Structural Mechanics Analysis Of Old Asphalt Pavement Overlaying And Reconstruction Considering The Gradient Change Of Material Modulus

The usual way to rebuild old asphalt pavement is to overlay the asphalt surface.Asphalt materials are often regarded as isotropic materials for the design of asphalt pavement structure,but their existence ignores the limitation of the influence of the transverse isotropic characteristics of asphalt mixture on the mechanical behavior of asphalt pavement structure.In this paper,the finite element analysis method is used to analyze the road structure of the old asphalt pavement with asphalt layer.The horizontal stress and strain of the asphalt layer bottom,the vertical compressive stress and strain,the driving direction stress and strain,the shear stress and the horizontal direction stress of the base layer are analyzed.Strain,vertical compressive stress and strain,stress and strain in the driving direction,shear stress and strain,and road surface deflection are used as analysis indicators.Considering the transverse isotropic properties of asphalt mixture materials and the gradient change characteristics of modulus under factors such as temperature and aging,it aims to provide a more comprehensive reference for the design of asphalt pavement structures on old asphalt concrete pavements.Based on the basic equations of isotropic elastic axisymmetric statics,an equation suitable for transversely isotropic is established.The ratio of the transverse and longitudinal modulus is the transverse isotropy coefficient α,which represents the degree of transverse isotropy.The mechanical behavior of the old asphalt pavement overlaying asphalt layer structure under different degrees of transverse isotropy is compared and analyzed.The transverse isotropy coefficient α=1 is isotropic.After determining the value of the transverse isotropy coefficient α,determine the low temperature gradient model,high temperature gradient model,and aging gradient model under the influence of temperature in sequence.Furthermore,the effects of transverse isotropy,temperature aging modulus gradient model and aging modulus gradient model on the mechanical behavior of the old asphalt pavement with asphalt layer pavement structure are analyzed separately.The calculation found that when the value of the transverse isotropy coefficient a is in the range of 0.75≤α<1.0,it is more reasonable to evaluate the transverse isotropy of asphalt materials.Take the transverse isotropy coefficient α=0.8 for follow-up research.Under low temperature conditions,the horizontal stress S11,vertical compressive strain E22,and driving direction stress S33 of the two-wheel load position at the bottom of each functional layer all increase,while the vertical compressive stress S22 and shear stress S12 all decrease.Under high temperature conditions,the horizontal stress and strain S11/E11,vertical compressive stress and strain S22/E22,E33 and shear stress and strain S12 at the bottom of the asphalt layer under the two-wheel load position of the asphalt layer increased,and the stress S33 in the direction of the vehicle decreased slightly;The horizontal stress and strain S11/E11 at the bottom of the layer,the stress and strain S33/E33 in the driving direction and the shear stress and strain S12 all increase,and the stress S22 in the driving direction decreases slightly;the road surface deflection increases.The aging modulus gradient analysis found that the stress and strain at the bottom of each functional layer have been reduced,and the vertical compressive stress and strain S22/E22 and the shear stress and strain S12/E12 fluctuate slightly.The pavement design should focus on the changes in asphalt modulus caused by aging,and road surface deflection as an acceptance index also shows a decreasing trend.Finally,this article affirmed the influence of the transverse isotropy of asphalt mixture on its mechanical behavior,and obtained the best value range of the transverse isotropy coefficient a in this state.And under the influence of temperature and aging,the mechanical behavior of the old asphalt pavement with asphalt layer is obtained respectively.The road structure verification passed,indicating the feasibility of the old asphalt pavement paving and reconstruction structure.Therefore,in the process of constructing new and old pavements considering the transverse isotropic characteristics of asphalt mixtures,the pavement structure of this article has reference significance.