An exploration of positron annihilation spectroscopy as a new evaluation tool for structure steel coatings

Polymer coatings are the primary line of protection against deterioration of structural steel. Two general problems exist in the current coating systems. (1) The design lifetime of structures is much longer than that of protective coating systems. (2) In last two decades, regulations from the Environment Protection Agency have more stringent limitation on volatile organic compounds and the use of certain metallic pigments. New generations of coating systems with longer life span that comply with new regulations are in urgent demand. However, lack of a service lifetime prediction methodology that can be conducted in a relatively short time frame is needed to expedite development of new generation coatings. Furthermore, there is also a need for in-situ testing methodologies that can predict remaining lifetime of coatings.; This Dissertation investigates positron annihilation spectroscopy (PAS) for the assessment of structural steel coating systems. This methodology characterizes free volume defects in polymer coating systems. Specifically, commercial coatings were applied to steel samples and exposed to three different weathering environments. A fourth set was subjected to cyclic tensional strain. Doppler Broadening Energy Spectra, and Positron lifetime annihilation spectra, were used to assess deterioration of the coatings after exposure. Electron spin resonance spectroscopy and mechanical tests were also conducted for identification of chemical process and engineering performance of the coatings.; A common decrease in the S-parameter was observed as a function of exposure time for all samples. Based on the change of S-parameter, the durability of different polymer coatings was assessed and found to be consistent with observed durability performance. The durability of coatings was analyzed as a function of exposure time, depth and different exposure environments as well. Other parameters, such as measured positron lifetime, density, free volume fraction and distribution were also investigated.; This research showed that positron annihilation spectroscopy is most suited as a service-lifetime prediction method. Additionally, this study advances the knowledge of free volume changes associated with weathering and stress related processes.; This research was conducted under a grant by the National Science Foundation, Grant Number CMS-9812717.