Graduation Year


Document Type




Degree Name

Doctor of Philosophy (Ph.D.)

Degree Granting Department

Civil and Environmental Engineering

Major Professor

Alberto A. Sagüés, Ph.D.

Co-Major Professor

Christopher Alexander, Ph.D.

Committee Member

Gray Mullins, Ph.D.

Committee Member

Dmitry Goldgof, Ph.D.

Committee Member

Michael Celestin, Ph.D.

Committee Member

Myung K. Kim, Ph.D.


Corrosion, Non-destructive, strand envelope, Tomagraphy, voids


Post-tensioned (PT) bridges have had severe corrosion issues with tendons that fail suddenly without prior notice. The corrosion of external post-tensioned tendons has been associated with grout deficiencies/anomalies from inadequate grouting. Deficiencies include voids, regions of chalky low strength grout, and regions where excessive water content or even free water is present. In those zones mechanical bonding of strand to the grout is degraded and, of more concern, the strand steel risks corrosion failure reducing the expected lifespan of the structure. As tendons are critical structural components, it is important to detect those deficiencies during inspection preferably by a cross section imaging method that can be readily deployed. Thus the method should be non-destructive, rapid, economical, easy to replicate, with a small and safe device not requiring specialized operator training. To that end, here a magnetic sensing approach to image the position of the steel strand bundle is combined with an electric impedance method to evaluate the condition of the grout space. Both are embodied in a device that images the tendon’s cross section. The magnetic sensor travels around the circumference of the tendon and measures the force of attraction to the steel strands, from which an image of the strand pattern inside the tendon is created. Simultaneously, a traveling plate rotates around the tendon and variations of the electric impedance between plate and strands identify grout deficiencies. The impedance and strand position data create a complete color-coded image of the tendon cross section flagging grout deficiencies. This dissertation details the relevant prior technical literature, and presents calculations, modeling and experiments to develop and validate the magnetic and impedance components of the method. The work culminates with the integration of both techniques in a working prototype and its performance evaluation as well as confirming comparison with the results of independent Gamma Ray Tomography tests performed on a reference group of test specimens.