Internal structure evolution of asphalt mixtures during freeze-thaw cycles

This paper is an attempt to identify the internal structure evolution within asphalt mixtures under freeze-thaw cycles. Three types of asphalt mixtures were fabricated in the laboratory. X-ray computed tomography technology was employed to capture internal structure within samples before and after the freeze-thaw test. A set of image analysis procedures for extracting the internal structure properties was used to analyze the changes in air void distributions and to evaluate the internal structure evolution under freeze-thaw cycles. Results of X-ray CT image processing illustrated a dramatical degradation in internal structure after the freeze-thaw tests. The change in internal structure mainly occurs in three ways: (1) expansion of existing individual voids, (2) coalescing of two separated air voids, and (3) formation of new voids. Interestingly, the internal structure properties for three types of asphalt mixtures differs from each other and results in various forms of internal structure evolution and micro-crack formation under freeze-thaw cycles. In addition, the differences in internal structure degradation were also evaluated with the levels of water saturation and design void content, indicating their important role in the study of freeze-thaw damage of asphalt mixtures and in the design of asphalt mixtures in cold regions.