Method for avoiding temperature influence on airport cement concrete pavement deflection test

Abstract

This invention discloses a method for testing the deflection of airport cement concrete pavement to avoid the influence of temperature. The method includes the following steps: estimating the equivalent linear temperature gradient of the pavement; constructing a finite element model; analyzing and calculating the critical positive and negative temperature gradients at the center, edges, and corners of the slab; comparing the temperature gradient distribution with the three critical temperature gradients; identifying the time periods during which the maximum deflection at the three load positions is unaffected by the temperature gradient; selecting the intersection of the three time periods as the time for testing the airport cement concrete pavement deflection; and then conducting the pavement deflection test according to specifications. This method establishes a quantitative relationship between temperature and test time, effectively reducing the influence of temperature on the pavement deflection test results. This allows the test results to more accurately reflect the actual condition of the pavement and scientifically guide pavement quality evaluation and maintenance strategy development.

Description

Technical Field

[0001] This invention relates to the field of airport pavement performance testing, and specifically to a method for testing the deflection of airport cement concrete pavement that avoids the influence of temperature. Background Technology

[0002] Deflection is crucial for evaluating the performance of airport cement concrete pavement structures. Obtaining effective deflection values ​​is essential for correctly assessing the performance of airport pavement structures and formulating appropriate pavement pre-maintenance measures.

[0003] Pavement deflection is influenced by a variety of factors, primarily including intrinsic and extrinsic factors. Intrinsic factors include the geometric dimensions of the cement slab, the flexural modulus and Poisson's ratio of the slab, the load transfer capacity of the joints, and the reaction modulus of the base course (or the elastic modulus and Poisson's ratio of the foundation, depending on the selected foundation model). Extrinsic factors include load and temperature. Among all factors affecting deflection, intrinsic factors are the focus of deflection testing and evaluation. Loads are controllable, and their impact on deflection can be uniquely determined by the applied load. Temperature, however, is significantly affected by climate and is difficult to measure, resulting in uncertainty regarding its impact on deflection; it is the most uncontrollable factor in actual pavement deflection testing experiments.

[0004] The effect of temperature on the deflection of cement concrete pavement is mainly reflected in the expansion, contraction, and warping of the cement concrete pavement slab under temperature influence. Expansion and contraction occur when the air temperature changes slowly, with the internal temperature of the cement concrete pavement slab rising and falling uniformly. This causes the slab to expand and contract uniformly along its cross-sectional depth, leading to changes in joint width. Joints primarily transfer loads through aggregate interlocking and load transfer rods. The aggregate interlocking effect is directly related to the joint width, while the deflection of the slab edges and corners is significantly affected by the load transfer effect of the joints. Therefore, the expansion and contraction of the cement concrete slab caused by temperature has a significant impact on the deflection of the slab edges and corners. Warping occurs when the air temperature changes rapidly, creating a temperature difference between the top and bottom surfaces of the slab. Consequently, the magnitude of expansion and contraction deformation at the top and bottom of the slab differs. When the temperature rises, the temperature of the top surface of the board is higher than that of the bottom surface (positive temperature gradient), and the expansion deformation of the top surface is greater than that of the bottom surface, resulting in bulging in the middle of the board. At this time, the deflection in the middle of the board is more affected by temperature, while the deflection at the corners and edges is smaller. When the temperature drops, the temperature of the top surface of the board is lower than that of the bottom surface (negative temperature gradient), and the expansion deformation of the bottom surface is greater than that of the top surface, resulting in warping at the edges and corners. At this time, the deflection in the middle of the board is less affected by temperature, while the deflection at the corners and edges is larger.

[0005] Current pavement structural performance evaluations are based on pavement deflection testing. However, temperature-induced changes in the shape of cement concrete pavement panels can introduce significant errors into deflection testing. To obtain effective deflection data, the influence of temperature must be eliminated. Both the "Technical Specification for Evaluation and Management of Civil Airport Pavement" (MH / T 5024) and the US "Airport Pavement Design and Evaluation" (ACNo: 150 / 5320) stipulate that deflection testing should ideally be conducted in the early morning or evening to minimize the impact of temperature. This practice severely limits the testing time, and since airports are generally closed at night, it is difficult to meet the required testing time. In fact, research shows that the influence of temperature on pavement deflection has a critical threshold. Based on temperature gradient prediction and critical temperature gradient analysis, an accurate testing time can be determined. This allows deflection testing to be conducted within the appropriate time frame after airport closure, avoiding the influence of temperature on pavement deflection testing, which has significant practical and engineering value. Summary of the Invention

[0006] The purpose of this invention is to provide a method for testing the deflection of cement concrete pavement that avoids the influence of temperature. This method can determine the deflection test time of pavement that avoids the influence of temperature, thereby enabling deflection testing, improving the accuracy of deflection test results, and providing scientific guidance for pavement quality evaluation and maintenance strategy formulation.

[0007] The first aspect of this invention discloses a method for testing the deflection of airport cement concrete pavement to avoid the influence of temperature, comprising the following steps: S1. Predict the pavement temperature gradient during the deflection test using the following pavement equivalent linear temperature gradient prediction model, and plot the pavement temperature gradient distribution curve for the entire day based on the results:

[0008] In the formula, ELTG This represents the equivalent linear temperature gradient of the pavement surface. The surface temperature of the pavement, in °C; The average atmospheric temperature, in °C, is the atmospheric average temperature over the consecutive 24 hours preceding the time of temperature gradient prediction. x The time for predicting the temperature gradient is h; The thickness of the track panel is in cm; S2. Construct a finite element analysis model based on the pavement structure, and perform numerical analysis based on the finite element analysis model. Calculate the positive and negative temperature gradients at the load positions of the slab edge and corner, respectively, where the maximum deflection is unaffected by temperature, as well as the positive temperature gradient at the load position in the middle of the slab (theoretical analysis shows that the negative temperature gradient is unaffected and can be ignored). These are used as the critical temperature gradients of the pavement slab at the corresponding load positions in this area. S3. Compare the predicted temperature gradient distribution curve with the critical temperature gradient at the three load positions (center, edge, and corner) of the slab to determine the time period during which the maximum deflection at the three load positions is not affected by the temperature gradient. Select the intersection of the three time periods as the time for the airport cement concrete pavement deflection test. S4. Conduct deflection tests on the airport's cement concrete pavement at the selected time.

[0009] There are critical temperature gradients that affect deflection at different load positions on the pavement. When the temperature gradient is less than the critical temperature gradient, deflection is not affected by temperature. However, when the temperature gradient exceeds the critical temperature gradient, deflection and temperature gradient show a positive linear correlation.

[0010] Furthermore, when using the equivalent linear temperature gradient prediction model described in S1, the pavement panel thickness, pavement surface temperature, air temperature, and time are taken as influencing parameters.

[0011] Preferably, referring to the "Technical Specification for Evaluation and Management of Civil Airport Pavement" (MH / T 5024), the deflection test method described in S4 is the method of using a falling weight deflectometer.

[0012] The second aspect of this invention discloses the application of the pavement deflection test method in the deflection test of cement concrete pavement in airports.

[0013] Deflection testing is typically conducted after airport operations cease at night. The method described in this invention allows for the determination of the optimal time or range for deflection testing. Firstly, it effectively avoids the influence of temperature on the test results, optimizes the testing process, and ensures that the test results more accurately reflect the actual condition of the pavement. Secondly, it reduces disruption to normal airport inspection operations caused by testing and facilitates the advance planning of other related airport work and personnel, effectively improving operational efficiency.

[0014] Secondly, deflection test results are core indicators for judging the load transfer efficiency of cement concrete pavement joints, the void condition at the bottom of the slab, the bearing capacity, and predicting service life. Their accuracy directly affects the quality evaluation conclusions and the formulation of maintenance plans. The method described in this invention can reduce the distortion of deflection data caused by temperature interference, which may lead to situations where "qualified pavements are mistakenly judged as unqualified" or "pavements with hidden dangers are missed," and consequently, problems of over-maintenance or under-maintenance.

[0015] Finally, the method described in this invention has a wide range of applications and can ensure the reliability of test results in extreme climate regions or environments with large temperature fluctuations. By establishing the correlation between temperature and test time through quantitative analysis, the operation time is clarified, and technical support is provided for the future development of relevant specifications and standards in the industry. Attached Figure Description

[0016] Figure 1This is a schematic diagram of the test method for pavement deflection under the influence of temperature.

[0017] Figure 2 This is a finite element analysis model of the pavement structure, where (a) is a top view and (b) is a side view.

[0018] Figure 3 This is the temperature gradient distribution curve of the pavement panel in area R4A of runway (16L / 34R) of airport A.

[0019] Figure 4 This is the temperature gradient distribution curve of the pavement panel in area R1A of runway (07L / R25) at airport B.

[0020] Figure 5 The results of the continuous deflection test of the runway pavement panel at Airport B change over time. Detailed Implementation

[0021] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, examples, and comparative examples. The following examples and comparative examples are only used to more clearly illustrate the technical solutions of the present invention, so that those skilled in the art can better understand and utilize the present invention, and are not intended to limit the scope of protection of the present invention.

[0022] The experimental methods, production processes, instruments, and equipment involved in the embodiments and comparative examples of this invention are all conventional names in the art, and are very clear and distinct in the relevant application fields. Those skilled in the art can understand the conventional process steps and apply the corresponding equipment based on the names, and implement them according to conventional conditions or conditions recommended by the manufacturer.

[0023] Example 1: Deflection test of cement concrete pavement of airport runway A.

[0024] Airport A's runway (16L / 34R) was initially constructed in 2012. It is 60m wide and 3800m long, with pavement panels measuring 5m x 5m. The transverse joints are dummy joints (contraction joints) without dowel bars. For ease of management, the airport authorities divided the runway into three zones based on structural condition and construction time; the specific names and corresponding structural parameters are shown in Table 1. Foot survey results indicate that the overall condition of the runway surface is good. Furthermore, based on actual operational data, the runway primarily handles A330-200 & 300, A340-200 & 300 & 500 & 600, A380, and B747 series aircraft. (Reference) Figure 1 The process involves conducting experiments.

[0025]

[0026] 1) Plot the temperature gradient distribution curve of the runner panel: After selecting the R4C evaluation area, continuously monitor the pavement surface temperature and atmospheric temperature under the current environmental conditions (for 24 hours, with hourly testing as estimated). Estimate the hourly pavement surface temperature gradient using the following formula:

[0027] In the formula, ELTG This represents the equivalent linear temperature gradient of the pavement surface. The surface temperature of the pavement, in °C; The average atmospheric temperature, in °C, is the atmospheric average temperature over the consecutive 24 hours preceding the time of temperature gradient prediction. x The time for predicting the temperature gradient is h; The thickness of the track panel is in cm.

[0028] Based on the calculation results, the temperature gradient distribution curve of the runner panel under the final test environment conditions is plotted, as follows: Figure 3 As shown.

[0029] 2) Construct a finite element analysis model of the pavement structure, such as Figure 2 As shown, the critical temperature gradient was analyzed. The analysis of the three load positions (center, edge, and corner) used the dimensions of a nine-slab pavement structure. Solid models were used for the pavement panels and base course, and a Winkler foundation was adopted. Given the small average temperature variation during the testing period, the variation in load transfer efficiency at the joints was ignored. Model parameters were obtained through modulus inversion of the deflection at the center of the slab. The final model analysis parameters are shown in Table 2. Furthermore, the Carl Bro HWD load pattern was used in the model, with a peak load of 140 kN and a loading mode of a 30 ms half-sine pulse. Similarly, to facilitate element division, the circular load was equivalent to a 26.6 cm × 26.6 cm rectangular load using an area equivalence method. Based on finite element numerical analysis, the critical negative temperature gradient and critical positive temperature gradient at the edge of the plate in this region are calculated to be -10.2℃ / m and 29.6℃ / m, respectively; the critical negative temperature gradient and critical positive temperature gradient at the corner of the plate are -6.9℃ / m and 40.8℃ / m, respectively; and the critical positive temperature gradient in the middle of the plate is 20.1℃ / m.

[0030]

[0031] ☆Note: The stiffness of the shear spring is determined by inverse calculation.

[0032] 3) Comparing the temperature gradient distribution with the critical temperature gradients at the three load positions (center, edge, and corner) of the slab, and considering the airport's closure status, the final test was conducted at night, when the pavement slab is subjected to a negative temperature gradient, and the deflection at the load position in the center of the slab is not affected by the temperature gradient. (Refer to...) Figure 3 The final determined test time for spatial deflection was between 0:00 and 3:00.

[0033] 4) Between 0:00 and 3:00, pavement deflection tests shall be conducted in accordance with the Technical Specifications for Evaluation and Management of Civil Airport Pavement (MH / T 5024).

[0034] Example 2: Deflection test of cement concrete pavement of airport runway B.

[0035] Airport B's runway (07L / R25) was initially constructed in 1993. It is 50m wide and 2400m long, with each pavement panel measuring 5m x 5m. The transverse joints are dummy joints (contraction joints) without load-bearing bars. Referring to Example 1, the runway was divided into four zones based on structural condition and service life, with specific names and corresponding structural parameters shown in Table 3. Foot survey results indicate that different zones of the runway exhibit varying degrees of damage to the joint sealant, but the overall structure remains intact and the appearance is good. Furthermore, based on actual operational conditions, the runway primarily handles aircraft such as the A330-200, A340-200, A340-500, and B-737-300.

[0036]

[0037] 1) Plot the temperature gradient distribution curve of the runner panel: After selecting the R1A evaluation area, continuously monitor the pavement surface temperature and atmospheric temperature under the current environmental conditions (for 24 hours, with hourly measurements as needed). Estimate the hourly pavement surface temperature gradient using the following formula:

[0038] In the formula, ELTG This represents the equivalent linear temperature gradient of the pavement surface. The surface temperature of the pavement, in °C; The average atmospheric temperature, in °C, is the atmospheric average temperature over the consecutive 24 hours preceding the time of temperature gradient prediction. x The time for predicting the temperature gradient is h; The thickness of the track panel is in cm.

[0039] Based on the calculation results, the temperature gradient distribution curve of the runner panel under the final test environment conditions is plotted, as follows: Figure 4 As shown.

[0040] 2) Construct a finite element analysis model. Based on finite element numerical analysis, calculate the critical negative temperature gradient and critical positive temperature gradient at the edge of the plate in this region as -7.3℃ / m and 24.7℃ / m, respectively; the critical negative temperature gradient and critical positive temperature gradient at the corner of the plate as -4.8℃ / m and 34.2℃ / m, respectively; and the critical positive temperature gradient in the middle of the plate as 16.6℃ / m.

[0041] 3) This airport is generally closed at night, therefore the test was conducted at night. At this time, the pavement slab is subjected to a negative temperature gradient, and the deflection at the load-bearing location is not affected by the temperature gradient. Based on the above analysis and the airport's closure status, and referring to... Figure 4 The final test time was determined to be between 0 and 4 o'clock.

[0042] 4) Conduct pavement deflection tests in accordance with the Technical Specifications for Evaluation and Management of Civil Airport Pavements.

[0043] Finally, during on-site testing, continuous deflection tests were conducted on the same panel, with testing time ranging from 0 to 6 hours. The results are as follows: Figure 5 As shown. From Figure 5 It can be seen that after 4:30, the deflection in the middle of the plate remained basically unchanged, while the maximum deflection at the edge and corner of the plate showed an increasing trend, indicating that the effect of the temperature gradient had become apparent. This proves the effectiveness of the present invention.

[0044] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for testing the deflection of airport cement concrete pavement to avoid the influence of temperature, comprising the following steps: S1. Predict the pavement temperature gradient during the deflection test period according to the following pavement equivalent linear temperature gradient prediction model, and plot the pavement temperature gradient distribution curve for the whole day based on the results: In the formula, ELTG This represents the equivalent linear temperature gradient of the pavement. The surface temperature of the pavement, in °C; The average atmospheric temperature, in °C, is the atmospheric average temperature over the consecutive 24 hours preceding the time of temperature gradient prediction. x The time for predicting the temperature gradient is h; The thickness of the track panel is in cm; S2. Construct a finite element analysis model based on the pavement structure, and perform numerical analysis based on the finite element analysis model. Calculate the positive and negative temperature gradients of the maximum deflection at the load positions of the slab edge and corner, which are unaffected by temperature, as well as the positive temperature gradient of the maximum deflection at the load position in the middle of the slab. These are used as the critical temperature gradients of the pavement slab at the corresponding load positions in this area. S3. By comparing the temperature gradient distribution curve with the critical temperature gradients at the three load positions (center, edge, and corner) of the slab, determine the time period during which the maximum deflection at the three load positions is not affected by the temperature gradient, and select the intersection of the three time periods as the time for the airport cement concrete pavement deflection test. S4. Conduct deflection tests on the airport's cement concrete pavement at the selected time.

2. The pavement deflection test method according to claim 1, wherein when using the equivalent linear temperature gradient prediction model described in S1, the pavement panel thickness, pavement surface temperature, air temperature, and time are taken as influencing parameters.

3. The pavement deflection test method according to claim 1, wherein the deflection test method in S4 is a method using a falling weight deflectometer.

4. The application of the pavement deflection test method according to claim 1 in the deflection test of airport cement concrete pavement.

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