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Concrete Maintenance Guidelines

John Poullain, P.E.


Course Outline

This one-hour online course provides general guidelines and methods used for the maintenance of concrete. Concrete maintenance includes the repair of cracks, joints and surface damage. Maintenance also includes the removal of stains and the protection of surfaces with coatings and sealers. Among the coatings and sealers discussed are silicones, cements, urethanes, epoxies, latexes and polyesters. The necessary surface preparations prior to application of a sealer or coating are discussed. Concrete cleaning methods include water washing, steam cleaning, water and abrasion blasting and mechanical, flame and chemical cleaning. Stains commonly encountered are iron, oil, dirt, mildew, asphalt, efflorescence and graffiti. Repair and rehabilitation of concrete are not discussed here.

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 three-hour course, the student will:


Intended Audience

This course is intended for civil engineers and planners.


Benefit to Attendees

The student will become familiar with the general guidelines for the methods and materials commonly used to remove various types of concrete stains along with any adverse effects. The student will also have an understanding of the types of concrete coatings and sealing compounds and the proper surface preparation to use prior to applying concrete protection. The advantages and disadvantages of the available methods and materials used are discussed.


Course Introduction

Preventive maintenance of concrete is an essential part of an O & M plan of a project. Deferred maintenance will lead to more expensive repairs or rehabilitation of a structure. Concrete stains do not usually adversely affect a structure but should be removed for esthetical reasons, for decorative types of concrete such as exposed aggregate and prior to sealing or re coloring colored concrete. A topping or overlay will not bond properly unless any sealer, coating or stain is removed first. Concrete cleaning is performed by several methods depending on the type of stain and degree of surface penetration. Methods commonly used are water washing, water and abrasive blasting and steam, flame, mechanical and chemical cleaning. The advantages and disadvantages and the most appropriate method for stain removal are discussed. Some methods will damage the concrete surface unnecessarily if not administered correctly. For some stain removal it may be necessary to make a trial run to gauge the affect of the cleaning agent and the method used. A degreaser may work all right on colored concrete but an acid cleaner may affect the surface texture of the concrete.

Ground in dirt and stains from oil and grease are difficult to remove. For removal of oil or dirt containing oil, preliminary measures include using portland cement or hydrated lime followed by scrubbing with scouring powder or strong soaps such as trisodium phosphate, sodium orthophosphate or sodium phosphate. For very difficult stain removal degreasers may be necessary for complete removal. Degreasers work by penetrating the surface to soften, lift and remove oil, dirt buildup, grease and other difficult to remove stains or contaminants. A degreaser must be checked for compatibility with bonding properties of a sealer product.

Graffiti can be very difficult to remove. There are several available proprietary cleaners which contain methylene chloride or potassium hydroxide which may be safer to use but require a subsequent application of an acid neutralizer. Sodium bicarbonate abrasives have been used with power washers as well as metered quantities of sand that may however etch the concrete surface.

Concrete surfaces can be protected from deterioration from chemicals, acids, water penetration and dusting by the application of an appropriate coating or sealing compound. Some coating and sealer applications serve as decorative systems such as a "wet look". Decorative concrete includes colored concrete, sprayed on decorative finishes, stamping and applications of various toppings and dressings. A surface coating will help extend the life of the finish and protect such an investment. Reapplication of a sealer may require only alight cleaning on surfaces previously sealed. Depending on the chemicals used and contaminates removed from the concrete; water runoff may not be allowed to enter storm sewers. Some municipal codes, local and state EPA regulation will determine the safe disposal of cleaning activity discharges. Care must be taken for the safety of the workers and to protect the physical site conditions.

Selection of a sealer or coating depends on the exposure to the environment, interior or exterior application, present condition of the concrete and cost. Sealers are differentiated from coatings by their properties and performance, which include thickness, durability, water repellence, dusting, and resistance to chemical attack, resistance to physical abrasion and decorative systems. Coatings can be defined as sealers, which include sacrificial coatings on the surface as a barrier to water, oil or dirt. Sealers serve as a durable water proffer for self-leveling toppings and for refurbishing older concrete flat work.

Thickness
Sealers are generally thinner than most coatings, however thin coatings may fall within the same thickness range as sealers. The concrete should have a smooth, sound surface for application.

Coatings have thickness which range from 2 mils to 125 mils (3 mm). Some coatings can bridge small cracks and fill and smooth minor surface irregularities. An epoxy sealer can be 12-16 mils thick and more economical than an epoxy coating 20-30 mils thick. A coating can fill and smooth minor surface irregularities.

Durability
Sealers are usually acrylic, silicone, silane or resin based and may be susceptible to freeze-thaw cycles. Sealers can have a durability of up to 10 years or more provided there is no hydrostatic pressure and they have UV protection for exterior applications. Sealers will protect from water and salts and some offer abrasion protection but not to the same degree as coating made of epoxies, urethanes or polyesters. They are not suitable for surfaces that show signs of water damage. Some polymer sealers however retard corrosion of reinforced concrete by converting the rust or iron oxide on the rebars into iron phosphate.

Coatings will provide longer service life, a hard durable surface and are more resistant to chemicals, abrasion and traffic for warehouses, food facilities, and shopping malls and garage floors. Some have other materials applied for skid resistance, durability or appearance.

Water Repellence and Dusting
Sealers may penetrate (impregnate) ½ inch to several inches into the concrete surface to form a physical and chemical bond to the substrate rather than sealing the surface with a film as some do. Sealers usually do not tolerate hydrostatic pressure as well as most coatings and may fail.

Coatings of epoxy or polyurethane may adhere better than sealers and are more suitable for waterproofing surfaces in contact with earth or below grade.
Sealers and coatings protect from concrete dusting and provide easier to clean surfaces. Sealers are an economical solution with lower initial costs but would require subsequent applications during the life of a structure.

Decorative Systems
Sealers can provide an esthetically pleasing surface; dirt resistant and application in occupied facilities. Some serve as primers for paints. Without proper application they may not be uniform in appearance.

Coatings provide the same attributes as sealers but will have a more uniform color and texture and more durable surface.

Maintenance of concrete joints minimizes water intrusion through the joints, which will reduce subgrade problems, damage to structures and dirt collection in the joints and arrests vegetative growth.

Course Content

This course is based on Chapter 7 of the US Army Corps of Engineers Manual, "Evaluation and Repair of Concrete Structures", EM 1110-2-2002 (1995 Edition, 8 pages), PDF file. This course is also based on Chapter 4 (pages 4-12 to 4-17) of the Caltrans Division of Maintenance Guide for “Joint Resealing and Crack Sealing” (2006 publication, 6 pages), PDF file.

The link to the Engineers Manual in PDF form is "Evaluation and Repair of Concrete Structures".

The link to the Caltrans Guide in PDF form is "Joint Resealing and Crack Sealing".

You are required to study Chapter 7 of the manual " Maintenance of Concrete" and the Caltrans Guide.

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

Course Summary

This course considers the methods and materials used to remove stains, oil, dirt, asphalt, efflorescence and soot from concrete surfaces. The advantages and disadvantages of various removal methods are discussed. Protective concrete coating and sealers and the necessary surface preparation methods are presented. Proper procedures and safety measures must be understood for workers safety and to prevent damage to the site and adjacent surfaces. ASTM standards for etching, cleaning, coating and abrading concrete are listed.

References

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

http://www.kleinandhoffman.com/Pages/21evaluating.html
Provides information for successful concrete repair and maintenance.

http://www.concretenetwork.com
The website has information on concrete cleaning, resurfacing, staining and other concrete treatments and finishes.

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.