Page 260 - Challenges in Corrosion Costs Causes Consequences and Control(2015)

238 CORROSION CONTROL AND PREVENTION

4.9.2.3 Overcoating Overcoating has become a more attractive option as the cost
of full removal and repainting has increased. This approach limits the amount of sur-
face preparation to the specific areas that have failed paint and corrosion. These areas
are spot-primed, and one or two coats of paint are applied over the entire structure
for uniformity of color. This approach can be effective in relatively less corrosive
environments.

4.9.2.4 Metal Spray Coatings These are nontraditional bridge coating systems
with potential long-term performance benefits. Metallized coatings appear to have
excellent long-term corrosion resistance. Although the metallized coatings are expen-
sive, the changing overall economics of bridge repainting operations has made their
use more competitive in terms of life-cycle cost.

4.9.2.5 Coating Installation Maintenance Costs It is not easy to define the cost of
coating system installation. The significant aspect is the dramatic increases in envi-
ronmental and worker protection regulations that impact these operations. The use
of containment structures to capture hazardous waste and pollutants generated dur-
ing removal of old coatings and the gradual institutionalization of worker health and
safety practices associated with hazardous materials removal have contributed to the
high cost of these operations.
The problem of applying protective coatings to steel bridges to prevent corrosion
involves the removal of the existing lead-based paint in compliance with environmen-
tal regulations. All wastes must be treated in accordance with congressional regula-
tions.
According to the 1992 NCHRP data, nearly 80% of the bridges have been
coated with lead-based paints. About 4100–$130 million is spent on painting
annually. Lead paint removal generates an estimated 181 million kg (200,000 ton) of
lead-contaminated abrasives.
The overall cost of coating consists of the cost of material, surface preparation, and
application of the coating. The costs of some coating systems are given in Table 4.18.
The service life of the coating systems is significantly affected by service condi-
tions. For example, a two-coat alkyd primer with the topcoat exposed to a rural or
residential area would last only 3 years. The triple system of moist-cured urethane
zinc-rich coat, a high-build acrylic urethane coat, and an acrylic urethane top coat
will last 15 years.

TABLE 4.18 Cost of Alkyd, Epoxy, and Epoxy/Urethane Coatings
Cleaning Material Application Total System
cost cost cost cost Life Cost/Year
System $1m 2 $1m2 $1m 2 $1m 2 (Years) $1m 2
Two-coat alkyd 5.92–9.15 1.08 5.38 12.38–15.61 3–6 4.09–2.58
Two-coat epoxy 5.92–9.15 1.72 6.46 14.10–17.38 7.5–10.5 1.83–1.61
Two-coat epoxy 9.15–10.76 2.26 7.00 18.41–20.02 10.5 1.94
urethane