Analysis On Micromechanical And Road Performance Of Asphalt Mixture After UV-aging Based On Mortar Character

Ultraviolet aging is one of the main forms of the each grade highway asphalt pavement aging in China's western region.It affects the asphalt pavement performance and shorten the service life.Therefore,based on the mortar character,these physical performance,rheological properties and micro-structure evolution of the asphalt mortar in ultraviolet aging process are studied.And the low temperature fracture properties of the modified asphalt mixture under UV aging were analyzed by particle flow numerical simulation method from the perspective of Micro-mechanics.In order to lay the foudation to establish the performance evaluation system for the UV aging of asphalt pavement,the filler-asphalt ratio is put forward and further underst and the mechanism of asphalt pavement degradation.These main contents and results in this paper were as follows:1.The filler in the composition of mortar was regarded as the starting point.Under the condition of quantitative UV irradiation,the content of filler affected the anti-aging property of asphalt was studied.Through these pavement performance test and rheologic cal properties test of these mortar,these difference of anti-aging ability between base asphalt mortar and modified asphalt mortar were analyzed.Further,the change of the filler-asphalt ratio was taken as the starting point,the influence of the filler to bitumen ratio on the water stability,the low-temperature anti-cracking property and high temperat ure stability in asphalt mixture was studied.By using the least residual sum of square method,the optimum ratio of powder to asphalt mixture was obtained.The results show that the addition of appropriate content of mineral powder could improve the anti-ultravi olet aging properties of asphalt.The UV aging reduces the anti-fatigue performance andlow temperature rheological properties of the asphalt mortar.Under the ultraviolet aging,the filler-asphalt ratio of these asphalt mixture was less affected by ultraviolet light in the following range,of which these filler-asphalt ratio of modified asphalt mixture was1.040,and the ratio of the matrix asphalt mixture was 1.245.2.Based on the Verhulst model,the nonlinear equation for characterizing these asphalt pavement performance deterioration was established under UV aging.Using the LM and the least squares algorithm to identify the relevant parameters,the reliability and correctness of the nonlinear equations under these two parameters are verified by the low temperature crack resistance experiments and the high temperature stability experiments under the different gradation asphalt mixtures.Two characteristic values which characterize the attenuation cofficient of the road performance of the mixture were presented:UV aging rate and UV aging residual index,which provide guidance for the conservation of asphalt pavement in ultraviolet region.3.By means of Fluorescence microscopy,Component separation,Fourier transform infrared spectrum and Gel Permeation Chromatography,these effects of mortar micro-structure and mineral content on the chemical properties of asphalt mortar were studied under UV aging.The relationship between macroscopic physical properties and characteristic parameters of molecular weight distribution was studied by gray entropy correlation analysis.The results show that the degree of UV aging of modified asphalt mortar depends on the interaction between polymer SBS,asphalt phase and filler.With the increasing content of filler,the mass average molecular weight Mw of macro-molecule SBS was related to macroscopic physical.And the UV aging of matrix asphalt mortar mainly depended on the effect of filler content on the number average molecular weight Mn in matrix asphalt4.Based on the coarse aggregate particle polygon algorithm combined with the numerical simulation of particle flow,a two-dimensional beams digital specimen of modified asphalt mixture was established,and was carried out the virtual bending fracture test.By monitoring the evolution of the internal cracks in the specimen and the change of the contact force between the particles,the mechanism of the formation of cracks in the asphalt pavement was revealed under UV aging.The results show that the crack was mainly occured in the interior of the asphalt mortar or the interface betweenthe asphalt mortar and the aggregate.The crack propagation rate of the sample after aging was greater than that before aging,and the change of the normal contact force between the particles after UV aging was most significant.