- How It Works
- Why ZRC
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ZRC Cold Galvanizing Compound is used by the Massachusetts Department of Public Works to protect hot-dip galvanized rebar under the Massachusetts Avenue ramp of the Fitzgerald Expressway in Boston; to protect the steel deck of the Fifth Street Bridge in Montague, Mass.; and to prevent rust on guardrails and galvanized sign supports throughout the state.
Galvanic Protection Extends Rebar Life
Because it is a sacrificial coating providing true cathodic protection, ZRC prevents the spread of corrosion and increases the life span of the steel rebar inside all concrete pilings under the Massachusetts Avenue ramp of the Fitzgerald (Southeast) Expressway. The expressway is Boston's central artery to the south. ZRC is a liquid compound with 95% zinc content in the dried film, meeting Commonwealth of Massachusetts Department of Public Works Specification No. M.07.02.61, Research & Material Section, Epoxy Ester Based Zinc Rich Primer, found in the DPW Guide Book.The contract for repairing the rebar in all pilings was awarded to RDA Construction Corp., Milton, Mass. Jackhammers were used to chip away concrete and expose the rebar for coating. Surface preparation was commercial sandblasting to SSPC-SP-6. One coat of ZRC 11/2-mils thick was applied by brush. Once the ZRC dried, the rebar was reencapsulated in concrete.
In the past, the porous nature of concrete had allowed moisture to penetrate and corrode the unprotected rebar. Now that ZRC has been applied, the zinc in the ZRC will slowly corrode to galvanically protect the substrate. As the zinc is sacrificed, insoluble by-products are formed, which fill voids and pores in the coating film. This forms an insoluble barrier to contaminants which further protects the substrate from corrosion.
ZRC Protects Steel on Bridges
ZRC protects the entire deck of a steel truss bridge in the western Massachusetts town of Montague. ZRC was used to coat the steel deck of the Fifth Street Bridge (Mass. Bridge #M28-15) in accordance with the same DPW Specification as Boston's Massachusetts Avenue ramp (No. M.07.02.61). The general contractor for the project was Warner Brothers, Sunderland, Mass. The steel contractor was I.K.G. Greulick, Cheswick, Penn., and the painting contractor was Osterling Sandblasting, Butler, Penn.
The new steel deck of the bridge has 10,000 square feet of surface area. Surface preparation consisted of SSPC-SP10 near-white sand-blasting. ZRC was applied to the decking by the fabricator as a preconstruction primer, followed by an epoxy mastic midcoat and an aliphatic urethane topcoat applied in-place at the job site. A graphic example of the vulnerability of unprotected steel to corrosion was seen when, during the three weeks the new deck sections were exposed during construction, the ends to be welded (where ZRC was not yet applied) developed visible rust.
The steel grid sections were welded together after being placed on the bridge. The new deck was welded onto the steel trusses of the bridge and was then filled with concrete. The ZRC zinc-rich primer is expected to increase the life of the deck significantly by preventing rust even in an application where high moisture and harsh New England winters create a corrosive atmosphere.