Damage analysis of cold recycled mixture under freeze-thaw environment based on CT technology

The development of meso-damage of cement stabilized cold recycled mixture under freeze-thaw environment was revealed by indoor test, and the effects of cement and recycled asphalt pavement material (RAP) on its damage in different freeze-thaw cycles were analyzed. The specimen after freeze-thaw cycle was scanned by CT machine, and the batch of 2D slice images were obtained. The cross section was analyzed by using the image processing technology, and the damage variable was introduced based on the change of the CT mean value in the image. The results show that with the increase of the number of freeze-thaw cycles, the average CT of mixture cross section increases at first and then decreases. On the other hand, the damage variable first decreases and then increases, which reflects the whole process of cement stable cold recycled mixture from initial meso damage to macroscopic damage in freeze-thaw environment, which can be divided into four stages, i.e. N \leqslant 1, 1 <N \leqslant 3, 3 < N \leqslant 7 and 7 < N \leqslant 9. When the number of freeze-thaw cycles is less than 7, the cement content has a significant effect on the specimen damage, and the addition of cement can improve the adhesion and early strength of the mixture. When the number of freeze-thaw cycles is more than 7 times, the damage of the specimen is mainly affected by the content of RAP, and the excessive content of RAP will aggravate the damage of the mixture.