Mechanical Calculation Method of LSAM-50 Full-depth Asphalt Pavement Considering Low-temperature Temperature Field

Abstract

The present invention relates to a mechanical calculation method for LSAM-50 full-depth asphalt pavement considering low-temperature temperature field. Temperature sensors are buried at different depths of the in-service pavement, and an intelligent meteorological acquisition station is established to collect the temperatures at different depths of the pavement structure in real time. Taking the lowest temperature at each layer as the characteristic temperature, a pavement temperature-pavement depth model is established, the asphalt pavement structure layer and structural sub-layer are divided, the calculation temperature corresponding to different calculation depths is determined according to the pavement temperature-pavement depth model, and according to the rebound modulus-temperature model of various asphalt mixtures, the different calculated rebound moduli corresponding to different calculated temperatures are determined; according to the determined rebound moduli of the asphalt mixtures in each structural sub-layer, the elastic layer continuous system theory under the action of double-circle uniform vertical load is used to calculate the mechanical indexes of the pavement structure. This method can calculate the mechanical response of LSAM-50 full-depth asphalt pavement more accurately.

Description

Technical Field

[0001] The present invention belongs to the field of traffic civil engineering, and particularly relates to a mechanical calculation method for LSAM-50 full-depth asphalt pavement considering low-temperature temperature field. Background Art

[0002] Currently, the "Code for Design of Highway Asphalt Pavements" (JTG D50-2017) in China stipulates that the elastic layered continuous system theory under the action of double-round uniformly distributed vertical loads should be used to calculate the mechanical indexes of pavement structures. For the structural check of full-depth asphalt pavement structures, the modulus values of structural layers should adopt the modulus under the conditions of 20°C and 10 Hz for asphalt surface layers, and the modulus under the conditions of 20°C and 5 Hz for asphalt base layers. However, the existing design specifications have the following deficiencies in calculating the mechanical response of LSAM-50 (Large Stone Asphalt Mixture-50) full-depth asphalt pavement:

[0003] (1) During the actual service process, with the seasonal change of the outside air temperature, the temperature field in the asphalt pavement structural layer changes complexly, and the temperature distribution of each structural layer changes periodically with time and the environment. As a typical viscoelastic-plastic body, the mechanical properties such as the resilient modulus of asphalt mixture have strong temperature dependence, that is, during the actual service process of asphalt pavement, the resilient modulus of each asphalt mixture material will change with the pavement temperature field. However, the existing design specifications usually use the empirical value or representative value of the resilient modulus at one temperature to characterize the performance of pavement materials, without considering the change of the asphalt pavement temperature field, which does not conform to the actual service process.

[0004] (2) The mechanical strength and fatigue cracking of LSAM-50 full-depth asphalt pavement have strong temperature sensitivity. However, the existing design specifications do not consider the fatigue cracking of the pavement structure at different temperatures, that is, the existing specifications do not consider the temperature sensitivity of LSAM-50 full-depth asphalt pavement. Summary of the Invention

[0005] Aiming at the above technical problems existing in the existing design specifications, the purpose of the present invention is to provide a mechanical calculation method for LSAM-50 full-depth asphalt pavement considering low-temperature temperature field.

[0006] To achieve the above task, the present invention adopts the following technical solutions:

[0007] A mechanical calculation method for LSAM-50 full-depth asphalt pavement considering low-temperature temperature field, characterized in that this method considers the actual low-temperature temperature field of the pavement, and can calculate the mechanical response of LSAM-50 full-depth asphalt pavement more accurately compared with the existing design specifications. The specific steps are as follows:

[0008] Step 1: Collect the temperature field of the service pavement

[0009] To study the temperature field distribution of the LSAM-50 full-depth asphalt pavement, temperature sensors and temperature data loggers with a test temperature range of not less than -50°C to 130°C and a test accuracy of not less than 0.1°C are selected. Considering various factors such as terrain, landform, light, wind speed, and wind direction, a suitable location is chosen to establish an intelligent weather station; according to the pavement structural layer position and mechanical calculation requirements, the burial depth of the temperature sensing wire is designed. The intelligent weather station is used to collect the temperature at different depths of the pavement structure in real time.

[0010] Step 2: Construct a model for the change of the low-temperature temperature field of the in-service pavement with pavement depth

[0011] The lowest temperature from December of each year to January of the following year is selected as the representative period of low temperature for the analysis of the low-temperature temperature field of the asphalt pavement. According to the low-temperature data of different layers recorded by the intelligent weather station, considering the most unfavorable situation, the lowest temperature of each layer is used as the characteristic temperature to establish a pavement temperature - pavement depth model. The constructed model adopts a linear model, and R 2 is not less than 0.90.

[0012] Step 3: Test the indoor resilient modulus of asphalt mixtures at different temperatures

[0013] Cylindrical specimens of asphalt mixtures are formed indoors. The asphalt mixtures used are the same as those of the asphalt surface layer and the LSAM-50 flexible base course materials respectively. The resilient modulus values of the asphalt mixtures at different temperatures are tested to establish a resilient modulus - temperature dependence model for different asphalt mixtures. The constructed model adopts an exponential model, and R 2 is not less than 0.90.

[0014] Step 4: Divide the structural layers and structural sub-layers of the asphalt pavement

[0015] The structural layers of the LSAM-50 full-depth asphalt pavement can be divided into a surface functional layer, a bonding layer, and an LSAM-50 flexible base course. Among them, the thickness of the surface functional layer is divided into 2 - 4 cm, the thickness of the bonding layer is divided into 6 - 8 cm, and the thickness of the LSAM-50 flexible base course is relatively large, and there are large differences in temperature and modulus inside its structure. The LSAM-50 flexible base course is divided into structural sub-layers, and the thickness of each structural sub-layer is 5 - 10 cm.

[0016] Step 5: Determine the temperature and mechanical parameters of the structural layers and structural sub-layers

[0017] Based on the pavement temperature - pavement depth model constructed in Step 2, for the surface functional layer, the calculation depth is the depth from the road surface to the mid - layer; for each structural sub - layer of the bonding layer and the LSAM - 50 flexible base course, the calculation depth is the depth from the road surface to the layer top. According to the model in Step 2, determine the calculation temperature corresponding to different calculation depths; based on the resilient modulus - temperature models of various asphalt mixtures constructed in Step 3, substitute each calculation temperature to determine the calculated resilient modulus corresponding to each calculation temperature.

[0018] Step 6: Conduct mechanical response calculation of the LSAM - 50 full - depth asphalt pavement

[0019] According to the resilient modulus of each structural sub - layer determined in Step 5, use the elastic layered continuous system theory under the action of a uniformly distributed double - circle vertical load to calculate the pavement structure mechanical indexes.

[0020] The mechanical calculation method of the LSAM - 50 full - depth asphalt pavement considering the low - temperature temperature field of the present invention can conduct more accurate mechanical response calculation of the LSAM - 50 full - depth asphalt pavement because it considers the internal temperature field distribution of the LSAM - 50 full - depth asphalt pavement during the actual service process. Description of the Drawings

[0021] Figure 1 is the pavement depth - pavement temperature model;

[0022] Figure 2 is the resilient modulus - temperature dependence model of asphalt mixtures, where Figure (a) represents the resilient modulus - temperature dependence model of AC - 13, Figure (b) represents the resilient modulus - temperature dependence model of AC - 20, and Figure (c) represents the resilient modulus - temperature dependence model of LSAM - 50;

[0023] Figure 3 is the schematic diagram of the uniformly distributed double - circle vertical load;

[0024] Figure 4 is the low - temperature mechanical response of the pavement, where Figure (a) represents the relationship between the maximum bottom tensile stress and the pavement depth, and Figure (b) represents the relationship between the maximum bottom tensile strain and the pavement depth;

[0025] Figure 5 is the low - temperature mechanical response of the pavement with different LSAM - 50 flexible base course thicknesses, where Figure (a) represents the relationship between the maximum bottom tensile stress and the LSAM - 50 flexible base course thickness, and Figure (b) represents the relationship between the maximum bottom tensile strain and the LSAM - 50 flexible base course thickness;

[0026] Figure 6 is the low - temperature mechanical response of the pavement with different subgrade resilient moduli, where Figure (a) represents the relationship between the maximum bottom tensile stress and the subgrade resilient modulus, and Figure (b) represents the relationship between the maximum tensile strain and the subgrade resilient modulus.

[0027] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Specific embodiments

[0028] In this embodiment, a test section of a super-large-size LSAM-50 flexible base asphalt pavement is paved relying on the newly built G347 project, and a mechanical calculation method for the full-depth LSAM-50 asphalt pavement considering the low-temperature temperature field is given. This method considers the actual low-temperature temperature field of the pavement and can calculate the mechanical response of the full-depth LSAM-50 asphalt pavement more accurately compared with the existing design specifications. The specific steps are as follows:

[0029] Step 1: Collect the temperature field of the in-service pavement

[0030] To study the temperature field distribution of the full-depth LSAM-50 asphalt pavement, temperature sensors and temperature data loggers with a test temperature range of not less than -50°C to 130°C and a test accuracy of not less than 0.1°C are selected. Considering factors such as terrain, landform, light, wind speed, and wind direction, a suitable location is selected to establish an intelligent weather station. According to the pavement structure layer position and mechanical calculation requirements, the burial depths of the temperature sensing lines are determined to be 2 cm, 7 cm, 12 cm, 17 cm, 22 cm, 27 cm, 32 cm, 37 cm, 44 cm, and 51 cm at the road shoulder. Using the intelligent weather station, the temperature at different depths of the pavement structure is collected in real time.

[0031] Step 2: Build a model of the low-temperature temperature field of the in-service pavement changing with the pavement depth

[0032] The temperature of the asphalt pavement is the lowest in winter. In this embodiment, the lowest temperature from December 2021 to January 2022 of the G347 test section is selected as the representative low-temperature period for analyzing the low-temperature temperature field of the asphalt pavement. According to the low-temperature data of different layers recorded by the intelligent weather station, considering the most unfavorable situation, the lowest temperature of each layer is used as the characteristic temperature to establish a pavement temperature - pavement depth model. The established model adopts a linear model, and the R 2 is 0.9643. The relationship between pavement temperature and pavement depth is shown in Figure 1 .

[0033] Step 3: Test the indoor resilient modulus of asphalt mixture at different temperatures

[0034] For the G347 new project, the surface functional layer of the LSAM-50 full-depth asphalt pavement uses AC-13 asphalt mixture, the bonding layer uses AC-20 asphalt mixture, and the LSAM-50 flexible base layer uses LSAM-50 asphalt mixture. Asphalt mixture cylindrical specimens are formed indoors, and the asphalt mixtures used are the same as those of the asphalt surface layer and the LSAM-50 flexible base layer materials respectively. The resilient modulus values of the asphalt mixtures at different temperatures are tested, and a resilient modulus-temperature dependence model for different asphalt mixtures is established. The model constructed uses an exponential model, and R 2 is not less than 0.90. The resilient modulus-temperature dependence models of AC-13, AC-20, and LSAM-50 are shown in Figure 2 .

[0035] Step 4: Divide the structural layers and structural sub-layers of the asphalt pavement

[0036] For the LSAM-50 full-depth asphalt pavement of the G347 new project, the structural layers are divided into a surface functional layer, a bonding layer, and an LSAM-50 flexible base layer. Among them, the surface functional layer is 4 cm of AC-13, the bonding layer is 6 cm of AC-20, and the thickness of the LSAM-50 flexible base layer is 40 cm. There are large differences in the internal temperature and modulus of its structure. The LSAM-50 flexible base layer is divided into structural sub-layers, and the thickness of each structural sub-layer is 5 cm. The pavement structural layer positions and the layered results of the calculation model are shown in Table 1.

[0037] Table 1: Pavement structural layer positions and calculation model layering

[0038]

[0039] Step 5: Determine the temperature and mechanical parameters of the structural layers and structural sub-layers

[0040] According to the pavement temperature-pavement depth model constructed in Step 2, the calculation depth of the surface functional layer is the depth from the middle of the layer to the road surface, and the calculation depth of each structural sub-layer of the bonding layer and the LSAM-50 flexible base layer is the depth from the top of the layer to the road surface. According to the model in Step 2, the calculation temperatures corresponding to different calculation depths are determined; according to the resilient modulus-temperature models of various asphalt mixtures constructed in Step 3, substituting each calculation temperature, the calculation resilient moduli corresponding to each calculation temperature are determined. The calculation depths, calculation temperatures, and calculation resilient moduli are shown in Table 2.

[0041] Table 2: Temperature and mechanical parameters of pavement structural layers and structural sub-layers

[0042]

[0043]

[0044] Step 6: Perform mechanical response calculations for the LSAM-50 full-depth asphalt pavement

[0045] Based on the resilient modulus of each structural sublayer determined in step 5, the elastic layered continuous system theory under the action of double circular uniformly distributed vertical loads is adopted to calculate the mechanical indexes of the pavement structure.

[0046] The "Code for Design of Highway Asphalt Pavements" (JTG D50-2017) stipulates that the elastic layered continuous system theory under the action of double circular uniformly distributed vertical loads should be adopted to calculate the mechanical indexes of the pavement structure. The schematic diagram of the double circular uniformly distributed vertical loads is shown in Figure 3 , the x-axis is the driving direction. The distance between the centers of the two wheels is 319.5 mm. The coordinates of points A, B, C, D, and E under the action of the standard axle load BZZ-100 are shown in Table 3. The radius of the load circle is 106.5 mm, and the unit of the coordinates of the calculation points is m.

[0047] Table 3: Coordinates of each calculation point under the action of BZZ-100 load

[0048] Calculation parameters Coordinates of point A Coordinates of point B Coordinates of point C Coordinates of point D Coordinates of point E Parameter value (0,0) (-0.0266,0) (-0.0533,0) (-0.1598,0) (-0.2663,0)

[0049] The mechanical calculation indexes of the pavement structure are selected as the bottom tensile stress and the bottom tensile strain.

[0050] In this embodiment, the mechanical response of the LSAM-50 full-depth asphalt pavement is calculated from the following three aspects:

[0051] ① The variation law of stress with depth at different calculation points;

[0052] ② The influence of the thickness of the LSAM-50 flexible base on the mechanical response of the pavement structure under low-temperature conditions;

[0053] ③ The influence of the resilient modulus of the subgrade on the mechanical response of the pavement structure under low-temperature conditions.

[0054] First, in this embodiment, the mechanical response of the pavement structure with a 40-cm-thick LSAM-50 flexible base and a subgrade resilient modulus of 60 MPa under the low-temperature temperature field is calculated, and the variation law of stress with depth at different calculation points is obtained as shown in Figure 4 . From Figure 4 (a), it can be seen that when the pavement depth ≤ 25 cm, the pavement is horizontally compressed under the load, and the maximum stress (<0.6 MPa) appears at the road surface; as the depth increases, the stress values at each calculation point tend to be the same and the stress experiences a change from compression to tension. The bottom of the asphalt layer at point A is the point with the largest tensile stress, and the maximum horizontal tensile stress at the bottom can reach 0.25 MPa. From Figure 4As can be seen from (b), the variation law of the tensile strain at different positions with depth is roughly the same as that of the horizontal tensile stress. When the pavement depth ≤ 15 cm, the pavement produces compressive strain under the action of the load; when the depth continues to increase, the strain values at each calculation position tend to be the same and the strain experiences a change from compression to tension; the bottom of the asphalt layer at point A is the position with the largest tensile strain, and the maximum horizontal tensile strain at the layer bottom can reach 55 με. The maximum values of both the horizontal tensile stress and the tensile strain are at the bottom of the flexible base layer at point A.

[0055] Second, in this embodiment, to explore the influence of the thickness of the LSAM-50 flexible base layer on the mechanical response of the pavement structure under low-temperature conditions, the thicknesses of the LSAM-50 flexible base layer are proposed to be 10 cm, 15 cm, 20 cm, 25 cm, 30 cm, 35 cm, 40 cm, and 50 cm, and the mechanical response of the pavement is shown in Figure 5 . As can be seen from Figure 5 (a), under low-temperature conditions, increasing the thickness of the LSAM-50 flexible base layer can significantly reduce the maximum tensile stress and maximum tensile strain of the pavement. The maximum tensile stress and maximum tensile strain of the pavement change in a negative exponential function with the change of the thickness of the LSAM-50 flexible base layer, and the reduction amplitude of the tensile stress and tensile strain is larger when the thickness is small. When the thickness of the LSAM-50 flexible base layer increases from 10 cm to 15 cm, the maximum tensile stress decreases from 0.99 MPa to 0.73 MPa, with a decrease of 26%. After the thickness of the LSAM-50 flexible base layer increases to 40 cm, the maximum tensile stress of the pavement is only 23.7% of that at 10 cm. As can be seen from Figure 5 (b), the variation law of the tensile strain is similar to that of the tensile stress. After the thickness of the LSAM-50 flexible base layer increases to 40 cm, the maximum tensile strain of the pavement is only 24.2% of that at 10 cm. Under low-temperature conditions, cracking failure is the main failure form, and controlling the tensile stress and tensile strain of the low-temperature pavement is the main basis for long-life asphalt pavements.

[0056] Third, in this embodiment, to explore the influence of the resilient modulus of the soil subgrade on the mechanical response of the pavement structure under low-temperature conditions, the resilient moduli of the soil subgrade are proposed to be 10 MPa, 20 MPa, 30 MPa, 40 MPa, 50 MPa, 60 MPa, 70 MPa, and 80 Mpa, and the mechanical response of the pavement is shown in Figure 6 . As can be seen from Figure 6 (a), under low-temperature conditions, increasing the resilient modulus of the soil subgrade can significantly reduce the maximum tensile stress and maximum tensile strain of the pavement. The maximum tensile stress and maximum tensile strain of the pavement change in a negative exponential function with the change of the resilient modulus of the soil subgrade, and the reduction amplitude of the tensile stress and tensile strain is larger when the resilient modulus of the soil subgrade is low. When the resilient modulus of the soil subgrade increases from 10 MPa to 20 MPa, the maximum tensile stress decreases from 0.32 MPa to 0.29 MPa. After the resilient modulus of the soil subgrade increases to 60 MPa, the maximum tensile stress of the pavement is only 70% of that at 10 MPa. As can be seen from Figure 6(b) It can be seen that the variation law of the tensile strain is similar to that of the tensile stress. After the resilient modulus of the subgrade increases to 60 MPa, the maximum tensile strain of the pavement is only 74% of 10 MPa. Cracking failure is the main failure form under low-temperature conditions. Controlling the tensile stress and tensile strain of the pavement at low temperature is the main basis for long-life asphalt pavements.

[0057] The above content is a further detailed description of the present invention in combination with specific implementation manners. It cannot be determined that the specific implementation manners of the present invention are limited thereto. For those of ordinary skill in the technical field to which the present invention belongs, without departing from the concept of the present invention, several simple deductions or substitutions can still be made, which should all be regarded as falling within the protection scope defined by the claims of the present invention.

Claims

1. A mechanical calculation method for the full-depth LSAM-50 asphalt pavement considering the low-temperature temperature field, characterized in that, The specific steps are as follows: Step 1: Collect the temperature field of the in-service road surface Select a temperature sensor and a temperature data collector with a test temperature range of not less than -50°C to 130°C and a test accuracy of not less than 0.1°C. Considering various factors such as terrain, landform, light, wind speed, and wind direction, select a suitable location to establish an intelligent meteorological station; design the burial depth of the temperature sensing line according to the pavement structure layer position and mechanical calculation requirements, and use the intelligent meteorological station to collect the temperature at different depths of the pavement structure in real time; Step 2: Construct a model for the change of the low-temperature temperature field of the in-service road surface with the pavement depth Select the lowest temperature from December of each year to January of the following year as the representative period of low temperature for the analysis of the low-temperature temperature field of the asphalt pavement. According to the low-temperature data recorded at different layers by the intelligent weather station, considering the most unfavorable situation, take the lowest temperature of each layer as the characteristic temperature, and establish a pavement temperature-pavement depth model. The constructed model adopts a linear model, and the correlation coefficient R 2 is not less than 0.90; Step 3: Test the indoor resilient modulus of asphalt mixture at different temperatures Cylindrical specimens of asphalt mixture are formed indoors. The asphalt mixtures used are the same as those for the asphalt surface course and the LSAM-50 flexible base course materials respectively. The resilient modulus values of the asphalt mixtures at different temperatures are tested, and a resilient modulus-temperature dependence model for different asphalt mixtures is established. The model constructed adopts an exponential model, and the correlation coefficient R 2 is not less than 0.90; Step 4: Divide the asphalt pavement structure layer and structural sub-layers The LSAM-50 full-depth asphalt pavement structure layer can be divided into a surface functional layer, a bonding layer, and an LSAM-50 flexible base layer. Among them, the surface functional layer is divided with a thickness of 2 cm to 4 cm, the bonding layer is divided with a thickness of 6 cm to 8 cm, and the LSAM-50 flexible base layer has a relatively large thickness, and there are large differences in temperature and modulus inside its structure. The LSAM-50 flexible base layer is divided into structural sub-layers, and the thickness of each structural sub-layer is 5 cm to 10 cm; Step 5: Determine the temperature and mechanical parameters of the structure layer and structural sub-layers According to the pavement temperature - pavement depth model constructed in Step 2, the surface functional layer uses the depth from the middle of the layer to the road surface as the calculation depth, and the bonding layer and each structural sub-layer of the LSAM-50 flexible base layer use the depth from the top of the layer to the road surface as the calculation depth. According to the model in Step 2, determine the calculation temperature corresponding to different calculation depths; according to the resilient modulus - temperature model of various asphalt mixtures constructed in Step 3, substitute each calculation temperature to determine the calculated resilient modulus corresponding to each calculation temperature; Step 6: Conduct mechanical response calculations for the LSAM-50 full-depth asphalt pavement; According to the resilient modulus of each structural sub-layer determined in Step 5, use the elastic layered continuous system theory under the action of a double-circle uniformly distributed vertical load to calculate the pavement structure mechanical indexes.

2. The method according to claim 1, characterized in that, The surface functional layer uses AC-13 asphalt mixture, and the bonding layer uses AC-20 asphalt mixture.

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