Study On Micro State Of Blending Of Aged And Virgin Asphalt In Recycling Asphalt Mixture Based On Trace Method

More and more pavements need to be maintained and rebuilt with the highway system completing.It is an important research issue to reuse the reclaimed asphalt pavement.One of the key questions is the degree of blending of aged and virgin asphalt in recycling asphalt mixture which has a notable influence on peformance.Researchers can’t form a clear cognition about it.There are less research on it in China,while foreign studies mostly take indirect means.This article makes an effort to study status of the blending of aged and virgin asphalt from micro viewpoint directly.First,this paper propose several markers and detection methods based on the principle of tracing and the purpose of study.In order to use element tracing, cobaltous naphthenate and 2-Ethylhexanoic acid are chosen to be markers,and EDS is used to detect the mapping of trace element.Different indexes are used to evaluate uniformity of the dispersion of different tracer proportion and mixing time in virgin asphalt. Results show that tracers can be well-distributed in asphalt which builds foundation of detection in mixture.This paper propose means to prepare mixture sample for EDS detection,and analysis many samples.But the mapping and line scanning results are interfered since content of trace element is low and heavy elments are high.The point detection results show that the degree of blending of two asphalt is high overall,while locally is lower.The fluorescence effect of epoxy can be observed by laser scanning confocal scanning microscope.This paper obtain the image of micro status of asphalt mastic in recycling asphalt mixture,and results show that virgin and aged asphalt can blend overall but in some area they don’t blend.This indicates that the degree of blending of two asphalt is not 100 percent.And inhomogeneity occurs not only in the film thickness direction, also occurred in the perpendicular to the thickness direction. Mixing nonuniformity is a three-dimensional existence.The research also tries to analysis the blending question in a quantifiable way. Using CTBN as tracer, a standard curve of characteristic peak area ratio and the amount of CTBN was established.CTBN content of the sample points can be backcalculated through the curve.Thus it is possible to analysis the average blending ratio of two kinds of asphalt.The research shows that blending ratio is high but not 100 percent. Orthogonal experiment was designed to study the influence of three factors on the average degree of blending. The results showed that the influence factors from high to low are as follow: mixing temperature, mixing time, dosage of RAP.This study builds foundation to improve the content of RAP.This paper for the first time prove that blending of two kinds of asphalt in recycling asphalt mixture is not complete in a direct way,and also obtain micro image of the existing status of virgin and aged asphalt.The experiments indicate that tracing method can be applied in this study.