Concrete Removal and Repair-Methods and Materials - a PDH Online Course for Engineers and Surveyors

Concrete Removal and Repair-Methods and Materials

Course Outline

This three-hour online course provides general guidelines for the removal of damaged or disintegrated concrete, preparation of surface after removal and the methods and materials used for concrete and reinforcement steel repair. Methods commonly used for concrete removal, blasting, crushing, cutting, impacting, milling and presplitting and their uses, advantages and limitations are discussed. Repair methods and materials consist of various grouts, polymer coatings, overlays and injections, types of cement, concrete and admixtures. Also considered are the preparation of concrete surfaces and reinforcement steel preparation and the replacement and addition of reinforcement steel for a successful and durable concrete repair. Monitoring techniques for damage to the remaining concrete after completing removal work are presented. The existing condition and cause or causes of damages are considered for the selection of suitable methods and materials for repair. Concrete damages include 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:

Have an understanding of the methods used for concrete removal along with the appropriate selection, advantages and limitations of each method. The techniques for removal methods are discussed and summarized;
Understand the measures for preparation of concrete surfaces and reinforcing steel to provide sound surfaces for bonding the replacement materials. Preparation measures include chemical, mechanical and blasting cleaning, shot blasting and acid etching;
Consider surface appearances for clues to the underlying cause of damages and to select a repair method for those cases where the damages will continue;
Understand the types of concrete damages such as disintegration, movement, erosion, seepage and spalling. Typical situations are included;
Be aware of the various methods, devises and examinations used to evaluate the condition of the remaining concrete after removing the damaged concrete;
Be familiar with important properties of repair materials, general considerations, advantages and limitations and factors to consider for durable concrete repair. Commonly used repair materials include fiber-reinforced concrete, shotcrete, shrinkage compensating concrete and silica-fume concrete;
Consider the importance of proper handling and disposal of waste materials and liquids generated by concrete removal activities;
Be familiar with the materials and methods for anchoring replacement concrete to existing concrete;
Be familiar with various techniques such as crack arresting, drilling and plugging, drypacking, flexible sealing and gravity soaking used for crack repair and their applications, limitations and procedures; and
Be familiar with various repair methods, jacketing, grouting, overlays, coatings and injections.

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 available concrete repair methods, materials, advantages, limitations and procedures are discussed. Repair methods include jacketing, grouting, overlays, coatings and injections. The methods used for concrete removal along with the selection, advantages and limitations of each method are discussed. Important properties of repair materials and factors to guide in selection are given and proper handling and disposal of waste materials are discussed. Commonly used materials include fiber-reinforced concrete, shotcrete, overlays, various grouts, coatings, cements and sealers. Causes for concrete damages include accidental loading, chemical attack and temperature changes. The student will understand the measures required preparing concrete surfaces and reinforcement steel for sound and durable damage repairs.

Course Introduction

Planning and design for successful and durable concrete repairs is a methodical process. The concrete's current condition must be evaluated for damages and causes. Condition surveys, underwater inspections, laboratory tests, investigations and nondestructive testing are used and problem areas are documented. The cause or causes related to the observed damage are then determined. Repair method and materials are then 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 resistance, 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.

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. Accidental loading, chemical attacks, improper construction or repairs and temperature changes can cause damages.

Unless periodical inspections are made of structures, deferred concrete maintenance would lead to expensive repairs or rehabilitation work. Judicious neglect or careful deferral of repairs is sometimes appropriate if there would be no immediate impact to the structure. 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 and improper preparation of concrete surfaces and reinforcement steel. Properties of newer repair materials such as the coefficient of thermal expansion and modulus of elasticity often differ from the existing concrete. If the repair 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 concrete or steel 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.

The condition of concrete left in place must be evaluated after removal work. Various methods ranging from visual inspections to tests for permeability, chloride ion, core compressive strength or pulse-velocity tests are performed. Petrographic exams with a microscope will show any brittle fractures or cracks caused by concrete removal methods.

Course Content

This course is based on Chapter 5 and 6 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 5 - Concrete Removal and Repair

Evaluation and Repair of Concrete Structures - Chapter 6 - Materials and Methods for Repair and Rehabilitation

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 defects. Methods and materials for repair of common types of concrete damages, which include cracking, deterioration and surface defects, are presented. Characteristics, advantages, limitations, possible problems to avoid such as incompatibilities of repair materials with existing concrete are discussed. Selection of the methods and materials for repair, removal of concrete and reinforcing steel, replacement and additional reinforcement are discussed and summarized.

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.concut.com/ot_mainmenu.htm
"Concrete Cutting and Breaking, Inc.", Information on various concrete removal methods.

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

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.