Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 4
5
CHAPTER 1
INTRODUCTION AND RESEARCH APPROACH
Zinc and aluminum have been used as steel coatings since tions (3). The excellent barrier properties and low rate of self-
the early 1900s, with early application of thermally sprayed corrosion for the aluminum coating make it attractive for sea-
metal coatings (TSMCs) to bridge structures in the 1930s (1). water exposure. Because TSMCs are porous, sealers are often
TSMCs have been used widely in the European bridge indus- specified to reduce the porosity and improve the service life
try, in the U.S. Navy, and on offshore oil exploration drill plat- of the coating. Common sealers include epoxies and vinyl
forms for quite some time. TSMCs of zinc, aluminum, and coatings. Because of the advances in coating technology, part
their alloys can offer substantial advantages when compared of this study was to investigate other sealer materials.
with other coatings typically used to protect steel pilings.
Organic coatings can fail prematurely as a result of corrosion
progression from coating defects. Transportation, handling, Quality Assurance Requirements
installation, or simple long-term material deterioration may
cause these defects. TSMCs offer advantages in generally TSMC materials are sensitive to surface preparation and
higher mechanical damage resistance, low self-corrosion rates, application conditions (4). Most specifications require sur-
and the ability to provide steel corrosion control via cathodic face preparation and application conditions that meet the
protection at coatings defects. The objective of this research Society for Protective Coatings Surface Preparation Specifi-
was to develop a guide for highway agency personnel on the cation 5 (SSPC-SP-5), "White Metal Blast Cleaning," for
selection and use of TSMCs for highway pilings that would application of a TSMC (5). This can be difficult to achieve in
be suitable as an AASHTO reference. The Thermally Sprayed all conditions, especially if field coating is being considered
Metal Coating Guide, containing all of the information gath- rather than shop coating. Other parameters, such as abrasive
ered from the literature, industry research, and laboratory test- type for surface preparation, required profile range, and accep-
ing, is the primary product of this research. tance environmental conditions, can affect porosity, adhesion,
The extensive body of information on TSMCs, including and corrosion performance of the coating.
existing guides, was researched so as not to repeat basic
research and development work or conflict with industry
standards where those standards are applicable. Applicable Damage Tolerance of the Coating
portions of existing materials were used in the preparation of
A key aspect of the coatings is their resistance to damage
the Thermally Sprayed Metal Coating Guide. This study also
in transportation, handling, and installation. Regardless of
sought to resolve any issues that were unclear concerning the
whether shop or field coatings are used, there is a tendency
use of TSMCs on steel pilings.
for there to be impact and flexure damage to the coatings.
The performance of the alternative alloys and application
conditions must be qualified in these regards.
ISSUES OF CONCERN
Alloy Selection
RESEARCH PLAN
There are several TSMC alloys available. Most commonly
The research plan consisted of eight tasks, briefly
used metals for the protection of steel are anodic to steel. This
described below.
eliminates the need for a completely pinhole-free barrier
because the TSMC provides sacrificial protection to the steel
substrate (2). Zinc, aluminum, and alloys of the two metals Task 1--Collect and Review Domestic and
are thus favored for the protection of steel. Ideally, the alloy Foreign Literature and Information
should have a very low self-corrosion rate and be an efficient
and effective sacrificial anode. Aluminum TSMCs have been The review of existing literature and other information
found to protect steel well under seawater immersion condi- included the following:
OCR for page 5
6
· Existing specifications and guides on coatings for steel the information available to date and delineating areas requir-
pilings and for metallizing in general, ing further research. They also asked that a second interim
· Published research studies of metallized coating perfor- report be prepared.
mance in immersion environments,
· Interviews with suppliers of metallizing materials and
application equipment and review of their literature, Task 5--Work Plan Execution
· A visit by researchers to a coating fabrication shop where
steel piles were being coated, The work plan execution consisted of conducting laboratory
· Laboratory studies to perform certain basic testing on tests to provide additional information about the effectiveness
TSMC, and of sealers, different sealer materials, surface preparation mate-
· Interviews with coating applicators. rials, and the application variables on performance. The tests
consisted of both standard laboratory tests and seawater expo-
sure tests. Researchers also intended to perform field inspec-
Task 2--Evaluate and Summarize the Literature tions of several TSMC structures, including some existing
structures operated by the U.S. Army Corps of Engineers. The
This consisted of the evaluation of information gathered in inability to access these structures without extensive dewa-
Task 1 to determine the completeness and relevance of exist- tering procedures prevented this from occurring.
ing information. From this evaluation, a detailed work plan
was developed that would provide the information necessary
for the guide to TSMCs. Task 6--Final Guide to TSMCs
This task consisted of preparing the final guide on the
Task 3--Develop a Detailed Experimental basis of the combined results of the literature search and
Work Plan laboratory tests.
The purpose of Task 3 was to develop an experimental
work plan built around key issues related to TSMC perfor- Task 7--Long-Term Validation Plan
mance. It was anticipated that the work plan would consist of
laboratory tests designed to provide information to supple- The objective of this task was to develop a long-term
ment the literature in the areas of surface preparation, seal- implementation plan for the use of TSMCs for pilings. The
ers, and application parameters. plan was to have the guide to TSMCs accepted as an
AASHTO guide by demonstrating the usefulness and appli-
cability of the guide and TSMCs to state DOT officials.
Task 4--Interim Report
The interim report presented the results of Tasks 1 through Task 8--Final Report
3. As a result of the interim report, the panel determined that
an expanded literature search was needed. The panel directed This report contains a discussion of all of the work
that a draft guide to TSMCs be prepared incorporating all of described in Tasks 1 through 7.
