X-ray microtomography for fracture studies in cement-based materials

In this study we are interested in microstructure-property relationships in portland cement-based materials. Specifically, we are interested in relating microfracture and damage to bulk mechanical properties. To do this a high resolution three-dimensional scanning technique called x-ray microtomography was applied to measure internal damage and crack growth in small mortar cylinders loaded in uniaxial compression. Synchrotron-based microtomography allows us to resolve internal features that are only a few microns in size. Multiple tomographic scans were made of the same specimen at different levels of deformation, the deformation being applied through a custom built loading frame. Three-dimensional image analysis was used to measure internal crack growth during each deformation increment. Measured load-deformation curves were used to calculate the non-recoverable work of load on the specimen. Incremental non-recoverable work of load was related to measured incremental change in crack surface area to estimate work-of-fracture in three dimensions. Initial results indicate a nearly constant work-of-fracture for the early stages of crack growth. These results show that basic fracture mechanics principles may be applied to concrete in compression, however we must think in terms of 3D multiple crack systems rather than traditional 2D single crack systems.