Evaluation of Surface Preparation Methods to Remediate Chlorides on Bridges

From JPCL, January 2017

By Bobby Meade, Greenman-Pedersen, Inc.; Michael Baase, Kentucky Transportation Cabinet; and Theodore Hopwood Ii and Sudhir Palle, University Of Kentucky

The cost of maintaining a protective coating during the service life of a bridge can approach the cost of the original construction. The authors describe a KYTC-funded research project that assessed steel panels prepared by application of 32 different cleaning methods for quantity and deposition of retained chlorides....

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Tagged categories: Bobby Meade; Bridges; Chlorides; Contaminants; Greenman-Pedersen, Inc.; Kentucky Transportation Cabinet; Performance testing; Salt contaminant levels; Soluble salts; Sudhir Palle; Surface Preparation; Theodore Hopwood II; Wet abrasive blasting

Comment from James Miller, (3/8/2017, 5:54 AM)

Method 28-Crushed glass should be used at lower pressure than the testing, 80-90 PSI max

Comment from John Brodar, (3/8/2017, 2:28 PM)

My compliments to Bobby Meade, Michael Baase, Theodore Hopwood II and Sudhir Palle on their article “Evaluation of Surface Preparation Methods to Remediate Chlorides on Bridges”. I found it interesting, nicely documented and well written. It has been added to my collection of “Chloride” articles. I sincerely hope that it is well received and helps educate the painting world to the problems of chloride contamination. For several decades I have stated that chloride contamination (and other “soluble salt” contaminants) are the single largest problem facing the paint and coating industry for the 21st century. The following quote from your article is extremely significant. The underlined portions is the area I wish to address. The protective coatings industry has long recognized that chlorides are detrimental to protective coatings. Recent efforts by the Kentucky Transportation Center (KTC) for the National Surface Treatment Center – Conductivity Testing and Comparative Analysis have documented that there are no reliable field test methods for identifying problematic distribution of chlorides. Currently available field test methods accurately quantify the chlorides within the test area but do not identify concentrations or “hot spots” of chlorides. You are performing MAINTENANCE painting. You have a built in method of “identifying problematic distribution of chlorides”: rusted areas. On your painted bridge structure, every area showing rust is contaminated with chlorides. Non rusted areas are not contaminated. It is really that simple. The difficult part is to change the mind set and contracting practices to properly decontaminate and repair the rusted areas instead of simply repainting the entire bridge. It is much easier to estimate repainting an entire structure than it is to estimate the PROPER decontamination and recoating of the rusted areas. I don’t expect the industry to change overnight, but spending the maintenance dollar on the problem instead of simply repainting the entire structure is the long term solution. Many of my other chloride decontamination concepts and methods are documented in my article “Coating the Reactivator Tank: A Step Into the Future”, published in the September 2011 Coatings Pro magazine. Several practices are directly applicable to your bridge painting. There are “Before”, “During” and “After” photos. “After” photos are after one year water immersion. At the time of the last inspection in March 2016, after 7 years water immersion service, the tanks still look the same, and without a single rust spot. Much to my dismay I have not had a single inquiry since publication. By the way, spreading a salt solution over clean steal is not the same as a chloride contaminated surface. I do know how to reliably and repeatedly contaminate steel surfaces with chlorides and will be happy to consider commercial development. I would be pleased to discuss soluble salt decontamination further, with anyone, jmbrodar@srpnet.com John Brodar P.E.

Comment from Regis Doucette, (3/10/2017, 7:50 AM)

Your study of chloride removal from metal surfaces was flawed by not following the directions of the acidic soluble salt remover of which I am very familiar. You applied with a hand sprayer a chemical treatment that the label and the directions clearly state the requirement of application with 3,000 PSI zero-degree rotary tip pressure wash of the potable water diluted solution. This methodology by the manufacturer, and that is successfully used in the field internationally on a daily basis, does clean out the pits your study focused upon. When properly used, this approved acidic soluble salt remover decontaminates surfaces to specified or non-detectable levels of chloride.

Comment from Tom Swan, (3/13/2017, 9:03 AM)

It would also be useful to point out the the other non-acidic salt remover also requires pressure washing for proper application. Minimum 1500 to 3000 psi. Higher pressures are especially critical on pitted surfaces to get the water into the pitted areas as well as the valleys in a blast profile. These products work by reducing the surface tension of the water to fully wet out the areas and it requires application under pressure to fully wet out the area for soluble salt removal. Except in a few rare situations, application by hand sprayers are never recommended.

Comment from Regis Doucette, (3/14/2017, 12:07 PM)

The purpose of the study was to remediate soluble salts and not a focus on visual standards after a coating is removed. The product you, Tom, cited has a pH of 10.2 which is alkaline. It is well documented that alkaline products do not remove surface adsorbed salts but rather mask them by developing a blanketing inhibiting layer as documented in NACE 6G186. Further, ISO 8502-2 states that amine inhibitors, which is the generic definition of the product to which you refer, “form a hydroxide boundary layer over the substrate” which prevent contact with the underlying salt. For decades the pipe coating and auto industries have used an acidic solution to decontaminate surfaces of residual surface salts, followed by an alkaline treatment to prevent flash rust. These two functional chemical steps are mutually exclusive. Therefore, the use of your product would have required an extra step to properly prepare the metal for measuring the residual salts not removed. The application of a biodegradable and coating manufacturer approved solution with a pH that is an acid, not a base, chelates and removes surface salts.

Comment from bobby meade, (3/14/2017, 10:27 PM)

The surface preparation methods evaluated were not all inclusive and were methods considered most likely to be used by the Kentucky Transportation Cabinet. The methods selected were approved by KYTC. KTC employed those methods as described and reported the results. If there is documentation of any surface preparation method that eliminates soluble salt contamination, the industry would surely be interested. KYTC has used the chemical additives included in this laboratory study on field projects with the manufacturer representative present and following his advise for application. Chlorides were reduced but not eliminated on the field application.

Comment from Tom Swan, (3/15/2017, 9:36 AM)

Regis, I suggest you read a chemistry book and not your marketing material. The only thing required to remove water soluble salts is Water. (That is why they are called soluble salts). Low or High pH has no effect on soluble salts The hydroxide boundary layer is nonscientific BS based on extracting one line out of a chemistry book out of context. Both cleaning products work by reducing the surface tension of the water to help the water get to the salts. pH has nothing to do with the removal of "soluble" salts, only how the products are formulated. This Bad chemistry has been floating around our industry way too long. I do not mind discussing different methods as long as the discussion is based on real chemistry. Bobby - weather or not salts are removed to non detectable levels depends on how they were tested. The detection levels have improved to where I never tell users to state less than detected or zero levels. Despite the difference of opinion between Regis and myself, neither product is designed to use with a hand sprayer and testing using this methodology does not represent how these products are used in the field.

Comment from Regis Doucette, (3/15/2017, 11:42 AM)

Tom, water does remove some surface salts for sure and because your material is diluted in water, but it cannot remove the salts down to the levels required to prevent premature coating failures. Why? Because the salts of concerns are those embedded and bonded to the steel and not dislodged with just a water flushing. This study’s revelations about pitted corrosion are key to preservation efforts. The ISO and NACE publications I have cited are not marketing materials as you say, but consensus documents from our trade and professional societies. Your claim that I crafted words previously means you have not read those documents where those phrases are found. In addition to the industry examples cited earlier (pipe coating and auto) the metal tooling and fabrication industry has followed a rigorous and disciplined approach to surface cleaning and decontamination which is abbreviated as the A-A-A process. A for an alkaline degreasing and dirt removal step to start, followed by a second A, an acidic solution to remove and decontaminate surface salts, and lastly another A, an alkaline flash rust inhibiting step. Each step is mutually exclusive and none can be combined from a chemical functionality standpoint. If a combination were possible, the industry would have done so years ago to save millions of dollars spent annually on this process. To summarize, your alkaline material does not dislodge salts to levels required in specifications but rather can mask their presence with a blanketing inhibitor layer. The result – coating failures long before achieving proper life cycle performance.

Comment from Lydia Frenzel, (3/15/2017, 2:17 PM)

Hopwood and Meade and I have discussed for years the merits of a "low technology for maintaining bridges, in other words, can you maintain with spot blasting, pressure washing or water blasting- not UHP WJ, use some of the cleaning agents? This article is a summary of many choices. I suggest Mark Schilling's papers in NACE, Corrosion 2009, Paper 09023, Material Performance, Mar, 2007, p. 32, or his two papers in Corrosion and Materials, Australasian Corrosion Association, Vol 31, No 5 and No 6, 2006. All deal with the problems of the Junk Science in Corrosion. There is bad chemistry and bad physical chemistry in our NACE, and SSPC articles. They come about because a mis-statement is made and it is repeated over and over again until it becomes a "Fact" and is not referenced back to the original source. For an example, I have been in committee where the chair wanted a vote on an equation. The majority wanted to vote yes on iron oxide will spontaneously break down to iron and oxygen. I had to forcibly point out to them that this doesn't happen in nature. By voting on an incorrect statement for inclusion doesn't make it real. Articles on salt and cleaning additives appear to me to be particularly susceptible to this problem. When I read the Meade and Hopwood article, I remembered Harlan Kline's words in 1997 when he said that both water and dry blasting removed salts. The water method was about 4 times as effective as the normal one-time blasting. Harlan was a senior technologist with Ameron. This was a generality- give at a Naval Industry event. So I looked at the article for the results of the multiple blast for cleaning efficiency.

Comment from Tom Swan, (3/16/2017, 10:27 AM)

I generally try to stay out of these discussions and my initial post was to agree with what you said as far as the application of the chemical salt removers.  I will never win this argument because there is real chemistry and the chemistry that has been being pushed by a long running series of articles in technical journals.  You cannot win an argument when  people make up chemistry rather than using actual chemistry,  There is little in your last statement that has any relationship to real chemistry and as Lydia pointed out there is a lot of bad information published in the technical journals and in some standards.  Acidic and alkalinecleaners do not remove water soluble salts.   You can find no better soluble salt remover than DI water,  The cleaners do not remove the salts, the water does. The cleaners just hep get the water to the salts. Try doing your laundry just using soap an no water and see how clean they get.  I am not sure how a 100% volatile cleaner can leave a film that masks anything if it is 100% volatile.  If you don't understand the word volatile, look it up in a chemistry book.  This is supposed to be a noncommercial forum and we should stick to facts, few of which are in your last post and most of them are wrong.  Unfortunately our industry has few Mark Schilling.s who dedicated his life to combating junk science of which your post is an excellent example.  I just got an email from NACE with an article on salts that had bad chemistry in it.  I can only encourage the industry to put more pressure on technical publications to get it right and not just publish it because they need content or because they are written by  paid advertisers in the publications. A while back I had a discussion with one of the technical editors for a major industry technical publication.  I pointed out some articles that had chemistry inaccuracies and he said they did not want to edit opinion.  I pointed out to him that Chemistry is not opinion, it is either right or wrong.  If you want an example of wrong chemistry read Regis's last post. 

Comment from regis doucette, (3/17/2017, 7:15 AM)

Tom, Lydia did not impugn published standards. Our standards are what I quoted and referenced, so your accusation THEY are involved with junk science insults all those societies. Your choice of repeated personal attacks here indicates a combination of desperation and denials observed in other parts of society these days, but I find it humorous that you chose to contradict yourself in the last posting. At one point you cite water as the best cleaner and then praise chemical additives. What I will gladly share with the community is a published US Navy study that presented a specific acidic soluble salt remover not only did a better cleaning of soluble salt contaminants than DI water, but that it also enhanced the coating adhesion by 20 to 50%. You are all over the logic here preaching about articles that are not the focus of this study and comments. Your statement of “no better soluble salt remover than DI water” clearly has been proven wrong by many specifications and studies that have been in place for years without failures in the field. I am focused on agreed principles and standards. An acidic additive to a wash water solution in accordance with the manufacturer’s instructions effectively cleans substrates of soluble salts.

Comment from Tom Swan, (3/20/2017, 9:37 AM)

It is impossible to "win" this argument so if there is any more than the three of us in this thread, I caution you to not believe everything you read in technical journals, in blogs or on the internet. Even text books can be prone to errors and omissions. Beware of statements taken out of context: "don't drink acid, it could kill you" (I hope you didn't drink orange juice this morning). It is up to the members of our industry to educate themselves. If you chose to believe that 1 + 1 = 3 then we will not get anywhere in our industry or in life. I encourage technical journals and professional organizations to better fact check information they publish. I cannot control what people choose to believe. And I will end the discussion with this.

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