Method for testing thermal conductivity of ultra-high performance concrete at ultra-low temperature

Abstract

This invention proposes a method for testing the thermal conductivity of ultra-high performance concrete (UHPC) at ultra-low temperatures, belonging to the field of thermal performance testing of UHPC. Based on Fourier's one-dimensional thermal conductivity law, a flat plate thermal conductivity model, quasi-state thermal conductivity testing equipment, and a comprehensive physical property testing system (PPMS) are used to directly apply an ultra-low temperature environment to UHPC specimens, and the relationship between heat, temperature, and thermal conductivity is measured, realizing the testing of UHPC thermal conductivity at ultra-low temperatures. The accuracy of the measured thermal conductivity is verified through the flat plate thermal conductivity model, PPMS equipment, and temperature field measurement and calculation methods. This invention solves the problem of the lack of testing and calculation methods for UHPC thermal conductivity at ultra-low temperatures, which cannot meet the requirements for temperature field analysis and insulation material calculation of UHPC-LNG storage tanks at ultra-low temperatures.

Description

Technical Field

[0001] This invention belongs to the field of thermal performance testing of ultra-high performance concrete (UHPC), specifically, it relates to a method for testing the thermal conductivity of ultra-high performance concrete at ultra-low temperatures. Background Technology

[0002] Liquefied natural gas (LNG) is typically stored in full-capacity tanks, with the inner tank made of 9% nickel steel and the outer tank made of prestressed concrete. Some countries have experimented with using concrete for the inner tanks, which can significantly shorten the construction period and reduce costs. However, the concrete outer tank carries a risk of cracking. Ultra-high performance concrete (UHPC) possesses high strength, high toughness, and high durability. If UHPC is used to replace the traditional steel inner tank and prestressed concrete outer tank, forming a UHPC-LNG storage tank, it will effectively avoid cracking of the concrete outer tank, increase the storage capacity, and reduce the cost of the storage tank.

[0003] The thermal conductivity of ultra-high performance concrete (UHPC) in ultra-low temperature environments is crucial for calculating the temperature field of UHPC-LNG storage tanks and designing insulation materials. However, methods for testing and calculating its thermal conductivity are currently lacking. Furthermore, the impact of coarse aggregates and steel fibers added to UHPCs, depending on requirements, on their thermal conductivity remains unclear. While methods exist for calculating the thermal conductivity of ordinary concrete (strength grades C40-C60) at ultra-low temperatures, the thermal conductivity of ordinary concrete at room temperature and lower temperatures (20℃ to -5℃) is often determined using the heat flow method, which is difficult to apply to concrete at ultra-low temperatures. Although the national standard "Technical Specification for Application of Concrete in Low-Temperature Environments" (GB 51081-2015) provides the thermal conductivity of concrete at ultra-low temperatures, this is an indirect estimate, and direct scientific testing methods are still lacking. Some scholars have also used the laser flash method to study the low-temperature thermal conductivity of C60 high-strength concrete gel, but the lowest temperature of this method is -90℃, which cannot meet the requirement of liquefied natural gas at an ultra-low temperature of -165℃. The thermal conductivity measured by this method differs greatly from the value recommended by the national standard, and the thermal conductivity is 25% to 30% of the value recommended by the national standard.

[0004] Compared to ordinary concrete, UHPC has higher strength, lower water-cement ratio, higher cementitious material content, and different types and contents of aggregates. It may also incorporate steel fibers. Therefore, the testing and calculation of the thermal conductivity of UHPC will inevitably differ significantly from that of ordinary concrete. Furthermore, methods for testing and calculating the thermal conductivity of UHPC at ultra-low temperatures are very limited, making it impossible to provide scientific support for temperature field analysis and insulation material design in UHPC-LNG storage tank projects. Summary of the Invention

[0005] To address the aforementioned issues, this invention proposes a method for testing the thermal conductivity of ultra-high performance concrete (UHPC) at ultra-low temperatures. This method addresses the lack of testing and calculation methods for the thermal conductivity of UHPC at ultra-low temperatures, which prevents the analysis of the temperature field and calculation of insulation materials for UHPC-LNG storage tanks at ultra-low temperatures.

[0006] This invention is achieved through the following technical solution: A method for testing the thermal conductivity of ultra-high performance concrete at extremely low temperatures, the method specifically includes the following steps: S1. Quasi-steady-state flat plate thermal conductivity test: The thermal conductivity of the UHPC sample is tested at room temperature to obtain the reference value of the thermal conductivity at room temperature; S2. Comprehensive physical performance measurement: The UHPC sample was subjected to ultra-low temperature environment conditioning and programmed temperature rise and fall control to test the thermal conductivity of UHPC at multiple target temperature points in the ultra-low temperature to room temperature range. S3. Compare the UHPC thermal conductivity obtained at multiple target temperature points in S2 with the baseline value in S1 to verify the data accuracy of the ultra-low temperature test system. S4. For UHPC containing coarse aggregate, the thermal conductivity of UHPC with and without coarse aggregate at ultra-low temperature was measured separately, and the ultra-low temperature thermal conductivity of UHPC containing coarse aggregate was calculated. S5. Prepare a UHPC specimen with built-in temperature sensing element, conduct actual measurements of the internal temperature field of the specimen under ultra-low temperature conditions, and cross-compare the results with numerical simulation results to verify the correctness of the final thermal conductivity result.

[0007] Furthermore, in S1, a flat UHPC sample is used, and a one-dimensional steady-state thermal conduction condition is established on both sides of the sample through a heater. When the thermoelectric potential no longer changes and remains stable, a quasi-steady state is reached, and the thermal conductivity of UHPC at room temperature is calculated.

[0008] Furthermore, in S2, the UHPC sample is selected as a cylinder or a prism; During the test, the test chamber is first cooled to the initial ultra-low temperature target temperature, and then heated at a constant rate. Multiple target temperature points are set, and the temperature is kept constant at each target temperature point for a preset time. After the sample temperature is consistent with the ambient temperature inside the chamber, the thermal conductivity at the corresponding temperature is tested.

[0009] Furthermore, in S3, when the error between the two sets of room temperature thermal conductivity test results is within the allowable range, the test data is deemed valid; if the error exceeds the allowable range, the measurement is repeated until the error requirement is met.

[0010] Furthermore, in S4, based on Maxwell and considering the volume ratio of coarse aggregate in the UHPC, the ultra-low temperature thermal conductivity of the UHPC containing coarse aggregate was calculated.

[0011] Furthermore, in S5, a UHPC specimen with a pre-embedded ultra-low temperature thermocouple is used. The specimen is cooled to the target ultra-low temperature through a cryogenic chamber with liquid nitrogen as the medium, and then placed in a room temperature environment to naturally warm up. Temperature change data at characteristic locations inside the specimen are collected. When the error between the numerical simulation result and the measured result of the temperature field is within the preset allowable range, the thermal conductivity test result is determined to be reliable.

[0012] A testing system for the thermal conductivity of ultra-high performance concrete at extremely low temperatures; The system includes a quasi-steady-state flat plate thermal conductivity testing module, a comprehensive physical property measurement module, a comparison and verification module, a coarse aggregate measurement module, and a result verification module. The quasi-steady-state flat plate thermal conductivity test module performs room temperature thermal conductivity test on the UHPC sample and obtains the room temperature thermal conductivity reference value. The comprehensive physical performance measurement module performs ultra-low temperature environment regulation and programmed temperature rise and fall control on the UHPC sample, and tests and obtains the thermal conductivity of UHPC at multiple target temperature points in the ultra-low temperature to room temperature range. The comparison and verification module compares the UHPC thermal conductivity at multiple target temperature points obtained by the comprehensive physical performance measurement module with the benchmark value of the quasi-steady-state flat plate thermal conductivity test module to verify the data accuracy of the ultra-low temperature test system. The coarse aggregate measurement module measures the thermal conductivity of UHPC with and without coarse aggregate at ultra-low temperatures, and calculates the ultra-low temperature thermal conductivity of UHPC with coarse aggregate. The result verification module prepares a UHPC specimen with a built-in temperature sensing element, performs an actual measurement of the internal temperature field of the specimen under ultra-low temperature conditions, and cross-compares the results with the numerical simulation results to verify the correctness of the final thermal conductivity result.

[0013] A computer device system includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the above-described method. A computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implement the steps of the above-described method.

[0014] A computer program product includes a computer program / instructions that, when executed by a processor, implement the steps of the method described above.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows: 1. A method was proposed to use a flat plate thermal conductivity model and quasi-state thermal conductivity testing equipment, combined with PPMS equipment, to realize the thermal conductivity testing of UHPC specimens at ultra-low temperatures.

[0016] 2. The accuracy of the measured thermal conductivity was verified by using a flat plate thermal conductivity model, PPMS equipment, and temperature field measurement and calculation methods.

[0017] 3. A method for calculating the thermal conductivity of UHPC at ultra-low temperatures considering the influence of coarse aggregates is proposed. This solves the problem of the lack of testing and calculation methods for the thermal conductivity of UHPC at ultra-low temperatures, which was insufficient for temperature field analysis and insulation material calculation of UHPC-LNG storage tanks at ultra-low temperatures.

[0018] 4. The PPMS equipment used possesses ultra-low temperature and high-precision measurement capabilities. Through precise temperature control technology, the system can stably provide ultra-low temperature environments as low as 1.9K or even lower, and can perform continuous and precise temperature control within a wide temperature range of 2K to 400K. This ensures high accuracy and repeatability of the intrinsic thermal conductivity data of UHPC under extreme low-temperature conditions. The automation and integration of the PPMS system improve experimental efficiency and data reliability. The system's built-in fully automated measurement software supports simultaneous measurement of multiple physical properties, enabling efficient completion of complex experiments without human intervention.

[0019] Based on Fourier's one-dimensional thermal conductivity law, this invention uses a comprehensive physical property testing system to directly apply an ultra-low temperature environment to UHPC specimens, and measures the relationship between heat, temperature and thermal conductivity, thus realizing the testing of UHPC thermal conductivity at ultra-low temperatures.

[0020] The thermal conductivity of a flat plate at room temperature was tested and cross-validated with the thermal conductivity of a UHPC measured at ultra-low temperatures. A method for calculating the thermal conductivity of UHPC at ultra-low temperatures, considering the influence of coarse aggregate, was proposed. Based on the measured thermal conductivity, the temperature field of a UHPC cube at ultra-low temperatures was calculated, and the result showed good agreement with the measured temperature field of UHPC at ultra-low temperatures, thus providing a second verification of the thermal conductivity and proving the correctness of both the testing method and the measured data. This invention solves the dual problem of lacking both testing and calculation methods for the thermal conductivity of UHPC in the construction of UHPC-LNG storage tanks. Attached Figure Description

[0021] Figure 1 For the thermal conductivity model of a flat plate; Figure 2 This is a top view of the UHPC sample in the flat plate thermal conductivity model. Figure 3 This is a schematic diagram of Fourier's law of heat conduction. Figure 4 The principle of using PPMS to measure the thermal conductivity of UHPC at ultra-low temperatures is shown in Table 4; the mix proportions of UHPC groups A, B, E, and F are listed in Table 4. Figure 5 These are the measured results of thermal conductivity of different UHPCs at ultra-low temperatures; Figure 6 Comparison of measured temperature field and simulation results for UHPC cubic specimens. Detailed Implementation

[0022] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Unless otherwise specified, the experimental methods used in the following examples are conventional methods. Unless otherwise specified, the materials, reagents, methods, and instruments used are all conventional materials, reagents, methods, and instruments in the art, and can be obtained commercially by those skilled in the art.

[0024] Combination Figures 1 to 6 The method for measuring the thermal conductivity of UHPC at ultra-low temperatures in this invention is as follows: Step 1: Using a flat plate thermal conductivity model and quasi-state thermal conductivity testing equipment, the thermal conductivity of the UHPC specimen is tested at room temperature. The flat plate thermal conductivity model (e.g., Figure 1 As shown), the plate thickness is 2h, and the initial temperature is... T 0. There is a uniform heat source on both sides of the plate. q c Under the action of a uniform heat source, the specimen is a flat sample with dimensions of 95mm × 95mm × 10mm. The specimen mounting profile (e.g.) Figure 2 As shown in the image, the temperature gradually increases; The quasi-steady-state thermal conductivity testing equipment includes a testing host, a cold junction, and a 6.0V thermocouple heater.

[0025] The flat plate thermal conductivity model establishes a one-dimensional steady-state thermal conductivity condition by having the heat generated by the heater enter the sample from the hot end and exit from the cold end.

[0026] The thermoelectric potential difference between the center surface and the heated surface increases gradually over time. The system inputs current to the heater for approximately 30 minutes. When the thermoelectric potential difference no longer changes and remains stable, it is considered to have reached a quasi-steady state. The value at this point is recorded. .

[0027] The quasi-steady-state thermal conductivity testing equipment systematically monitors the heat flowing through the sample per unit time. and the temperature difference between the two ends of the sample .

[0028] Fourier's law (such as...) Figure 3(As shown) When applied to the sample, the thermal conductivity λ of UHPC at room temperature can be calculated using formula (1).

[0029]

[0030] To reach the quasi-steady state, the thermoelectric potential The heating voltage is 6V. The cross-sectional area of ​​the specimen. For the specimen thickness, The resistance value of the center surface thermal resistor is 150.25Ω. The proportionality coefficient (40) ); The flat plate thermal conductivity model can only be used to measure the thermal conductivity of UHPC at room temperature. It cannot be used to measure the thermal conductivity of UHPC at extremely low temperatures by subjecting UHPC specimens to ultra-low temperatures. To solve the above problems, a comprehensive physical performance measurement system (PPMS) and a temperature field testing system need to be introduced.

[0031] The flat plate thermal conductivity model can only be used to measure the thermal conductivity of UHPC at room temperature. It cannot be used to measure the thermal conductivity of UHPC at extremely low temperatures by subjecting UHPC specimens to ultra-low temperatures. To solve the above problems, a comprehensive physical performance measurement system (PPMS) and a temperature field testing system need to be introduced.

[0032] Step 2: The UHPC sample was cooled using a Physical Properties Measurement System (PPMS), and its thermal conductivity at ultra-low temperatures was measured. The PPMS has a test temperature range of 1.9K to 400K, with a temperature stability of ±0.1% when T < 20K and ±0.02% when T > 20K.

[0033] Due to the size limitations of the PPMS system test chamber, UHPC specimens can be selected as cylindrical specimens with a diameter not exceeding 4 mm and a height of 2-3 times the diameter, or prism specimens with a side length not exceeding 5 mm and a height of 2-3 times the diameter.

[0034] The Physical Properties Measurement System (PPMS) places the test sample inside the PPMS chamber and introduces liquid nitrogen to lower the temperature inside the chamber to an initial target temperature (-168°C), then heats up at a rate of 10 K / min. Five to eight target temperatures can be set as needed; for example, -168°C, -120°C, -80°C, -40°C, -20°C, 0°C, and 20°C can be selected as seven target temperatures. Each target temperature is held constant for 10 minutes to ensure that the sample temperature matches the ambient temperature inside the test chamber.

[0035] The principle of using PPMS to test the thermal conductivity of UHPC specimens at ultra-low temperatures is as follows: Figure 4 As shown, applying Fourier's law to UHPC samples at ultra-low temperatures allows us to calculate the thermal conductivity λ of UHPC at ultra-low temperatures using formula (4). In this formula,

[0036] In the formula, To measure the amount of heat flowing through the specimen per unit time in the system, To test the temperature difference between the two ends of the specimen, It is the distance and temperature difference between the two thermocouple measuring points. It is the cross-sectional area of ​​the specimen.

[0037] Step 3: The thermal conductivity of different UHPC specimens at ultra-low temperatures can be measured using equation (4), as shown in Table 1. Comparing the thermal conductivity at 20℃ obtained by equation (4) with that obtained by equation (1) verifies whether the UHPC thermal conductivity test data at room temperature is correct. If the error between the two is within 10%, it is considered correct, and step 4 can be performed. If the error between the two exceeds 10%, steps 1 and 2 need to be repeated until the error between the two meets the requirements.

[0038] Step 4: Since the steel fiber's geometric dimensions are Φ0.18mm × 13mm, which are very small compared to the UHPC thermal conductivity sample, the effect of the steel fiber on the thermal conductivity can be directly measured by PPMS. However, the coarse aggregate size (continuously graded coarse aggregate with a particle size of 1mm~5mm) is relatively large compared to the UHPC thermal conductivity sample, and the effect of the coarse aggregate on the UHPC thermal conductivity needs to be further considered. The consideration method is as follows: the thermal conductivity of the coarse aggregate at ultra-low temperatures is measured by PPMS. The thermal conductivity of UHPC without coarse aggregate at ultra-low temperature was measured using PPMS. , The thermal conductivity of UHPC containing coarse aggregate was calculated using equation (5). The thermal conductivity values ​​of UHPC with different components at ultra-low temperatures are as follows: Figure 5 As shown.

[0039]

[0040] In the formula, Based on Maxwell's consideration of the thermal conductivity of coarse aggregate UHPC; , Let be the thermal conductivity of material 1 and material 2, respectively; This represents the volume percentage of material 2; if This represents the volume percentage of coarse aggregate, and its value shall not exceed 30%.

[0041] Step 5: Further verify the accuracy of the thermal conductivity of UHPC at ultra-low temperatures, and conduct temperature field tests and calculations on UHPC specimens at ultra-low temperatures.

[0042] Fabricate 2-3 100mm×100mm×100mm cube or 100mm×100mm×300mm prism UHPC specimens with embedded thermocouples. Embed two thermocouples at the center and one at the diagonal of a quarter section of the UHPC specimen, respectively. The thermocouples should be cryogenic, capable of measuring temperatures from -200℃ to 100℃. The cooling system uses a cryogenic chamber with liquid nitrogen as the cooling medium, achieving cooling through gas thermal circulation.

[0043] The test method is as follows: Place 2-3 UHPC specimens with pre-embedded thermocouples into a cryogenic chamber for cooling. Record the ambient temperature changes in the cryogenic chamber. When the temperature reaches -170℃ at both the center and the diagonal of the quarter-body of the specimen (the specimen is frozen through), remove the specimen from the cooling device and place it in a room temperature environment (around 20℃) to allow it to warm up naturally. Measure the temperature data at the center and the diagonal of the quarter-body of the specimen.

[0044] Based on steps 1 to 4 above, the measured thermodynamic parameters of UHPC (Tables 1 to 3) are input into the temperature field calculation software to simulate the temperature field of the UHPC specimen. The calculated temperature field values ​​are compared with the measured values, for example... Figure 6 As shown, the error between the calculated and measured temperature field values ​​is within 15%. Through mutual verification between numerical analysis and measured temperature field data, the thermal conductivity measured in Table 1 is proven to be correct. A comparison of the measured UHPC with relevant experimental results is shown below. Figure 6 As shown.

[0045] Table 1. Thermal conductivity results of UHPC at different temperatures (W / K·m)

[0046] Table 2. Parameters used in the temperature field simulation of the UHPC test block.

[0047] Table 3. Specific heat capacity of UHPC at different temperatures

[0048] Experimental system / equipment for studying the thermal conductivity of ultra-high performance concrete (UHPC) at -165℃ to -20℃: including a comprehensive physical performance measurement system (PPMS), a flat plate thermal conductivity model, and quasi-state thermal conductivity testing equipment.

[0049] Quasi-steady-state thermal conductivity tests were conducted on UHPC samples with three different mix proportions (A, B, and E) at room temperature. By controlling the material to enter a "quasi-steady-state" state under constant temperature difference and heating rate, thermal conductivity can be measured. This method is suitable for measuring the thermal conductivity of UHPC samples. The thermal conductivity measurement under the quasi-steady-state method is based on the one-dimensional infinite flat plate heat conduction theory. The mix proportions are shown in Table 4.

[0050] Table 4. Mixing ratios of different UHPCs

[0051] like Figure 2 The conductivity model is shown below; assuming a plate thickness of 2h, an initial temperature of T0, and uniform heat sources qc on both sides of the plate; under the action of the uniform heat sources, the sample gradually heats up. When the temperature difference between the sample surface and the center remains constant, the system enters a quasi-steady state.

[0052] A flat sample test block with dimensions of 95×95×10 mm was fabricated, and experiments were conducted at room temperature; Before the experiment, connect the circuit, zero the main unit, and select a heating voltage of 6.0V. The cold junction is used to maintain a constant temperature of the thermocouple during the experiment.

[0053] Turn on the thermocouple heater, maintain symmetry, and place four samples with the same composition into the thermocouple heater.

[0054] Heating begins, and the change in the electromotive force reading due to the temperature difference between the central surface and the heated surface is used to determine whether the sample has reached a quasi-steady state.

[0055] When the electromotive force reading remains stable, the system is considered to have reached a quasi-steady state. Record the temperature difference ΔT between the central plane and the heated surface at this point, and calculate the thermal conductivity λ.

[0056] Table 5 compares the thermal conductivity of UHPC measured at room temperature using the plate method and PPMS. It can be seen that the test results for UHPC specimens of different sizes at room temperature (20℃) are basically consistent.

[0057] Table 5 Comparison of thermal conductivity of UHPC at room temperature using the plate method and PPMS measurement

[0058] However, the plate method is only suitable for measuring the thermal conductivity of UHPC at room temperature and cannot be used to measure the thermal conductivity of UHPC at ultra-low temperatures.

[0059] To address this issue, the thermal conductivity of UHPC at ultra-low temperatures was tested using PPMS. Although the specimen size was small, it contained coarse aggregate and steel fibers, and the test results from both methods at room temperature were similar, indicating that PPMS testing is feasible. The measured thermal conductivity of UHPC at ultra-low temperatures is listed in Table 6.

[0060] Table 6 Comparison of thermal conductivity of different UHPCs at ultra-low temperatures

[0061] A computer device system includes a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the above-described method. A computer-readable storage medium having a computer program / instructions stored thereon, which, when executed by a processor, implement the steps of the above-described method.

[0062] A computer program product includes a computer program / instructions that, when executed by a processor, implement the steps of the method described above.

[0063] The above provides a detailed description of the method for testing and calculating the thermal conductivity of ultra-high performance concrete at ultra-low temperatures proposed in this invention, and elucidates the principles and implementation methods of this invention. The descriptions of the above embodiments are only for the purpose of helping to understand the method and core ideas of this invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this invention. Therefore, the content of this specification should not be construed as a limitation of this invention.

Claims

1. A method for testing the thermal conductivity of ultra-high performance concrete at ultra-low temperatures, characterized in that: The method specifically includes the following steps: S1. Quasi-steady-state flat plate thermal conductivity test: The thermal conductivity of the UHPC sample is tested at room temperature to obtain the reference value of the thermal conductivity at room temperature; S2. Comprehensive physical performance measurement: The UHPC sample was subjected to ultra-low temperature environment conditioning and programmed temperature rise and fall control to test the thermal conductivity of UHPC at multiple target temperature points in the ultra-low temperature to room temperature range. S3. Compare the UHPC thermal conductivity obtained at multiple target temperature points in S2 with the baseline value in S1 to verify the data accuracy of the ultra-low temperature test system. S4. For UHPC containing coarse aggregate, the thermal conductivity of UHPC with and without coarse aggregate at ultra-low temperature was measured separately, and the ultra-low temperature thermal conductivity of UHPC containing coarse aggregate was calculated. S5. Prepare a UHPC specimen with built-in temperature sensing element, conduct actual measurements of the internal temperature field of the specimen under ultra-low temperature conditions, and cross-compare the results with numerical simulation results to verify the correctness of the final thermal conductivity result.

2. The method according to claim 1, characterized in that: In S1, a flat UHPC sample is used. A one-dimensional steady-state thermal conductivity condition is established on both sides of the sample through a heater. When the thermoelectric potential no longer changes and remains stable, a quasi-steady state is reached. The thermal conductivity of UHPC at room temperature is then calculated.

3. The method according to claim 2, characterized in that: In S2, the UHPC sample is selected as a cylinder or a prism; During the test, the test chamber is first cooled to the initial ultra-low temperature target temperature, and then heated at a constant rate. Multiple target temperature points are set, and the temperature is kept constant at each target temperature point for a preset time. After the sample temperature is consistent with the ambient temperature inside the chamber, the thermal conductivity at the corresponding temperature is tested.

4. The method according to claim 3, characterized in that: In S3, the test data is considered valid when the error between the two sets of room temperature thermal conductivity test results is within the allowable range; if the error exceeds the allowable range, the measurement is repeated until the error requirement is met.

5. The method according to claim 4, characterized in that: In S4, the ultra-low temperature thermal conductivity of UHPC containing coarse aggregate was calculated based on the volume ratio of coarse aggregate in the Maxwell bound UHPC.

6. The method according to claim 5, characterized in that: In S5, a UHPC specimen with a pre-embedded ultra-low temperature thermocouple is used. The specimen is cooled to the target ultra-low temperature in a cryogenic chamber with liquid nitrogen as the medium, and then placed in a room temperature environment to recover naturally. Temperature change data at characteristic locations inside the specimen are collected. When the error between the numerical simulation result and the measured result of the temperature field is within the preset allowable range, the thermal conductivity test result is determined to be reliable.

7. A system for testing the thermal conductivity of ultra-high performance concrete at extremely low temperatures, characterized in that: The system is based on the method for testing the thermal conductivity of ultra-high performance concrete at ultra-low temperatures as described in any one of claims 1 to 6. The system includes a quasi-steady-state flat plate thermal conductivity testing module, a comprehensive physical property measurement module, a comparison and verification module, a coarse aggregate measurement module, and a result verification module. The quasi-steady-state flat plate thermal conductivity test module performs room temperature thermal conductivity test on the UHPC sample and obtains the room temperature thermal conductivity reference value. The comprehensive physical performance measurement module performs ultra-low temperature environment regulation and programmed temperature rise and fall control on the UHPC sample, and tests and obtains the thermal conductivity of UHPC at multiple target temperature points in the ultra-low temperature to room temperature range. The comparison and verification module compares the UHPC thermal conductivity at multiple target temperature points obtained by the comprehensive physical performance measurement module with the benchmark value of the quasi-steady-state flat plate thermal conductivity test module to verify the data accuracy of the ultra-low temperature test system. The coarse aggregate measurement module measures the thermal conductivity of UHPC with and without coarse aggregate at ultra-low temperatures, and calculates the ultra-low temperature thermal conductivity of UHPC with coarse aggregate. The result verification module prepares a UHPC specimen with a built-in temperature sensing element, performs an actual measurement of the internal temperature field of the specimen under ultra-low temperature conditions, and cross-compares the results with the numerical simulation results to verify the correctness of the final thermal conductivity result.

8. A computer device system, comprising a memory, a processor, and a computer program stored in the memory, characterized in that, The processor executes the computer program to implement the steps of the method according to any one of claims 1 to 6.

9. A computer-readable storage medium having a computer program / instructions stored thereon, characterized in that, When the computer program / instructions are executed by the processor, they implement the steps of the method according to any one of claims 1 to 6.

10. A computer program product comprising a computer program / instructions, characterized in that, When executed by a processor, the computer program instructions implement the steps of the method according to any one of claims 1 to 6.

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