Method for determining rutting damage conversion point based on full-scale asphalt pavement life cycle test

Abstract

The present application relates to a kind of rut damage conversion point determination method based on full-size asphalt pavement full life cycle test, belong to road engineering technical field, the method of the present application, based on full-size asphalt pavement full life cycle test, with the interrelation of rut depth and equivalent design axle load, timely find the conversion point in the service performance damage evolution process of asphalt pavement in full life cycle, when service performance damage decay is about to enter acceleration period, take effective maintenance and repair measures to improve pavement serviceability, can greatly extend the service life and service life of asphalt pavement, it has important practical significance for improving pavement durability, reducing the use cost in full life cycle etc..

Description

Technical Field

[0001] This invention relates to the field of road engineering technology, and in particular to a method for determining rutting damage transition points based on full-scale asphalt pavement life cycle tests. Background Technology

[0002] During the entire service life of asphalt pavement, the pavement structure and materials gradually deteriorate and accumulate damage due to long-term vehicle loads and the natural environment. When the accumulated damage reaches a certain level, the asphalt pavement will eventually fail, rendering it unusable. If the transition points in the evolution of asphalt pavement performance damage can be identified in time throughout its life cycle, and effective maintenance and repair measures are taken to improve pavement condition as the damage is about to accelerate, the service life and service life of asphalt pavement can be significantly extended. This is of great practical significance for improving pavement durability and reducing the overall cost of use. The entire life cycle of asphalt pavement generally refers to the entire process from pavement construction to final failure. According to relevant provisions in my country's design specifications, for highways, the service life should be at least 15 years, or equivalent to 50 million cycles of the equivalent design axle load.

[0003] Rutting is a key indicator of the service performance of asphalt pavements. Currently, in the field of road engineering technology, there is still a lack of corresponding methods to determine the service performance transition points during the rutting damage evolution process of asphalt pavements throughout their entire life cycle. This makes it impossible to accurately pinpoint the moment when rutting damage decay is about to enter an accelerated phase, and also prevents timely and effective maintenance measures to improve pavement service condition. Furthermore, although some scholars have conducted research on the rutting damage evolution process and behavior of asphalt pavements throughout their entire life cycle, and have developed some representative methods, such as theoretical analysis, semi-theoretical and semi-empirical analysis, and empirical methods, these methods all have certain limitations in describing and expressing the rutting evolution behavior of asphalt pavements throughout their entire life cycle.

[0004] Among them, the theoretical analysis method is mainly based on the theory of layered elastic system or viscoelastic system. It calculates the stress in the pavement system through analytical solutions or finite element method, and uses the relationship between the permanent strain and stress of pavement asphalt mixture to calculate the permanent strain of pavement, and then determines the rutting. Representative methods include Shell method, VESYS method, finite element method, etc. Because this method is a purely theoretical calculation method, it does not establish a corresponding method based on the long-term evolution behavior of rutting deformation of real road structure under load and environmental action, resulting in a large error between the predicted and measured values ​​of rutting.

[0005] The semi-theoretical and semi-empirical analysis method generally first uses the theory of elastic layered systems or viscoelastic systems to solve the stress and displacement of the pavement, and then combines relevant indoor and outdoor tests to statistically derive empirical relationships between the permanent deformation of the asphalt layer, material performance parameters, and loads to predict rutting. Representative methods include those proposed by American scholar Jacob Uzan, the methods in the MEPDG design guidelines, and those proposed by Chinese scholars Xu Shifa, Zhang Dengliang, Yang Liqi, and Wang Haiyan. Because this method is generally based on the results of rutting tests on small-sized indoor specimens or scaled-down indoor and outdoor structures, there is a significant difference between these results and the actual rutting depth variations of pavement structures, leading to inaccurate rutting depth predictions with large errors.

[0006] The empirical method, mainly based on statistical principles, relies on extensive observation data from test road sections. It establishes mathematical relationships between asphalt mixture deformation and factors such as material properties, traffic load, and environmental conditions using rutting test results. By constructing a rutting prediction model, it predicts the rutting depth of asphalt pavement under various complex factors. Representative methods include prediction methods proposed by domestic and foreign scholars based on rutting tests using APT accelerated loading test equipment such as ALF, MLS, and HVS. Since this method is generally based on rutting tests on actual pavement structures, it can consider the influence of certain external environments, pavement structures, and materials. The rutting prediction results obtained are more accurate than theoretical analysis methods and semi-theoretical and semi-empirical analysis methods. However, it also has some problems, mainly reflected in the following aspects. First, the simulation time is relatively short, which cannot cover and reflect the long-term evolution of rutting depth throughout the entire life cycle of the pavement structure. The obtained rutting depth test data is also relatively scarce, and the prediction methods established based on this data are unreliable and have poor extrapolation. As mentioned earlier, the so-called full life cycle of asphalt pavement generally refers to the entire process from pavement construction to final failure. According to the relevant provisions in my country's design specifications, for highways, the service life should be at least 15 years, or equivalent to 50 million times of cumulative equivalent design axle load. However, existing APT accelerated loading test equipment such as ALF, MLS, and HVS can generally only obtain hundreds of thousands to millions of times of cumulative equivalent design axle load, which does not meet the requirements of the full life cycle and can only obtain a segment of the entire service process of asphalt pavement. Secondly, existing APT accelerated loading tests such as ALF, MLS, and HVS generally only conduct limited-time rutting tests at specific test temperatures (such as 45℃, 60℃, etc.) or during the hottest season of the year. The test environment is relatively simple and cannot simulate the real-time changes in the natural environment of the actual road surface structure and the alternation of the four seasons. It cannot reflect the influence of temperature on rutting depth. Existing research has found that changes in the natural environment have a significant impact on service performance, sometimes even exceeding the effect of load. Thirdly, the vehicle loads used in the test are too simplified. ALF, MLS, HVS and other APT accelerated loading test devices generally simplify the vehicle load to a single wheel of half axle, a double wheel of half axle, or only a few tires, which is not the full vehicle load on actual roads. The loading method generally adopts reciprocating cyclic loading rather than unidirectional travel, which is significantly different from the unidirectional, channelized traffic load on actual roads. The operating speed of the load is also low, generally with a maximum speed of only about 20km / h, which is a very low-speed travel state and seriously inconsistent with the actual driving speed on roads.

[0007] Therefore, in order to extend the service life of in-service asphalt pavements and to take timely and effective maintenance measures to improve pavement condition when rutting damage decay is about to enter an accelerated phase, it is necessary to find the inflection point of service performance transition during the rutting damage evolution process of asphalt pavements throughout their entire life cycle. At the same time, to ensure accurate and complete rutting evolution behavior throughout the entire life cycle of asphalt pavements, rutting performance tests should be conducted under actual-sized or full-scale road structures, actual service natural and load environments, and test conditions covering the entire life cycle. This ensures that the rutting service performance evolution process is consistent with and matches the rutting damage evolution behavior of the actual pavement structure. Only by establishing the rutting damage transition point on this basis can the accuracy and reliability of the results be guaranteed. Summary of the Invention

[0008] To address the aforementioned issues, this invention proposes a method for determining rutting damage transition points based on full-scale asphalt pavement life-cycle testing. This method identifies key nodes in the evolution of rutting damage throughout the life-cycle of asphalt pavement, enabling timely and effective maintenance and repair measures to improve pavement condition, enhance pavement durability, extend service life, and reduce life-cycle operating costs.

[0009] The method for determining the rutting damage transition point based on full-scale asphalt pavement life cycle testing includes the following steps:

[0010] 1) Based on the basic conditions of the road to be evaluated for rutting damage evolution, determine the road's highway grade, design service life, traffic load grade, cumulative number of equivalent design axle loads within the design service life that meets the full life cycle requirements of asphalt pavement, as well as the asphalt pavement structure type and material type of each structural layer.

[0011] 2) Construct a full-scale pavement with the same structure and materials as the road to be evaluated in an open natural environment. The full-scale pavement shall be at least 7.5m wide (equivalent to two lanes), at least 50m long, and all structural layers shall be of the same thickness as those of the road to be evaluated. The pavement materials shall be constructed using normal construction techniques.

[0012] 3) Use actual vehicles as test loading devices. The vehicle type is a truck with two or more axles. Loading is carried out in a one-way, channelized traffic manner. The vehicle running speed is 60-80km / h. Formula (1) is used to convert the axle load of each axle of the loaded truck into the equivalent design axle load action number. The number of loaded trucks is not less than 4.

[0013]

[0014] Where: N i — The number of equivalent design axle loads applied to the i-th axle of the truck;

[0015] C1—Shaft group coefficient. When the distance between the front and rear shafts is greater than 3m, it is calculated as a single shaft. When the distance between the shafts is less than 3m, the coefficient is 2.1 for double shafts and 3.2 for triple shafts.

[0016] C2 – Wheelset coefficient, 1 for dual-wheelset and 4.5 for single-wheelset;

[0017] P i —The axle load of the i-th axle of the truck, in kN;

[0018] 4) Conduct long-term loading tests on full-scale road surfaces using a test loading device;

[0019] 5) Every time the cumulative number of times the design axle load is applied (approximately 1-1.2 million equivalents), the rut depth of the full-scale road surface should be measured once using a vehicle-mounted laser profiler.

[0020] 6) Stop loading when the cumulative number of equivalent design axle loads that meet the requirements of the entire life cycle of asphalt pavement has been completed;

[0021] 7) Compile and organize all rut depth test data and the cumulative number of equivalent design axle loads during the full-life-cycle loading test of the full-scale pavement, and draw a graph;

[0022] 8) Establish the correlation between the two types of data in step 7) according to formula (2), determine the regression coefficient by fitting, and perform error analysis. The average relative error should not be greater than 10%.

[0023]

[0024] In the formula: y—rut depth, in mm;

[0025] x — the logarithm of the cumulative number of equivalent design axle loads, base 10;

[0026] k1, k2, k3, k4 — regression coefficients;

[0027] 9) Differentiating equation (2) yields equation (3);

[0028]

[0029] 10) After setting equation (3) to 0 and solving it, we can obtain two roots x1 and x2 of the independent variable x. The location of these two roots is the rutting damage transition point. The transition point x1 is located in the early stage of pavement service. Before the transition point, the pavement will increase rutting faster due to compaction. When the compaction deformation reaches a certain level, the rutting tends to stabilize. The transition point x2 is located in the middle and late stages of pavement service. Rutting damage reaches a certain level under continuous accumulation. Rutting damage after the transition point enters the accelerated development stage. It can be used as the time when the asphalt pavement is about to make a maintenance decision.

[0030] In step 5), after approximately 150,000 to 600,000 equivalent design axle loads have been applied cumulatively, the rut depth of the full-scale road surface is measured once using a vehicle-mounted laser profiler.

[0031] The test loading device is a four-axle, five-axle, or six-axle trailer.

[0032] The test loading device increases the axle load of the truck to 1.5-2 times the design axle load by adding counterweights inside the truck bed.

[0033] Each test involves more than six parallel tests, and the average value of the rut depth of the left and right wheel tracks in the lane is taken as the rut depth of the cross section.

[0034] The full-scale road surface is 9m wide and is divided from left to right by markings into: a 1m wide left shoulder, a 3.75m wide overtaking lane, a 3.75m wide driving lane, and a 1m wide right shoulder. The driving lane is used as the test loading lane, and the overtaking lane is used as the test comparison lane. The full-scale road surface is 60m long.

[0035] The method of this invention can promptly identify the transition points in the service performance damage evolution process of asphalt pavement throughout its entire life cycle. When the service performance damage is about to enter the accelerated phase, effective maintenance and repair measures can be taken to improve the pavement's condition, which can greatly extend the service life and service life of asphalt pavement. This has important practical significance for improving pavement durability and reducing the cost of use throughout its entire life cycle. Attached Figure Description

[0036] Figure 1 This is a schematic diagram of the asphalt pavement structure and materials of a certain highway.

[0037] Figure 2 This is a full-scale road lane marking diagram.

[0038] Figure 3 This is the rutting damage evolution curve of asphalt pavement throughout its entire life cycle. Detailed Implementation

[0039] Taking the evaluation of the rutting damage evolution process of an asphalt pavement on a highway as an example, the technical solution of the present invention is explained in detail.

[0040] 1) Based on the relevant technical documents for the design and construction of this expressway, the basic conditions of the road for which the rutting damage evolution process evaluation is to be conducted can be determined as follows: the road grade is expressway, the design service life is 15 years, the traffic load level is extra-heavy traffic, and the cumulative number of equivalent design axle loads within the design service life that meets the full life cycle requirements of asphalt pavement is not less than 50 million cycles. The asphalt pavement structural type and material types of each structural layer are as follows: Figure 1 As shown, from bottom to top, the layers are: a 20cm thick cement-stabilized soil subbase, a 20cm thick cement-stabilized crushed stone base, an 18cm thick cement-stabilized crushed stone base, an 8cm thick A70 asphalt concrete lower layer, a 6cm thick SBS modified asphalt concrete intermediate layer, and a 4cm thick SBS modified asphalt concrete upper layer, with a total pavement structure thickness of 76cm.

[0041] 2) Constructed in an open-air natural environment and Figure 1 A full-scale pavement with identical structure and materials to the asphalt pavement. The full-scale pavement is 9.5m wide. Figure 2 As shown, from left to right, the road is divided by road markings into: a 1m wide left shoulder, a 3.75m wide overtaking lane, a 3.75m wide driving lane, and a 1m wide right shoulder. The driving lane serves as the test loading lane, and the overtaking lane serves as the test control lane. The full-scale pavement is 60m long. The thickness of each structural layer of the full-scale pavement is... Figure 1 The proposed road has the same thickness for each layer. During construction, asphalt mixing plants and water-stabilized mixing plants are used to produce the pavement materials, and pavers and rollers are used for on-site construction.

[0042] 3) A six-axle trailer was used as the test loading device. The loading mode was one-way, channelized traffic, and the average speed of the vehicle was 70 km / h. In order to improve the test loading efficiency, six loading trucks were used to load simultaneously in all weather conditions. Precast cement concrete standard counterweights were used in the truck bed of the six-axle trailer for counterweighting. Each counterweight had a dry weight of 1 ton, and the total number of counterweights was 65. According to formula (1), the cumulative number of equivalent design axle loads applied by each loading truck when passing through the full-length road surface is approximately 72.

[0043] 4) Conduct long-term loading tests on full-scale road surfaces using six-axle trailers.

[0044] 5) Every time approximately 200,000 equivalent design axle loads are accumulated, the rut depth of the full-scale road surface is tested once using a vehicle-mounted laser profiler. Six parallel tests are performed for each test, and the average value of the rut depth of the left wheel track and the right wheel track is taken as the rut depth of the profile.

[0045] 6) When the cumulative number of equivalent design axle loads that meet the full life cycle requirements of the asphalt pavement of the road structure to be evaluated is completed, the loading test will be temporarily stopped. The specific number of times is 50.37 million.

[0046] 7) Summarize and organize all rutting depth test data and the cumulative number of equivalent design axle load applications during the full-life-cycle loading test of the full-scale pavement, as shown in Table 1. Plot the full-life-cycle rutting service performance evolution data from Table 1, as shown below. Figure 3 As shown.

[0047] Table 1. Rutting depth test data for full-scale road surface throughout its entire life cycle.

[0048]

[0049]

[0050]

[0051]

[0052] 8) By fitting the correlation between the two types of data in Table 1 according to Equation (2), the values ​​of regression coefficients k1, k2, k3, and k4 are 4.6455, -95.678, 659.07, and -1511.8, respectively. Substituting these values ​​into Equation (2) yields the specific expression, as shown in Equation (4). The average relative error of Equation (4) is 4.59%, which meets the requirement that the average relative error should not exceed 10%. Therefore, Equation (4) has a small error, high accuracy, and good reliability.

[0053] y = 4.6455·x 3 -95.678·x 2 +659.07·x-1511.8(4) Where: y——rut depth, in mm;

[0054] x — the logarithm of the cumulative number of equivalent design axle loads, base 10;

[0055] k1, k2, k3, k4 — regression coefficients;

[0056] 9) Differentiating equation (4) yields equation (5);

[0057]

[0058] 10) After setting equation (5) to 0 and solving it, we can obtain two roots of the independent variable x: x1 = 6.67 and x2 = 7.52, corresponding to the cumulative number of equivalent design axle loads: 4.68 million and 33.11 million, respectively. The locations of these two roots are the rutting damage transition points. Transition point x1 is located in the early stage of pavement service. Before the transition point, the pavement will experience rapid rutting due to compaction. When the compaction deformation reaches a certain level, the rutting tends to stabilize. Transition point x2 is located in the middle and late stages of pavement service. Rutting damage accumulates to a certain level. After the transition point, the rutting damage enters an accelerated development stage, which can be used as the time when maintenance and repair decisions will be made for the asphalt pavement.

Claims

1. A method for determining the rutting damage transition point based on full-scale asphalt pavement life-cycle testing, comprising the following steps: 1) Based on the basic conditions of the road to be evaluated for rutting damage evolution, determine the road's highway grade, design service life, traffic load grade, cumulative number of equivalent design axle loads within the design service life that meets the full life cycle requirements of asphalt pavement, as well as the asphalt pavement structure type and material type of each structural layer. 2) Construct a full-scale pavement with the exact same structure and materials as the road to be evaluated in an open, natural environment. The full-scale pavement has a width of at least 7.5m for two lanes, a length of at least 50m, and the thickness of each structural layer of the full-scale pavement is exactly the same as the thickness of each layer of the road to be evaluated. The pavement material is constructed using normal construction techniques. 3) Use actual vehicles as test loading devices. The vehicle type is a truck with two or more axles. Loading is carried out in a one-way, channelized traffic manner. The vehicle running speed is 60-80km / h. Formula (1) is used to convert the axle load of each axle of the loaded truck into the equivalent design axle load action number. The number of loaded trucks is not less than 4. Where: N i —The number of equivalent design axle loads applied to the i-th axle of the truck; C1—Shaft group coefficient. When the distance between the front and rear shafts is greater than 3m, it is calculated as a single shaft. When the distance between the shafts is less than 3m, the coefficient is 2.1 for double shafts and 3.2 for triple shafts. C2 – Wheelset coefficient, 1 for dual-wheelset and 4.5 for single-wheelset; P i —The axle load of the i-th axle of the truck, in kN; 4) Conduct long-term loading tests on full-scale road surfaces using a test loading device; 5) Every time the cumulative number of axle load applications of 1-1.2 million equivalent design loads is completed, the rut depth of the full-scale road surface shall be measured once using a vehicle-mounted laser profiler. 6) Stop loading when the cumulative number of equivalent design axle loads that meet the requirements of the entire life cycle of asphalt pavement has been completed; 7) Compile and organize all rut depth test data and the cumulative number of equivalent design axle loads during the full-life-cycle loading test of the full-scale pavement, and draw a graph; 8) Establish the correlation between the two types of data in step 7) according to formula (2), determine the regression coefficient by fitting, and perform error analysis. The average relative error should not be greater than 10%. y = k1·x 3 +k2·x 2 +k3·x+k4(2) Where: y——rut depth, in mm; x — the logarithm of the cumulative number of equivalent design axle loads, base 10; k1, k2, k3, k4 — regression coefficients; 9) Differentiating equation (2) yields equation (3); 10) After setting equation (3) to 0 and solving it, we can obtain two roots x1 and x2 of the independent variable x. The location of these two roots is the rutting damage transition point. The transition point x1 is located in the early stage of pavement service. Before the transition point, the pavement will increase rutting faster due to compaction. When the compaction deformation reaches a certain level, the rutting tends to stabilize. The transition point x2 is located in the middle and late stages of pavement service. Rutting damage reaches a certain level under continuous accumulation. Rutting damage after the transition point enters the accelerated development stage. It can be used as the time when the asphalt pavement is about to make a maintenance decision.

2. According to the determination method of claim 1, in step 5), every time the cumulative number of times the equivalent design axle load is applied is completed, the rut depth of the full-scale road surface is detected once using a vehicle-mounted laser profiler.

3. The determination method according to claim 1, wherein the test loading device is a four-axle, five-axle, or six-axle trailer.

4. According to the determination method of claim 1, the test loading device increases the axle load of the truck to 1.5-2 times the design axle load by adding counterweights in the truck bed.

5. According to the determination method of claim 1, in step 5), more than 6 parallel tests are performed for each test, and the average value of the rut depth of the left wheel track and the rut depth of the right wheel track is taken as the rut depth of the cross section.

6. According to the determination method of claim 1, the full-scale road surface is 9m wide and is divided from left to right by markings into: a 1m wide left shoulder, a 3.75m wide overtaking lane, a 3.75m wide driving lane, and a 1m wide right shoulder. The driving lane is used as the test loading lane, and the overtaking lane is used as the test comparison lane. The full-scale road surface is 60m long.

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