Spalling Concrete due to rusting steel

By
Home Inspector with Charles Buell Inspections Inc.

     In modern construction the use of steel reinforcement in concrete has become the norm.  It was not always this way.  There are not usually too many problems that arise as a result of doing this as long as the concrete is of good quality and the steel is far enough away from the surface.  The concrete itself Bird on a rusting postcreates an environment that “naturally” protects the concrete from corrosion.  If a pathway for water and other corrosive elements like salt can find there way to the steel, rusting can then happen.  As steel rusts, the oxides build up on the surface causing the steel to expand.  This causes the concrete around the steel to “spall”----to peel away.  This then exposes the steel to even more direct adverse conditions leading to an even faster rate of corrosion. 

     In this first picture one can see where the surface of the wall has been pushed away exposing the rusting steel.

Spalling concrete due to rusting steel

     In brick homes, steel lintels over doors and windows can cause the same sort of problem resulting in lifting of the bricks that cause diagonal cracks that radiate away from the ends of the steel.

     I saw some of the most extreme examples of this condition at Fort Jefferson in the Dry Tortugas.  This fort utilized tons of iron to reinforce the areas around the gun ports----to provide greater protection to these areas of they were to be struck by cannon balls.  Previous to this fort’s design giant pieces of stone work were used instead of steel.

     If someone were to sit down and figure out how they could install steel in such a way as to cause its quickest demise, they would come up with “Fort Jefferson.”  None of this steel was truly encased in protective concrete.  Instead it was installed in the very porous coral fill behind the brick veneer and within the brick veneer itself.  It was also vulnerable to round-the-clock “condensation.”

Huge section of the facade spalling away

     The roof of the ramparts all around the fort were covered with earth and easily allowed rains to be absorbed into the structure where it would find its way to the steel.

View from the top of the fort

     These conditions mean that the steel reinforcement is continually being attacked from within and without.

     In most cases the reinforcement was not small diameter rods like we use in modern construction but was instead massive iron plates weighing hundreds of pounds.  Take a look at this picture.  We can see three gun ports.  The one on the right has been rebuilt and appears pretty much as intended----minus the gun sticking out.  The two ports at the left show extreme spalling all around the ports and much of the brick and steel is in the moat.  If you look carefully you can see several of the massive steel billets that used to be around the ports.  They measured approximately 6” x 16” x 48”----approximately 1500 lbs each.

Spalling of the brick facing

     This next picture is one of the gun ports close up showing the large heavy iron plates around the openings.

Iron work around the gun port

     As these metal components rust and expand they simply push all the bricks and themselves right into the moat.  The complexity of maintaining such a structure is immense.  Hopefully as they rebuilt the areas around the ports they are not replacing the iron but are instead utilizing materials that are more conducive to the environment----given that the gun ports are not likely to come under heavy cannon fire any time soon.

For more information on Fort Jefferson and Dry Tortugas National Park see my previous post:  Dry Turtles! Florida Keys and the Dry Tortugas

 

Charles Buell

 

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Rainmaker
1,244,561
Steven L. Smith
King of the House Home Inspection, Inc. - Bellingham, WA
Bellingham WA Home Inspector

Mr Charles,

I find that very interesting stork by far the most intersting feature of this old building blog.

Nutsy

Dec 18, 2009 10:47 AM #10
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Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Nutsy you are storkraving mad!

Dec 18, 2009 11:54 AM #11
Rainmaker
176,535
Jim Allhiser
Perfection Inspection, Inc. - Salem, OR
Salem, Oregon Home Inspector

Thanks for that, fantastic blog Charles.   Just can't stop that blog machine can you?

Dec 18, 2009 04:42 PM #12
Rainmaker
564,223
Steve, Joel & Steve A. Chain
Chain Real Estate Investments & Mortgage, Steve & Joel Chain - Cottonwood, CA

Charles, Did you notice the new IBC does not require rebar in residential foundations?

Dec 19, 2009 12:16 AM #13
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Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Jim, I am just out of control:)

Steve and Joel---do you have a code reference number for that?

Dec 19, 2009 12:46 AM #14
Rainer
215,888
Diane Williams
Pell City, AL

This is very interesting. It is also sad to see it falling apart. You have shot some great pictures.

Dec 19, 2009 02:13 AM #15
Rainmaker
1,846,865
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

Oh, spAlling!  I thought you wanted me to look for the bricks that were spIlling into the water.  I didn't find any until I read your comments...

 

 

(;>)

Dec 19, 2009 05:30 AM #16
Rainmaker
1,846,865
Jay Markanich
Jay Markanich Real Estate Inspections, LLC - Bristow, VA
Home Inspector - servicing all Northern Virginia

What a great trip!

Dec 19, 2009 05:30 AM #17
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Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Diane, thanks----sometimes falling apart things are more beautiful than when they were new:)

Jay---it was a great trip

Dec 19, 2009 11:03 AM #18
Rainmaker
1,052,687
Barbara S. Duncan
RE/MAX Advantage - Searcy, AR
GRI, e-PRO, Executive Broker, Searcy AR

There you were on vacation and doing an inspection!  A fort inspection.  Great pictures.

Dec 19, 2009 11:04 AM #19
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Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Barbara there really is not too much difference between what I do for a living and how I live while I am doing:)

Dec 19, 2009 11:10 AM #20
Rainmaker
564,223
Steve, Joel & Steve A. Chain
Chain Real Estate Investments & Mortgage, Steve & Joel Chain - Cottonwood, CA

Charles, The code is 2007 CBC ( adopted from IBC for California). Implimented January 2008.

Steve

Dec 19, 2009 03:21 PM #21
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Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Steve that seems so odd.  Here IBC is not for residential---more commercial projects and I am not very familiar with it.  Certainly the IRC which covers residential construction in most areas requires rebar in most everything----even in areas of low seismic activity.

Dec 19, 2009 03:35 PM #22
Rainmaker
564,223
Steve, Joel & Steve A. Chain
Chain Real Estate Investments & Mortgage, Steve & Joel Chain - Cottonwood, CA

Charles,  We develop in numerous areas with different county and city agencies.  They all handle this differently.  This was the result of post-earthquake analysis of buildings in CA.  They discovered that the buildings weren't failing as much from foundation failure as from bracing problems. So the minimum "brace panel" frequency was increased, but the requirement for rebar went away (unless the building designer calls for it).  One agency "suggests" rebar not for today's code, but "incase" it changes back.  One agency will forgo the required soil report if rebar is installed.   That being said we design most of the homes we build in-house and still choose to use rebar in our designs.  I thought you would get a kick out of this.

Steve

Dec 20, 2009 12:31 AM #23
Rainer
407,371
Sean Allen
International Financing Solutions - Fort Myers, FL
International Financing Solutions

Hey Charles,

Fort Jefferson is on my "To do" list before I die. Have always wanted to visit it.

Sean

Dec 20, 2009 08:04 AM #24
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Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Steve----interesting.  I remember seeing some post quake pictures of failed bridges with the rebar cages still intact with the concrete shaken off them:)

Sean----you better get your butt out there while it is still standing:)

Dec 21, 2009 05:30 AM #25
Rainer
166,615
Andy Chaudoir
Professional Inspection Services - Georgetown, Texas - Georgetown, TX
Your Home Inspection Connection in Central Texas

Hello Charles - Thanks for the great post.  I ran into this problem in an inspection last week.  Thanks again!

Jan 01, 2010 12:32 PM #26
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Charles Buell
Charles Buell Inspections Inc. - Seattle, WA
Seattle Home Inspector

Andy, hopefully not as bad as the fort:)

Jan 01, 2010 02:03 PM #27
Anonymous
James

I would think another cause of the corrosion would be that they used salt water to mix the mortar for the fort.

Aug 15, 2010 01:19 AM #28
Anonymous
Daemyon Zatarga

Building practices of the 19th Century aside, it's a great location to take a date for a picnic! I seriously doubt you'd be interrupted or even see another person if you picked the right day to sail a boat over and anchor behind the fort...

Sep 29, 2010 02:14 AM #29
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