Study On Mechanism And Prediction Of The Distress Of Punchout In Continuously Reinforced Concrete Pavement Based On Two Scale Model

Punchout is the area which is surrounded by two transverse cracks with short distance(less than 0.6m), short longitudinal crack and the edge of pavement or longitudinal joint. Punchout is the main distress of continuously reinforced concrete pavement(CRCP). The pavement shows fine quality and the punchout has little effect on the comfort and safety of driving at the beginning of punchout formation stage. But if the punchout area under repeated effect of environment and vehicle loading, spalling and another crack will appear which have great influence on the comfort and safety of driving, and the pavement needs to be repaired. Thus, the punchout is divided into two stages by the time when longitudinal crack appears. The first stage is the form of longitudinal crack and the second stage is the degeneration of punchout area. There are a lot of research on the punchout of CRCP at domestic and abroad and obtaining great achievements, but these researchs almost about the first stage of punchout in macro-scale, and little study was done on the degeneration of punchout area and maintenance critetion based on two-scale model. CRCP is one of the importanr forms of high grade highway. Thus, to adapt to the development of the high grade highway, the studies on punchout of CRCP have great practical value.Based on the numerical simulation test and the indoor test, the degeneration of punchout area and maintenance criterion will be researched from the macro-scale and micro-scale model. Main research contents are as follows:Firstly, the vibration of punchout area is taken into consideration, the vehicle vibration model in puchout area is established and the coupling vibration of human-vehicle-road is analyzed. Impact load and passenger acceleration are obtained and influence factors are analyzed. Then, the subsequent cracking and concrete spalling mechanism can be studied based on the impact load, and maintenance criterion for punchout area can be studied based on acceleration of passenger.Secondly, the cement concrete which is constituted by aggregates, cementing materials and their interfaces is taken into consideration, and compressive strength test, flexural tensile strength test and shear strength test in meso-scale are simulated by using the discrete element method software. The formation of strength and mechanism of destruction for concrete are studied, and the compressive strength, elastic modulus, flexural tensile strength and shear strength of concrete are obtained. Considering the characteristics of punchout area and combining the elastic modulus which is obtained by the compressive strength test, the mechanics model of CRCP is established by the finite element method software and the flexural stress at the bottom of pavement in punchout area under vehicle load, temperature and moisture gradient is analyzed. Combining the flexural tensile strength which is obtained by the research on concrete in meso-scale, the subsequent cracks in punchout area are studied and the influence of the constitution of concrete factors in meso-scale and pavement factors in macro-scale are analyzed.Thirdly, based on the analysis of formation reasons for concrete spalling, the spalling is classified into shear spalling and delamination spalling, and the mathematical model of delamination spalling is built. Considering the characteristics of punchout area, the mechanics model of CRCP is established by the finite element method software and the shear stress at crack and the flexural stress at delamination place under vehicle load, temperature and moisture gradient are analyzed. Combining the shear strength and flexural tensile strength which are obtained by the study on concrete in meso-scale, the spallings in punchout area are studied and the influence factors of the constitution concrete factors in meso-scale and pavement factors in macro-scale are analyzed.Fourthly, considering the influence of cracks at the edge of punchout area on concrete performance, the acceleration loading test, dry-wet cycle test and freeze-thaw cycles test are conducted to study the degeneration of concrete. Then, according to the analysis of flexural strength, shear strength and cement concrete model test in meso-scale, the degeneration mechanism of concrete in second stage punchout area is studied, and the prediction method of the degeneration of second stage punchout area is given.Finally, the concept of step height at punchout area is put forward, the vibration of vehicle passing through punchout area is instantaneous is taken into consideration and the maximum transient vibration value(MTVV) is chosen as the riding comfort evaluation index. Then, according to the research on riding comfort evaluation criterion of transient vibration and the influencing factors of riding comfort, the method and procedure of the maintenance criterion of punchout area are given. According to the study on degradation mechanism and indoor test, the delaying measures for the degeneration of second stage punchout area are reserched.