HALF-SLAB SLIPPAGE PROBLEM 3

[JBP00]

We are a retailer of Prestressed Concrete Strands 9.5mm (ASTM A416). Our customer experienced slippage on their Precast Half Slab and bonding problem with concrete due to oiled Strands. Our supplier informed us that they applied Water-Soluble Oil and it will be dried by natural air drying for 2-3days. After several days out in the open-air, there is still oil/grease residue on the strands as seen in attached image and our customer has lost confidence of using the remaining stocks of strands which is 88 metric tons (16 coils).

I would like to receive your insights and solution on how to remove the oil, what type of chemical to apply to it and speed up the process to remove it totally to salvage the remaining affected stocks of strands.

 

[Ingenuity]

JBP00:

This can be a serious problem - both the strand slippage/deficient bond issue, and the removal of the residual oil.

In my area of practice, about 10 years ago one of the local precaster's experienced strand bond slippage and it was due to the residual coating that was left-over by the manufacturing process. I understand the strand was rejected and remaining stock was returned.

What is the country of origin of the strand?

The US-based TRANSPORTATION RESEARCH BOARD authored a document in 2008 entitled "Acceptance Tests for Surface Characteristics of Steel Strands in Prestressed Concrete". It is very detailed on matters related to strand surface, and may address part of your problem. Free downloaded copy is available here: Link

Part copy of paragraph from page 7 of the above document:

I would be placing the onus on the manufacturer to directly address the issue - bypass the supplier and get answers from the manufacturer.

In the past, have any of your other customers experienced similar issue with the same strand manufacturer?

 

[dik]

Ingenuity... there may not be any contractual relationship with the manufacturer, only the supplier.

Dik

 

[Ingenuity]

dik, probably true, however, if the manufacturer does not step up to the plate they will not only have a irate supplier, but an end-user that will never purchase such a brand again...along with telling all precast competitors of the issue.

Too many players in this situation: user-retailer-supplier-manufacturer.

When I used to purchase strand in large quantities (typically from Japan and the US manufacturers) it was always preferable to go as close to the manufacturer as possible. Most times you have to go through a distributor - but we often had a direct link to the manufacturer to check on production/supply delays.

When we used to purchase product by Florida Wire and Cable in Jacksonville. We purchased directly from them. Made it easier to get resolution on a 100t consignment that rolled over in containers due to inadequate tie downs.

 

[JBP00]

Ingeniuty,

Thank you for your response. Our Manufacturer is from China and we have sourced to them with 4 shipments before and only now our customer(end-user) has experienced this issue. Our Manufacturer informed us that we shall apply kerosene and wipe cloth after to clean the residue.

May I ask if you have a swiftly way to remove the oil residue from the strands?

 

[dik]

Does not kerosene leave an oily residue... not positive, but seem to recall. Acetone may be a better choice... but, if you have miles of the stuff... can you dip the rolls in a solvent?

Dik

 

[JBP00]

Our manufacturer informed us that we shall apply kerosene and wipe it after to dry it out. If we dip the whole coil in solvent(acetone), should we wipe it off after or just let it dry?

Dik,

Which solvent do you think we can dip it into and not wipe it off after to reduce work? Thank you.

 

[Ingenuity]

Does not kerosene leave an oily residue... not positive, but seem to recall.

dik: I think you are correct.

JBP00: If I was the end-user I would REJECT the strand. Period. The effort to clean and the risk/liability that it was indeed satisfactory, is too great, in my opinion.

Our Manufacturer informed us that we shall apply kerosene and wipe cloth after to clean the residue.

A 3-ton coil of 1/2" dia strand is 12,000 feet long, so 9.5mm would be even longer. Using a wipe-cloth to remove any residual kerosene or any other applied liquid/cleaner, will take a long time to execute, and it is only practical to clean it after the strands are laid in the bed (but prior to stressing) - but very laborious.

I have de-greased and re-greased many UNbonded strand tendons using a custom-made automated system, but your issue is very different.

If the oil is indeed 'water-soluble oil' then clean and wipe with water will work, BUT, you run the risk that water will fill the interstices between the outer 6-wires and the central king-wire, and may promote future corrosion. One of the reasons why the manufacturing process uses drying processes.

7-wire strand manufacture is a complex one. Don't mess with the end-product.

 

[JBP00]

Ingeniuty,

Thank you for you advice. Since the coils cannot be returned to China, we shall degrease the coils as our customer wants to solve this issue as soon as possible. May you advice us how to degrease the coil without harming the strands and not take too much labor?

 

[TehMightyEngineer]

Low concentration sodium hydroxide bath followed by clean water bath and then followed immediately by heating to remove moisture? I agree with Ingenuity that this is going to be a lot of work to even come close to guaranteeing that the final wire will perform without any corrosion issues and have all the oil removed with an easy to implement process.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[dik]

Can anyone suggest a means of salvaging the coil(s) of strand? Is it possible to dip in a solvent to remove the oil? provide sufficient corrosion resistance and maintain any certification?

Dik

 

[TehMightyEngineer]

dik, that's why I suggested the sodium hydroxide (aka lye or caustic soda, essentially oven cleaner) as probably the most effective industrial strength degreaser I can think of that would require little manual labor. I'm no chemist but I believe sodium hydroxide reacts with most water soluble oils and fats by turning them into soap. This way the oils the sodium hydroxide removes are trapped in solution and wont re-adhere to the wires. The other advantage is sodium hydroxide is available on an industrial scale and would be much cheaper than trying a solvent like acetone (which may not fully clean the strands depending on the oil).

Sodium hydroxide is corrosive though so some small trial batches should be done to establish the minimum concentration required to remove all the oil and verify no corrosion concerns exist following the treatment. Then a hot water bath to remove any remaining sodium hydroxide solution or maybe an acid bath as this would help pickle the steel and neutralize the sodium hydroxide. Then a propane heater to heat dry the coils and you're done.

It's the most effective way I can think of to degrease a large quantity of strand with minimal manual labor, rapid cleaning, and a controllable process to keep degradation of the wires to a minimum.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/

 

[dik]

Were you able to resolve this problem. If so, what was the solution?

Dik

 

[JBP00]

Hello Dik,

We have tapped degreasing firms that also supply rust preventive Oil. They informed me that dipping process with caustic solution is not possible since the strands should be uncoiled and not applicable on this process and will not penetrate the inside of the coil. The strands cannot be uncoiled as per our customer.

The degreasing firm have sampled to me wiping with cloth dipped with solution (alkaline or CL I am not sure) and it removed the oil totally. Although this process is laborious, I think this is the only Solution.

Ingeniuty,

May you inform me your automated solution for degreasing?
"I have de-greased and re-greased many UNbonded strand tendons using a custom-made automated system, but your issue is very different."

Regards.

 

[Ingenuity]

May you inform me your automated solution for degreasing?

Unfortunately I cannot as I am in the process of applying for a patent on the equipment and technique I developed. Sorry.

 

[JBP00]

Ingeniuty,

Thank you for the response, this technique your are applying for a patent can degrease the strands even the coil is intact?

JBP

 

[Ingenuity]

No, it is for existing/installed strands within a building floor systems that utilize UNbonded (greased and sheathed) 7-wire strands.

 

[JBP00]

Hello everyone,

One of degreasing firm here informed me that it is possible to dip the coils in an emulsifiable degreaser. I would like to ask for your insights regarding the penetration of the degreaser for the whole coil on degreasing bath.

TYPICAL CHARACTERISTICS:
Specific Gravity @ 15.6 °C 0.797
Appearance Clear
Flash Point, TCC, °C 40.6
Color, ASTM + 28
Appearance of Emulsion Milky White


Regards,
JBP

 

[dik]

Based on the information you provided, we can offer no opinion (speaking on behalf of everyone).

Dik

 

[TehMightyEngineer]

I'll join with dik; that doesn't tell me anything particularly useful about the degreaser.

Professional Engineer (ME, NH, MA) Structural Engineer (IL)
American Concrete Industries

https://www.facebook.com/AmericanConcrete/