Evaluation of Micro-damage of Concrete Specimens under Cyclic Uniaxial Loading by X-ray CT Method

Abstract

The X-ray CT method was applied to evaluate micro-damage – namely, deterioration of concrete specimens under cyclic uniaxial loading tests. The μ-focus X-ray CT scanner was used. Concrete cylinders with a diameter of 50 mm and a length of 100 mm were prepared as specimens. Cyclic uniaxial loading tests were conducted on the specimens. The X-ray CT images of the specimens were taken at the loading level 0, 60, 70, 80 and 90 percent of their uniaxial compressive strength. For three dimensional CT images of the specimen, the Three Dimensional Medial Axis Analysis (3DMA) method was applied to evaluate porosity and width, length, persistence of cracks which represent deterioration of the specimen. As the results, slight micro-fracturing occurs until a loading level R = 60%, and starts to increase at R of 60% to 70%. The cracking occurs in a part of the mortar near boundary between aggregate and mortar, and the crack links to another crack with increasing loading level. The degree of cracking varies according to the position dependent on the final apparent fracture surface of the specimen. It is concluded that the X-ray CT method with 3DMA is effective for not only evaluating the state of micro-cracking within the specimen, but also estimating the process of deterioration of the specimen with an increasing loading level.