Structure Evaluation And Life-extensional Design Method Of Existingasphalt Pavement

By the end of 2018,the total mileage of highways had reached 4,846,500 kilometers,in which the expressways reached 142,600 kilometers in China.With development of national highways,highway network has been continuously optimized.Some roads have reached their service life.The maintenance investment for the existing roads has grown rapidly.According to statistics,the maintenance investment reached 338.99 billion yuan in 2015.The proportion of medium maintenances and overhauls is over 15% in the repairing projects of highways.The total repairing mileage has reached more than 500,000 kilometers and the costs have reached hundreds of billions yuan every year.Asphalt pavement accounts for more than 90% of the national trunk highways in China.The design life of asphalt pavement is generally 10 to 15 years,and the structural overhaul is required when the service life is reached.It is of great economic and social significance to do a right maintenance of asphalt pavement.The scientific decision on structural overhaul is related to the sustainable development of transportation infrastructure construction.At present,the value of existing asphalt pavement has not been systematically studied,and a design method for overhaul and maintenance of asphalt pavement has not yet been formed.Due to lack of technology in the detection of pavement structure damage,lack of indicators in the evaluation of pavement structure,lack of methods in the design of existing pavement life extension,the traditional maintenance technology can not achieve the appreciation of asphalt pavement.The typical diseases and damage characteristics of asphalt pavement have been analyzed.The methods and theories,such as neural network technology,non-destructive testing methods,continuous damage mechanics theory,shakedown theory,real-time sensor monitoring,have been adopted.Pavement comprehensive performance classification,structural condition assessment,life extension design indicators and methods are studied.The classification evaluation and life-extensional design method of existing asphalt pavement was established.It has theoretical significance for improving the design method of pavement maintenance in China.Based on the data of asphalt pavement in the past 30 years,the data of pavement was analyzed by multi-features and multi-dimensional.Based on the mechanical analysis of typical structures of highways and expressways,it was found that the structural performance of expressway’s pavement is generally superior to highways.Asphalt pavement of expressways is maybe long-life pavement.The effect of thickness on the fatigue life of the pavement is greater than the modulus of the material.A functional relationship between the thicknesses of surfaces and the service life can be established.The service life of asphalt pavement can be extended byoverlaying surface courses.The main diseases of the asphalt pavement in the overhaul projects were surveyed in Beijing,it is found that the main disease of the existing asphalt pavement is the net-shaped cracks,and the life-extensional design to asphalt pavement must identify an indicator to characterize the fatigue cracks.The asphalt pavement is coupled some factors such as traffic load,external environment and material aging.Based the cluster analysis to comprehensive performance of asphalt pavement,it is found that the comprehensive performance of pavement can be classified into four different modes.The asphalt pavements of Class A and Class B are the result of comprehensive effects of high-quality materials,reasonable structure,strict quality control and preventive maintenance.Structural detection method integrated modern non-destructive testing technology and lossy testing technology.Through the evaluation and verification of typical pavements,a multi-index classification evaluation system was established.Aiming at the problem that GPR cannot accurately detect the thickness of thin layer pavement,a method based on the signal processing of GPR is proposed for the first time.The overlapping signals gradually appear to realize the distinction between the different levels of the asphalt surface layers.The maximum relative error of the layer thicknesses is less than 5%.Two new indicators of pavement damage,pavement damage index(PDI)and modulus of pavement structure(Ep),were proposed for the first time.the surface damage index(SDI)and the base damage index(BDI)of the expressway are two structural evaluation indicators.The four indicators form an automatic discrimination technology for the damages of asphalt pavement based on FWD deflection basin data.The discrimination accuracy was verified by the field cores.Accuracy is 89.88% for pavements of expressways.Accuracy is 96.02% for pavements of highways.It provides a technical mean for the diagnosis and classification evaluation of the invisible disease of pavement.Based on the three-stage performance evolution of semi-rigid base and the four evolution modes of existing asphalt pavements,a four-classification method for the existing asphalt pavement was proposed,The evaluation criteria and classification treatment strategy were established.For the A and B pavement with good structural conditions,the life-extensional design method can be appled to control the fatigue damage and structural rutting of asphalt pavement.Two design indexes are fatigue damage of the semi-rigid base and shakedown load of the overlay structure.The modulus of semi-rigid base is an important design parameter.A method for extending the life of existing asphalt pavement was established.Through the long-term performance monitoring and sensor monitoring data analysis of the test section,the structural safety and structural shakedown of the existing pavement were verified during life extension.The life-extensional design method can reasonably increase surface layer,which can effectively extend the service life of existing pavement.Themethod is suitable for extending the service life by more than one time on the basis of the Class A and Class B pavements.It provides a theoretical basis for pavements’ value preservation and increment,which will promote the improvement of road maintenance level in China.