Adhesion Improvement between RAP and Emulsified Asphalt by Modifying the Surface Characteristics of RAP

Recycled asphalt pavement (RAP) can be used in highway engineering again by cold recycled technology. Due to the aged asphalt on the surface of RAP, some problems such as poor adhesion between emulsified asphalt and RAP and the low properties of emulsified asphalt recycling mixture are easy to occur. This work aims at analyzing the aging degree of asphalt from RAP surface and improving the poor adhesion between RAP and emulsified asphalt by modifying the surface characteristics of RAP. In this work, a new device was designed to delaminate off the asphalt on the surface of RAP. The aging degree of asphalt at different layers was studied then by physical properties and molecular weight distribution. Slurry of hydrated lime (Ca(OH)2) (S-Ca) and slurry of silane coupling agent (SCA) modified Ca(OH)2 (S-Si-Ca) were used to modify the asphalt on the surface of RAP, respectively. The adhesion between emulsified asphalt and RAP was studied by contact angle and boiling method. Results show that the asphalt on the RAP surface can be successfully stripped into four layers through the self-designed RAP delaminating and stripping device. The aging degree of asphalt wrapped around the surface of the RAP showed a tendency to be gradually severe from outside to inside. However, asphalt at the innermost layer (L4) shows abnormal situation due to the fact that the light components are absorbed by the aggregate. In addition, reasonable dosage of SCA is determined as 3.0% in Ca(OH)2 powder mass. Both S-Ca and S-Si-Ca can effectively reduce the contact angle and thus improve the adhesion between emulsified asphalt and RAP. Moreover, S-Si-Ca possesses the most obvious modification effect attributed to the formation of asphalt-SCA-Ca(OH)2 structure.