Building Management Hawaii - April/May 2012 - (Page 14)
Ask an Expert
Epoxy vs. Regular Rebar
By Jon Brandt At my building, we are currently doing a spall repair project. Sometimes when the broken concrete is pulled off, the reinforcing is so rusted that it needs to be replaced. Would the repair last longer if the contractor used epoxy reinforcing?
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I assume that these repairs are happening at the leading edge of a lanai or walkway. This is where we usually find reinforcing bars with the most damage. My firm does not specify epoxy-coated reinforcing for these conditions, but there are several contractors who do use it—regardless of what is specified. It’s not a problem if epoxy reinforcing is used for leading edge conditions, but let me explain why I do not use it. Through experience I have determined that proper spall repair preparation and repair mortar placement is actually more important than the type of bar. If the contractor does a poor job preparing the area for the repair mortar or improperly places the repair mortar, it doesn’t really matter what the reinforcing is; the repair will fall apart quickly. So the focus should be put on the repair preparation and mortar placement. Another issue is the quality of the epoxy coating. I’ve been told by suppliers that the marine-grade epoxy coatings have greatly improved since the ‘90s, but I still have questions about the product’s durability. Rust on reinforcing is caused by a chemical reaction between the steel bar and the chloride contaminated concrete (chloride comes from our local marine environment). The epoxy coating is designed to protect the
Hot-dip galvanized (HDG) rebar.
reinforcing bars against rust—except when a chip occurs in the coating. Chips can happen for a number of reasons. Wherever a small section of the reinforcing is chipped and exposed, rust will grow rapidly. And, the rust will occur at the same rate as if the whole bar was exposed to the concrete. If the bar had no coating, the same reaction would occur, but it would occur over the full length of the bar. This means that an uncoated bar will last a lot longer than a chipped epoxy-coated bar. Another reason I have stayed away from the epoxycoated bars is that studies from the mid-1990s showed that the epoxy coating tends to come loose from the steel about 10 years after the concrete has cured. In order for a reinforced concrete structure to maintain its strength, its steel needs to be bonded to the concrete. So I have concerns about that strength if the epoxy between the steel and concrete becomes loose. At the leading edge conditions noted, the reinforcing is typically for crack control during the curing of the concrete. So it isn’t a problem in that situation. Still, the best way to deal with the spalling is proper repair preparation and mortar placement. The International Concrete Repair Institute provides standards. If you have concerns about spalling repairs, check with your design professional.
Jonathan Brandt, S. E., is the principal of JPB Engineering, Inc. and has engineering licenses in Hawaii, California and Guam. He has worked in both the construction and engineering fields and has more than 10 years of engineering experience. Visit www.jpbengineering.com.
Epoxy-coated steel reinforcing bar (rebar) is designed to protect the reinforcing bars against rust.
April - May 2012
Table of Contents for the Digital Edition of Building Management Hawaii - April/May 2012
Contents Building Management Hawaii, April/May 2012
DEPARTMENTS: Concrete Restoration
If You’re Not Testing, You’re Guessing. Diagnose your concrete woes to save time and money.
Corroding Rebar and Spalling Concrete. Why zinc can be a spalling solution.
Top Five Fixes for Spalling. Preventing the corrosion of your building.
Trees – Our Green Assets. How not to plant the wrong tree in the wrong place.
Watts Up? Watts Down!. What you don’t know about parking lots could cost you big bucks.
Covered Parking & Photovoltaics: A Symbiotic Relationship. Covered Parking & Photovoltaics: A Symbiotic Relationship
Fire Prevention & Response
Top 10 Fire Fighters. Preventing fires is a job for everyone, but condo boards and property managers have a particular responsibility.
Keep a Clean Chute. Maintainance of trash chutes prevents serious high-rise fires
Stop, Drop & Go Wireless. New technology aids in fast response and saving lives.
Insurance: Do Condo Owners ‘Get’ Your Master Policy?
EDITORIAL: Editor’s Note
Ask An Expert: Epoxy vs. Regular Rebar
Movers & Shakers
Resource Guide: Concrete Restoration & Asphalt
Building Management Hawaii - April/May 2012