Resaerch On The Effect Of Aggregate Morphology On Affnity Between Bitumen And Aggregate

The appearance of potholes, stripping and other damages reduce the life of asphalt pavement. Adhesion failure of bitumen-aggregate caused by hydrodynamic pressure is the main reason that induces moisture damage in pavement structure. The surface morphology characteristics of aggregate have close relationship with the interfacial adhesion performance. The surface morphology characteristics of the aggregate refers to micro geometrical morphology remained on the surface after the aggregate is produced in the quarry. Carrying out the research on bitumen-aggregate adhesion mechanism caused by hydrodynamic pressure based on the aggregate morphology characteristics is one important way to deepen the moisture damage theory of asphalt concrete pavement.In this study, a new test method of bitumen-aggregate adhesion is established. The ultrasound is used for the simulation of the stripping of bitumen from aggregate surface under hydrodynamic pressure caused by high speed flow impact, and the test method of bitumen-aggregate adhesion based on ultrasound is designed. Ten kinds of coarse aggregate with one kind of bitumen are used for studying the adhesion based on ultrasound test method. It can be seen from the test results, the performance of bitumen-aggregates adhesion is not based on the type of aggregate(siliceous or carbonate) alone. Also, the adhesion is related with the surface morphology factors of aggregate.In order to reduce the subjective influence and improve precision of the adhesion test method, the automatic digital image acquisition and processing system is built up. The system is composed of the illumination, image acquisition and image processing. In the system, black box is used to decrese the effect of natural light, LED modules are symmetrically embedded in the inner surface of a black box as the directional light source improving the contrast of bitumen and aggregate, increasing the light intensity and reducing the shadow. Black is used as color of the inner surface of the black box to absorb unnecessary scattered light in the system. White is choosed as color of the test platform to increase the sharpness of aggregate profile. Then digital images of test sample are analyze and process by Image Pro-plus software. Then the ratio of the area of bitumen to aggregate can be calculated which is the bitumen residue rate on the aggregate surface, namely asphalt-aggregate adhesion test results.Three-dimensional laser scanner is used to describe aggregate’s surface morphology. MATLAB software program is used to rebuild three-dimensional topography of aggregate surface. Fractal theory is used to represent aggregate surface roughness of three-dimensional topography. The prism volume covering algorithm is used to calculate the fractal dimension of aggregate surface. The larger the fractal dimension, the texture of aggregate is more complicated and the surface is rougher. The fractal dimension is correlated with the bitumen-aggregate adhesion. The aggregate with a higher fractal dimension can obtain better adhesion.Polishing technology is used to change roughness of aggregate surface. Then the relationship between the roughness of aggregate surface and the bitumen-aggregate adhesion is analyzed. With the increasing polishing time, the aggregate surface is getting smoother. After a certain time, the fractal dimension of aggregates tends to be a constant value. When the roughness of aggregate surface is decreased, the bitumen-aggregate adhesion becomes worse. It is proved again that aggregate roughness is one important factor affected adhesion.