature control system is used.

[0016] S5. Pour grouting agent into the model specimen according to the determined maintenance strategy. Obtain the curve of the change of the surface temperature of the model specimen and the center temperature of the grouting agent under different voltages through experiments, and select the voltage value that stabilizes the center temperature of the grouting agent within the range set in S3.

[0017] S6: After the power module begins powering the entire system, it checks whether the center temperature of the grouting agent is within the upper and lower limits determined in S3. If so, it executes S7. If not, it returns to S5 to reconfirm the voltage value. If, after trying all available voltage values ​​in S5, it is still not within the upper and lower limits determined in S3, it returns to S4 to reconfirm the maintenance strategy, and then executes S5 and S6 in sequence. If, after trying all maintenance strategies in S4, it is still not within the upper and lower limits determined in S3, it returns to S1 to re-acquire the specifications of the heating wire, adjust the material, surface material, winding spacing and other specifications of the heating wire, and then execute S2-S6 in sequence. Returning to S5, S4, and S1 in sequence according to the situation can confirm the appropriate parameters in a minimum of steps, improving efficiency and reducing costs.

[0018] S7: Prepare a test block based on the prestressed beams of an actual bridge. Connect a heating module and a temperature detection module to the test block. Grout the test block according to a curing strategy confirmed in S4. After curing, core the test block and perform compression and flexural tests on the grouting agent core sample to determine whether the test results meet the requirements. If they do, execute S8. If they do not, return to S5 to reconfirm the voltage value and execute S6 and S7 in sequence. If the requirements are still not met after trying all available voltage values ​​in S5, return to S4 to reconfirm the curing strategy and execute S5-S7 in sequence. If the requirements are still not met after trying all curing strategies in S4, return to S1 to re-acquire the heating wire specifications, adjust the heating wire material, surface material, winding spacing, and other specifications, and then execute S2-S7 in sequence. Returning to S5, S4, and S1 in sequence as appropriate can confirm the appropriate parameters in a minimal number of steps, improving efficiency and reducing costs.

[0019] S8. After confirming that the requirements are met through S7, the heating wire specification parameters confirmed by S1, the maintenance strategy confirmed by S4, and the voltage value determined by S5 are put into practical use.

[0020] The present application also provides an electric bellows grouting agent curing temperature control calibration system, which can be integrated with a model specimen to implement an electric bellows grouting agent curing temperature control calibration method.

[0021] It includes a heating module, a temperature detection module, a temperature control module, and a power supply module.

[0022] Specifically, the heating module includes a corrugated tube, a heating wire wound on the corrugated tube, and a connection cable connected to the heating wire.

[0023] Specifically, the heating wire is a heating wire made of carbon fiber material.

[0024] Specifically, the temperature detection module includes a temperature control probe arranged on the bellows, which can be an infrared probe.

[0025] Specifically, the temperature control module includes a transformer connected to the heating module, a temperature controller connected to the transformer, and a control switch connected to the transformer.

[0026] Specifically, the power module is electrically connected to the temperature control module to provide power for the entire system.

[0027] Specifically, the temperature control module sets a temperature control range in the thermostat, and the temperature control probe transmits the measured temperature to the thermostat. When the measured temperature is lower than the set temperature range, the control switch automatically opens, and after the heating wire is energized, heat is transferred to the bellows, and the temperature inside the bellows gradually rises. When the measured temperature is higher than the set temperature range, the control switch is closed, the circuit is disconnected, the heating wire stops working and no longer generates heat, thereby ensuring that the temperature inside the tube is within the set temperature range.

[0028] Specifically, the heating wire skin material is any one of PVC skin material, Teflon skin material, and silicone skin material, and the specific material needs to be analyzed based on the ambient temperature and the beam structure.

[0029] Specifically, the heating wire is wound around the corrugated tube in a single spiral manner, with a winding pitch of d mm. The d value is selected based on the ambient temperature and the heat dissipation characteristics of the beam body. The d value can be determined based on cost reduction considerations.

[0030] Specifically, the voltage output by the power module is any one of 180V~380V, which needs to be determined based on site conditions (such as residential electricity or industrial electricity).

[0031] Specifically, the temperature detection module can detect a temperature range of -50°C to 50°C, which can meet the needs of most usage scenarios.

[0032] Specifically, the thermostat has a temperature control range of -55°C to 125°C, with an accuracy of ±0.1°C. The upper and lower thresholds are calibrated to X°C and Y°C, where X depends on the ambient temperature and the thickness of the protective layer, and Y depends on the minimum active temperature of the grouting agent used. The thermostat automatically adjusts the upper and lower thresholds based on the ambient temperature and the type of grouting agent.

[0033] Specifically, one end of the heating wire and one end of the cable are inserted into the same metal sleeve. The metal sleeve is filled with conductive adhesive, and the outside of the metal sleeve is covered with insulating wrapping material, which is then filled with insulating material. The metal sleeve is copper, the conductive adhesive is silver-filled conductive adhesive, the insulating wrapping material is double-layer heat shrink tubing (including an adhesive layer), and the insulating material is high-temperature resistant epoxy resin.

[0034] Specifically, the heating wire is made of carbon fiber. When the heating wire leaves the factory, in order to protect one end from being damaged, the end of the heating wire will be coated with epoxy resin for protection. When in use, it is necessary to remove the epoxy resin on the end and connect the cable to the heating wire. Align the surface of the heating wire end and the surface of the cable end after treatment, insert the copper sleeve and press the two ends of the sleeve with crimping pliers, then fill the sleeve with silver-filled conductive glue (the silver-filled conductive glue fills the cable gap in the sleeve, and the silver particles in the silver-filled conductive glue increase the conductivity between the two wires through the tunneling effect), put a double layer of heat shrink tubing (including glue layer) at the connection between the two wires, and encapsulate with high-temperature resistant epoxy resin to ensure waterproofness and insulation. The connection method is:

[0035] After stripping the heating wire, use high-grit sandpaper to polish the end of the heating wire until the surface is flat and smooth, remove the epoxy resin on the surface, and then soak the polished heating wire end in strong acid to remove any residual epoxy resin. After stripping the cable, scrape it down to the copper core, then use high-grit sandpaper to polish the cross-section of the cable end flat and smooth. Use sandpaper to grind a notch around the cable end. Closely align the surface of the heating wire end with the surface of the cable end. Insert the copper sleeve and press the ends of the sleeve tightly with crimping pliers. Then fill the sleeve with silver-filled conductive glue. The silver particles in the silver-filled conductive glue increase the conductivity between the two wires through the tunneling effect. Cover the connection between the two wires with a double layer of heat shrink tubing (including the glue layer) and pot it with high-temperature resistant epoxy resin to ensure waterproofing and insulation. Finally, perform a conductivity test.

[0036] Specifically, it also includes an analysis module, which is connected to the temperature control module and is used to calculate the temperature field and stress field of the beam under different ambient temperatures, and generate corresponding temperature control strategies based on this to achieve stable thermal insulation and temperature control effects.

[0037] The present application provides a method and system for curing temperature control calibration of an electric heating bellows grouting agent. The method determines appropriate heating wire specification parameters, curing strategy, and input voltage through model specimens and finite element modeling analysis, and then applies the same curing method to the construction of prestressed pipes in prestressed concrete bridges. The system for curing temperature control calibration of an electric heating bellows grouting agent includes a heating module, a temperature detection module, a temperature control module, and a power module. Compared with the existing technology, the dynamic and precise temperature control of the heating module and the temperature control module ensures that the slurry of prestressed pipes in bridges in cold areas is fully hydrated during the solidification process, improves the reliability of grouting quality, effectively prevents the slurry from freezing and expanding in low-temperature environments, and avoids structural cracking problems caused by frost heave. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0039] Figure 1 This is a step diagram of a method for temperature control calibration of an electric heating bellows grouting agent according to an embodiment of the present application;

[0040] Figure 2 This is a schematic diagram of a temperature control calibration system for curing a grouting agent using an electric heating bellows according to an embodiment of the present application;

[0041] Figure 3 This is a schematic diagram of the connection between the cable and the heating wire in an embodiment of the present application;

[0042] Figure 4 This is a diagram showing the temperature rise of heating wires with different outer skins at different powers according to an embodiment of the present application;

[0043] Figure 5 This is a temperature rise curve diagram of the center point E of the grouting agent in the embodiment of the present application;

[0044] Figure 6 This is a temperature rise curve diagram of point O on the outer surface of a concrete model specimen according to an embodiment of the present application;

[0045] Figure 7 It is the dimension drawing of simulated hollow slab beam;

[0046] Figure 8 This is a graph showing the center temperature of the bellows at different ambient temperatures according to an embodiment of the present application;

[0047] Figure 9 This is a diagram of the temperature rise of the specimen under different voltages in the embodiment of the present application.

[0048] 1. Heating module; 11. Bellows; 12. Heating wire; 13. Cable; 14. Copper casing; 15. Silver-filled conductive adhesive; 16. Double-layer heat shrink tubing; 17. High-temperature resistant epoxy resin; 2. Temperature detection module; 21. Temperature control probe; 3. Temperature control module; 31. Transformer; 32. Thermostat; 33. Control switch; 4. Power module; 41. Power supply. DETAILED DESCRIPTION

[0049] The following will clearly and completely describe the technical solutions in the embodiments of this application in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0050] It should be noted that when an element is referred to as being “fixed on” or “set on” another element, it can be directly on the other element or indirectly set on the other element; when an element is referred to as being “connected to” another element, it can be directly connected to the other element or indirectly connected to the other element.

[0051] It should be understood that the terms "length", "width", "up", "down", "front", "back", "first", "second", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as a limitation on the present application.

[0052] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or implicitly specify the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" or "several" means two or more, unless otherwise specifically defined.

[0053] It should be noted that the structures, proportions, sizes, etc. illustrated in the drawings of this specification are only used to match the contents disclosed in the specification for people familiar with this technology to understand and read, and are not used to limit the conditions under which this application can be implemented. Therefore, they have no substantive technical significance. Any structural modification, change in proportional relationship or adjustment of size should still fall within the scope of the technical content disclosed in this application without affecting the efficacy and purpose that can be achieved by this application.

[0054] like Figures 1 to 9 As shown, a method and system for curing temperature control of an electric bellows grouting agent provided in an embodiment of the present application are described in detail through specific embodiments and their application scenarios.

[0055] Figure 1 This is a step diagram of a method for curing temperature control of an electric heating corrugated pipe grouting agent, comprising the following steps:

[0056] S1. Determine the specification parameters of the heating wire 12 of the electric heating bellows 11, such as material, surface material, winding spacing, etc.

[0057] Specifically, the heating wire 12 is a heating wire 12 made of carbon fiber material. The surface, specifications and winding spacing of the heating wire 12 are determined. The bundle specification of the heating wire 12 is n K, and 1K means that 1000 carbon fiber filaments form a bundle, and the winding method is single helical.

[0058] S2. Prepare a model specimen according to the prestressed beam of an actual bridge, integrate the model specimen with the electric heating bellows grouting agent curing temperature control calibration system, and connect the heating module 1 and the temperature detection module 2 to the model specimen.

[0059] Specifically, the method for preparing the model specimen is to cut a section of the prestressed beam of the actual bridge to manufacture the model specimen, and connect the heating module 1 and the temperature detection module 2 into the model specimen. The temperature control module 3 can adjust the temperature of the heating module 1 according to the temperature detection result.

[0060] S3. Use finite element modeling to perform structural analysis on the model specimen. During the modeling process, the external ambient temperature T is loaded. The internal temperature t after heating by the heating module is analyzed through modeling calculation. The temperature difference between the inside and outside of the model specimen (Tt) is analyzed. The stress conditions inside the model specimen at different external temperatures and the temperature of the heating module 1 are analyzed to determine the upper limit of the calibration temperature of the thermostat 32. Then, the lowest curing temperature for complete hydration of the grouting agent inside the model specimen is taken as the lower limit of the calibration temperature of the thermostat 32.

[0061] Specifically, the upper temperature limit in S3 is the value at which the maximum principal tensile stress on the beam surface reaches the concrete tensile strength, and is determined by calculating whether the maximum principal tensile stress on the beam surface reaches the standard value of concrete tensile strength using a finite element model.

[0062] S4. Determine multiple fixed temperatures between the upper and lower temperature limits determined in S3, divide the ambient temperature into multiple temperature ranges based on the fixed temperatures, determine a different maintenance strategy for each temperature range, and determine one of the maintenance strategies based on the experimental environment.

[0063] Specifically, different maintenance strategies use different grouting agents. Two fixed temperatures i℃ and j℃ are determined according to the ambient temperature from high to low, and the ambient temperature is divided into three temperature ranges: high temperature (higher than i℃), medium temperature (j℃-i℃), and low temperature (lower than j℃). In terms of maintenance strategy, ordinary grouting agent is used in the high temperature range, ordinary grouting agent plus electric heating bellows heating temperature control system is used in the medium temperature range, or low-temperature grouting agent is used, ordinary grouting agent plus electric heating bellows heating temperature control system is used in the low temperature range, or low-temperature grouting agent plus electric heating bellows heating temperature control system is used.

[0064] S5. Pour grouting agent into the model specimen according to the determined maintenance strategy. Obtain the curve of the change of the surface temperature of the model specimen and the center temperature of the grouting agent under different voltages through experiments, and select the voltage value that stabilizes the center temperature of the grouting agent within the range set in S3.

[0065] S6. After the power module 4 starts to supply power to the entire system, it detects whether the center temperature of the grouting agent is within the upper and lower limits determined by S3. If so, execute S7; if not, return to S5 to reconfirm the voltage value; if after trying all available voltage values ​​in S5, it is still not within the upper and lower limits determined by S3, return to S4 to reconfirm the maintenance strategy, and execute S5 and S6 in sequence; if after trying all maintenance strategies in S4, it is still not within the upper and lower limits determined by S3, return to S1 to re-acquire the specification parameters of the heating wire 12, adjust the material, surface material, winding spacing and other specification parameters of the heating wire 12, and then execute S2-S6 in sequence.

[0066] S7. Prepare a test block according to the actual prestressed beam of the bridge, connect the heating module 1 and the temperature detection module 2 to the test block, and perform grouting and curing on the test block according to a curing strategy confirmed in S4. After curing, drill core samples of the test block and perform compression and flexural tests on the grouting agent core samples to determine whether the test results meet the requirements. If the requirements are met, execute S8; if the requirements are not met, return to S5 to reconfirm the voltage value, and execute S6 and S7 in sequence; if the requirements are still not met after trying all available voltage values ​​in S5, return to S4 to reconfirm the curing strategy, and execute S5-S7 in sequence; if the requirements are still not met after trying all curing strategies in S4, return to S1 to re-acquire the specifications of the heating wire 12, adjust the specifications of the heating wire 12 such as the material, surface material, winding spacing, etc., and then execute S2-S7 in sequence.

[0067] S8. Confirm through S7 that the requirements are met, and put the specification parameters of the heating wire 12 confirmed by S1, the maintenance strategy confirmed by S4, and the voltage value determined by S5 into actual use.

[0068] Figure 2This is a schematic diagram of the temperature control calibration system for curing grouting agents for electric heating corrugated pipes. The heating wire 12 is wound around a plastic corrugated pipe 11 for prestressed concrete bridges in a single spiral with a spacing of d mm (the distance is generally determined based on actual conditions), forming the heating module 1 of this system.

[0069] The temperature detection module 2 is an external temperature control probe 21 , which is used to detect the temperature of the slurry in the plastic bellows 11 .

[0070] The temperature controller 32 receives the temperature from the external temperature control probe 21. The temperature control range of the temperature controller 32 is -55°C to 125°C, and its temperature control accuracy is ±0.1°C. The upper limit threshold of the temperature control calibration is X°C, and the lower limit threshold is Y°C. X depends on the external temperature of the structure and the thickness of the structural protective layer, and Y depends on the minimum active temperature of the grouting agent used. Together with the adjustment of the control transformer 31 and the opening and closing of the control switch 33, they constitute the temperature control module 3 of the system.

[0071] The power module 4 is a power source and a cable 13, which provides electrical energy for the entire system.

[0072] Figure 3 This is a diagram showing the connection between the cable 13 and the heating wire 12. When the heating wire 12 leaves the factory, epoxy resin is applied to the end of the heating wire 12 to protect it from damage. When using it, you need to remove the epoxy resin from the end and connect the cable 13 to the heating wire 12. The connection method is as follows:

[0073] First, after peeling the heating wire 12, use high-grit sandpaper to polish the end of the heating wire 12 until the surface is flat and smooth to remove the epoxy resin on the surface. Then, soak the polished end of the heating wire 12 in strong acid to remove the residual epoxy resin.

[0074] After peeling the cable 13, scrape it down to the copper core, then use high-grit sandpaper to polish the cross-section of the cable 13 end to make it smooth and flat, use sandpaper to polish a notch around the cable 13 end, align the end surface of the heating wire 12 closely with the surface of the cable 13 end, insert the copper sleeve 14 and press the two ends of the sleeve with crimping pliers, then fill the sleeve with silver-filled conductive glue 15, and the silver-filled conductive glue 15 fills the notch of the cable 13 in the sleeve. The silver particles in the silver-filled conductive glue 15 increase the conductivity between the two wires through the tunneling effect. Put a double layer of heat shrink tubing 16 (including glue layer) at the connection between the two wires, and potting with high-temperature resistant epoxy resin 17 to ensure waterproofness and insulation. Finally, perform a conductivity test.

[0075] A method and system for curing temperature control of electric bellows grouting agent is described using a hollow slab beam with a standard span of 20m at an ambient temperature of -20℃.

[0076] 1. Structural description and external environment description: The external environment temperature is -20℃, the structural dimensions and cross-section are as follows: Figure 7shown.

[0077] 2. Determine the specifications of the heating wire 12 of the electric heating bellows 11 , specifically the surface, specifications, and winding spacing of the heating wire 12 .

[0078] A heating wire 12 made of carbon fiber with a common specification of 24K tow on the market is selected as the heating wire 12 of the heating module 1 .

[0079] 3. Manufacturing model specimens and integrating them with the temperature control calibration system for curing electric bellows grouting agents: (1) The experiment uses heating wires 12 with three specifications of outer skin, PVC, silicone, and Teflon, to conduct temperature rise comparison tests at different powers. The length of the heating wire 12 used in the experiment is 12.5m, the resistance is 17Ω / m, and the wire bundle is 24K. The laboratory temperature is 17.0℃. First, the heating wire 12 is suspended to avoid contact with other objects and reduce heat loss. The temperature sensor is fixed on the heating wire 12, and the temperature sensor reading is recorded every 30s. The test power is 15min long. The different powers in the test are changed by changing the test voltage. The current and power values ​​of the heating wire 12 with the same length at different voltages are shown in Table 1. The temperature rise test results of the heating wire 12 with different outer skins at room temperature are shown in Table 1. Figure 4 shown.

[0080] Table 1 Current and power values ​​of heating wires of the same length at different voltages

[0081]

[0082] Depend on Figure 4 It can be seen that as the heating time gets longer, the temperature of the heating wires 12 with different outer skins gets higher and higher, and finally the temperature of the heating wire 12 will be maintained at a stable state. Figure 4 From the figures a) b) and c) in the figure, it can be seen that the heat generated by the heating wire 12 with different skins is proportional to the input power. The greater the input power, the higher the temperature of the heating wire 12. Figure 4 Figure d) shows that when the three materials reach 30°C at the same power, PVC heating wire 12 takes the shortest time and also reaches a higher stable temperature than the other two materials. At -20°C, the hollow slab beam has thin walls, a large surface area, and convection of cold air in the cavity, resulting in faster heat dissipation. Therefore, a higher-heating heating wire 12 is required, and PVC-coated heating wire 12 should be selected as the calibration material for the heating temperature control system.

[0083] (2) Cast three groups of The empty tube calibration model specimen has an outer protective layer of concrete with a thickness of 60mm and is made of ordinary silicate cement. The corrugated pipe 11 adopts a prestressed bridge special plastic corrugated pipe 11 with a diameter of 60mm. The corrugated pipes 11 of the three groups of specimens are respectively wound with heating wires 12 with a spacing of 30mm, 60mm, and 90mm. The winding method is a single spiral. The specifications of the heating wire 12 are a resistance of 17Ω and a wire of 24K. The three groups of empty tube concrete specimens are placed in a -20℃ refrigerator (simulating the negative temperature in the high-altitude cold area). Except for the rectangular symmetrical surface, the model specimen is wrapped with polystyrene foam board on all sides to more realistically simulate the hollow slab beam. After standing for one day, when the temperature of the three groups of specimens reaches -20℃, grouting agent is poured into the corrugated pipe 11, and the temperature sensor is inserted into the middle of the corrugated pipe 11 to the grouting agent. The power of the heating wire 12 is turned on and the temperature of each point in the specimen is recorded. When the heating wire 12 is connected to a voltage of 220V, Figure 5 is the temperature rise curve of the grouting agent center, Figure 6 This is the temperature rise curve of the outer surface of the concrete specimen.

[0084] Depend on Figure 5 It can be seen that the temperature rise curve of the center point of the grouting agent goes through three stages: decline, rise, and flattening; when the 20°C temperature grouting agent enters the -20°C corrugated tube 11, the temperature of the grouting agent drops; when the temperature of the grouting agent drops to a certain extent, as the heating wire 12 heats up and the grouting agent hydrates and releases heat, the temperature of the grouting agent rises, and finally the temperature of the grouting agent gradually stabilizes. The center temperature of the grouting agent with a heating wire 12 winding spacing of 30mm is 3.2°C lower than the two groups with winding spacings of 60mm and 90mm. It is higher than -3°C with a spacing of 60mm and -5.7°C with a spacing of 90mm. Its stable temperature is 41.6°C, which is much higher than 11.5°C with a spacing of 60mm and 2.1°C with a spacing of 90mm. Figure 5 It can be seen that as the working time of the heating wire 12 increases, the outer surface temperature of the concrete model specimen will gradually rise and finally reach a steady state. The outer surface steady-state temperatures of the concrete model specimens with the heating wire 12 winding spacing of 30mm, 60mm, and 90mm are 33.3℃, ​​7.5℃, and -1.4℃, respectively.

[0085] The heating wire 12 with a winding spacing of 30mm generates significantly more heat than the other two in the same time. Under low temperature conditions of -20℃, the hollow slab beam has a thin wall, a large surface area, and cold air convection in the cavity, which results in faster heat dissipation. Therefore, a winding spacing with a larger heat output is required. Therefore, the electric bellows grouting agent curing temperature control calibration system calibrates the heating wire 12 with a winding spacing of 30mm.

[0086] 4. Determine the upper and lower limits of the temperature control of the thermostat 32: Use the finite element model to simulate and calculate the temperature field and stress field of the hollow slab beam under different power inputs of the heating wire 12, and infer the center temperature of the grouting agent when the surface stress of the beam is about to exceed the limit. This temperature is used as the upper temperature limit of the thermostat 32.

[0087] The dimensions of the hollow slab beams used in the experimental simulation are as follows: Figure 7 As shown, the exterior is made of C40-strength concrete, the internal grouting agent is made of C50-strength concrete, and the prestressed corrugated pipe 11 is made of high-density polyethylene (HDPE). For ease of calculation, the model of the hollow slab electric heating corrugated pipe 11 is simplified. The raised annular threads on the surface of the corrugated pipe 11 are not considered, and the corrugated pipe 11 is equivalent to a circular pipe with a diameter of 60 mm and a wall thickness of 3 mm. The influence of the steel strands within the pipe is ignored. Due to the symmetrical structure of the hollow slab beam, half of the actual hollow slab beam structure is used for the model calculation. Table 2 below shows the parameters of the hollow slab electric heating corrugated pipe 11.

[0088] Table 2 Material parameters.

[0089]

[0090] The comprehensive heat transfer coefficient in the finite element model is calculated using the following formula:

[0091]

[0092]

[0093]

[0094] is the comprehensive heat transfer coefficient, is the heat exchange coefficient between the bridge surface and the outside air, represents the radiation heat transfer coefficient of the bridge surface, is the average wind speed in a day, Indicates blackness, which is 0.94 in this embodiment. is the Stefan-Boltzmann constant, take , is the temperature of the beam surface, The absolute zero is -273°C. is the atmospheric temperature in °C.

[0095] The surface heat flux of the heating wire 12 in the temperature field boundary condition of the finite element model is calculated using the following formula:

[0096]

[0097] is the surface heat flux of the heating wire 12, in W / ㎡, is the power of the heating wire 12, in W / m; r is the radius of the heating wire 12, in m. The radius of the heating wire 12 in this model is 2.5 mm and the resistance is 17 Ω.

[0098] The boundary conditions of the modulus stress field of the finite element model are to apply fixed supports on the two rubber bases.

[0099] According to the specification JTG / T 3650-2020 "Technical Specifications for Highway Bridge and Culvert Construction", during the grouting process and within 48 hours after grouting, the temperature of the concrete of the structure or component and the ambient temperature shall not be lower than 5°C, otherwise insulation measures should be taken. According to the above specifications, for ordinary grouting agents, when the temperature in the pipeline is lower than 5°C, measures need to be taken to perform electric heating maintenance on the grouting agent. For low-temperature grouting agents, when the temperature in the pipeline is lower than -10°C, the grouting agent needs to be electrically cured. Due to the thermal insulation effect of concrete and the fluctuation of the external temperature of hollow slab beams, the internal temperature of the beam body has a certain lag compared to the external temperature of the beam body. The temperature in the pipeline is divided into three groups with 5°C, -5°C, and -10°C as the lower limit of fluctuations. The three groups are calculated to determine the three corresponding ambient temperatures. The results are as follows Figure 8 In the figure, A, B, and C refer to the ambient temperature, and T1 and T2 refer to the center point temperatures of the upper and lower bellows 11 in the model respectively.

[0100] according to Figure 8 It can be seen that the temperature inside the bellows 11 will increase with the increase of the external ambient temperature, but the internal temperature has a certain hysteresis. Figure 8 As shown in Figure a), when the external environment fluctuates in the range of -3.8℃ to 26.9℃, the temperature inside the bellows 11 fluctuates in the range of 5.2℃ to 16.9℃; when the external environment temperature fluctuates in the range of -14.6℃ to 18.0℃, the temperature inside the bellows 11 fluctuates in the range of -5.0℃ to 8.4℃; when the external environment temperature fluctuates in the range of -18.4℃ to 12.0℃, the temperature inside the bellows 11 fluctuates in the range of -10.0℃ to 2.5℃.

[0101] Materials are subject to thermal expansion and contraction. When the temperature rises, the material expands. When this expansion is restricted, temperature stress is generated. This temperature stress has a significant impact on the stability of the structure. A finite element model of the hollow slab beam was established. By assigning different temperatures to the corrugated tube 11, the maximum principal tensile stress on the hollow slab beam surface was calculated. This was compared with the allowable tensile stress of the material to ultimately determine the appropriate temperature for the heating wire 12. The stress calculation conditions are shown in Table 3.

[0102] Table 3 Stress calculation conditions

[0103]

[0104] Finite element model calculation simulation shows that the temperature around the bellows 11 is the highest.

[0105] Through the finite element model calculation simulation, it can be seen that the maximum principal tensile stress value on the outer wall of the beam appears in the concrete near the corrugated pipe 11. Due to the high temperature near the corrugated pipe 11, temperature stress is generated. The stress calculation results are shown in Table 4:

[0106] Table 4 Stress calculation results

[0107]

[0108] According to the concrete structure design specification, the standard value of the tensile strength of C50 concrete is 2.64 MPa. Therefore, when the carbon fiber heating wire 12 is used to heat and cure the grouting agent, the tensile stress on the beam surface should be lower than 2.64 MPa. Combined with the analysis in Table 4, it can be seen that when the ambient temperature is B (-14.6℃~18.0℃), the calibrated temperature upper limit of the temperature control module 3 is set at 30℃, and when the ambient temperature is C (-18.4℃~12.0℃), the calibrated temperature upper limit of the temperature control module 3 is set at 20℃.

[0109] The lower limit of the calibration temperature of the temperature control module 3 is the lowest temperature at which the grouting agent can be smoothly hydrated.

[0110] 5. Determine the maintenance strategy at different temperatures: Through the finite element analysis in the previous step, Figure 8 It can be seen that when the outside temperature is higher than -3.8°C, the temperature inside the bellows 11 is higher than +5.2°C; when the outside temperature is higher than -18.4°C, the temperature inside the bellows 11 is higher than -10°C. Since the curing temperature of ordinary grouting agents shall not be lower than 5°C, and the curing temperature of low-temperature grouting agents shall not be lower than -10°C, when ordinary grouting agents are used for curing, if the outside environment is lower than -3.8°C, the electric heating bellows grouting agent curing temperature control calibration system should be used for heating and curing; when low-temperature grouting agents are used for curing, if the outside environment is lower than -18.4°C, the electric heating bellows grouting agent curing temperature control calibration system should be used for heating and curing.

[0111] The ambient temperature is divided into three ranges: high temperature range (T≥-3.8℃) using ordinary grouting agent, medium temperature range (-3.8℃>T≥-18.4℃) using ordinary grouting agent plus electric heating bellows heating temperature control system, or low temperature grouting agent, low temperature range (<-18.4℃) using ordinary grouting agent plus electric heating bellows heating temperature control system, or low temperature grouting agent plus electric heating bellows heating temperature control system.

[0112] Therefore, under the external temperature condition of -20℃, the prestressed pipe of the 20m span hollow slab beam is maintained by using ordinary grouting agent plus electric heating bellows heating temperature control system, or low-temperature grouting agent plus electric heating bellows heating temperature control system.

[0113] 6. Determine the input voltage of the temperature control calibration system of the electric heating bellows 11 grouting agent.

[0114] 7. Determine whether the temperature rise range of the model specimen is within the upper and lower limits of temperature control.

[0115] 8. Check the feasibility of the system through flexural and compressive tests: 6 groups of Empty tube concrete test blocks, 6 groups of empty tube concrete test blocks are numbered 1 to 6, and after curing, they are placed in a freezer and cooled to -20℃ (simulating the negative temperature environment in high-altitude cold areas), and connected to the electric heating corrugated pipe grouting agent curing temperature control calibration system. Ordinary grouting agent is poured into the 1st to 3rd group of corrugated pipes 11, and each group is connected to 180, 220, and 300V voltage respectively. Low-temperature grouting agent is poured into the 4th to 6th group of corrugated pipes 11, and each group is connected to 180, 220, and 300V voltage respectively. After three days of curing, the cured grouting agent is taken out by the core drilling method. The core sample size is , conduct compression and flexural strength tests on the core samples to check whether the test results meet the specification requirements.

[0116] The specific test conditions are as follows:

[0117] Table 5 Test conditions

[0118]

[0119] Under 180V, 220V and 300V voltages, the temperature rise patterns of the surface temperature O of different specimens and the temperature rise patterns of the grouting agent center E are as follows: Figure 9 .

[0120] The compressive strength results and specification strength are shown in the following table:

[0121] Table 6 Compressive strength results and standard strength

[0122]

[0123] The flexural strength results and standard strength are shown in the following table:

[0124] Table 7 Flexural strength results and standard strength

[0125]

[0126] pass Figure 9It can be seen that when the voltage is 180V or 220V, regardless of whether the grouting agent is an ordinary grouting agent or a low-temperature grouting agent, the electric heating bellows grouting agent curing temperature control calibration system can control the grouting agent temperature within the set temperature range. When the voltage is 300V, due to the high voltage, the electric heating bellows grouting agent curing temperature control calibration system generates too much heat, and the grouting agent temperature is difficult to stably control below the set temperature of 20°C.

[0127] As shown in Table 6, under 180V electric heating curing, the 3d compressive strength of both the conventional grouting agent group and the low-temperature grouting agent group did not meet the specification requirement of ≥20MPa. Under 220V and 330V electric heating curing, the 3d compressive strength of both the conventional grouting agent group and the low-temperature grouting agent group met the specification requirement of ≥20MPa.

[0128] It can be seen from Table 7 that the 3d flexural strength of ordinary grouting agents with voltages of 180V, 220V, and 300V under electric heating curing meets the standard strength, but the 3d flexural strength of ordinary grouting agents and low-temperature grouting agents under electric heating curing at a voltage of 180V is significantly lower than the 3d flexural strength under standard curing. The 3d flexural strength of the low-temperature grouting agent with a voltage of 180V under electric heating curing does not meet the standard strength of greater than or equal to 5MPa.

[0129] Therefore, the calibration voltage of the electric bellows grouting agent curing temperature control calibration system is 220V, and the temperature rise of the specimen is within the upper and lower limits of the temperature control temperature. The experiment proves the feasibility of the electric bellows grouting agent curing temperature control calibration system.

[0130] The above description of the disclosed embodiments is intended to enable one skilled in the art to implement or use the present application. Various modifications to these embodiments will be readily apparent to one skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application is not limited to the embodiments shown herein, but is intended to conform to the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for calibrating the curing temperature of an electric heating bellows grouting agent, characterized in that: The steps include: S1, obtaining the specification parameters of the heating wire (12); S2, preparing a model specimen according to the prestressed beam of an actual bridge, and connecting a heating module (1) and a temperature detection module (2) into the model specimen; S3, obtaining the external environment temperature T, modeling and analyzing the internal temperature t of the heating module (1) after heating, calculating the temperature difference between T and t, modeling and analyzing the stress conditions inside the model specimen under different temperature differences to determine the upper limit of the calibration temperature of the temperature controller (32), and then taking the lowest curing temperature at which the grouting agent inside the model specimen is completely hydrated as the lower limit of the calibration temperature of the temperature controller (32), wherein the upper limit of the temperature is the value at which the maximum principal tensile stress on the surface of the model specimen reaches the tensile strength of concrete; S4. Determine the first temperature and the second temperature inside the model specimen between the upper and lower temperature limits determined in S3, calibrate the first temperature and the second temperature to obtain fixed temperatures i°C and j°C corresponding to the ambient temperature, and divide the ambient temperature into multiple temperature ranges based on the fixed temperatures, wherein the temperature range includes three temperature ranges: higher than i°C, j°C-i°C, and lower than j°C. Different curing strategies are determined for each temperature range, and one of the curing strategies is determined according to the experimental environment, wherein the curing strategies corresponding to each temperature range include: when the ambient temperature is higher than i°C, use a common grouting agent; when the ambient temperature is within the range of j°C-i°C, use a common grouting agent plus an electric heating bellows heating temperature control system, or use a low-temperature grouting agent; when the ambient temperature is lower than j°C, use a common grouting agent plus an electric heating bellows heating temperature control system, or use a low-temperature grouting agent plus an electric heating bellows heating temperature control system; S5. In accordance with the curing strategy determined in S4, a grouting agent is poured into the model specimen, and a curve of the surface temperature of the model specimen and the center temperature of the grouting agent at different voltages is obtained through experiments to confirm the voltage value that stabilizes the center temperature of the grouting agent within the range set in S3; S6. After power supply is started, the center temperature of the grouting agent is detected to see if it is within the upper and lower limits determined in S3. If so, S7 is executed. If not, the voltage value is returned to S5 to be reconfirmed. If the voltage value is still not within the upper and lower limits determined in S3 after adjustment in S5, the maintenance strategy is returned to S4 to be reconfirmed. If the voltage value is still not within the upper and lower limits determined in S3 after adjustment in S4, the maintenance strategy is returned to S1 to adjust the specification parameters of the heating wire and reconfirm the specification parameters. S7, prepare a test block according to the prestressed beam of an actual bridge, connect the heating module (1) and the temperature detection module (2) in the test block, perform grouting and curing on the test block according to a curing strategy confirmed in S4, drill core samples from the test block after curing, perform compression and flexural tests on the core samples, and judge whether the test results meet the requirements. If so, execute S8; if not, return to S5 to reconfirm the voltage value; if it still does not meet the requirements after returning to S5 for adjustment, return to S4 to reconfirm the curing strategy; if it still does not meet the requirements after returning to S4 for adjustment, return to S1 to adjust the specification parameters of the heating wire and reconfirm the specification parameters; S8. Put the various parameters and maintenance strategies determined in S1, S4, and S5 into practical use.

2. A method for calibrating the curing temperature of an electric heating bellows grouting agent according to claim 1, characterized in that: The specification parameters in S1 include surface material, specification size, and winding spacing.

3. The method for temperature control calibration of an electrothermal bellows grouting agent according to claim 1, characterized in that: In S6, the temperature control probe (21) transmits the detected temperature to the temperature controller (32). When the detected temperature is lower than the set temperature range, the control switch (33) is turned on. When the detected temperature is higher than the set temperature range, the control switch (33) is turned off.

4. A method for calibrating the curing temperature of an electric heating bellows grouting agent according to claim 1, characterized in that: The connection between the heating wire (12) and the heating module (1) comprises the following steps: Remove the protective materials from the ends of the heating wire (12) and the cables (13) in the heating module (1), and process the surfaces of the ends until they are flat and smooth; Grind a notch around each end of the cable (13), insert the end of the heating wire (12) and the surface of the end of the cable (13) into the metal sleeve and align them tightly; Pressing the two ends of the metal sleeve tightly, filling the metal sleeve with conductive glue so that the conductive glue fills the gap of the cable (13); An insulating wrapping material is provided outside the metal sleeve, and an insulating material is encapsulated inside the insulating wrapping material.

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