An analytical–empirical investigation of the bleeding mechanism of asphalt mixes

• The bleeding of asphalt concrete is investigated using image analysis.
• An X-ray CT system was used to capture the internal structure of the specimens.
• We characterize the air voids distribution in asphalt mixes.
• We evaluate the influence of gradation on air voids distribution.

In literature on asphalt mixes, bleeding is considered to occur mostly due to poor construction practices. Also, other than empirical and qualitative observations, there have been little attempts to understand its mechanism. The aim of this study was to evaluate the analytical–empirical bleeding mechanism of asphalt mixes. This evaluation is based on the distribution of air voids in asphalt mixes. An X-ray computed tomography (X-ray CT) system was used to capture the internal structure of the specimens and image analysis techniques were used to quantify the distribution of air voids. The method used was based on image analysis. Firstly, the specimen was scanned using X-ray CT. Then, dynamic loading was applied at temperatures 5, 25, 40 and 60 °C and the specimens were scanned again after loading. At the end, image processing and analysis software were used to quantify the distribution of air voids in the X-ray CT images. The stress–strain results obtained from dynamic loading and the variations in the distribution of air voids in specimens clearly demonstrate the influence of the distribution of air voids on asphalt bleeding.