The Influence Of Interlayer Pattern On The Structure And Performance Of Double Layer Porous Asphalt Mixture

In the double-layer drainage pavement structure,the lower layer with lager pores has the traditional drainage and noise reduction functions,while the upper layer with smaller pores prevents external debris from entering the deeper pores,which improves the service life of the pavement and reduces the difficulty of pavement maintenance.The interlayer shape between the upper and lower layers plays a decisive role in the structure integrity and internal void connectivity of the double-layer drainage pavement.In this paper,the interlayer shape of double-layer drainage mixture is taken as the research object,and the influence of the interlayer shape of different molding processes on the interlayer mechanical properties,interlayer void connectivity characteristics and anti-clogging is studied,so as to provide reference for the design and construction process optimization of double-layer drainage mixture.Firstly,the number of concave and convex points and the average undulating heights on the interlayer of double-layer drainage mixtures under different molding processes were collected by oil absorption papers and aluminum sheets.Based on the W-M fractal function,the virtual interlayer shape models were generated,which conforms to the characteristic of the real interlayer;According to the results,the values of scale parameter G and fractal dimension D of the interlayer shapes are 1e-12～1e-10 and 2.300～2.386,respectively.The lager G and the smaller D are,the fewer concave and convex points are,and the higher the average fluctuation height is.Next,the real shape aggregate model library is established by using 3D modeling software,and the Bubble-Pack algorithm in PFC3D software is used to fill the aggregate template to obtain the aggregate particle model;The parameters of burger`s model at ordinary temperature and high temperature were determined by uniaxial creep test and dynamic shear rheological test;Based on the hot-on-cold method,hot-on-warm method,hot-on-hot method,the virtual specimens corresponding to the interlayer shape model were formed;Through the self-developed pore visualization function,the porosities along the depth direction in the virtual specimens are determined and compared with those in the real specimens.The results show that the interlayer fluctuation height:hot-on-cold method<hot-on-warm method<hot-on-hot method,while the transition degree of plane porosity along the depth direction in the interlayer is opposite.Then,the type,number and angle of force chain at the interface of the specimens under different interlayer shapes are analyzed,and the formation mechanism of interlayer strength of the double-layer drainage mixture is revealed;The virtual shear test and pull-out test were designed,and effect of interlayer shape on the interlayer mechanical properties was analyzed;The procedure of tack coat oil sprayed was simulated,and the effect of different spraying amount on the distribution of tack coat oil,effective force chain related tack coat oil was analyzed;The simulation results were verified by shear and pull-out tests.The results show that with the increase of the fractal dimension D of interlayer shape,the number and distribution angle range of the interlayer force chains decrease,and the interlayer shear and tensile resistance become worse.When the amount of tack coat oil is about 0.3kg/m~2,the interlayer bonding strength reaches the best,and the number of effective force chains reaches maximum.Finally,the interlayer connected voids of specimens with different interlayer shapes are obtained by using the self-developed function algorithm;CT scanning was carried out on the double-layer drainage mixture under different molding processes,and the threshold value based on Otus method was modified to obtain the binary slice image;Avizo software is used to visualize the internal connected void structure of double-layer drainage mixture.In the discrete element software,spherical particles with the same radius are used to replace the void pixels to obtain the interlayer connected void model,and the accuracy is further verified by constant head seepage test;Based on the interlayer connected void models of virtual and real specimens,the pavement models with only interlayer connected void structure are constructed.The clogging behavior of the double-layer drainage mixture with different interlayer shape and different tack coat oil content is revealed,and the influence of the interlayer shape on the drainage performance and anti-clogging is determined.The result show that without tack coat oil,the lager the fractal dimension D is,the lager the interlayer connected porosity is,the better the drainage performance is,but the worse the anti-clogging is.The increase of the amount of tack coat oil will lead to the decline of drainage performance and the improvement of anti-clogging.In this paper,the research results reveal the relationship between the interlayer shape and the molding process of the double-layer drainage mixture,and put forward the change law of interlayer mechanical properties,drainage properties and anti-clogging with the interlayer shape,which has reference significance for the selection and design of the molding process of double-layer drainage mixture.