The evolution and spatial distribution of internal random pore structure are key factors in damage mechanism and macro-mechanical properties of concrete material under freeze-thaw (F-T) environment. This paper was presented to discover the deterioration mechanism of concrete under F-T actions. Through the experiment, visual examination was employed to evaluate the surface damage; the degradation considering the mass loss and uniaxial compressive strength of concrete was statistically analyzed under F-T environment. Moreover, X-ray tomography was adopted to characterize the concrete internal structure subjected to F-T cycles. The specimens exposed to F-T environment were scanned at regular intervals. Coupled with CT test, the pore space was characterized in terms of porosity and pore distribution by image analysis. And the relationship between the pore structure and the F-T cycles was described quantitatively by the fractal theory. The results indicated that the fractal dimension of the pore structure presented "down-up" trend with the number of F-T cycles increasing. The pore structure evolution changed from chaos to order and then to a process of disorder. The results demonstrated that F-T cycles accelerated the generation of meso-damage in concrete, which leads to more severe damage under F-T cycles.

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Three-dimensional printing (3DP) technology has undergone a rapid development in the last few years and become a useful tool in many research fields. This study applied 3DP technology to prepare solid specimens simulating rock-type materials combined with computed tomography scanning and 3D image processing. 3DP specimens with pre-existing flaws in different inclina-