Effect of FTC on the interface between soil materials and asphalt concrete using a direct shear test

The process of freezing and thawing has a great effect on different aspects of materials in cold regions. Due to the complex behavior of materials under the impact of freezing and thawing, several studies conducted on the individual behavior of soil materials or asphalt concrete on this condition. In the present study, the impact of freezing and thawing on the strength characteristics and interaction ratio of soil materials from classes GC (clayey gravel) and GP (poorly graded gravel) at the interface between asphalt and soil materials was assessed. The particle size distribution of the aggregate used in this study was within the grading range recommended by the International Commission on Large Dams (ICOLD) and Fuller's ideal grading curve used in the construction of Mijran Dam, Mazandaran Province, Iran. First, granular materials and asphalt concrete were subjected to weight loss test and durability study, respectively, according to AASHTO-T103 and Iranian Standard 12728. Then, utilizing a large-scale direct shear machine, the contact surface element (interface between granular materials and asphalt concrete) was evaluated under dry and saturated conditions as well as under various freeze-thaw cycling (FTC). The results demonstrate that an increase in the number of FTC let to a decrease in the maximum shear stress under dry and saturated circumstances for both clayey gravels and poorly graded gravels materials at interference with asphalt concrete. In GC materials at the contact surface with asphalt concrete, the interaction ratio reduces by 0.22 % under dry conditions and by 0.54-1.2 % under saturated conditions, relative to its value in the tenth cycle, as the number of FTC increases. In GP materials at the interface with asphalt concrete, as the number of FTC increases, the interaction ratio drops between 9.2 % and 33.61 % in dry conditions and by 20.62 % in saturated situations compared to the value that occurred in 10 cycles.