Corrosion of Prestressed Reinforcing Steel in Concrete Bridges: State-of-the-Art

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Title: Corrosion of Prestressed Reinforcing Steel in Concrete Bridges: State-of-the-Art

Author(s): M. Nagi and D. Whiting

Publication: Special Publication

Volume: 151

Issue:

Appears on pages(s): 17-42

Keywords: bridges (structures); chlorides; concretes; corrosion; grout; hydrogen; prestressed concrete; prestressing steels; rehabilitation; reinforcing steels; stress corrosion resistance; Structural Research

Date: 7/1/1994

Abstract:
The practice of prestressing steel has proven to be a very successful method of construction compared to conventional reinforced concrete in increasing load-carrying capacity, improving crack control, and slenderizing structural elements. However, corrosion in prestressed concrete has much more serious consequences than in normal reinforced concrete. Tendons are subjected to high mechanical stresses (often up to 70 to 80 percent of their tensile strength). Under an FHWA contract dealing with rehabilitation of prestressed concrete bridge components by nonelectrical methods, a comprehensive technology review focusing on corrosion of prestressing steel in highway structures was conducted and is summarized in this paper. Types of corrosion and recent theories explaining stress corrosion and hydrogen embrittlement are presented. Susceptibility of prestressing steel to corrosion in prestressed and post-tensioned concrete structures is covered. Factors such as concrete materials, prestressing steel, and environments, which may influence such corrosion, are categorized. Laboratory and field studies dealing with a variety of corrosion issues in pretensioned and post-tensioned concrete are also presented. These issues include the development and improvement of grout materials for bonded tendons in post-tensioned concrete members, use of epoxy-coated prestressing wires, and corrosion of unbonded tendons under severe exposure. Selected case histories and field evaluation of concrete bridges subjected to corrosion are also included. This study gives an overview of corrosion problems in prestressed concrete members and should help engineers to diagnose causes of corrosion and select the right methods and materials to be used for rehabilitation as well as in new constructions.