Localized Damage Analysis of Cement Mortar Using X-ray Computed Tomography In Situ Compressive Loading and Digital Volume Correlation

In this study, X-ray computed tomography (X-ray CT) in situ compressive loading was used, in combination with digital volume correlation (DVC), to analyze the localized damage behavior of cement mortar, the cracking process, microstructural changes, and strain distribution. By using X-ray CT, it was possible to identify the three-dimensional structure and two-dimensional internal morphology of compressed cement mortar. The development of localized damage was significantly influenced by the unhydrated cement. Cracks in the material did not always expand with an increasing load, and the formation of new cracks made old ones become extruded. After conducting a DVC calculation, it was found that the loading procedure contained bias. The bias during loading and the non-homogeneity of the material can cause uneven strain distribution. The maximum principal strains are all tensile, causing tensile damage. To reflect the damage inside the specimen, the gray value of the CT image and the damage index determined by the maximum primary strain were used. A localization factor was introduced to characterize the damage failure process in three dimensions. The internal localization damage of the material occurred earlier than that on the surface, and the damage develops from the inside out, according to the results of the CT image's gray value, damage index, and localization factor. The damage develops from the inside out, which may be caused by the phenomenon of a compression load or bias pressure. In order to reach a reliable conclusion, more research is required.