Concrete Repair - Selection of Repair Methods

John Poullain, P.E.


Course Outline

This three-hour online course provides general guidelines for diagnosing concrete defects and selecting the methods and materials for repair of damaged concrete. The existing condition and cause or causes of defects and damages are evaluated to select the suitable method or methods and materials for a successful and durable concrete repair. The types of investigations, testing, analysis and inspections used to determine the extent and possible causes of concrete damages are discussed. Typical causes and symptoms are explained and the best repair method and materials are presented. Concrete deficiencies include several types of cracking, surface deterioration, construction faults, joint damages, erosion, seepage and spalling.

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:


Intended Audience

This course is intended for civil engineers, planners and contractors.


Benefit to Attendees

The student will become familiar with the guidelines for selecting the methods and materials commonly used to repair or rehabilitate defective concrete. The student will have an understanding of the terms used to describe cracking, general physical conditions, current structure and crack movements and other defects. Causes for concrete deficiency such as accidental loading, chemical attack, improper construction or design and temperature changes and the typical symptoms and preventative measures are described. Descriptive examples and representative photos of the various types of concrete defects are presented. The student will also gain an understanding of the general procedures, equipment and tests used for core drilling, underwater inspection and nondestructive testing. Examples of advantages and limitations of the available repair methods and materials are discussed.


Course Introduction

Planning and design for successful and durable concrete repairs is a methodical process of several steps. The first step is to evaluate the concrete's current condition and identify and document concrete defects and deterioration. Condition surveys, underwater inspections, laboratory tests, investigations and nondestructive testing are used and problem areas are noted according to type, size and location. The cause or causes related to the observed damage are then determined. In the next step the repair method and materials are selected based on the findings and data already collected and evaluated and also from the lessons learned from similar repairs.

Concrete is a construction material with many attributes and disadvantages that should be carefully designed for good construction and rehabilitation work. 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. 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 admix 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.

Other common causes of concrete defects and damages are discussed in this course. Correct diagnosis of the cause or causes is essential in order to select the appropriate method and materials for a successful repair. For instance if rust stains are not visible, then deterioration of the concrete may be caused by freeze-thaw cycles, not from steel corrosion and thus concrete removal would not be as extensive. 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. It will then be necessary to determine the underlying cause to select the suitable method and materials for repair. The types of investigations, testing, analysis and inspection required to determine the extent and causes of concrete damages are discussed. Accidental loading, chemical attacks, improper construction or repairs and temperature changes can cause damages. Typical damages and the mechanism of damage are explained and the symptoms, preventative measures and examples are described. Representative photos of typical concrete damages are shown.

Unless periodical inspections are made of structures, deferred concrete maintenance would lead to expensive repairs or rehabilitation work. Spalls or other surface defects may be indicative of more serious structure damage entering into buildings' structure. Repair work required inside a building are expensive and may require shoring, bracing of walls and protective measures for interior spaces.

Planning for concrete repair should include factors such as the quality of the existing concrete, repair materials' compatibility, properties, manufacturer data, surface preparation, application methods and service conditions. Knowing the mix design of the existing concrete aids in selecting repair materials. Concrete repairs often fail because of poor selection of repair materials. Properties of newer repair materials such as the coefficient of thermal expansion and modulus of elasticity often differ from the existing concrete. If the material is not physically or chemically compatible with the existing concrete, debonding, cracking or failure may occur. The damaged area must be properly prepared and the details for removal carefully planned. If the entire defective concrete and corrosion product from the reinforcing steel is not removed, the repairs may fail because of inadequate surface preparation. And just as importantly, knowing the quality of the concrete helps in predicting the possibility of further deterioration and to plan and budget for current and future repairs.

Course Content

This course is based on Chapter 2, 3, and 4 of the US Army Corps of Engineers Manual, "Evaluation and Repair of Concrete Structures", EM 1110-2-2002 (1995 Edition, 43 pages), PDF file.

The link to each chapter of the Engineers Manual in PDF form is

Evaluation and Repair of Concrete Structures - Chapter 2: Concrete Evaluation

Evaluation and Repair of Concrete Structures - Chapter 3: Causes of Distress and Deterioration of Concrete

Evaluation and Repair of Concrete Structures - Chapter 4: Planning and Design of Concrete Repair

You need to open or download above documents to study this course.

Course Summary

This course considers the methods and materials appropriate for repair of concrete damages. Planning for repair work consists of evaluating the current conditions, relating possible cause or causes to the observations and tests performed and then selecting from possible repair methods and materials based on evaluations and observations of the defectives. The common types of concrete damages, including several types of cracking, deterioration and surface defects, their causes, symptoms and preventative measures are presented. Characteristics, advantages, limitations, possible problems to avoid, incompatibilities of repair materials with existing concrete are discussed. Diagram and tables methods helpful for selection of the methods and materials are presented.

The appropriate ASTM and ACI standards are noted in the text.

References

For additional technical information related to this subject, please refer to:

http://www.kleinandhoffman.com/Pages/21evaluating.html
"Laying the groundwork for a successful repair program"


http://www.aci-int.org
Archived research papers, seminars, publications for concrete repair and advancement by the American Concrete Institute.

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.