Research On Asphalt Concrete Pavement Thermal Stress And Low Temperature Cracking

Low temperature cracking of asphalt concrete pavement is widespread in coldregions of northern China, after a cold winter, transverse cracks often appear at acertain intervals in the road surface, with other cold regions of the world, thisphenomenon also occurs frequently. The appearance of cracks for water enter to theroad structure provides favorable conditions, resulting in lower bearing capacity andservice life of the road structure, so the analysis of asphalt pavement thermal stress ofthe cold regions has a very important practical significance.In this paper, firstly according to the measured temperature data of the road,using finite element software ANSYS to simulate temperature field substep along theroad depth direction, at the same time calculate the structure temperature gradient.The results show that the greater temperature difference between the road surface andthe soil basal surface, the greater temperature gradient within the structure; withincreasing of the road depth, the absolute value of the temperature gradient getssmaller and smaller; the temperature gradient of the road structure in summer andautumn is the positive temperature gradient, the temperature gradient of the roadstructure in winter is the negative temperature gradient.Then, in reference to a large number of domestic and foreign literatures and onthe basis of research achievements, establish asphalt pavement thermal—structurecoupling three—dimensional finite element model under low temperature to analyzecooling rate, parameters of asphalt surface and base influence law of the thermalstress, in addition considering influence of contact condition between surface and baseon the thermal stress. The results show that the maximum thermal stress of asphaltpavement appears in the road surface, if exceeds ultimate tensile strength of asphaltmixture, there will be cracks; the greater cooling rate, the larger thermal stressgenerated within structure; increasing thickness of surface layer can reduce thermalstress, but the effect is not obvious; the influence of surface modulus to thermal stress of road surface, bottom of the top and the bottom layer is more noticeable, along withincreasing of surface layer modulus also increases as the thermal stress, while to thebottom of base and subbase thermal stress had little effect; when asphalt surfacetemperature shrinkage coefficient increases, the thermal stress of road surface, bottomof the top and the bottom layer are increased, the maximum thermal stress is largelyincreased half of the original, while the bottom of base and subbase thermal stresschanges little; the effect of variation of base thickness and modulus on thermal stressis very small; through contact element to simulate interlayer contact conditions, whenthe contact state is not the same between bottom layer and base, changes of thethermal stress is very obvious at different contact conditions, because of stressresponse of contact model is more in line with actual road working condition, so whenmaking asphalt pavement structure design, the proposed contact model for analysis.Finally, based on the analysis of influence factors of asphalt pavement thermalcracking, according to the different influence factors on the analysis of the thermalstress, the method was proposed for predicting the crack spacing in the asphaltpavement. Through the finite element analysis shows that the lager cooling rate of theroad environment temperature, the smaller road pavement crack spacing; increasingthickness of asphalt surface and base can reduce the crack spacing, but contributelittle; with increase of surface layer modulus, the crack spacing shortened; withincrease of the surface layer temperature shrinkage coefficient, the crack spacinggradually shortened; change modulus at base, the crack spacing is constant. Thus itcan be seen that the crack of asphalt pavement is not only related to the nature of thematerial itself, but also related to the road structure conditions.