Date of Award

8-2011

Level of Access

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Civil Engineering

Advisor

Eric N. Landis

Second Committee Member

William G. Davids

Third Committee Member

Edwin Nagy

Abstract

X-ray microtomography (XMT) was used to create three dimensional images of 4-5 mm diameter split cylinder concrete specimens with 0.006 mm voxel resolution. The concrete specimens have a water to cement ratio of 45% and contain glass bead aggregates with a nominal diameter of 0.5 mm. Two different mixes were used: 10% unetched glass bead by weight and 10% etched glass bead by weight. A custom load frame was designed so that the specimens could be scanned while under load in the XMT system. The load frame allowed for measurement of load and displacement in real time and the ability to scan the image while it was under load. XMT scans were taken with no load and then at incremental loads until failure, when a final scan was taken of the damaged specimen. A software toolbox was developed in MATLAB to analyze these images. It contains tools to: remove ring artifacts caused by non-linearities in the XMT detector, segment the specimen from the background, identify pore space inside the specimen, locate glass beads and calculate their centroids and radii, measure surface area of a binary image volume, track glass beads between scans, measure the location of pore space relative to beads, calculate full displacement fields at sub-voxel accuracy, calculate strain from a displacement field, and calculate strain energy from load-displacement data. The displacement vector algorithm was tested with artificially translated data and against displacement curves from the load frame. It was found to be stable to 0.10 voxel accuracy. Viewing the displacement fields between the unloaded scan and the final scan before peak load showed that both specimens rotated relative to the platens; this was verified by tracking the beads. Strain was calculated using a point-wise least squares algorithm extended to three dimensions. The maximum localizations of the components of strain parallel and perpendicular to the load appeared to be concentrated slightly inside the boundaries of the specimen. Deformations that indicate the formation of a crack were identified at the platens in one specimen.

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