Analyze The Thermal Stresses Of Asphalt Pavement In Circular Low Temperature Environment

Asphalt surface will be cracking in low temperature, it has always been a main form of pavement diseases in the road engineering in north China, even in the Yangtze river which has relatively mild climate, when the cooling rate is too fast, the asphalt surface will be cracking because of the stress relaxation ability is insufficient. But, so far our country current highway asphalt pavement design specification still lack of the corresponding control parameters、indicators and methods which can control the craze due to the low temperature. On the one hand, the selection of the material parameters is completely in accordance with the requirements of specification using the uniform modulus when the asphalt pavement structure is designed, but in fact, the asphalt mixture is a kind of environment sensitive material, which means the change of the external environment will cause the non-uniform change of the material parameters in the pavement depth direction, so the method in the conventional pavement design and mechanics calculation which think the design and calculation of material parameters is always uniform has a great gap with the usage of the actual pavement. On the other hand, how the structure factors such as interlayer contact state will influence the temperature stress of the pavement structure has not yet been to carry out systematic research work. Therefore to establish a suitable model for the stress analysis of asphalt pavement structure under low temperature load has great significance for the improvement of the low temperature anti-crack design methods of the asphalt surface.At first, this paper studies the temperature stress problem of the ice-snow road under circular low temperature environment with state space method on the elastic foundation, meanwhile, perform parametric analysis, the temperature on the road length direction will present non-uniform distribution at this time, the results show that under the low temperature environment the tensile stress in the pavement structure are greatly, when the temperature stress reaches the tensile strength, the pavement structure will produce low temperature shrinkage crack; and the tensile stress in the pavement structure are different at different times because of the big temperature gap between day and night in a day, when the temperature changes in a daily cycle、a annual cycle, which means the road surface temperature will rise and fall repeatedly,it can cause temperature fatigue cracks, the pavement structure layer which is more close to the surface will be more vulnerable to the influence of road surface temperature rise and fall repeatedly, and more prone to temperature fatigue cracks.Secondly, the static problem of each structural layer of FGM pavement model under the low temperature load is studied under the condition of considering the weak bonding between pavement structure layers, the non perfect of the bonding surface is described by using a linear elastic model, through a numerical example, this paper discusses how the non perfect of the bonding surface will influence the temperature stress of pavement structure, and this paper compares and analyzes the surface model which considering the weak interlayer bonding and which regardless of the weak interlayer bonding, on the other hand this paper also compares and analyzes the calculation results with the consideration of material characteristic and without the consideration of material characteristic. Results show that when the flexibility coefficient of road surface is not taken into account,the evaluating of the temperature stress is likely to underestimate the tensile stress of pavement which will cause to pavement early cracking, pavement temperature stress by traditional homogeneous model sometimes will lead to the misdiagnosis phenomenon that is pavement structure actually not to crack but are thought to have craze.Finally, when the low temperature load is uniformly distributed, this paper studies the temperature stress distribution of pavement structure layer. The results show that the temperature of pavement structure changes in the different depth is mainly caused by the periodic changes of environmental factors, and the heat in the process of transfer is accompanied by energy attenuation. The temperature stress of the surface layer will increase with the increase of the equivalent modulus parameters of the foundation, and finally tends to a stable value, we should choose the equivalent shear modulus parameters and the equivalent spring modulus parameters according to the actual situation when calculating the foundation, lest cause to the difference between the pavement structure temperature stress by calculated and the actual value is too large, which will result in pavement design is unreasonable and cause the temperature crack of pavement.