Print this page Corrosion Control of Reinforced Concrete
John Poullain, P.E.
Course Outline
This three-hour online course summarizes research by the Federal Highway Administration for developing various corrosion protection systems for reinforced concrete bridges and structures. The nature of the corrosion process and the success of control measures are described. It describes materials and measures used and cover topics including design and construction considerations, post-tensioned concrete, types of grout, corrosion inhibitors, epoxy-coated and corrosion resistant reinforcing bars. ASTM standards for corrosion resistance and tests performed on post-tensioned concrete are described.
The topics covered in this course include:
- The electrochemical process, which corrodes steel reinforcing, bars in concrete, and the conditions, which initiate and propagate it.
- Concretes’ natural protection or resistivity and design which provide protection from corrosion.
- Factors to consider in selecting a reinforced concrete corrosion protection method.
- Factors that influence the rate of corrosion and deterioration.
- Corrosion inhibitors and additives used for concrete protection.
- Pretension and post-tensioned concrete considerations.
- Types of grouts used for bonded post-tensioned concrete.
- Performance and field results of epoxy-coated reinforcing steel and corrosion resistant bar.
This course includes a multiple-choice quiz at the end, which is designed to enhance the understanding of the course materials.
Learning Objective
At the conclusion of this course, the student will have covered these topics:
- The electrochemical process, which corrodes steel reinforcing, bars in concrete and the conditions, which initiate and propagate it;
- Concretes’ natural protection or resistivity and mixes which provides protection from corrosion;
- Sources of chloride which make reinforcing bars susceptible to corrosion;
- Factors for good design to reduce corrosion of reinforced concrete;
- Factors to consider in selecting a reinforced concrete corrosion protection method;
- Factors that influence the rate of corrosion and deterioration;
- Corrosion inhibitors and additives used for concrete protection;
- Pretension and post-tensioned concrete considerations;
- Types of grouts used for bonded post-tensioned concrete;
- Performance and field results of epoxy-coated reinforcing steel and corrosion resistant bars; and
- ASTM and ACI standards for the materials and methods used to test for corrosion control and testing performance.
Intended Audience
This course is intended for materials and civil engineers, reinforced concrete specialists, planners and contractors.
Benefit to Attendees
The student will become familiar with the guidelines for selecting the methods and materials commonly used in new reinforced concrete construction. Causes for concrete deterioration such as chemical attack, improper construction or design and temperature changes and the preventative measures used in new construction are described. The student will also gain an understanding of the general procedures, equipment and tests used to test post-tensioned concrete. Examples of advantages and limitations of the available corrosion control methods and materials are discussed.
Course Introduction
Concrete is a construction material with many attributes and disadvantages that should be carefully designed for good construction. Some defective concrete can be attributed to the addition of reinforcement steel since corrosion of imbedded steel is one of the most frequent causes of concrete damage. Concrete is highly alkaline with electrical resistant, which gives imbedded steel some corrosion protection. Theoretically carbon steel rebar is protected from corrosion when imbedded in the high alkalinity of concrete. However it is a porous material and over time is not very resistant to acidic chemicals. Deicer chlorides and also chemical reactions within the concrete destroy the protection. In addition to other means there are two types of corrosion inhibitors attracting interest for concrete repairs. One, calcium nitrate, an admixture for fresh concrete that has been used for several years with good results. Other inhibitors are applied externally on hardened concrete. They function by migrating through the concrete covering the reinforcement steel. Their effectiveness however is uncertain for the long term.
Salt and deicer chlorides have caused the deterioration of about 80,000 bridges in the Federal-aid system (1997) and a considerable economic burden. The adoption of protection measures, such as good design and construction practices, concrete cover depths, low permeability concrete, corrosion inhibitors in new construction help to delay corrosion. Because concrete has a tendency to crack, chloride ions intrude into the concrete and reinforcement. Joints also provide access into the concrete. Uses of barrier systems like epoxy; metallic coatings and an alloy becomes the last line of defense for corrosion control.
Reinforced concrete deterioration may not be caused from corrosion of rebar. If rust stains are not visible, then deterioration of the concrete may be caused by freeze-thaw cycles, not from steel corrosion. If cracks appear, the cause could be reinforcing steel corrosion, drying shrinkage, thermal movement or structural stress. If caused by drying shrinkage, the crack will eventually stabilize and repair with a rigid material may be suitable. However cracks caused by structural stress will continue. Accidental loading, chemical attacks, improper construction or repairs and temperature changes also damage concrete.
Course Content
This course is based on US Department of Transportation Publication FHWA-RD- 00-081, “Materials and Methods for Corrosion Control of Reinforced and Prestressed Concrete Structures in New Construction” (2000 Edition, 76 pages), PDF file.
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Course Summary
This course considers the methods and materials used to control the corrosion of reinforced concrete in new construction. Course topics include the effects of good design and construction, types of grout, concrete admixtures, corrosion inhibitors, and epoxy-coated reinforcement bars. Characteristics, advantages, limitations, and possible problems to avoid with the materials and methods commonly used are discussed. Factors, diagrams and tables helpful for selecting the appropriate methods, materials and ASTM standards are described in the text.
Related Links
For additional technical information related to this subject, please refer to:
http://aec.engr.wisc.edu/resources/rsrc07.html University of Wisconsin, “Why Do Concrete Repairs Fail”
http://www.concretenetwork.com Concrete admixes, rebars, grouts etc.
http://www.actonrust.com Equipment and products for concrete corrosion control.
Quiz
Once you finish studying the above course content, you need to take a quiz to obtain the PDH credits.
DISCLAIMER: The materials contained in the online course are not intended as a representation or warranty on the part of PDH Center or any other person/organization named herein. The materials are for general information only. They are not a substitute for competent professional advice. Application of this information to a specific project should be reviewed by a registered architect and/or professional engineer/surveyor. Anyone making use of the information set forth herein does so at their own risk and assumes any and all resulting liability arising therefrom.
