Effect Of Surface Microstructure Of Limestone Aggregate On Adhesiveness Of Aggregate To Asphalt

Due to the difference of physical properties of aggregates,there will be insufficient adhesion between aggregates and asphalt,resulting in the destruction of asphalt pavement.The aggregate-asphalt adhesion is directly related to the loose spalling,water damage,durability of asphalt pavement,strength of asphalt mixture,low temperature crack resistance and so on.However,most of the research on aggregates is still at the micro and macro level,and the research on the micro-structure of aggregates is less,and the research on the physical micro-structure of aggregates is still in the blank stage.In this paper,the same aggregate is scratched by means of corrosion simulation,the method of extracting pore structure and the macro-test of adhesion are used to realize the pertinence of aggregate micro-structure to the adhesion of aggregate to asphalt.Firstly,hydrochloric acid corrosion was used to simulate the pore structure on aggregate surface,and the pore structure difference was characterized according to the different corrosion concentration and corrosion time.The micro-pore(micro-pore)structure images of corrosion simulation specimens were obtained by field emission scanning electron microscopy(SEM).In order to ensure the multi-scale and omni-directional extraction of micro-pore structure on aggregate surface,four observation multiples were selected to photograph the micro-pore structure.Because of the complexity of pore on aggregate surface,the stability of pore structure eigenvalues can be guaranteed only by taking 8 pictures at each scale using single factor cumulative average criterion.Secondly,the image processing software is used to recognize the SEM micro-image of the pore structure,extract the basic data of the pore structure(area,average diameter,perimeter,length,width),and calculate the pore characteristic structure index(aspect ratio,shape factor).The pore structure is analyzed from three angles: the pore shape is relatively stable under different corrosion degree and different observation scales through the analysis of pore structure eigenvalue,and the pore size shows greater discreteness with the reduction of observation rate;the main pore height of each figure is similar based on the analysis of frequency histogram of pore characteristic index and score map of principal component factor.Most of them are irregular micro-cracks and elliptical grooves.There are also a few large holes,long cracks and circular grooves.At the same time,in order to study the influence of microporous structure on aggregate-asphalt adhesion,the macro-test was used to characterize the aggregate-asphalt adhesion.The adhesion force between aggregate and asphalt is measured directly by drawing test,and the contact angle between aggregate and asphalt is measured by surface energy theory.The surface energy of aggregate and asphalt is calculated,and the adhesion work between aggregate and asphalt is obtained by Young's equation.Finally,the relationship between aggregate micro-structure and aggregate-asphalt adhesion is established,and the concrete influence of aggregate micro-pore structure on aggregate-asphalt adhesion is obtained.Based on grey correlation analysis and principal component regression analysis,the relationship between them is established from qualitative and quantitative levels.According to the grey correlation degree,it is concluded that the pore size has greater influence on the aggregate-asphalt adhesion work than the pore shape.Principal Component Regression(PCR)analysis of regression equation shows that the size of nano-pore is the primary factor affecting aggregate-asphalt adhesion,and the shape of micro-pore is the main factor affecting adhesion.