3-D X-ray CT Image Analysis of Concrete Microstructure and Fracture

The ultimate research goal focused on cementitious materials is to characterize, simulate, predict, diagnostic and rehabilitate the behavior of quasi-brittle materials. Typical quasi-brittle include, but are not limited to, concrete, cementitious composites, sea-ice, cohesive and frozen soils, and toughened ceramics. However, a wide variety of other materials (e.g. macromolecular based polymers, biomedical materials, and nano composite materials) feature quasi-brittle behavior when analyzed at length scales (micro- and nano-scale) smaller than the usual engineering scale (macro-scale).

We have been developing various computational technologies for the simulation of the mechanical behavior of quasi-brittle materials under severe loading and environmental conditions. The ultimate objective is to provide the engineering industry applicable model based simulation tools that will improve the performance of structures to mane-made and natural hazards, as well as enhance the disaster resilience properties.

This research developed the first three-dimensional digital sliced images of the 3-D cracking X-Ray CT images acquired from Landis. We achieved an isotropic resolution (844X844X623) of cubic voxel at 6 micrometers on a side, which is the highest resolution achieved in a cement concrete microstructure. Using software Iso2mesh, phases were also individually segmented and reconstructed to create three-dimensional geometry. Additional quantitative information including, volume, surface areas, and mean gray scale intensities were also determined. High-quality volume tetrahedral mesh and surface triangle mesh are both generated using mesh-generator MeshVol, developed by the authors.

3-D views from one end of the specimen set C4 and two 3-D Side views of the specimen C4, volume rendering without segmentation

3D view of the specimen set C4 and display in Orthoslice mode

2-D Crack patterns of certain image slice

Set 3 # 533/580 [XY]

Set 5 # 533/580 [XY]

Set 7 # 533/580 [XY]

A high resolution three dimensional (3D) scanning technique called X-ray Microtomography was used to measure internal crack growth in small mortar cylinders under compressive loading. Tomographic scans were made at different load increments in the same specimen. All the currently used sliced image sets are obtained from Prof. Landis at University of Maine. 3D image analysis is used to measure internal crack growth during each load increment. Load-deformation curves were used to measure the corresponding work of the external load on the specimen. Separate components for crack formation energy and secondary toughening mechanisms are proposed. The secondary toughening mechanisms were found to be about three times the initial crack formation energy.

2-D sliced image of cracked sample set C4 after image segmentation

3-D reconstruction of the crack microstructure, view from the top

3-D reconstruction of the crack microstructure, view from side

3-D Crack network profile

3-D tetrahedral elements are created on the 3-D cracked concrete specimen

Durability induced concrete damage modeling

Concrete service life models have proliferated in recent years due to increased interest in designing infrastructure elements with at least a 75-year service life, along with greater emphasis on life cycle costing in general. While current models consider a variety of concrete material and environmental factors, at varying levels of complexity, in predicting the time until the onset of chloride-induced corrosion of the steel reinforcement, the influence of cracking is generally beyond their current scope. This research presents a preliminary strategy for examining the influence of transverse cracking on chloride ion penetration into concrete that includes a graphical approach for adjusting the service life provided by current models to reflect this influence. Comparison to experimental data indicates that the contributions of binding of the chloride ions by the cement paste play a significant role in slowing the ingress of chlorides and should be accounted for in any modeling efforts.

This is a fine mesh created from a 3-D sliced images. It contains 103881 tetrahedral elements and 19857 nodes.

3-D diffusion and reaction analysis with a cracked concrete structure considering the microstructure