Research On Evolution Mechanism Of Pore Structure In Porous Asphalt Mixture Based On Aggregate Morphological Characteristics

Functional properties of porous asphalt mixture(PAM),such as performance of draining water and noise reduction,maily depend on rich pore structure.However,in engineering applications,this pore structure is easy to be clogged by suspended particles in surface run-off or occur deformation under traffic load,which will lead the reduction in the spatial morphology,and thereby partly or completely lose functional properties of PAM.Therefore,the investigation on evolution mechanism of pore structure in PAM is significant for the structural design and maintenance of permeable pavement.Nevertheless,existing researches almost focus on the relationship between pore structure characteristics and mixture performances,ignoring the influence of coarse aggregate morphology.In fact,coarse aggregate is main medium that constitutes the pore boundary,and its morphology directly affects pore structure characteristics of PAM.Therefore,based on multi-scale technical methods,this article proposed a comprehensive research system that focused on the closed-loop study from aggregate morphology to pore structure characteristics to mixture performances and then back to aggregate morphology,for revealing the evolution mechanism of pore structure in PAM.Firstly,a 3D image analysis method for morphological characteristics of coarse aggregate was developed using industrial CT scanning,image processing and visual reconstruction technology,which could realize the integrated processing of the collection,extraction and geometric reconstruction of three-dimensional aggregate morphological characteristics.Based on this method,the distribution of aggregate morphological characteristics and correlations between each other were statistically analyzed.Meanwhile,a discrete element model(DEM)database of coarse aggregate was established for subsequent simulation research.Secondly,in order to clarify the strength mechanism of porous asphalt mixture against void attenuation under traffic load from the perspective of aggregate morphology,a threedimensional simulation method for coarse aggregate skeleton structure(CASS)was proposed using DEM database and virtual scan imaging technology.And this method was valicated to solve the difficulties of aggregate morphology combination in experimental researches and the transform to pore structure in simulation process effectively.Then,the distribution law of pore structure characteristics(porosity,equivalent pore diameter and fractal dimension)in CASS was analyzed along the longitudinal and radial direction.Meanwhile,the influence mechanism of coarse aggregate morphology on characteristics of CASS was quanlified using GA-BP neural network.Thirdly,a multiscale study was conducted on the evolution mechanism of PAM.From a macro perspective,a short-term rapid clogging(SRC)test and long-term cyclic clogging(LCC)test were designed.On this basis,SRC process of PAM was divided into four stages,and the characteristics of each stage were analyzed.In addition,the relationship between clogging index and clogging cycles during LCC process was established using Mistcherlich growth model.Moreover,the orthogonal test for PAM was conducted to reveal the influence of coarse aggregate integrated morphology on the anti-clogging performance of pore structure.From a mesoscopic perspective,pore structure meso-characteristics were evaluated by interconnected porosity,cross-sectional equivalent pore diameter and pore tortuosity,the longitudinal distribution and correlation of which were analyzed based on digital image processing technology.Moreover,the cross-sectional pore area and clogging index were chosen to investigate the evolution behavior of the pore structure in PAM during LCC process,and four longitudinal feature regions were determined according to cross-sectional clogging index.After that,the linear function correlation was discovered between the anti-clogging performance and each pore structure meso-characteristic.Lastly,the DEM analysis model of pore structure meso-characteristics was established on the basis of aggregate morphological characteristics,and thereby the interaction among aggregate morphology,pore structure characteristics and mixture performances(skeleton strength and anti-clogging performance)was quantified.In addition,considering the optimization of mixture performances,the value restriction of aggregate morphological characteristics was explored to give the corresponding technical requirements.Research conclusions quantify the correlation mechanism among aggregate morphology,pore structure characteristics and resistance to void attenuation,and also can surport the optimization design of aggregate morphology characteristics to strengthen the long-term service performance of PAM.In the future,the correspondence between the indoor research conditions and real traffic environment will be further determined using the on-site data,for promoting the precise implementation of PAM maintenance.