Image analysis for detecting aggregate gradation in asphalt mixturefrom planar images

The mechanical properties of bituminous mixture strongly depend on the gradation of the aggregate thatrepresents the mineral skeleton of the mixture, since for open and gap-graded mixtures, stresses due tovehicles in movement on the pavement are mainly transmitted through their contacts. Internal structureof bituminous mixture is, therefore, of great interest for road and infrastructure engineering and it isappropriate to study it with recently developed image analysis method. The purpose of this study wasto finalize an effective analysis of asphalt section image for automatically extracting aggregate gradationwithout the need of separation of the bitumen from the aggregate. This paper proves that, thanks to thesynergic use of different segmentation methods of the digital images taken on slices of cores from thepavement, it is possible to obtain a reliable gradation of the mineral skeleton of the mixture. The proposedmethodology allows one to estimate the aggregate gradation that, otherwise, it would be necessaryto establish via specially equipped laboratory, undertaking time-consuming tests that also imply healthrisks for the operators, due to the use of solvents and other hazardous materials.