Research On The Structure Stress And Reflection Cracking Of AC+CRC Composite Pavement

In the last twenty years, the highway construction of our country has beendeveloping rapidly. Along with the fast increase in traffic volume, the vehicles in roadtransportation are becoming larger and heavier, requiring stronger pavement structure.Thus, it is urgent to develop a high performance pavement structure with larger loadcapacity, longer durability and higher service level.Asphalt concrete (AC)+continuously reinforced concrete (CRC) compositepavement is a new type of pavement structure with high-performance. It is known thatCRC has higher strength and longer durability and that AC pavement is superior inriding quality and convenient to maintain and repair. AC+CRC composite pavementcombines the advantages of these two pavements. The AC layer plays the role offunction level and the CRC layer acts as the load-bearing course. Since China is rich incement and short in asphalt resource，it is suggested that composite pavement with ACfor the upper surface and CRC for the lower layer should be for considerations ofapplicability and economy.Based on the project of AC+CRC pavement for Changsha to Xiangtan Expressway,this thesis performs theoretical analyses on the structure design of AC+CRC compositepavement. Firstly Reinforcement in composite pavement is treated as an orthogonalanisotropy thin layer unit, and a3D finite element model is established using the FEMsoftware. Through calculation and analysis for different load position, the critical loadposition is found under different length of crack space. That is the transverse crack ofone side or in the middle part of the longitudinal joint. Effects of pavementconstruction factors such as transverse crack spacing, thickness and modulus of AClayer and CRC layer, steel ratio on load stress and thermal stress are studied. In theanalysis of thermal stress, the finite element model of ther mal stress is established. Theinfluences of pavement construction factors on the thermal warping stress are thendetermined.Secondly, base on the theory of fracture mechanics, the stress analysis model isestablished to simulate the continuously reinforced concrete with asphalt concreteoverlay composite pavement using the FEM software. The corresponding normal stressand shear stress are analyzed under the effect of symmetry load and bias load. Thestress intensity factors of load are calculated and effects of structure thickness and modulus, steel ratio and inter-layer conditions on reflection cracking in AC layer areanalysed. Results of the analysis show that increasing AC layer thickness, increasingsteel ratio, and improving interlayer bonding conditions have certain effects ondelaying reflection cracking, while the thickness and modulus of CRC layer andmodulus of AC layer have little effects on cracking propagation. These results couldprovide a theoretical basis for design of AC+CRC composite pavement.Lastly, with respect to the pavement construction of Changsha to XiangtanExpressway, material quality requirements and construction techniques are discussed.Pertinent suggestions are made for assuring construction quality of the AC+CRCcomposite pavement.