fib Bulletin No. 64

Title: Effect of zinc on prestressing steel

Category: Technical report

Year: 2012

Pages: 22

Format approx. DIN A4 (210x297 mm)

ISBN: 978-2-88394-104-5

Abstract:

Concerns have been raised regarding the durability of galvanized prestressing steels in contact with cementitious grout, and regarding the use of galvanized ducts for grouted tendons or galvanized inserts or components in contact with prestressing steel inside concrete. These concerns are mainly based on the assumption that the hydrogen formed on the zinc surface when exposed to the fresh cementitious grout for a short period of time represents a risk of hydrogen induced stress corrosion for the prestressing steel. Basic research has demonstrated that hydrogen induced stress corrosion may indeed occur with prestressing steels which are sensitive to hydrogen induced stress corrosion.

The use of galvanizing for high strength steels exposed to atmosphere is less controversial. However, under certain conditions hydrogen may develop also and potentially damage the high strength steel.

This report provides a summary and evaluation of the relevant parameters on the corrosion behaviour of high strength wires, strands and bars when in contact with zinc with and without the presence of fresh cementitious grout or concrete. Both, tendons made of prestressing steels used in structural concrete and cables under atmospheric conditions are considered. The main groups of applications discussed in the report are:

• A Zinc-coated high strength steel for applications in atmospheric corrosion conditions
• B Zinc-coated prestressing steel embedded in fresh cementitious grout or concrete
• C Bare prestressing steel (no zinc coating) embedded in fresh cementitious grout or concrete in direct contact with, or indirect contact in the immediate vicinity of galvanized components embedded in the grout or concrete (e.g. galvanized ducts, galvanized reinforcing steel, galvanized fastenings / dowels, etc).

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