Method for the Evaluation of the Homogeneity of Asphalt Mixtures by 2-Dimensional Image Analysis

A Novel Evaluation Method of Construction Homogeneity for Asphalt Pavement Based on the Characteristic of Component Distribution

To effectively evaluate the construction homogeneity of asphalt pavement, the tomography image of a core sample of asphalt pavement was obtained via industrial computed tomography (CT) equipment. According to the characteristics of CT images, an improved separation algorithm based on annular partition and Nobuyuki Otsu (OTSU) threshold segmentation was proposed. Based on the distribution of aggregates, voids and asphalt mortar, and the area ratio of each part in the CT images inside the pavement, a novel evaluation method for the distribution homogeneity of asphalt pavement components was put forward, and the validity of the evaluation index was also verified. The results show that the aggregates, voids and asphalt mortar in CT images can be effectively segmented by annular partition combined with the OTSU threshold separation algorithm. By superimposing the segmented image on the original image, the segmentation and identification effects of aggregates, voids and asphalt mortar in the CT image are confirmed. Compared with a non-segregated specimen, the average values of the horizontal heterogeneity coefficients of high, medium, light and fine-aggregate-segregated mixtures increased by 72.0%, 48.3%, 34.7% and 16.1%, respectively, where the change range is in accordance with the segregation degrees of several mixtures. The indirect tensile strength of fine-aggregate-, light-, medium- and high-segregated asphalt mixtures decreased by 8.3%, 16.7%, 25.0% and 45.8%, respectively, when compared with the non-segregated asphalt mixture. The index of the vertical heterogeneity coefficient has good correlation with the indirect tensile strength of segregated asphalt mixtures. The construction quality homogeneity of asphalt pavement in different regions can be reliably evaluated by the horizontal heterogeneity coefficient and vertical heterogeneity coefficient.

Characterization of Rutting Damage by the Change of Air-Void Characteristics in the Asphalt Mixture Based on Two-Dimensional Image Analysis

In the process of the rutting test, the air-void characteristics in asphalt mixture specimens are a dynamic change process. It is of great significance to systematically study the correlation between the change of air-void characteristics and the depth of the rutting slab and establish a relationship with damage. In this paper, the air-void information of rutting specimen sections with different loading cycles (500, 1000, 1500, 2000, 2500, and 3000 times) is obtained by two-dimensional image technology. The dynamic change process of the micro characteristics of internal air voids of two graded asphalt mixtures (AC-13 and AC-16) under cyclic wheel load is analyzed, and it is used as an index to characterize the microstructure damage of the asphalt mixture. The results show that the variation of air-void distribution, air-void shape characteristics, and air-void fractal dimension with the loading process can well characterize the permanent deformation law of the rutting slab. The fractal dimension of the air void increases with the increase in load. It is a dynamic process in which the air-void content changes with crack initiation and propagation. After rutting deformation, the total air-void area and average air-void size of the sample increase, and the total air-void number decreases. Because microcracks are formed in the specimen after rutting damage, the aspect ratio of the air void increases, and the roundness value decreases.