ACI 423.4R-98 became effective February 23, 1998. Copyright  1998, American Concrete Institute. All rights reserved including rights of reproduction and use in any form or by any means, including the making of copies by any photo process, or by electronic or mechanical device, printed, written, or oral, or recording for sound or visual reproduc- tion or for use in any knowledge or retrieval system or device, unless permission in writing is obtained from the copyright proprietors. ACI Committee Reports, Guides, Standard Practices, and Commentaries are intended for guidance in planning, design- ing, executing, and inspecting construction. This document is intended for the use of individuals who are competent to evaluate the significance and limitations of its content and recommendations and who will accept responsibility for the application of the material it contains. The American Concrete Institute disclaims any and all responsibility for the stated principles. The Institute shall not be liable for any loss or damage arising therefrom. Reference to this document shall not be made in contract documents. If items found in this document are desired by the Architect/Engineer to be a part of the contract docu- ments, they shall be restated in mandatory language for in- corporation by the Architect/Engineer. 423.4R-1 This report gives general information regarding the evaluation of corrosion damage in structures reinforced with unbonded single strand post-tension- ing tendons. Historical development of those parts of the building code dealing with durability and corrosion protection is explained. Evolution of the types and components of unbonded tendons is described. Specific aspects of corrosion in unbonded single strand tendons are described, and common problems in structures reinforced with these tendons are discussed. Methods are presented for repairing, replacing, and supplementing tendons. Keywords: allowable stresses; anchorage; carbonation; concrete con- struction; corrosion; corrosion protection; cover; durability; embrittle- ment; external post-tensioning; grease; inspection; post-tensioned concrete; pre-stressed concrete; repair; sheathing; single strand tendons; surveys; tendons; tests; unbonded post-tensioning. CONTENTS Chapter 1—Introduction, p. 423.4R-2 1.1—General 1.2—Background 1.3—Scope 1.4—Limitations Chapter 2—Review of code requirements and changes, p. 423.4R-3 2.1—General 2.2—Cover requirements for unbonded tendons 2.3—Allowable tensile stresses in concrete 2.4—Protection of unbonded tendons Chapter 3—Unbonded tendons, p. 423.4R-5 3.1—Evolution of unbonded tendons 3.2—Sheathing problems 3.3—Detailing practices 3.4—Storage, handling, and construction problems 3.5—Deterioration mechanisms 3.6—Performance record Corrosion and Repair of Unbonded Single Strand Tendons ACI 423.4R-98 Reported by ACI/ASCE Committee 423 Charles W. Dolan Chairman Henry J. Cronin Jr. Secretary Kenneth B. Bondy † Catherine W. French Gerard J. McGuire † David H. Sanders Robert N. Bruce Jr. Clifford Freyermuth Mark Moore † Thomas C. Schaeffer Dale C. Buckner William L. Gamble Antoine E. Naaman Morris Schupack † Ned H. Burns † Hans R. Ganz Kenneth Napior Kenneth Shushkewich Gregory P. Chacos * Mohammad Iqbal Thomas E. Nehil * Khaled S. Soubra Jack Christiansen Francis J. Jaques Mrutyunjaya Pani Patrick J. Sullivan Todd Christopherson Daniel P. Jenny Kent H. Preston Luc R. Taerwe Steven R. Close L.S. Paul Johal Denis C. Pu Carl H. Walker Thomas E. Cousins Susan N. Lane Julio A. Ramirez Jim J. Zhao Apostolos Fafitis Ward N. Marianos Jr. Ken B. Rear Paul Zia Mark W. Fantozzi Leslie D. Martin David M. Rogowsky Martin J. Fradua † Alan H. Mattock Bruce W. Russel * Co-chairmen of subcommittee responsible for preparation of report † Member of subcommittee responsible for preparation of report.