Effect of the contact structure characteristics on rutting performance in asphalt mixtures using 2D imaging analysis

The contact structure of asphalt mixtures has been considered as an important micromechanical mixture property related to the rutting performance. In this study, a two-dimensional (2D) image acquisition and processing procedure was utilized to acquire the contact structure of asphalt mixtures with varying compactness, gradation types, nominal maximum aggregate sizes (NMAS) and binder types. New indices for contact structure of different asphalt mixtures were developed based on three aspects: contact distance distribution, contact length distribution and contact orientation, including average contact distance (dave), proportion for contact distance no more than 0.5 mm (Pd⩽0.5mm), proportion for contact distance no more than 1 mm (Pd⩽1mm), total contact length (Lsum), number of contact (No. contact), average contact length (Lave), the average contact angle of inclination θ and the vector magnitude Δ. Flow number and strain rate from dynamic creep test were determined to be the rutting indicators for varying asphalt mixtures. A linear regression model was used to investigate the relationship between new contact indices and rutting indicators. The results indicated that the contact structure of varying mixtures could be successfully differed by the new indices proposed. New indices, such as Lsum, Lave and dave, could be ranked in a similar trend as the flow number. Furthermore, a more comprehensive index represented the contact structure of asphalt mixtures was developed to better uncover the mechanism of rutting in micromechanical perspective.