Research on the homogeneity of asphalt pavement quality using X-ray computed tomography (CT) and fractal theory

This paper presents an imaging method to assess the homogeneity of asphalt concrete using X-ray computed tomography, the improved OTSU image method, and fractal theory. Specifically, this research attempts to analyse the principles of X-ray computed tomography (CT) and to discover the cause of "dead pixels" in CT images. They are further processed by combining the annular block and OTSU methods. For this, the image is divided into several annular regions of similar brightness. The OTSU method divides the image into two parts, the object and the setting, for which the largest variance equals the least mistakes. Fractal theory can effectively calculate the complexity of the curves. Then, the fractal dimension can be calculated using the box-counting dimension method. This article applies pavement-quality indicators to test asphalt pavement and to choose four specimens with various degrees of segregation. A segregation evaluation standard based on fractal dimensions and the imaging method was established. By testing the physical indices, including the density, air void, strain, fatigue life and stiffness modulus of the specimens, it was concluded that the fractal dimension can define the 3D segregation of asphalt pavement well. The analysis also indicates that when the fractal dimension is relatively small, the boundary characteristics of the aggregate and mucilage will be relatively simple, and the uniformity coefficient will be larger with a shorter fatigue life. (C) 2014 Elsevier Ltd. All rights reserved.