| As the service time of highway continues to extend,the traffic load and environment factors continues to accumulate,the transverse cracks condition of semi-rigid base asphalt pavement is becoming more and more serious.According to the existing pavement design theory,a large proportion of the national highway sections,respresented by the Jiangsu Provincial Highway,have reached or are close to the design life,and the service condition of the semi-rigid base asphalt pavement has been completely presented in the whole design life,or even beyond the design life.However,the development law of transverse cracks in semi-rigid base asphalt pavement with service time is still not completely clear;the key factors influencing the anti-cracking performance of asphalt mixture in different layers and the decay law with service time are not clear,and the effective relationship between the anti-cracking performance of asphalt mixture and the development of transverse cracks has not been established.In addition,the existing prediction models of asphalt pavement transverse cracks do not realize the coupling between traffic load,environmental factors,pavement structure information,base performance and service time,and cannot accurately reflect the actual development condition of pavement transverse crack.Therefore,relying on Jiangsu province highways,this paper carries out in-depth research on the development law and prediction of transverse cracks in semi-rigid base asphalt pavement,providing technical support for making scientific pavement maintenance decision,so the research of this paper is of great significance.Firstly,based on the pavement structural materials information,the transverse crack data,maintenance historical data,traffic load data,and environmental data of the Jiangsu highway network for more than 20 years and exceeds 20,000km single lane mileage,the Python platform and big data analysis method are applied to establish the muli-feature and multi-dimensional variation process of transverse cracks spacing（TCS）with service time,the development of TCS under different combinations of road sections and traffic loads is compared;The number of transverse cracks and the crack pattern of some unmaintained sections of more than 10 highways are counted to reveal the development law of transverse cracks of semi-rigid base asphalt pavement,and the results show that:with the growth of service time,the development of transverse cracks of semi-rigid base asphalt pavement generally exists in four stages,namely:（1）transverse crack initiation stage（2）rapid development stage（3）gentle development stage（4）secondary accelerated development stage.In the first three stage,more than 80%of transverse cracks are bottom-up type cracks,while the fourth stage is dominated by top-down type cracks,and increase rapidly.Due to the high level of research and management in Jiangsu province,the transverse cracks in most road sections have not entered the secondary accelerated development stage,so this paper focuses on the study of transverse cracks features before it enters the secondary accelerated development stage.Because of the complexity of transverse cracking,this paper carries out a multi-dimensional in-depth study on the anti-cracking performance of materials used in different asphalt layers and semi-rigid base layer respectively,and explores the decay law and key influencing factors along with the service time,so as to provide a basis for establishing the transverse crack prediction model of the semi-rigid base asphalt pavement.Secondly,the anti-cracking performance of the surface,middle and bottom asphalt layers was studied in depth from three scales of mixtures,meso-structure of asphalt mixture,and asphalt binder,the evaluation models of the anti-cracking performance of the surface,middle and bottom asphalt layers were established.From the macro mixtures perspective,the decay laws of the anti-cracking performance for three asphalt layers core samples with service time and the influencing factors were analyzed by applying the SCB（Semi-circular bending）test at 15℃,50mm/min loading frequency.The results show that the CRI（Crack Resistance Index）index can effectively evaluate the anti-cracking performance of the core samples for different asphalt layers.The CRI decay laws of the surface,middle and bottom asphalt layers with service time are revealed,with the increase of ESALs,the CRI decay rate of surface asphalt layer is significantly faster than that of the middle and bottom asphalt layers.There is a certain positive correlation between the CRI of surface asphalt layer and the TCS,combined with the service time and the TCS development law,it is found that the surface asphalt layer mixture anti-cracking performance test can predict in advance the time of transverse cracks into the second accelerated development stage,so as to avoid the pavement large area damage caused by the rapid development of fatigue cracks,for example.The key influencing factors of the CRI for three asphalt layers are different,the surface and middle asphalt layers are affected significantly by both internal factors（mixture type,whether the modified asphalt binder is used or not）and external factors（traffic load,environmental factors,service age）,the influence is ranked as:the asphalt mixture type of surface（middle）layer>traffic load>service age,while the bottom asphalt layer mixture is more sensitive to internal factors（including whether the modified asphalt binder is used or not in bottom asphalt layer and air void）.From the meso-scale of asphalt mixture,the asphalt mixture meso-structures of three asphalt layers have been analyzed utilizing high-precision two-dimensional image scanning technology and Matlab image processing method,selecting the meso-scale characteristics parameters that have significant effect on the anti-cracking performance of three asphalt layers,and the variation laws of meso-scale characteristic parameters with service time for three asphalt layers were established.The results show that with the increase of service time,the coarse aggregate contact characteristic parameters of the mixture in the surface,middle and bottom asphalt layers show different decreasing trends.The meso-structure characteristics that have significant influence on the CRI for three asphalt layers CRI mainly include:the4.75mm sieve passage ratios,the average contact of distance and the total number of contact pairs.From the asphalt binder scale,asphalt binders are obtained from core samples of three asphalt layers through the rotary evaporator method,and the LAS（Linear Amplitude Sweep）test is applied to investigate the asphalt binder property parameters that have significant effect on the anti-cracking performance of asphalt layers and the variation law of asphalt binder property with service time.It is found that parameters A and B obtained from LAS test affect the CRI of three asphalt layers significantly.With the increase of service time,the performance of the surface layer asphalt binder gradually deteriorated.Three CRI evaluation models are established to evaluate the anti-cracking performance of the three asphalt layers by integrating the marco mixture,meso-scale structure,and asphalt binder factors that significantly affect the CRI of each asphalt layer.Then,the D20-D60 index was used as indicator to evaluate the structural load-bearing capacity of semi-rigid base and the base durability was also studied.The core samples from in-service semi-rigid base are used to explore the key factors affecting the anti-cracking performance of semi-rigid base layer using unconfined compressive strength test.The results show that,with the increase of service time,the structural condition of semi-rigid base layer in Jiangsu highway network is stable and the fatigue life of semi-rigid base layer is more than 50 years based on the current axle load level of Jiangsu highway.The factors that shows significant effects on the anti-cracking performance of semi-rigid base materials are:base material type,initial strength,and service time.Two evaluation models of the anti-cracking performance of cement-stabilized crushed stone base and lime-fly ash gravel base are obtained respectively,which will provide parameters related to the anti-cracking performance of base materials to the TCS prediction model.Finally,an analysis of the factors influencing TCS in Jiangsu highway network is carried out to identify the macro-factors that have significant influence on TCS,combined with significant influence factors for the anti-cracking performance of three asphalt layers and semi-rigid base material,the TCS prediction model of semi-rigid base asphalt pavement is constructed.The results show that the coefficient of variation between the predicted and measured values of TCS is less than 25%,could effectively distinguish the differences in transverse crack condition between different road sections（SMA-13 and OGFC-13 mixtures sections）,and the prediction model is suitable for predicting the transverse crack condition of semi-rigid base asphalt pavement before entering the secondary accelerated development stage.The research results of this paper provide a reference for the development and prediction of transverse cracks of similar pavement structures and an important basis for determining the asphalt pavement implementation time of structural preventive maintenance of highway. |
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