Electric heating corrugated pipe grouting agent health maintenance temperature control calibration method and system

Abstract

Compared with the prior art, the electric heating corrugated pipe grouting agent health maintenance temperature control calibration method and the electric heating corrugated pipe grouting agent health maintenance temperature control calibration system have the advantages that proper heating wire specification parameters, maintenance strategies and input voltage are determined through the model test piece and a finite element modeling analysis method; the same curing method is applied to prestressed concrete bridge prestressed pipeline construction. The electric heating corrugated pipe grouting agent curing temperature control calibration system comprises a heat supply module, a temperature detection module, a temperature control module and a power supply module. Compared with the prior art, through dynamic accurate temperature control of the heat supply module and the temperature control module, it is ensured that bridge prestressed pipeline slurry in the cold region is fully hydrated in the condensation process, the grouting quality reliability is improved, the slurry is effectively prevented from freezing and expanding in the low-temperature environment, and the problem of structural cracking caused by frost heaving is solved.

Description

Technical Field

[0001] This application relates to the technical field of prestressed concrete bridge prestressed duct construction, and specifically relates to a method and system for calibrating the temperature control of the curing of electrothermal corrugated pipe grouting agent. Background Art

[0002] In the existing construction of prestressed concrete bridges, the technical means for low-temperature grouting mainly rely on three types of 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, passive thermal insulation measures (such as covering thermal insulation materials and building temporary warm sheds). Although they can delay heat loss, in extremely low-temperature environments, the thermal insulation efficiency decays rapidly, and it is difficult to dynamically respond to external temperature fluctuations, and it is impossible to ensure that the grout continuously remains in the active temperature range. Third, active heating technologies (such as electric blanket curing and steam heating). When the external environment temperature is too low, their equipment generally has problems such as low temperature control accuracy and uneven temperature distribution, which are prone to cause thermal stress cracks in concrete. At the same time, due to the lack of systematic calibration matching the beam structure and environmental parameters, the heating strategy is out of touch with the actual working conditions. In addition, traditional heating devices are difficult to deploy in the construction of high-altitude long-span prestressed beams, and the problems of high installation complexity and high energy consumption further limit their engineering applicability.

[0003] In recent years, although there have been research attempts to introduce carbon fiber materials as heating elements to improve energy efficiency, their applications are mostly limited to the field of building heating, and an integrated temperature control solution for prestressed duct grouting has not been formed. In addition, the existing technology has insufficient quantitative research on the coupling relationship between the active temperature threshold of the grouting agent and the structural thermal stress, and it is difficult to avoid structural damage while ensuring the curing quality of the grout.

[0004] Therefore, there is an urgent need to develop a method and system for calibrating the temperature control of the curing of the grouting agent that can accurately control the temperature and is highly adaptable to the prestressed duct. By modeling and analyzing the coupling relationship between the active temperature threshold of the grouting agent and the structural thermal stress, the technical bottleneck of bridge construction in alpine regions can be broken through, and the problems in the existing technology such as the heating strategy being out of touch with the actual working conditions, resulting in insufficient hydration of the grout and prone to thermal stress cracks in concrete can be solved. Summary of the Invention

[0005] In order to overcome the problems existing in the prior art, this application provides a method and system for calibrating the temperature control of the curing of electrothermal corrugated pipe grouting agent, which can keep the whole process of the grout in the prestressed duct of bridges in cold regions warm and control the temperature, ensure sufficient hydration of the grout, improve the reliability of the grouting quality, and avoid the problem of co-existing cracking of the structure due to frost heave of the grout.

[0006] The technical solutions provided by this application are as follows: This application provides a method for calibrating the temperature control of the curing of electrothermal corrugated pipe grouting agent, including the following steps: S1. Determine the specification parameters of the heating wire of the electric heating corrugated pipe, such as the material of the heating wire, the material of the skin, the winding pitch, etc.

[0007] Specifically, the heating wire can be a heating wire containing carbon fiber material. Determine the skin, specification and winding pitch of the heating wire. The 12-strand specification of the heating wire is n K, where 1K means that 1000 carbon fiber filaments form 1 bundle, and the winding method is single helix.

[0008] S2. Prepare model specimens according to the prestressed beam of the actual bridge. Integrate the model specimens with the electric heating corrugated pipe grouting agent curing temperature control calibration system, and connect a heating module and a temperature detection module in the model specimens.

[0009] Specifically, the method for preparing the model specimens is to cut a section according to the prestressed beam of the actual bridge to manufacture the model specimens. A heating module and a temperature detection module are connected in the model specimens, and the temperature control module can adjust the temperature of the heating module according to the temperature detection results.

[0010] S3. Conduct structural analysis on the model specimens using finite element modeling. Load the external environmental temperature T during the modeling process, analyze the internal temperature t after heating by the heating module through modeling calculation, analyze the temperature difference (T - t) between the inside and outside of the model specimens, and determine the upper limit of the thermostat calibration temperature by analyzing the stress conditions inside the model specimens under different external temperatures and heating module temperatures. Then, take the lowest curing temperature at which the grouting agent inside the model specimens is completely hydrated as the lower limit of the thermostat calibration temperature.

[0011] Specifically, the upper temperature limit in S3 is the value at which the maximum principal tensile stress on the surface of the beam reaches the tensile strength of the concrete, which is determined by calculating whether the maximum principal tensile stress on the surface of the beam reaches the standard value of the tensile strength of the concrete through the finite element model.

[0012] S4. Determine multiple fixed temperatures between the upper and lower temperature limits determined in S3. Divide the environmental temperature into multiple temperature ranges according to the fixed temperatures, and determine different curing strategies for each temperature range. Determine one of the curing strategies according to the experimental environment.

[0013] Specifically, different curing strategies use different grouting agents. Determine two fixed temperatures i℃ and j℃ respectively according to the environmental temperature from high to low. Divide the environmental temperature into three temperature ranges: high temperature (higher than i℃), medium temperature (j℃ - i℃), and low temperature (lower than j℃). In terms of curing strategies, in the high temperature range, ordinary grouting agent is used; in the medium temperature range, ordinary grouting agent plus electric heating corrugated pipe heating temperature control system, or low temperature grouting agent is used; in the low temperature range, ordinary grouting agent plus electric heating corrugated pipe heating temperature control system, or low temperature grouting agent plus electric heating corrugated pipe heating temperature control system is used.

[0014] S5. Pour the grouting agent into the model specimen according to the determined curing strategy, obtain the curves of the surface temperature of the model specimen and the change of the center temperature of the grouting agent at different voltages through experiments, and select the voltage value that stabilizes the center temperature of the grouting agent within the range set in S3.

[0015] S6. After the power supply module starts to supply power to the entire system, detect whether the center temperature of the grouting agent is within the upper and lower limits determined in S3. If so, execute S7; if not within the upper and lower limits determined in S3, return to S5 to reconfirm the voltage value; if it is still not within the upper and lower limits determined in S3 after trying all available voltage values in S5, return to S4 to reconfirm the curing strategy, and execute S5 and S6 in sequence; if it is still not within the upper and lower limits determined in S3 after trying all curing strategies in S4, return to S1 to re-obtain the specification parameters of the heating wire, adjust the specification parameters such as the material of the heating wire, the skin material, and the winding pitch, and then execute S2 - S6 in sequence. Returning to S5, S4, and S1 according to the situation can confirm the appropriate parameters with the fewest steps, improve efficiency, and reduce costs.

[0016] S7. Prepare test blocks according to the prestressed beams of the actual bridge, connect the heating module and the temperature detection module in the test blocks, perform grouting curing on the test blocks according to a curing strategy confirmed in S4, drill core samples from the test blocks after curing, and conduct compressive and flexural tests on the extracted grouting agent core samples to determine whether the test results meet the requirements. If they meet the requirements, execute S8; if they do not meet the requirements, return to S5 to reconfirm the voltage value, and execute S6 and S7 in sequence; if it is still not satisfied after trying all available voltage values in S5, return to S4 to reconfirm the curing strategy, and execute S5 - S7 in sequence; if it is still not satisfied after trying all curing strategies in S4, return to S1 to re-obtain the specification parameters of the heating wire, adjust the specification parameters such as the material of the heating wire, the skin material, and the winding pitch, and then execute S2 - S7 in sequence. Returning to S5, S4, and S1 according to the situation can confirm the appropriate parameters with the fewest steps, improve efficiency, and reduce costs.

[0017] S8. After confirming that it meets the requirements through S7, put the specification parameters of the heating wire confirmed in S1, the curing strategy confirmed in S4, and the voltage value determined in S5 into actual use.

[0018] This application also provides an electrothermal corrugated pipe grouting agent curing temperature control calibration system, which can be integrated with the model specimen to implement an electrothermal corrugated pipe grouting agent curing temperature control calibration method.

[0019] It includes a heating module, a temperature detection module, a temperature control module, and a power supply module.

[0020] Specifically, the heating module includes a corrugated pipe, a heating wire wound around the corrugated pipe, and a wiring cable connected to the heating wire.

[0021] Specifically, the heating wire is a heating wire made of carbon fiber material.

[0022] Specifically, the temperature detection module includes a temperature control probe set on the corrugated pipe, and an infrared probe can be used.

[0023] Specifically, the temperature control module includes a transformer connected to the heating module, a thermostat connected to the transformer, and a control switch connected to the transformer.

[0024] Specifically, the power supply module is electrically connected to the temperature control module to provide power for the entire system.

[0025] Specifically, the temperature control module sets a temperature control range in the thermostat. The temperature measured by the temperature control probe is transmitted to the thermostat. When the measured temperature is lower than the set temperature range, the control switch automatically turns on. After the heating wire is powered on, heat is transmitted into the corrugated pipe, and the temperature inside the corrugated pipe gradually rises. When the measured temperature is higher than the set temperature range, the control switch turns off, the circuit is disconnected, and the heating wire stops working and no longer generates heat, ensuring that the temperature inside the pipe is within the set temperature range.

[0026] Specifically, the skin material of the heating wire is any one of PVC outer skin material, Teflon outer skin material, and silicone outer skin material, and it specifically needs to be analyzed according to the ambient temperature and the beam structure.

[0027] Specifically, the way the heating wire is wound around the corrugated pipe is single - spiral winding, and its winding pitch is d mm. The value of d is specifically selected according to the ambient temperature and the heat dissipation characteristics of the beam body. The determination of the value of d can be considered from the perspective of cost reduction.

[0028] Specifically, the voltage output by the power supply module is any one of 180V - 380V, and it needs to be determined from the on - site conditions (such as civil electricity or industrial electricity).

[0029] Specifically, the temperature range that the temperature detection module can detect is - 50°C to 50°C, which can meet the vast majority of usage scenarios.

[0030] Specifically, the temperature control range of the thermostat is - 55°C to 125°C, the temperature control accuracy is within ±0.1°C, the upper threshold value calibrated by the thermostat is X°C, and the lower threshold value is Y°C. X depends on the external temperature of the structure and the thickness of the structure protection layer, and Y depends on the lowest activation temperature of the grouting agent used. The thermostat supports automatically adjusting the upper and lower threshold values according to the ambient temperature and the type of grouting agent.

[0031] 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 an insulating wrapping material is sleeved outside the metal sleeve. The insulating wrapping material is filled with insulating material. The metal sleeve is a copper sleeve, the conductive adhesive is silver-filled conductive adhesive, the insulating wrapping material is a double-layer heat shrinkable tube (with a glue layer), and the insulating material is high-temperature resistant epoxy resin.

[0032] Specifically, the heating wire is a heating wire made of carbon fiber material. Since the heating wire is protected at one end with epoxy resin when leaving the factory to prevent damage, the epoxy resin at the end of the heating wire needs to be removed during use and the cable needs to be connected to the heating wire. After the surfaces of the heating wire end and the cable end are processed, they are closely aligned, inserted into the copper sleeve, and the two ends of the sleeve are clamped tightly with a crimping pliers. Then, the sleeve is filled with silver-filled conductive adhesive (the silver-filled conductive adhesive fills the cable gap in the sleeve, and the silver particles in the silver-filled conductive adhesive increase the conductivity between the two wires through the tunneling effect). A double-layer heat shrinkable tube (with a glue layer) is sleeved at the connection of the two wires, and high-temperature resistant epoxy resin is potted to ensure waterproof and insulation. The connection method is as follows: After peeling the heating wire, use high-grit sandpaper to polish the end of the heating wire until the surface is flat and smooth, removing the surface epoxy resin. Then, soak the polished end of the heating wire in strong acid to remove the remaining epoxy resin. After peeling the cable to expose the copper core, use high-grit sandpaper to polish the cross-section of the cable end until it is flat and smooth, and use sandpaper to grind out a notch around the cable end. Closely align the surface of the heating wire end with the surface of the cable end, insert it into the copper sleeve, and clamp the two ends of the sleeve tightly with a crimping pliers. Then, fill the sleeve with silver-filled conductive adhesive (the silver-filled conductive adhesive fills the cable gap in the sleeve, and the silver particles in the silver-filled conductive adhesive increase the conductivity between the two wires through the tunneling effect). A double-layer heat shrinkable tube (with a glue layer) is sleeved at the connection of the two wires, and high-temperature resistant epoxy resin is potted to ensure waterproof and insulation. Finally, conduct a conductivity test.

[0033] Specifically, it further includes an analysis module. The analysis module is connected to the temperature control module and is used to calculate the beam temperature field and stress field at different ambient temperatures, and generate corresponding temperature control strategies accordingly to achieve a stable heat preservation and temperature control effect.

[0034] A method and system for curing temperature control calibration of an electrothermal corrugated pipe grouting agent provided by the present application determine appropriate heating wire specification parameters, curing strategies, and input voltages through model specimens and finite element modeling analysis, and then implement the same curing method in the construction of prestressed concrete bridge prestressed ducts. The system for curing temperature control calibration of the electrothermal corrugated pipe grouting agent includes a heating module, a temperature detection module, a temperature control module, and a power supply module. Compared with the prior art, through the dynamic and precise temperature control of the heating module and the temperature control module, it is ensured that the grout in the prestressed ducts of bridges in cold regions is fully hydrated during the setting process, the reliability of the grouting quality is improved, the grout is effectively prevented from freezing and expanding in a low-temperature environment, and the structural cracking problem caused by frost heaving is avoided. Description of the Drawings

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0036] Figure 1 It is a flowchart of the steps of the method for curing temperature control calibration of the electrothermal corrugated pipe grouting agent in the embodiment of the present application; Figure 2 It is a schematic diagram of the system for curing temperature control calibration of the electrothermal corrugated pipe grouting agent in the embodiment of the present application; Figure 3 It is a schematic diagram of the connection between the cable and the heating wire in the embodiment of the present application; Figure 4 It is a graph of the temperature rise law of different outer-skin heating wires at different powers in the embodiment of the present application; Figure 5 It is a temperature rise curve graph of the center point E of the grouting agent in the embodiment of the present application; Figure 6 It is a temperature rise curve graph of the outer surface point O of the concrete model specimen in the embodiment of the present application; Figure 7 It is a simulated hollow slab beam size diagram; Figure 8 It is a graph of the center temperature value of the corrugated pipe under different ambient temperatures in the embodiment of the present application; Figure 9 It is a graph of the temperature rise law of the specimen under different voltages in the embodiment of the present application.

[0037] 1. Heating module; 11. Bellows; 12. Heating wire; 13. Cable; 14. Copper sleeve; 15. Silver-filled conductive adhesive; 16. Double-layer heat shrinkable tube; 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 supply module; 41. Power supply. Detailed implementation manners

[0038] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Apparently, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0039] It should be noted that when an element is referred to as being "fixed to" or "disposed on" another element, it can be directly on the other element or indirectly disposed 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.

[0040] It should be understood that the orientation or positional relationship indicated by the terms "length", "width", "upper", "lower", "front", "rear", "first", "second", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus cannot be understood as a limitation to the present application.

[0041] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present application, the meaning of "a plurality" and "several" is two or more, unless otherwise specifically defined.

[0042] It should be noted that the structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those who are familiar with this technology to understand and read, and are not used to limit the limiting conditions for the implementation of the present application. Therefore, they do not have technical substance. Any modification of the structure, change of the proportional relationship or adjustment of the size, without affecting the effects that the present application can produce and the purposes that can be achieved, should still fall within the scope that the technical content disclosed in the present application can cover.

[0043] Such as Figures 1 to 9As shown, a method and system for curing temperature control of an electrothermal corrugated pipe grouting agent provided by an embodiment of the present application are described in detail through specific embodiments and their application scenarios.

[0044] Figure 1 It is a flowchart of the steps of a method for curing temperature control of an electrothermal corrugated pipe grouting agent, including the following steps: S1. Determine the specification parameters of the heating wire 12 of the electrothermal corrugated pipe 11, such as material, skin material, winding pitch, etc.

[0045] Specifically, the heating wire 12 is specifically a heating wire 12 containing carbon fiber material. Determine the skin, specification and winding pitch of the heating wire 12. The wire bundle specification of the heating wire 12 is n K, where 1K means that 1000 carbon fiber filaments form 1 bundle, and the winding method is single helix.

[0046] S2. Prepare model specimens according to the prestressed beams of the actual bridge, integrate the model specimens with the electrothermal corrugated pipe grouting agent curing temperature control calibration system, and connect a heating module 1 and a temperature detection module 2 into the model specimens.

[0047] Specifically, the method for preparing the model specimens is to cut a section according to the prestressed beam of the actual bridge to manufacture the model specimens. A heating module 1 and a temperature detection module 2 are connected into the model specimens, and the temperature control module 3 can adjust the temperature of the heating module 1 according to the temperature detection result.

[0048] S3. Conduct a structural analysis on the model specimens using finite element modeling. During the modeling process, load the external environmental temperature T, calculate and analyze the internal temperature t after heating by the heating module through modeling, analyze the temperature difference (T - t) between the inside and outside of the model specimens, and determine the upper limit of the calibration temperature of the thermostat 32 by analyzing the stress conditions inside the model specimens at different external temperatures and temperatures of the heating module 1. Then, take the lowest curing temperature at which the grouting agent inside the model specimens is completely hydrated as the lower limit of the calibration temperature of the thermostat 32.

[0049] Specifically, the upper temperature limit in S3 is the value at which the maximum principal tensile stress on the beam surface reaches the tensile strength of concrete, which is determined by calculating whether the maximum principal tensile stress on the beam surface reaches the standard value of the tensile strength of concrete through the finite element model.

[0050] S4. Determine multiple fixed temperatures between the upper and lower temperature limits determined in S3, divide the environmental temperature into multiple temperature ranges according to the fixed temperatures, determine different curing strategies for each temperature range, and determine one of the curing strategies according to the experimental environment.

[0051] Specifically, different curing strategies use different grouting agents. Two fixed temperatures, i°C and j°C, are determined according to the environmental temperature from high to low. The environmental temperature is divided into three temperature ranges: high temperature (above i°C), medium temperature (j°C - i°C), and low temperature (below j°C). In terms of curing strategies, in the high-temperature range, ordinary grouting agent is used; in the medium-temperature range, ordinary grouting agent plus an electric heating corrugated pipe temperature control system is used, or low-temperature grouting agent is used; in the low-temperature range, ordinary grouting agent plus an electric heating corrugated pipe temperature control system is used, or low-temperature grouting agent plus an electric heating corrugated pipe temperature control system is used.

[0052] S5. Pour the grouting agent into the model specimen according to the determined curing strategy, and obtain the curves of the surface temperature of the model specimen and the change of the center temperature of the grouting agent at different voltages through experiments, and select the voltage value that makes the center temperature of the grouting agent stable within the range set in S3.

[0053] S6. After the power supply module 4 starts to supply power to the entire system, detect whether the center temperature of the grouting agent is within the upper and lower limits determined in S3. If so, execute S7; if not within the upper and lower limits determined in S3, 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 in S3, then return to S4 to reconfirm the curing strategy, and execute S5 and S6 in sequence; if after trying all curing strategies in S4, it is still not within the upper and lower limits determined in S3, then return to S1 to re-obtain the specification parameters of the heating wire 12, adjust the specification parameters such as the material of the heating wire 12, the skin material, and the winding pitch, and then execute S2 - S6 in sequence.

[0054] S7. Prepare test blocks according to the prestressed beams of the actual bridge, connect the heating module 1 and the temperature detection module 2 into the test blocks, and perform grouting and curing on the test blocks according to a curing strategy confirmed in S4. After the curing is completed, take core samples from the test blocks, and conduct compressive and flexural tests on the taken grouting agent core samples to determine whether the test results meet the requirements. If they meet the requirements, execute S8; if they do not meet the requirements, return to S5 to reconfirm the voltage value, and execute S6 and S7 in sequence; if after trying all available voltage values in S5, it still does not meet the requirements, then return to S4 to reconfirm the curing strategy, and execute S5 - S7 in sequence; if after trying all curing strategies in S4, it still does not meet the requirements, then return to S1 to re-obtain the specification parameters of the heating wire 12, adjust the specification parameters such as the material of the heating wire 12, the skin material, and the winding pitch, and then execute S2 - S7 in sequence.

[0055] S8. After confirming that it meets the requirements through S7, put the specification parameters of the heating wire 12 confirmed in S1, the curing strategy confirmed in S4, and the voltage value determined in S5 into actual use.

[0056] 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 the plastic corrugated pipe 11 for prestressed concrete bridges in a single spiral form with a spacing of d mm (the distance is determined according to the specific actual situation), forming a heating module 1 of this system.

[0057] 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 corrugated pipe 11 .

[0058] The temperature controller 32 receives the temperature transmitted by the external temperature control probe 21. The temperature control range of the temperature controller 32 is -55°C~125°C, and the 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 switch of the control switch 33, the temperature control module 3 of the system is composed.

[0059] The power module 4 is a power source and a cable 13, which provides electrical energy for the entire system.

[0060] Figure 3 The figure is a schematic diagram of the connection between the cable 13 and the heating wire 12. When the heating wire 12 leaves the factory, in order to protect one end from being damaged, the end of the heating wire 12 is coated with epoxy resin for protection. When using, it is necessary to remove the epoxy resin on the end and connect the cable 13 to the heating wire 12. The connection method is as follows: First, the heating wire 12 is peeled and then the end of the heating wire 12 is polished with high-grit sandpaper until the surface is flat and smooth to remove the epoxy resin on the surface. Then, the polished end of the heating wire 12 is soaked in a strong acid to remove the residual epoxy resin.

[0061] After the cable 13 is peeled, it is scraped to the copper core, and then the cross-section of the end of the cable 13 is polished flat and smooth with high-grit sandpaper, and a notch is polished around the end of the cable 13 with sandpaper, and the end surface of the heating wire 12 is closely aligned with the surface of the end of the cable 13, and the copper sleeve 14 is inserted and the two ends of the sleeve are pressed tightly with crimping pliers, and then the sleeve is filled with silver-filled conductive glue 15, and the silver-filled conductive glue 15 fills the gap 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, and a double-layer heat shrink tube 16 (including glue layer) is put on the connection between the two wires, and high-temperature resistant epoxy resin 17 is poured to ensure waterproof and insulation, and finally a conductivity test is performed.

[0062] A method and system for curing temperature control of electric heating corrugated pipe grouting agent is described using a hollow slab beam with a standard span of 20m at an ambient temperature of -20℃.

[0063] 1. Structural description and external environment description: The external environment temperature is -20℃, the structural dimensions and structural cross-section are as follows: Figure 7 shown.

[0064] 2. Determine the specification parameters of the heating wire 12 of the electric heating corrugated pipe 11, specifically the skin, specification, and winding pitch of the heating wire 12.

[0065] Select a heating wire 12 made of carbon fiber material with a common specification of 24K in the market as the heating wire 12 of the heating module 1.

[0066] 3. Integrate the manufacturing of model specimens with the curing temperature control calibration system for the electric heating corrugated pipe grouting agent: (1) In the experiment, heating wires 12 with three specifications of PVC, silicone, and Teflon on the outer skin are used to conduct temperature rise comparison tests at different powers. The length of the heating wire 12 selected for the test is 12.5 m, the resistance is 17 Ω / m, and the wire bundle is 24K. The laboratory temperature is 17.0 °C. First, suspend the heating wire 12 to avoid contact with other objects and reduce heat loss. Fix the temperature sensor on the heating wire 12 and record the readings of the temperature sensor every 30 s. The power-on duration of the test is 15 min. 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 test results of the heating wires 12 with different outer skins for heating and temperature rise at normal temperature are as Figure 4 shown.

[0067] Table 1 Current and power values of heating wires with the same length at different voltages

[0068] As Figure 4 can be seen, as the heating time gets longer and longer, the temperature of the heating wire 12 with different outer skins gets higher and higher, and finally the temperature of the heating wire 12 will maintain a stable state. From Figure Four Figures a), b), and c) in it, it can be obtained that the heat generation of the heating wire 12 with different outer skins is proportional to the input power. The greater the input power, the higher the temperature of the heating wire 12. From Figure Four Figure d) in it, it can be seen that when the three materials reach 30 °C under the same power, the PVC heating wire 12 takes the shortest time, and at the same time, the final stable temperature of the PVC heating wire 12 is also higher than the other two. Under the low-temperature condition of -20 °C, the wall of the hollow slab beam is thin, the surface area is large, and the cold air in the cavity convects, resulting in fast heat dissipation. Therefore, a heating wire 12 with a greater heat generation is required, and the PVC outer skin heating wire 12 should be selected as the material for the heating temperature control system calibration heating wire 12.

[0069] (2) Pour 3 groups in the laboratory with dimensions of Air traffic control calibration model specimens, with the concrete thickness of the external protective layer of the specimens being 60 mm, are made of ordinary Portland cement. The corrugated pipe 11 uses a special plastic corrugated pipe for prestressed bridges with a diameter of 60 mm. The heating wires 12 with pitches of 30 mm, 60 mm, and 90 mm are respectively wound around the outside of the corrugated pipes 11 of the 3 groups of specimens. The winding method is single helix. The specifications of the heating wires 12 are a resistance of 17 Ω and a wire of 24K. The three groups of air-filled concrete specimens are placed in a -20°C refrigerator (simulating negative temperatures in alpine regions). Except for the rectangular symmetry plane, the specimens are wrapped with polystyrene foam boards around to more realistically simulate the hollow slab beam. After standing for one day, when the temperatures of the three groups of specimens reach -20°C, grouting agent is poured into the corrugated pipe 11, and a temperature sensor is inserted into the middle of the corrugated pipe 11 into the grouting agent. The power supply of the heating wire 12 is connected and the temperatures at various points in the specimens are recorded. When the voltage connected to the heating wire 12 is 220V, Figure 5 It is the temperature rise curve graph of the center of the grouting agent, Figure 6 It is the temperature rise curve graph of the outer surface of the concrete specimen.

[0070] It can be seen from Figure 5 that the temperature rise curve of the center point of the grouting agent experiences three stages: decline, rise, and flat. When the grouting agent at 20°C enters the -20°C corrugated pipe 11, the temperature of the grouting agent drops. When the temperature of the grouting agent drops to a certain extent, with the heating of the heating wire 12 and the heat release of the hydration of the grouting agent, 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 the heating wire 12 wound at a pitch of 30 mm is 3.2°C, which is higher than -3°C of the 60 mm pitch and -5.7°C of the 90 mm pitch compared with the two groups with pitches of 60 mm and 90 mm. Its stable temperature is 41.6°C, which is much higher than 11.5°C of the 60 mm pitch and 2.1°C of the 90 mm pitch. It can be seen from Figure 5 that as the working time of the heating wire 12 increases, the temperature of the outer surface of the concrete model specimen will gradually rise and finally reach a steady state. The steady-state temperatures of the outer surfaces of the concrete model specimens with the heating wire 12 wound at pitches of 30 mm, 60 mm, and 90 mm are 33.3°C, 7.5°C, and -1.4°C respectively.

[0071] The heat generation of the heating wire 12 wound at a pitch of 30 mm is significantly greater than the other two within the same time. Under the low temperature condition of -20°C, the wall of the hollow slab beam is thin, the surface area is large, and the cold air in the cavity convects, resulting in fast heat dissipation. Therefore, a larger pitch with greater heat generation is required. Therefore, the heating wire 12 of the electrothermal corrugated pipe grouting agent curing temperature control calibration system is wound at a pitch of 30 mm.

[0072] 4. Determine the upper and lower temperature limits controlled by the thermostat 32: By simulating and calculating the temperature field and stress field of the hollow slab beam under different power inputs of the heating wire 12 through a finite element model, the central temperature of the grouting agent when the surface stress of the beam is about to exceed the limit is deduced, and this temperature is used as the upper temperature limit value of the thermostat 32.

[0073] The size of the hollow slab beam simulated in the experiment is as Figure 7 shown. The external part uses concrete with a strength of C40, the grouting agent in the pipe uses concrete with a strength of C50, and the prestressed corrugated pipe 11 uses HDPE high-density polyethylene material. For the convenience of calculation, the hollow slab electrothermal corrugated pipe 11 model is reasonably 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 strand in the pipe is ignored. Since the hollow slab beam is a symmetric structure, 1 / 2 of the actual structure of the hollow slab beam is used for model calculation. Table 2 below shows the parameters of the hollow slab beam electrothermal corrugated pipe 11.

[0074] Table 2 Material parameters.

[0075]

[0076] The comprehensive heat transfer coefficient in the finite element model is calculated using the following formula:

[0077]

[0078]

[0079] 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 during the day, represents the emissivity. In this embodiment, it is taken as 0.94, is the Stefan-Boltzmann constant, taken as , is the temperature of the beam surface, is the absolute zero temperature, with a value of -273 °C, is the atmospheric temperature, in °C.

[0080] The surface heat flux of the heating wire 12 in the temperature field boundary condition of this finite element model is calculated using the following formula:

[0081] is the surface heat flux of the heating wire 12, in W / ㎡, is the power of the heating wire 12, with the unit of W / m; r is the radius of the heating wire 12, with the unit of m. The radius of the heating wire 12 in this model is 2.5 mm and the resistance is 17 Ω.

[0082] The boundary condition of the stress field of the finite element model is to apply fixed supports to the two rubber bases.

[0083] According to the requirements of the specification JTG / T 3650—2020 "Technical Specification for Construction of Highway Bridges and Culverts": 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 heat preservation measures shall be taken. According to the above specification, for ordinary grouting agents, when the temperature in the pipeline is lower than 5 °C, measures need to be taken to electrically heat-cure 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 heat-cured. Due to the heat preservation effect of the concrete of the hollow slab beam and the volatility of the external temperature, the temperature inside the beam body has a certain lag compared to the temperature outside the beam body. The temperature in the pipeline is divided into three groups with lower limit values of 5 °C, -5 °C, and -10 °C for fluctuation, and the three groups are calculated to determine three corresponding ambient temperatures. The results are as follows Figure 8 , where A, B, and C in the figure refer to the ambient temperature, and T1 and T2 respectively refer to the temperatures at the center points of the upper and lower corrugated pipes 11 in the model.

[0084] According to Figure 8 it can be known that the temperature inside the corrugated pipe 11 will increase with the increase of the external ambient temperature, but there is a certain lag in the internal temperature. As can be seen from Figure 8 Figure a) of, when the external environment fluctuates within the range of -3.8 °C to 26.9 °C, the temperature inside the corrugated pipe 11 fluctuates within the range of 5.2 °C to 16.9 °C; when the external ambient temperature fluctuates within the range of -14.6 °C to 18.0 °C, the temperature inside the corrugated pipe 11 fluctuates within the range of -5.0 °C to 8.4 °C; when the external ambient temperature fluctuates within the range of -18.4 °C to 12.0 °C, the temperature inside the corrugated pipe 11 fluctuates within the range of -10.0 °C to 2.5 °C.

[0085] Materials will be affected by thermal expansion and contraction. When the temperature rises, the materials will expand. When the expansion is restricted, temperature stress will be generated, which will have a great impact on the stability of the structure. A finite element model of the hollow slab beam is established. By assigning different temperatures to the corrugated pipe 11, and then calculating the maximum principal tensile stress value on the surface of the hollow slab beam and comparing it with the allowable tensile stress value of the material, the appropriate temperature of the heating wire 12 is finally determined. The stress calculation conditions are as shown in Table 3 below.

[0086] Table 3 Stress calculation condition table

[0087] It can be known from the calculation and simulation of the finite element model that the temperature around the corrugated pipe 11 is the highest.

[0088] It can be known from the calculation and simulation of the finite element model 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 around the corrugated pipe 11, temperature stress is generated. The stress calculation results are shown in Table 4 below: Table 4 Results of stress calculation conditions

[0089] According to the concrete structure design code, the standard value of the tensile strength of C50 concrete is 2.64 MPa. Therefore, when heating and curing the grouting agent with the heating wire 12 made of carbon fiber material, the tensile stress on the beam surface should be lower than 2.64 MPa. Combining the analysis of Table 4, it can be seen that when the ambient temperature is B (-14.6°C to 18.0°C), the upper limit of the calibrated temperature of the temperature control module 3 is set at 30°C, and when the ambient temperature is C (-18.4°C to 12.0°C), the upper limit of the calibrated temperature of the temperature control module 3 is set at 20°C.

[0090] The lower limit of the calibrated temperature of the temperature control module 3 is the lowest temperature for the smooth hydration of the grouting agent.

[0091] 5. Determine the curing strategies at different temperatures: Through the finite element analysis and trial calculation in the previous step, it can be known from Figure 8 that when the outside temperature is higher than -3.8°C, the temperature inside the corrugated pipe 11 is higher than +5.2°C; when the outside temperature is higher than -18.4°C, the temperature inside the corrugated pipe 11 is higher than -10°C. Since the ordinary grouting agent cannot be cured below 5°C and the curing temperature of the low-temperature grouting agent cannot be lower than -10°C. When using the ordinary grouting agent for curing, when the outside environment is lower than -3.8°C, the electrothermal corrugated pipe grouting agent curing temperature control calibration system should be used for heating and curing; when using the low-temperature grouting agent for curing, when the outside environment is lower than -18.4°C, the electrothermal corrugated pipe grouting agent curing temperature control calibration system should be used for heating and curing.

[0092] The ambient temperature is divided into 3 ranges, namely the high-temperature range (T≥-3.8°C) using the ordinary grouting agent, the medium-temperature range (-3.8°C>T≥-18.4°C) using the ordinary grouting agent plus the electrothermal corrugated pipe heating temperature control system, or using the low-temperature grouting agent, and the low-temperature range (<-18.4°C) using the ordinary grouting agent plus the electrothermal corrugated pipe heating temperature control system, or using the low-temperature grouting agent plus the electrothermal corrugated pipe heating temperature control system.

[0093] Therefore, under the condition of an outside temperature of -20°C, the prestressed pipeline of the 20m-span hollow slab beam is cured using the ordinary grouting agent plus the electrothermal corrugated pipe heating temperature control system, or using the low-temperature grouting agent plus the electrothermal corrugated pipe heating temperature control system.

[0094] 6. Determine the input voltage of the temperature control calibration system of the electric heating bellows 11 grouting agent.

[0095] 7. Determine whether the temperature rise range of the model specimen is within the upper and lower limits of temperature control.

[0096] 8. Check the feasibility of the system through flexural and compression tests: pour 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 to cool to -20°C (simulating the negative temperature environment in high-cold areas), and connected to the electric heating bellows grouting agent curing temperature control calibration system. Ordinary grouting agent is filled into 1 to 3 groups of bellows 11, and each group is connected to 180, 220, and 300V voltages respectively. Low-temperature grouting agent is filled into 4 to 6 groups of bellows 11, and each group is connected to 180, 220, and 300V voltages respectively. After three days of curing, the cured grouting agent is taken out by the core drilling method and 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.

[0097] The specific test conditions are as follows: Table 5 Test conditions

[0098] Under 180V, 220V, and 300V voltages, the temperature rise rules of the surface temperature O of different specimens and the temperature rise of the grouting agent center E are as follows: Figure 9 .

[0099] The compressive strength results and standard strength are shown in the following table: Table 6 Compressive strength results and standard strength

[0100] The flexural strength results and standard strength are shown in the following table: Table 7 Flexural strength results and standard strength

[0101] pass Figure 9 It can be seen that when the voltage is 180V or 220V, no matter whether the grouting agent is ordinary grouting agent or low-temperature grouting agent, the electric 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 excessive voltage, the electric 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.

[0102] As can be seen from Table 6, under the electrothermal curing with a voltage of 180V, the 3-day compressive strengths of both the ordinary grouting agent group and the low-temperature grouting agent group do not meet the specification requirement of being greater than or equal to 20MPa. Under the electrothermal curing with voltages of 220V and 330V, the 3-day compressive strengths of both the ordinary grouting agent group and the low-temperature grouting agent group meet the specification requirement of being greater than or equal to 20MPa.

[0103] As can be seen from Table 7, the flexural strengths of the ordinary grouting agent under the electrothermal curing with voltages of 180V, 220V, and 300V for 3 days meet the specification strength. However, the flexural strengths of the ordinary grouting agent and the low-temperature grouting agent under the electrothermal curing with a voltage of 180V for 3 days are significantly lower than the flexural strength under the standard curing for 3 days. The flexural strength of the low-temperature grouting agent under the electrothermal curing with a voltage of 180V for 3 days does not meet the specification strength of being greater than or equal to 5MPa.

[0104] Therefore, the calibration voltage of the electrothermal 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 controlled temperature. Through experiments, the feasibility of the electrothermal bellows grouting agent curing temperature control calibration system is proved.

[0105] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but will be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A method for calibrating the temperature control during the curing of an electrothermal corrugated pipe grouting agent, characterized in that, It includes the following steps: S1. Obtain the specification parameters of the heating wire (12); S2. Prepare model specimens according to the prestressed beams of the actual bridge, and connect a heating module (1) and a temperature detection module (2) into the model specimens; S3. Obtain the external environmental temperature T, model and analyze the internal temperature t after the heating module (1) is heated, calculate the temperature difference between T and t, model and analyze the stress conditions inside the model specimens at different temperature differences to determine the upper limit of the calibration temperature of the thermostat (32), and then take the lowest curing temperature at which the grouting agent inside the model specimens is completely hydrated as the lower limit of the calibration temperature of the thermostat (32); S4. Determine multiple fixed temperatures between the upper and lower temperature limits determined in S3, divide the environmental temperature into multiple temperature ranges according to the fixed temperatures, determine different curing strategies for each temperature range, and determine one of the curing strategies according to the experimental environment; S5. Pour the grouting agent into the model specimens according to the curing strategy determined in S4, obtain the curves of the surface temperature of the model specimens and the change of the central temperature of the grouting agent at different voltages through experiments, and confirm the voltage value that can keep the central temperature of the grouting agent stable within the range set in S3; S6. After starting the power supply, detect whether the central temperature of the grouting agent is within the upper and lower limits determined in S3. If so, execute S7; if not within the upper and lower limits determined in S3, return to S5 to reconfirm the voltage value; If it is still not within the upper and lower limits determined in S3 after returning to S5 for adjustment, return to S4 to reconfirm the curing strategy; If it is still not within the upper and lower limits determined in S3 after returning to S4 for adjustment, return to S1 to reconfirm the specification parameters; S7. Prepare test blocks according to the prestressed beams of the actual bridge, connect the heating module (1) and the temperature detection module (2) into the test blocks, perform grouting curing on the test blocks according to one curing strategy confirmed in S4, take core samples by coring the test blocks after curing, perform compressive and flexural tests on the taken core samples, judge whether the test results meet the requirements. If so, execute S8; If the requirements are not met, return to S5 to reconfirm the voltage value; If it is still not met after returning to S5 for adjustment, return to S4 to reconfirm the curing strategy; if it is still not met after returning to S4 for adjustment, return to S1 to reconfirm the specification parameters; S8. Put the parameters and curing strategies determined in S1, S4, and S5 into actual use.

2. An electrothermal corrugated pipe grouting agent curing temperature control calibration method according to claim 1, characterized in that: The specification parameters in S1 include the skin material, specification size, and winding pitch.

3. An electrothermal corrugated pipe grouting agent curing temperature control calibration method according to claim 1, characterized in that: The upper temperature limit in S3 is the value at which the maximum principal tensile stress on the surface of the model specimen reaches the tensile strength of the concrete.

4. An electrothermal corrugated pipe grouting agent curing temperature control calibration method according to claim 1, characterized in that: In S4, two fixed temperatures i°C and j°C are determined respectively according to the ambient temperature from high to low, and the ambient temperature is divided into three temperature ranges of higher than i°C, j°C-i°C, and lower than j°C.

5. The method for curing temperature control of an electric heating bellows grouting agent according to claim 1 is 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 a 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.

6. A method for calibrating the temperature control during curing of an electrothermal corrugated pipe 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: Removing protective materials from the ends of the heating wire (12) and the ends of the cables (13) in the heating module (1), and treating the surfaces of the ends to make them 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 arranged outside the metal sleeve, and an insulating material is encapsulated inside the insulating wrapping material.

7. An electrothermal corrugated pipe grouting agent curing temperature control calibration system, comprising: The heating module (1), the temperature detection module (2), the temperature control module (3), and the power supply module (4) are characterized by: Can be used to implement the method described in any one of claims 1 to 5; The heating module (1) comprises a corrugated tube (11), a heating wire (12) wound around the corrugated tube (11), and a cable (13) connected to the heating wire (12); The temperature detection module (2) comprises a temperature control probe (21) arranged on the bellows (11); The temperature control module (3) comprises a transformer (31) connected to the heating module (1), a temperature controller (32) connected to the transformer (31), and a control switch (33) connected to the transformer (31); The power module (4) is electrically connected to the temperature control module (3) to provide power (41) for the entire system.

8. The temperature control calibration system for curing electric bellows grouting agent according to claim 7, characterized in that: It also includes an analysis module, which is connected to the temperature control module (3).

9. The temperature control calibration system for curing electric bellows grouting agent according to claim 7, characterized in that: One end of the heating wire (12) and one end of the cable (13) are inserted into the same metal sleeve; The metal sleeve is filled with conductive glue; The outer side of the metal sleeve is covered with an insulating wrapping material; The insulating wrapping material is filled with insulating material.

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