Interlocking property evaluation of dual skeleton in semi-flexible pavement material by micromechanical model and X-ray computed tomography

Abstract

Semi-flexible pavement (SFP) material has been proven to have more interlocking effect than its Porous Asphalt (PA) matrix because of the secondary skeleton consisting of interconnected grouting cement. However, because of the irregular, elongated and concave shapes conflicting with the requirement of aggregates, together with a stiffness much higher than that of asphalt binder (which can bear and transfer most of the load), it is hard to define whether cement grouted into air voids works mainly as a role of another aggregate or binder. Based on the X-ray computed tomography and digital image process method, this study aims to distinguish effective coarse aggregate-grouting cement contacts (cement working as aggregates) from noneffective ones (cement working only as binder). A contact classification method, as well as a fast contact calculation method, was proposed. The characteristics of different types of contacts were analyzed and two morphological interlocking indexes were established based on the concept of contact points and contact lines, respectively. A mechanical interlocking index was also back-calculated from a micromechanical model as a reference. The result reveals that there exists a good linear relationship between the mechanical and morphological interlocking indexes, verifying the validity of the contact classification method. Additionally, with a larger quantity than that of contacts between coarse aggregates, only one-sixth of aggregate-cement contacts are effective ones, the number of which is half of the coarse aggregates’ contacts. As for contact lines, while the average length of effective aggregate-cement contacts is the same as that of aggregate contacts, the length of the noneffective ones is only the half.