A semi-rigid base asphalt pavement crack cause diagnosis method

Abstract

The application discloses a kind of causes of semi-rigid base course asphalt pavement crack diagnostic methods, carry out crack data acquisition and semi-rigid base course asphalt pavement crack cause classification;Crack special cause diagnosis based on basic information investigation;Traffic, temperature external cause diagnosis based on index and threshold analysis;Material, structural internal cause diagnosis based on core sample test and field test;Comprehensive diagnosis semi-rigid base course asphalt pavement crack cause.The present application realizes the system, comprehensive diagnosis of semi-rigid base course asphalt pavement crack cause, provides theoretical support for subsequent crack targeted treatment and pavement maintenance.

Description

Technical Field

[0001] The present application relates to the technical field of pavement maintenance, and in particular to a method for diagnosing the causes of cracks in a semi-rigid base asphalt pavement. Background Art

[0002] With the sustained growth of the national economy, highway transportation, as a fundamental infrastructure of the national economy, has also flourished. With the rapid development of high-grade highway construction in my country, the transportation network is becoming increasingly complete. As of 2021, my country had built 169,100 kilometers of expressways, an increase of 8,100 kilometers. Of this total, 117,000 kilometers were national expressways, an increase of 4,000 kilometers. During the 14th Five-Year Plan period, my country will complete the construction and reconstruction of 25,000 kilometers of expressways. By 2025, my country will have achieved a total expressway mileage of 190,000 kilometers. In the construction of high-grade highways and expressways, my country primarily utilizes semi-rigid pavement. This pavement consists of a base layer stabilized with inorganic binders such as cement and lime, and an asphalt surface layer. It features high strength, high bearing capacity, and excellent integrity. However, after a period of operation, semi-rigid pavements will develop varying degrees of defects, such as cracks, slurry pumping, subsidence, voids, potholes, etc. Cracks are the most common, most prone to, and earliest-occurring defects among all types of asphalt pavement damage. They almost accompany the entire service life of the asphalt pavement and continue to worsen with the increase in road service life. The pavement performance will be significantly affected, and the pavement quality will be reduced, seriously affecting the appearance of the road and driving comfort. If not handled in time, it will affect the normal use of the pavement.

[0003] At present, my country's judgment on the causes of cracking problems on semi-rigid pavements still mainly relies on traditional experience-based decision-making methods. At the same time, due to the limitations of testing standards, most maintenance departments lack understanding of cracks and frequently adopt simple surface treatment methods, reducing "cracks" to "repairs" to achieve higher PCI values, but only treating the symptoms rather than the root cause. Summary of the Invention

[0004] In order to solve the technical problems mentioned in the above background technology, the present invention proposes a method for diagnosing the causes of cracks in semi-rigid base asphalt pavement.

[0005] In order to achieve the above technical objectives, the technical solution of the present invention is:

[0006] A method for diagnosing the causes of cracks in a semi-rigid base asphalt pavement comprises the following steps:

[0007] S1: Crack data collection and classification of crack causes in semi-rigid base asphalt pavement;

[0008] S2: Diagnosis of special causes of cracks based on basic information investigation;

[0009] S3: Diagnosis of external causes of traffic and temperature based on indicator and threshold analysis;

[0010] S4: Diagnosis of the internal causes of structure and materials based on core sample tests and field tests;

[0011] S5: Comprehensive diagnosis of the causes of cracks in semi-rigid base asphalt pavement.

[0012] Furthermore, in step S1, cracks existing in the road section are detected and classified, and the severity of different types of cracks in the road section is evaluated, and the causes of the cracks are graded and classified; including: first-level division of the causes of cracks, including Class I special factors, Class II special factors, Class III special factors, external causes, Class I internal factors, and Class II internal factors; second-level explanation of the causes of cracks, explaining Class I special factors as special factors of the road section location, Class II special factors as special factors of the crack generation location, Class III special factors as construction factors, external causes as environmental factors, Class I internal factors as material factors, and Class II internal factors as structural factors; third-level detailed explanation of the specific causes of the divided second-level causes, special factors of the road section location include the road section being located at a river embankment susceptible to water intrusion, the road section being located at a long longitudinal slope, the road section being located at a sharp bend, The road section is located in a semi-filled and semi-excavated area; special factors for the location of cracks include the occurrence of settlement cracks accompanied by pavement settlement, the occurrence of construction cracks at construction joints, and cracks at the crossing of structures; construction factors include insufficient compaction of the pavement subgrade, improper subgrade soil filling, asphalt mixture paving not meeting specifications, joint treatment not meeting specifications, and mixing and transportation of asphalt mixture not meeting specifications; environmental factors include overloading, heavy loading, and heavy traffic volume leading to fatigue reflection cracks in the bottom of the surface layer, i.e., fatigue cracks from bottom to top, low temperature leading to surface cracking, and temperature cycling leading to temperature fatigue cracks; material factors include asphalt aging leading to reduced crack resistance of the surface layer, poor asphalt mixture grading leading to reduced crack resistance of the surface layer, high base strength leading to shrinkage cracking of the base layer resulting in bottom-up reflection cracks, insufficient fatigue resistance of the asphalt mixture, which makes it easy to produce fatigue cracking of the surface layer from top to bottom, and insufficient fatigue resistance of the inorganic binder of the base layer leading to fatigue cracking of the base layer and bottom-up reflection cracks; structural factors include insufficient modulus of the structural layer, unreasonable thickness design of each structural layer, and poor adhesion of the structural layer.

[0013] Furthermore, in step S2, it specifically includes:

[0014] S21: Preliminary diagnosis of the causes of cracks based on historical maintenance data and crack morphology. Specifically, this includes analyzing the trend of crack density during annual maintenance to determine whether most of the cracks are fatigue cracks. Observing the pavement crack morphology, including width, direction, tortuosity, and number of branch joints, to determine whether the cracks are reflective cracks caused by thermal shrinkage of the base layer, low-temperature cracking of the surface layer, or longitudinal fatigue cracks running from top to bottom.

[0015] S22: Determination of Class I special factors based on the section characteristics investigation, specifically including analysis of the road section's location, geometric design, and surrounding environment to determine whether Class I special factors are the cause of the cracks;

[0016] S23: Determination of Class II special factors based on crack location analysis, specifically including observing the crack location to determine whether the cracks occur at joints, are accompanied by road surface settlement, or are located where structures cross the roadbed.

[0017] S24: Determination of Class III special factors based on construction log investigation, specifically including, based on construction log data, analyzing and eliminating factors that may cause cracks during the construction process, including whether the compaction of the roadbed and pavement meets the specifications, whether the asphalt mixture paving meets the specifications, whether the joint treatment meets the specifications, whether the original cracks in the pavement are properly treated, and whether the mixing and transportation of the asphalt mixture meet the specifications, to analyze and determine whether Class III special factors are the cause of the cracks.

[0018] Furthermore, in step S3, it specifically includes:

[0019] S31: Traffic load cause diagnosis based on index and threshold analysis, specifically using the cumulative number of equivalent design axle load actions (Ne) on a road section and the annual average daily traffic volume (AADTT) of vehicles with two axles and six wheels or more as comprehensive traffic load evaluation indicators. The relationship between each index and the set threshold is used to analyze and determine the load cause that leads to cracks.

[0020] S32: Diagnosis of temperature causes based on index and threshold analysis, specifically including taking the proportion of days with temperature below 0℃ in a year and the proportion of days with temperature greater than a℃ in a year as comprehensive temperature evaluation indicators in the area where the road section is located, and using the relationship between each index and the set threshold to analyze and determine the temperature cause of the cracks.

[0021] Furthermore, in step S4, it specifically includes:

[0022] S41: Class I internal cause determination based on core sample testing, specifically including taking cores from the analyzed road section, analyzing the material properties of the asphalt mixture and inorganic binder using core sample testing and material evaluation indicators to determine the material cause of the cracks;

[0023] S42: Class II internal cause determination based on field tests, specifically including conducting field tests on the analyzed road section, testing the road deflection using a drop weight deflectometer, analyzing the modulus and thickness of each structural layer of the road, and determining the structural cause of the cracks.

[0024] The beneficial effects brought about by adopting the above technical solution are:

[0025] The present invention realizes the systematic and comprehensive diagnosis of crack diseases in semi-rigid base asphalt pavement, effectively eliminates the influence of maintenance personnel's subjective judgment on objective evaluation standards, is more objective and accurate in evaluation content, and will effectively improve the prevention and control of cracks in asphalt pavement and the maintenance efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 is a flow chart of the method of the present invention;

[0027] Figure 2 It is a diagnostic reference for special causes of cracks based on basic information investigation;

[0028] Figure 3 It is a type I internal cause diagram judgment flow chart;

[0029] Figure 4 This is a photo of the core sample at the crack in the pavement of Xicheng section in the embodiment. Implementation Method

[0030] The present invention designs a method for diagnosing the causes of cracks in semi-rigid base asphalt pavement. The following will be combined with the accompanying drawings to further illustrate and explain the present invention. Figure 1 , the embodiment of the present invention includes the following steps:.

[0031] S1: Crack data collection and classification of crack causes in semi-rigid base asphalt pavement;

[0032] S2: Diagnosis of special causes of cracks based on basic information investigation;

[0033] S3: Diagnosis of external causes of traffic and temperature based on indicator and threshold analysis;

[0034] S4: Diagnosis of the internal causes of structure and materials based on core sample tests and field tests;

[0035] S5: Comprehensive diagnosis of the causes of cracks in semi-rigid base asphalt pavement.

[0036] In this embodiment, preferably, in step S1, cracks present on the road section are detected and classified. Video images of road cracks are captured using a highly integrated drone-mounted camera. The detected road section is divided into several smaller segments at 1 km intervals, with the final segment being rounded to 1 km if less than 1 km in length. A pixel threshold method is used for crack segmentation and concatenation, and crack parameter identification is performed, classifying cracks into transverse cracks, longitudinal cracks, block cracks, and network cracks. The severity of each crack type in the road section is then assessed. The severity of transverse cracks, longitudinal cracks, block cracks, and network cracks is assessed based on crack width, length, spacing, and affected area according to the "Highway Technical Condition Assessment Standard" (JTG5210-2018). Causes of road sections with severe crack damage are analyzed. To facilitate subsequent crack cause diagnosis, the crack causes are classified and graded. The classification of crack causes in semi-rigid base layers is shown in Table 1 below.

[0037] Serial number Primary classification of crack cause type Secondary classification of crack cause type Tertiary classification of crack cause type 1 Special factor of type I Special factor of road section location ① The road section is located in the river embankment prone to water intrusion; ② The road section is located in the long and large longitudinal slope; ③ The road section is located in the sharp bend; ④ The road section is located in the half fill and half excavation 2 Special factor of type II Special factor of crack generation location ① The appearance of settlement cracks is accompanied by pavement settlement; ② The appearance of construction cracks exists in the construction joint; ③ The cracks appear in the structure crossing 3 Special factor of type III Construction factor ① The pavement and subgrade compaction is insufficient; ② The roadbed soil filling is improper; ③ The asphalt mixture paving does not meet the specification; ④ The joint treatment does not meet the specification; ⑤ The asphalt mixture mixing and transportation does not meet the specification 4 External cause Environmental factor ① Overload, heavy load, and heavy traffic volume lead to surface layer bottom fatigue reflection cracks, i.e. fatigue cracks from bottom to top; ② Low temperature leads to surface layer cracking; ③ Temperature cycle leads to temperature fatigue cracks 5 Internal cause of type I Material factor ① Asphalt aging leads to reduced surface layer crack resistance; ② Poor asphalt mixture gradation leads to reduced surface layer crack resistance; ③ High base strength leads to base shrinkage cracks and reflection cracks from bottom to top; ④ Insufficient fatigue resistance of asphalt mixture leads to easy production of surface layer fatigue cracks from top to bottom; ⑤ Insufficient fatigue resistance of base inorganic binder leads to base fatigue cracking and reflection cracks from bottom to top 6 Internal cause of type II Structure factor ① Insufficient structure layer modulus; ② Unreasonable design of thickness of each structure layer; ③ Poor structure layer adhesion

[0038] Table 1 Classification of causes of cracks in semi-rigid base

[0039] In this embodiment, preferably, the above step S2 specifically includes four steps S21, S22, S23 and S24, such as Figure 2As shown. In step S21, a preliminary diagnosis of the cause is performed based on historical maintenance data and crack morphology. Specifically, if the annual maintenance crack density has maintained a relatively stable trend over the past three years and then suddenly increases, it can be roughly determined that the majority of the cracks are fatigue cracks. The pavement crack morphology is then observed. For transverse cracks, if the cracks are narrow at the top and wide at the bottom, appear continuously at regular intervals within the road section, run through the entire pavement, have high overall straightness, and have a small number of branch cracks with high continuity, they can be preliminarily diagnosed as reflective cracks caused by thermal shrinkage of the base layer. Short transverse cracks are preliminarily diagnosed as low-temperature cracking of the surface layer. For longitudinal cracks, if the cracks are located within the wheel track, are tortuous, and discontinuous, they are preliminarily diagnosed as shear fatigue. This serves as a reference for further cause determination. In step S22, a Class I special factor assessment based on the section characteristics survey is performed, specifically including whether the road section is located on a riverbank susceptible to water intrusion, on a long longitudinal slope, in a partially excavated and filled area, or on a sharp bend. Analyze and determine whether Class I special factors are the cause of the cracks. In step S23, a Class II special factor determination is made based on the analysis of the crack location. Specifically, if the cracks are accompanied by pavement settlement, they are preliminarily determined to be settlement cracks; if the cracks appear at a construction joint and their directions coincide, they can be determined to be joint cracks; if the cracks appear at a bridgehead embankment or when a structure crosses it, they can be determined to be caused by the structure. Analyze and determine whether Class II special factors are the cause of the cracks. In step S24, a Class III special factor determination is made based on the construction log survey. Specifically, based on the construction log data, factors that may have caused the cracks during construction are analyzed and eliminated, including whether the compaction of the roadbed and pavement meets the specifications, whether the roadbed soil filling is proper, whether the asphalt mixture paving meets the specifications, whether the joint treatment meets the specifications, whether the existing cracks in the pavement are properly treated, and whether the mixing and transportation of the asphalt mixture meet the specifications. The determination is then made as to whether Class III special factors are the cause of the cracks. Through the four steps S21, S22, S23 and S24, the special causes of cracks are analyzed.

[0040] In this embodiment, preferably, the above-mentioned step S3 specifically includes two steps, S31 and S32. In step S31, traffic load cause diagnosis is performed based on index and threshold analysis, specifically including, using traffic volume data obtained through ETC gantry data and the load weighing system of the technology company, using the equivalent design cumulative axle load action times Ne and the annual average daily traffic volume AADTT of vehicles with two axles and six wheels or more as comprehensive traffic load evaluation indicators, and when the equivalent design cumulative axle load action times Ne exceeds the set threshold or the annual average daily traffic volume AADTT of vehicles with two axles and six wheels or more exceeds the set threshold, it is determined that heavy load and heavy traffic are the main causes of the cracks; in step S32, temperature cause diagnosis is performed based on index and threshold analysis. Specifically, using data from the China Meteorological Data Network, the percentage of days with temperatures below 0°C and the percentage of days with a diurnal temperature range greater than a°C in a year are used as comprehensive temperature evaluation indicators. When the percentage of days with temperatures below 0°C exceeds a set threshold, low-temperature cracking is determined to be the primary cause of the cracks. When the percentage of days with a diurnal temperature range greater than a°C exceeds a set threshold, temperature cycle fatigue cracking is determined to be the primary cause of the cracks. Through steps S31 and S32, the external causes of the cracks are analyzed.

[0041] In this embodiment, preferably, the above step S4 specifically includes two steps, S41 and S42. In step S41, a Class I internal cause determination is performed based on the core sample test. Since it includes many steps, please refer to Figure 3Specifically, the process includes taking cores from a road section, measuring the penetration through an asphalt recovery test as an evaluation indicator and comparing it with a set threshold. If the penetration is less than the set threshold, the cracks are determined to be caused by asphalt aging leading to brittle cracking of the asphalt mixture; determining whether the mixture gradation is the cause of the cracks through an asphalt mixture extraction test; determining the splitting strength through an asphalt mixture splitting test as an evaluation indicator and comparing it with a set threshold. If the penetration is less than the set threshold, the cracks are determined to be caused by insufficient tensile strength of the asphalt mixture; determining the fatigue life through a four-point bending fatigue life test as an evaluation indicator and comparing it with a set threshold. If the penetration is less than the set threshold, the cracks are determined to be caused by insufficient fatigue resistance of the asphalt mixture; determining the unconfined compressive strength through an unconfined compression test as an evaluation indicator and comparing it with a set threshold. If the penetration is greater than the set threshold, the cracks are determined to be caused by excessive base layer strength leading to shrinkage cracking; and determining the fatigue life through a bending-tension fatigue test as an evaluation indicator and comparing it with a set threshold. If the penetration is less than the set threshold, the cracks are determined to be caused by insufficient fatigue resistance of the inorganic binder in the base layer. In step S42, a Class II internal cause determination is made based on the field test. Specifically, this involves conducting field tests on the analyzed road section, measuring pavement deflection using a drop weight deflectometer, back-calculating the SIDMOD structural layer modulus, and comparing the modulus and thickness of each structural layer. If the modulus is less than a set threshold, insufficient deformation resistance of the structural layer is the cause of the cracks. The appropriate thickness of the structural layer is then analyzed to determine whether an unreasonable thickness is the cause of the cracks. Through these two steps, S41 and S42, the intrinsic cause of the cracks is analyzed.

[0042] In this embodiment, preferably, the entire diagnostic process adopts the idea of ​​first analyzing and eliminating special factors, and then gradually screening conventional factors. All causes of cracks in the semi-rigid base asphalt pavement are eliminated step by step and superimposed step by step in combination with the analysis of road section characteristics. In step S5, the results of steps S1-S4 are combined to achieve a comprehensive diagnosis of the causes of cracks in the semi-rigid base asphalt pavement.

[0043] The following is a detailed description of the detection method based on specific application cases:

[0044] S1: The Xicheng section of the Guangjing-Xicheng Expressway in Jiangsu Province was used as the inspection area and divided into n small blocks at 1 km intervals. A multifunctional inspection vehicle was used to collect crack data and complete crack classification and evaluation. Among the crack disease types on the Xicheng section of the expressway, transverse cracks were the most common.

[0045] S2: Analyze historical maintenance data of the Xicheng section of the expressway to determine the occurrence of fatigue cracks in the road section. The Xicheng section of the expressway was mainly maintained on a daily basis from 2015 to 2017, and the annual maintenance crack density remained stable, making it impossible to determine whether the cracks were fatigue cracks. Observe the morphology of the pavement cracks to roughly determine the cause of the transverse cracks. Most of the transverse cracks in the Xicheng section of the expressway appear continuously at regular intervals within the road section, with high overall straightness, a small number of branch cracks, and a high degree of continuity. It is preliminarily determined that most of the transverse cracks in the Xicheng section of the expressway are reflective cracks. A section characteristic survey of the Xicheng section of the expressway was conducted, and it was found that it did not contain the conditions included in Class I special causes. The locations of cracks in the Xicheng section of the expressway were analyzed, and Class II special factors were determined. A small number of cracks were cracks at construction joints or cross-structure cracks. Based on the construction log, the construction status of the Xicheng section of the expressway was investigated, and Class III special factors were determined. It was found that it did not contain the conditions included in Class III special causes.

[0046] S3: Combined with highway cross-section traffic volume data and toll station traffic data, the equivalent design cumulative axle load action times were calculated. The impact of traffic load on the cause of cracks was analyzed by analyzing the relationship between the annual average daily traffic volume of vehicles with two axles and six wheels or more, the equivalent design cumulative axle load action times, and the set threshold. In 2017, the annual average daily traffic volume of vehicles with two axles and six wheels or more on the surveyed section of the Xicheng Expressway reached 20,920 vehicles / day, exceeding the set threshold. At the same time, the equivalent design cumulative axle load action times reached 671 million times, also exceeding the set threshold. Therefore, it can be inferred that heavy loads and heavy traffic volume are the causes of the transverse cracks on the Xicheng Expressway. The temperature data of Jiangyin City, Wuxi City, Jiangsu Province that year was obtained from the China Meteorological Data Network. The influence of temperature on the cause of cracks was analyzed. Jiangyin City has a mild and humid climate, with 9.3% of days below 0°C and 7.4% of days with a daily temperature difference greater than 20°C, both below the set threshold. Therefore, it can be concluded that low temperature is not the cause of the transverse cracks on the Xicheng Expressway, that is, the transverse cracks on the Xicheng Expressway are not low-temperature cracks.

[0047] S4: Core sampling was conducted at the crack site of a certain investigated section of the Xicheng Expressway. Material origin diagnosis was performed based on core sample tests such as asphalt recovery tests. Due to limited project funding, only asphalt recovery tests and unconfined compression tests were conducted. The asphalt penetration of the asphalt mixture of the Xicheng Expressway was less than the set threshold, and the unconfined compressive strength measured by the unconfined compression test was greater than the set threshold. This indicates that the insufficient crack resistance of the surface layer and base layer is the cause of the transverse cracks on the Xicheng Expressway. Please refer to the core sample diagram for details. Figure 4 ; Based on the on-site drop weight deflectometer test, the pavement structure cause diagnosis was carried out. The pavement structure strength PSSI of the Xicheng section expressway represents the deflection value and meets the pavement structure strength requirements. The deflection basin value meets the roadbed bearing capacity requirements. The inversely calculated pavement structure layer modulus and thickness are both less than the set threshold value. It can be judged that the transverse cracks of the Xicheng section expressway are not related to the pavement structure performance.

[0048] S5: Combining the diagnostic results of S1-S4, we analyzed and diagnosed the causes of cracks on the Xicheng section of the expressway. The cracks are primarily transverse reflective cracks caused by shrinkage cracking due to excessively high base modulus, and fatigue transverse cracks at the bottom of the surface layer due to heavy traffic and heavy loads. These cracks are primarily caused by heavy traffic volume, aging of the asphalt in the surface asphalt mixture, and excessive base strength, which predisposes to shrinkage cracking. A very small number of cracks are caused by cracks in joints or by cross-cutting structures.

[0049] The embodiments are only for illustrating the technical idea of ​​the present invention and cannot be used to limit the protection scope of the present invention. Any changes made on the basis of the technical solution in accordance with the technical idea proposed by the present invention shall fall within the protection scope of the present invention.

Claims

1. A method for diagnosing the causes of cracks in semi-rigid base asphalt pavement, characterized in that: The following steps are involved: S1: Crack data collection and classification of crack causes in semi-rigid base asphalt pavement; Detect and classify cracks existing on road sections, evaluate the severity of different types of cracks on the road sections, and classify the causes of cracks; including: first-level classification of crack causes, including Class I special factors, Class II special factors, Class III special factors, external causes, Class I internal causes, and Class II internal causes; The second-level explanation of the causes of cracks is given. The special factors of type I are explained as special factors of the road section location, the special factors of type II are explained as special factors of the crack location, the special factors of type III are explained as construction factors, the external causes are explained as environmental factors, the internal factors of type I are explained as material factors, and the internal factors of type II are explained as structural factors. The specific causes of the second-level causes are explained in detail at the third level. The special factors of the road section location include the road section being located at the river embankment that is susceptible to water intrusion, the road section being located at a long longitudinal slope, the road section being located at a sharp bend, and the road section being located at a half-filled and half-excavated area. The special factors of the crack location include the appearance of settlement cracks accompanied by road surface settlement, the appearance of construction cracks at construction joints, and the appearance of cracks at the crossing of structures. The construction factors include insufficient compaction of the roadbed, improper filling of the roadbed soil, and the appearance of asphalt concrete. The paving of the composite material does not meet the specifications, the treatment of the joints does not meet the specifications, and the mixing and transportation of the asphalt mixture do not meet the specifications; environmental factors include overloading, heavy loading, and heavy traffic volume leading to fatigue reflection cracks in the bottom of the surface layer, i.e., fatigue cracks from bottom to top, low temperature leading to cracking of the surface layer, and temperature cycling leading to temperature fatigue cracks; material factors include asphalt aging leading to reduced crack resistance of the surface layer, poor grading of the asphalt mixture leading to reduced crack resistance of the surface layer, high base strength leading to shrinkage cracking of the base layer resulting in bottom-up reflection cracks, insufficient fatigue resistance of the asphalt mixture leading to easy top-down fatigue cracking of the surface layer, insufficient fatigue resistance of the inorganic binder of the base layer leading to fatigue cracking of the base layer and bottom-up reflection cracks; structural factors include insufficient modulus of the structural layer, unreasonable thickness design of each structural layer, and poor adhesion of the structural layer; S2: Diagnosis of special causes of cracks based on basic information investigation; S3: Diagnosis of external causes of traffic and temperature based on indicator and threshold analysis; S4: Diagnosis of the internal causes of structure and materials based on core sample tests and field tests; S5: Comprehensive diagnosis of the causes of cracks in semi-rigid base asphalt pavement.

2. The method for diagnosing the causes of cracks in a semi-rigid base asphalt pavement according to claim 1, characterized in that: In step S2, it specifically includes: S21: Preliminary diagnosis of the causes of cracks based on historical maintenance data and crack morphology. Specifically, this includes analyzing the trend of crack density during annual maintenance to determine whether most of the cracks are fatigue cracks. Observing the pavement crack morphology, including width, direction, tortuosity, and number of branch joints, to determine whether the cracks are reflective cracks caused by thermal shrinkage of the base layer, low-temperature cracking of the surface layer, or longitudinal fatigue cracks running from top to bottom. S22: Determination of Class I special factors based on the section characteristics investigation, specifically including analysis of the road section's location, geometric design, and surrounding environment to determine whether Class I special factors are the cause of the cracks; S23: Determination of Class II special factors based on crack location analysis, specifically including observing the crack location to determine whether the cracks occur at joints, are accompanied by road surface settlement, or are located where structures cross the roadbed. S24: Determination of Class III special factors based on construction log investigation, specifically including, based on construction log data, analyzing and eliminating factors that may cause cracks during the construction process, including whether the compaction of the roadbed and pavement meets the specifications, whether the asphalt mixture paving meets the specifications, whether the joint treatment meets the specifications, whether the original cracks in the pavement are properly treated, and whether the mixing and transportation of the asphalt mixture meet the specifications, to analyze and determine whether Class III special factors are the cause of the cracks.

3. The method for diagnosing the causes of cracks in a semi-rigid base asphalt pavement according to claim 1, characterized in that: In step S3, it specifically includes: S31: Traffic load cause diagnosis based on index and threshold analysis, specifically using the cumulative number of equivalent design axle load actions (Ne) on a road section and the annual average daily traffic volume (AADTT) of vehicles with two axles and six wheels or more as comprehensive traffic load evaluation indicators. The relationship between each index and the set threshold is used to analyze and determine the load cause that leads to cracks. S32: Diagnosis of temperature causes based on index and threshold analysis, specifically including taking the proportion of days with temperature below 0℃ in a year and the proportion of days with temperature greater than a℃ in a year as comprehensive temperature evaluation indicators in the area where the road section is located, and using the relationship between each index and the set threshold to analyze and determine the temperature cause of the cracks.

4. The method for diagnosing the causes of cracks in a semi-rigid base asphalt pavement according to claim 1, characterized in that: In step S4, it specifically includes: S41: Class I internal cause determination based on core sample testing, specifically including taking cores from the analyzed road section, analyzing the material properties of the asphalt mixture and inorganic binder using core sample testing and material evaluation indicators to determine the material cause of the cracks; S42: Class II internal cause determination based on field tests, specifically including conducting field tests on the analyzed road section, testing the road deflection using a drop weight deflectometer, analyzing the modulus and thickness of each structural layer of the road, and determining the structural cause of the cracks.

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