| Issues Impacting Bridge Painting:
an Overview
Abstract
This final report documents the findings of
a research program designed to collect and critically assess
information
on issues impacting bridge
painting.
Life-cycle costs and performance were used
to assess the economics of maintenance painting. These assessments
are
made difficult (uncertain) because the performance data
and hidden application costs are extremely variable. The
variability
of coating performance can be improved by better control
of preparation quality.
Paint-removal assessments were made based largely
on field operations. A few tests involving environmental
chambers
were conducted. Test conditions and pros and cons of the
various procedures are critically summarized. Regarding
worker safety, recommendations are made for close monitoring
and
control of the particles generated during surface preparation,
especially when techniques such as steel-grit blasting
and laser ablation are used for cleaning.
Paint debris digestion procedures followed
by atomic absorption spectroscopy is the best way to determine
total lead in a
paint film. The toxicity characteristic leaching procedure
(TCLP) is currently the best method for classifying paint,
buy may not be a reliable indicator of future resistance
to leaching. Steel blast media is recyclable and stabilizes
lead; proprietary additives work well in reducing leachable
lead in the TCLP. Long-term stability of lead-containing
debris has not been validated.
With the exception of thermal spray coatings,
the lack of performance data, i.e., long-term durability
data, is
a major problem in using advanced coating systems. Advantages
and disadvantages of thermal spray coatings are summarized.
Modified accelerated testing procedures to determine coating
durability were identified that could improve the correlation
between laboratory tests and corresponding
field tests.
Several sensor technologies were considered
in an effort to identify techniques that could improve the
quality of
applied coatings. The methods evaluated included monochrome
CCD (to determine the degree of surface rusting), color
CCD to assess the cleanliness of blast-cleaned surfaces,
and
thermal-wave images to evaluate the condition of the substrate
beneath the coating prior to paint removal.
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