BajaNomad

rusty rebar

bledito - 7-9-2013 at 07:52 AM

I never hear about any cathodic protection installation for all the varrilla (rebar) used in building homes/resorts. I do hear about the rusty varrilla (rebar) that is used. Salts and heat increase the corrosion process and spalling of concrete due to the expansion of the metal rebar as it corrodes can wreck the structural integrity of a building. a few hundered bucks and some dilligence in insuring there is electrical continuity of the rebar would minimalize this corrosion. i guess most folks don't even know.

Rebar

J.P. - 7-9-2013 at 08:08 AM

After a lifetime of installing Rebar in all kind's of structures that's the first I ever heard of that . I Do know without Rebar most structures would have little or no integrity.
Because of the Salt used on the highways the rebar failed much earlier. The solution for that kind of failure was they tore the bridges out and rebuilt then using Teflon coated rebar

Islandbuilder - 7-9-2013 at 09:55 AM

The International Building Code require the use of clean re-bar. I have bonded re-bar to use it in place of driven ground rods for electrical panels, but never heard of it needing to be bonded to protect it from electrolysis.
In fact, unless you used a sacrificial anode (a zinc) bonding would just insure that the whole steel armature would rot out.
The new sealed re-bar protects against rust, not electrolysis.

bledito - 7-9-2013 at 10:16 AM

Point made (never heard about it). Many structures built without CP (cathodic protection) have had to be retrofitted with anodes to mitigate some of the effects of this corrosion after the fact. Non continuity of the rebar inside the concrete minimizes the universal effect of these installations, and only localized protection is acieved. The rebar areas that are in contact with the anodes.
fusion bonded epoxy coated rebar helps by elininating exposure of the metel to the elements, but no coating is perfect, dings in coating, material defects, etc.making the rebar contiuos electrically, and adding CP mitigates these minor flaws in coating by providing a sacraficial anode to deplete before the steel will.

Islandbuilder - 7-9-2013 at 11:24 AM

Wow. Good info bledito. That means that most of the concrete foundations in the world are just ticking time bombs.

I'm glad I'm old!

I see the epoxy coated stuff going into state and federal projects, but so far not in light commercial and residential. Perhaps a change in the codes is coming?

To meet codes there is (was? I've been out of construction for almost 10 years now) a 20x diameter overlap secured with at least 3 ties was required.

The union of vertical and horizontal runs had to be secured before the pour, not dug into the mud and "hooked" like we used to do it.

So, not bonded, but all steel in contact.

How does the cathodic protection work? An accessible anode tied into the steel? Doesn't it all need to be wet (and salty) to have molecular erosion?

Thanks for the new info, appreciate it! (even if it does scare the crap out of me!)

bledito - 7-9-2013 at 11:45 AM

concrete never fully cures, moisture is present. infiltration from rain, run off and the atmosphere can and will penetrate. Not looking to cause anyone to crap themselves. It's just the nature of the beast, metal will alway want to revert to its original state ore. and yes a accesable sacraficial anode, magnesium is less expensive,, can be dropped into your septic system providing activation of the anode. and bonded via copper wire to the rebar. this should work. a multi meter on dc volts should read above -.85v when attached to the wire and using a copper sulfate referance cell to obtain the reading.

bledito - 7-9-2013 at 11:48 AM

rust never sleeps, they wrote a song, I think it was neil young. it will take a long time but eventually it will cause failures.

woody with a view - 7-9-2013 at 11:53 AM

after our lifetimes, mostly. i can't vouch for the below the border work methods buts up north we're talking lifetimes if the correct material (coatings) and methods of installation are followed. nothing is perfect, concrete will crack and steel rusts.....

bledito - 7-9-2013 at 12:15 PM

north of the border things have definatly changed. south not so much. for my future generations i would want to insure structural integryty of the homes i build. the methods are simple and cp is easily achieved for minemal cost 17# magnesium anode could last 30+ years till it needs replacing.
an egg crate structure with deteriorated rebar inside it is not going to be structurally sound 50 60 years from now look at all the bridges and roads we're now completely replacing because this wasn't considered or known 60 years ago.

DavidE - 7-9-2013 at 12:23 PM

When I poured a patio slab 50' from crashing tropic waves I had ground up five dollars some odd cents worth of pennies and put them in a zip-loc. When the pour reached the varilla, I P-nched off the zinc a bit at a time and dusted along the rods. Better than bare steel I guess. i brought the pennies down to melt and hot dip galvanize reinforcing brackets for the patio wood railing. Pickled the metal in muriatic acid and then let cool. I had to go to three banks to get 20 dollars worth of zinc. Who knows if the zinc dust worked...the brackets resisted corrosion wonderfully.

TMW - 7-9-2013 at 02:24 PM

Sometimes on Sunday morning I turn on Science Fantastic on the radio. One time they talked about the buildings and bridges in Rome and why they have lasted for a couple thousand years. The rebar they used was not steel. It may have been copper or an alloy of some kind I don't remember. They went on to say that the concrete buildings built in the past couple of hundred used steel rebar that rusted and usually had a life span of 50 -100 years. In the last 20-30 years or so that has changed to using treated rebar to prevent the rust or to use a non-steel rebar.

I've always wondered why they always want to tear down a stadium and build a new one. Now I know.

bledito - 7-9-2013 at 02:24 PM

http://www.frpdistributors.com/gfrp-vs-steel/gfrp-vs-galvini...
here a link to what happens

bajagrouper - 7-9-2013 at 06:02 PM

I guess using salty beach sand mixed into the cement doesn't help either......

bledito - 7-9-2013 at 06:09 PM

it won't help stop the corrosion but it will probabally kill the METAL EATING MICROBES.

Ateo - 7-9-2013 at 06:30 PM

Interesting. No different than old Underground Storage Tanks (UST's) storing motor vehicle fueling.

Old tanks were steel and would corrode and leak. So they started using Cathodic Protection or Sacrificial Anodes to negate the effects of corrosion.

But a house won't leak and contaminate the soil. I guess it'll just fall over in an earthquake.


:biggrin::biggrin::biggrin:

bledito - 7-9-2013 at 06:51 PM

what about the problems with mismatched metals in the rivets on airplanes ?

woody with a view - 7-9-2013 at 07:15 PM

aluminum rivets in aluminum airplanes?

bledito - 7-9-2013 at 07:18 PM

with steel shanks oh my oh my.

woody with a view - 7-9-2013 at 07:42 PM

if it was an issue they'd use a steel rivet on the steel shank. how many planes have fallen out of the sky due to dissimilar rivets/metals?:yawn:

bledito - 7-9-2013 at 07:54 PM

http://en.wikipedia.org/wiki/Aloha_Airlines_Flight_243 only 1 or 2 so far

woody with a view - 7-9-2013 at 08:01 PM

anyway.....

"Investigation by the United States National Transportation Safety Board (NTSB) concluded that the accident was caused by metal fatigue exacerbated by crevice corrosion. The plane was 19 years old and operated in a coastal environment, with exposure to salt and humidity.[6][7]

According to the official NTSB report of the investigation, Gayle Yamamoto, a passenger, noticed a crack in the fuselage upon boarding the aircraft prior to the ill-fated flight but did not notify anyone."

luckily, there has never been another plane that has operated in such an environment since! maybe the Asiana flight had metal fatigue also when it's tail slammed against a rock jetty? prolly those cheap Chinese rivets!:light:

bledito - 7-9-2013 at 08:12 PM

so back to the varrilla (rebar) anyone seen anywhere you can get FBE fusion bonded epoxy coated varrilla (rebar) in baja.

Ken Bondy - 7-9-2013 at 08:37 PM

I've watched this thread with great interest. In my 50-year career as a structural engineer specializing in the design and construction of concrete building structures I have never specified cathodic protection, nor seen it used on any building in which I was involved. The primary method for providing corrosion protection for reinforcing steel in concrete is with adequate concrete cover over the bars. Hardened concrete is very alkaline (pH 12-13) and steel does not corrode in an alkaline environment. Certain concrete cover distances have been proven to be effective in preventing steel corrosion in various environments, and they are specified in all model buiding codes. Some structures in extremely corrosive environments, like bridges in areas where deicing salts are applied, require exceptional corrosion protection, and that's where you see special measures used, like epoxy-coated reinforcing bars and cathodic protection. But these things are not presently used in building construction, residential or commercial, and I see no signs that they will be used in the future.

J.P. - 7-9-2013 at 09:03 PM

Quote:
Originally posted by Ken Bondy
I've watched this thread with great interest. In my 50-year career as a structural engineer specializing in the design and construction of concrete building structures I have never specified cathodic protection, nor seen it used on any building in which I was involved. The primary method for providing corrosion protection for reinforcing steel in concrete is with adequate concrete cover over the bars. Hardened concrete is very alkaline (pH 12-13) and steel does not corrode in an alkaline environment. Certain concrete cover distances have been proven to be effective in preventing steel corrosion in various environments, and they are specified in all model buiding codes. Some structures in extremely corrosive environments, like bridges in areas where deicing salts are applied, require exceptional corrosion protection, and that's where you see special measures used, like epoxy-coated reinforcing bars and cathodic protection. But these things are not presently used in building construction, residential or commercial, and I see no signs that they will be used in the future.





I worked for many years on all kinds of reinforced concrete structures in the late 60's I worked on the One Shell Plaza which was the tallest reinforced concrete building in the South it topped out at 55 stories. as they used to say in the trade my body was wore out and beat up but my brain was like new because I never used it.
I don't know where this guy came up with this info. on rebar buy in all my years around Cal Trans engineers I never heard of it and if it was weird I am shure they would have specified it.
Retired Ironworker local.118 Sac. Ca

[Edited on 7-10-2013 by J.P.]

bledito - 7-10-2013 at 08:04 AM

http://www.corrpro.com/content/186/cathodic-protection-of-a-...
this is one example there are others. Just because some one has never used it in their trade does that make it a non issue. baja has a high corrosive enviorment high heat, salts, these salts make way into the concrete via sand mix, water, enviormental infiltration. I am not trying to sell anyone anything here. If you spend a bit of time researching the effects of corrosion on reinforced concrete in coastal and non coastal areas, or just look around the states at bridges and structures built you will find examples of spalled out supporting columns. I worked in an industry that utilized CP, natural gas transportation. i was involved in design and implementation of the cp systems. most of the steel i worked on had wall thickness of .50 or .375 sometimes less . have personally seen failures cause by corrosion. while I am not an engineer in CP, I have enough insight in this feild to consider the protection of building structural
steel a point to make. I plan on installing some type of cp on any structure I will build, for the cost, relativly inexpensive, why not.

Ken Bondy - 7-10-2013 at 10:50 AM

Quote:
Originally posted by bledito
.....most of the steel i worked on had wall thickness of .50 or .375 sometimes less...


I am puzzled by this statement bledito. Do you actually mean "diameter" instead of "wall thickness"? Also, are the units of the numbers ".50" and ".375" inches?? If the answer to both of those questions is "yes" then it appears you are talking about standard #4 and #3 bars.

Islandbuilder - 7-10-2013 at 11:30 AM

Seems like the larger concern would be starting with rusty rebar, that will have a reduced bond to the surrounding concrete due to the iron oxide on it surface. I built in the Pacific Northwest, with lots of rain and surface water, and it seems like this would be a far more likely environment for galvanic erosion than in Baja. Unless, you are using beach sand or sea water in your concrete mix.

I looked into using sea water for a remote island project, and found that it reduced the strength of the finished pour by less than 10%, which I figured I could counter by going to a 6-sack mix instead of the usual 5-sack. I decided to bring in a barge and transit mixers in the end.

Another concern I have had in watching Baja concrete pours is small batched being made, making consistency through an entire pour more challenging, and the high water content used to make the mix more user friendly. The more water, the weaker the finished product.

I always used retarding agents to slow the cure if it was sunny, a curing agent on all finished slabs which were poured over a doubled or tripled vapor barrier. All to slow the cure which also made a stronger finished pour.

In the heat of Baja, even in the winter, I would think those steps would be of greater importance than tossing a zinc in the septic tank.

But again, I know what I don't know, and this is certainly fits into that category.

Ken Bondy - 7-10-2013 at 11:47 AM

Quote:
Originally posted by Islandbuilder
Seems like the larger concern would be starting with rusty rebar, that will have a reduced bond to the surrounding concrete due to the iron oxide on it surface.


Actually a light layer of surficial rust improves bond. This has been demonstrated numerous times in testing performed by the Concrete Reinforcing Steel Institute (CRSI).

J.P. - 7-10-2013 at 11:57 AM

On some remodel jobs where the existing building was around 100 years old the demolition reviled old Rebar that that was Square. and it appeard to be in near perfect condition.

Ken Bondy - 7-10-2013 at 12:24 PM

The first deformed reinforcing bars used in concrete were square. I think they were used up through the 20s when they were replaced by round bars.

DENNIS - 7-10-2013 at 12:35 PM

Quote:
Originally posted by Ken Bondy
they were replaced by round bars.



I much prefer a round bar. It's easier to see everybody. :biggrin:
Start time at Sharky's in 25 minutes. SALUD

Ken Bondy - 7-10-2013 at 02:14 PM

Quote:
Originally posted by DENNIS
Quote:
Originally posted by Ken Bondy
they were replaced by round bars.



I much prefer a round bar. It's easier to see everybody. :biggrin:
Start time at Sharky's in 25 minutes. SALUD


I agree. In square bars I always ended up in the corner where it was hard to see anybody. And get the barkeep's attention.

Mexitron - 7-10-2013 at 02:55 PM

Quote:
Originally posted by Ken Bondy
Quote:
Originally posted by Islandbuilder
Seems like the larger concern would be starting with rusty rebar, that will have a reduced bond to the surrounding concrete due to the iron oxide on it surface.


Actually a light layer of surficial rust improves bond. This has been demonstrated numerous times in testing performed by the Concrete Reinforcing Steel Institute (CRSI).


That's what I had heard too...or else I've got a few patios and retaining walls to redo!
I've torn out old patios and walls at times and if the rebar was well ensconced in the concrete it was usually as shiny as new.

[Edited on 7-10-2013 by Mexitron]

Islandbuilder - 7-10-2013 at 03:50 PM

Yeah Ken, I understand. I was referring to flaky rusty bar, the kind you get when you leave the verticals stubbed out of the footing for a few years. Under UBC there was a threshold for rust that required really rusty bar to be removed. Seems like there's some language in the IBC that limits or prohibits rusty reinforcing steel, but leaves room for the inspector to make the call.

mulegemichael - 7-10-2013 at 05:42 PM

so...let's cut to the chase here....please....will i be able to outlive my patio?...is it at all possible?...i just built it...i would love to enjoy a few years with it.

bledito - 7-10-2013 at 05:50 PM

yep it'll last long enough. were those retarding agents and curing agents guys with hoses spraying down the concrete for a week or so.

Ken Bondy - 7-10-2013 at 05:50 PM

Quote:
Originally posted by mulegemichael
so...let's cut to the chase here....please....will i be able to outlive my patio?...is it at all possible?...i just built it...i would love to enjoy a few years with it.


As long as the rebar was properly installed with the appropriate concrete cover it should be good for 100 years :). Does it even have any rebar??

Islandbuilder - 7-10-2013 at 09:14 PM

Quote:
Originally posted by bledito
yep it'll last long enough. were those retarding agents and curing agents guys with hoses spraying down the concrete for a week or so.


No, the retarders were added to the mix, and the curing agents were sprayed on when the forms came off, or the slab was walkable. The only times we didn't use them was when the slab was going to be acid etched and dyed.