Exploring freeze-thaw damage distribution of asphalt mixture through DIC in combination with CT

Abstract

Open graded friction course (OGFC) is highly susceptible to environmental impacts such as load and clogging, due to its rich void structure and exposure to environments. Especially in cold regions, freeze–thaw (F-T) damage is inevitable for OGFC. While the existing analysis methods cannot specifically describe the material's micro-response to load or environment. Therefore, the digital image correlation (DIC) in combination with computed tomography (CT) was applied to closely examine the intricate process of F-T damage of OGFC in this research. Principal strain and strain energy were used to describe the F-T damage process and distribution. In addition, the effects of initial void content and immersion conditions on the temporal and spatial distribution of damage were discussed. The data demonstrated that the spatial distribution of F-T damage strain was uneven. During F-T cycles, the principal strain inside the OGFC during F-T cycles was generally increased, and the deformation of the sample gradually accumulated. According to the strain energy growth rate variation, the F-T damage could be divided into two stages during the 18 F-T cycles, namely, the development stage and the deceleration stage. Moreover, the crucial parts of F-T damage were determined to be at the end of the voids connected with the outside or the void interface between the aggregates and asphalt mortar. The larger initial void content would increase the strain of OGFC during F-T cycles, as well as the inhomogeneity of the strain. Furthermore, the strain energy increased considerably, and the development of F-T damage of OGFC accelerated. Under partial immersion conditions, the immersed part has large strain and strain energy due to the direct effect of F-T, and the increase in immersion depth aggravates the F-T damage.