Study On The Influence Of RAP Morphological Characteristics On The Performance Of Recycled Asphalt Mixture

As the skeleton structure of asphalt mixture,the morphological characteristics of aggregate affect the stability,adhesion,friction and strength of the mixture,and the morphological characteristics are usually manifested as the smoothness,needle shape and angularity of the aggregate.Asphalt mixture recycled material(RAP)is subjected to vehicle load,and internal mutual extrusion friction leads to surface wear,which will adversely affect the performance of recycled asphalt mixture.Therefore,the physical morphological characteristics of RAP will be analyzed by software and compared with the new aggregate,and then the morphological characteristics of the aggregate will be changed by changing the 9.5mm～16mm RAP content to design the proportion,and the performance of the recycled asphalt mixture will be affected.In this regard,the main research content and conclusions of this paper are as follows.(1)The asphalt content increased with the decrease of RAP particle size,and the gradation of recycled material after pumping was significantly changed,and the fine aggregate content increased after extraction,the coarse aggregate content decreased,and the particle refinement phenomenon appeared.And in the old asphalt performance test,it was found to be seriously aging.(2)The difference between the physical morphological characteristics of the same grade RAP material,the extracted old aggregate and the new aggregate was calculated and analyzed by IPP image processing software.The test results show that the needle-like degree of the old aggregate below 9.5mm after extraction is higher than that of the extraction,and the roundness,roughness and angular parameters decrease with the increase of particle size.Compared with the new aggregate,when the particle size of the aggregate is greater than 9.5mm,the six morphological characteristic parameters are different,and the differences in roundness and angularity parameters are particularly obvious.(3)The RAP was graded,and the fixed RAP content was 30%,and the 9.5mm～16mm RAP content was increased by reducing the 4.75mm～9.5mm RAP content,thereby changing the morphological characteristics of the 9.5mm～16mm synthetic aggregate.Subsequently,the total RAP content was increased by increasing the 9.5mm～16mm RAP content to design the matching ratio.Among the 9.5mm～16mm particle size morphological characteristic parameters of the synthetic aggregate of the two design methods,the roundness and angular parameters were smaller with the increase of RAP content,and the axial coefficient,convexity,fractal dimension and roughness did not change significantly.(4)The performance verification of recycled asphalt mixture shows that the total amount of RAP is first affected by the high temperature stability,low temperature crack resistance and water stability of recycled asphalt mixture,and the increase of the total amount of RAP will improve its high temperature stability,and weaken its low temperature crack resistance and water damage resistance.Secondly,the roundness and angular parameters in the morphological characteristic parameters of the aggregate,the increase of 9.5mm～16mm RAP,the roundness and angular parameters of the aggregate were significantly reduced,thereby reducing the high temperature stability,low temperature crack resistance and water stability of the recycled asphalt mixture.