Safeguarding Steel
by Rita Robison, Contributing Editor;Serial Information: Civil Engineering—ASCE, 1992, Vol. 62, Issue 4, Pg. 50-53
Document Type: Feature article
Abstract:
U.S. bridges are caught in the money squeeze. Painting has become a luxury few public agencies can afford and complying with EPA regulations has escalated costs even more. The paint/coatings industry has responded with high performance coatings that solve these problems but must be specified and used carefully. One type is a high-ratio zinc silicate that cures as it dries is based on a formulation developed by NASA. Many types contain a corrosion-inhibiting pigment additive, Micaceous iron oxide (MIO) has only recently been imported to the U.S. from Europe, where it is specified routinely by all government agencies. In the U.S., MIO is now included in proprietary coatings specified by 11 state DOTs and numerous federal agencies. Moisture cure is the key to a class of high performance coatings that can be applied in a wide range of humidities and temperatures. One such formulation (which includes MIO) was tested successfully in Oregon and is now mandated there for coastal bridges. (Oregon's test results are given for 10 systems.) Maine DOT successfully tested a single-coat water-based zinc silicate system on a coastal bridge. Other major issues are shop coatings and encapsulation. In New York, all steel for two viaducts is being coated off site with two coats of epoxy and a urethane topcoat. Painting over lead-based coatings is far less costly than safely removing them, according to many manufacturers. A bridge in Pittsburgh is cited as an example.
Subject Headings: Coating | Bridge tests | Zinc | Steel bridges | Silica | Sea water | Safety
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