Introducing a simple method to determine aggregate gradation of hot mix asphalt using image processing

The aggregate gradation is one of the most important parameters in the mechanical properties of hot mix asphalt (HMA). Thus, determining the aggregate gradation is a very significant subject in civil engineering. Usually, to estimate the aggregate gradation, it is required to separate the aggregate from the bitumen, and this operation can be time-consuming and even dangerous related to chemical solvents. Moreover, several computer-based methods have been established to model the internal structure of HMA in two- and three-dimensional methods and can be applied to determine the aggregate gradation, but these methods need special and expensive equipment. Therefore, in this study, a simple approach is introduced to quickly and easily determine the aggregate gradation of HMA from the prepared cross-section images of cylindrical samples using numerical and image-processing techniques such as fitting equation and colour space system. The obtained results indicate that the introduced method can detect the aggregate gradation with high accuracy and can be used as a satisfactory alternative to other expensive methods.