THE MATERIAL PRINCIPLE OF BLEEDING IN ASPHALT PAVEMENT

Based on discussions on the classic definitions of bleeding phenomenon in asphalt pavement and their mechanisms, the defects of three classic mechanism explanations are exposed. From the point of multi-polymers, the rheologic behaviors of asphalt，such as ‘climbing pole’ , ‘shearing dilution’, ‘expansion after extrusion’ and ‘tubeless siphon’, are analyzed. With the rheologic mechanism of bleeding put forward by LIU Lixin as a basis, ‘earthworm effect’ model for bleeding is presented. The theoretical and practical directions of ‘climbing pole’ of asphalt binder in pavement are deducted. Investigation of asphalt modification mechanism shows that chemical modification of asphalt changes the molecular structure of asphalt and strengthens its elastic behaviors, making bleeding easier in modified asphalt pavement under suitable condition. ‘Earthworm effect’ model satisfactorily explains the new bleeding phenomenon in some expressways. Finally, discussion of some important influential factors on bleeding, such as pavement temperature, quantity and velocity of shearing, fiber and mineral fillers, time, difference of asphalt containment between pavement layers, is made.