Evaluation methods and indexes of morphological characteristics of coarse aggregates for road materials: A comprehensive review

The morphological characteristics of coarse aggregates, namely shape profile, angularity and surface texture, have a significant effect on the mechanical properties of asphalt mixtures. The identification methods and evaluation indexes of the morphological characteristics are crucial for the coarse aggregates. First, the visual identification technologies, including charged coupled device (CCD) image processing, X-ray tomography imaging and laser scanning technology, are summarized in term of the characteristics, research status and existing problems. Based on the deficiencies of visual identification technologies, it is proposed to improve the three-dimensional reconstruction of aggregate particles by increasing the number of two-dimensional projection directions or scanning sections. Moreover, the evaluation indexes of coarse aggregate morphology were summarized from the three aspects, namely shape profile, angularity and surface texture. It is found that evaluation of the indexes based on two-dimensional profile images or unrelated to pavement performance could not adequately evaluate the morphological characteristics of coarse aggregates. Therefore, the evaluation methods and indexes of coarse aggregate morphological characteristics have been recommended based on the performance of asphalt mixtures in this paper, which is helpful to establish a complete set of an evaluation system for coarse aggregate morphology.