Petroleum resistant concrete 2

[gtrainor]

I'm about to place concrete for helicopter parking pads. All was well until the client pointed out that the existing concrete directly under the copters was scaling off due to the petroleum by products (hydraulic oil, fuels, lubricants...) leaking from the copters. He wants to make sure this doesn't happen to my concrete. Anybody have any suggestions to making concrete resistant to petroleum?

 

[RDK]

Spalling of concrete due to chemical attack is normally resisted by air entrainment. I have a fair bit of experience with airfield pavements(including helicopter sites) and have never seen concrete spalling due to petroleum products. Asphalt will deteriorate unless it is jet fuel resistive but not concrete.

Usually all parking and maneuvering areas of the airfield are concrete. This is for two reasons the first is strength. Asphalt will soften in hot weather and the tires or skids will sink into the surface. The other is that hydrocarbons will dissolve asphalt but not concrete.

Are you sure that the spalling is due to the petroleum and not some other cause like freeze thaw? Or some other chemical? You might want to have some cores tested to determine the cause of the deterioration. (have the lab check for air entrainment as well. If there is no air in the original mix this could be the cause of the problem.)

Where is this located? If you are in a location where freeze thaw is not usually a problem then air might not have been used in the original mix.

The DND Pavement Maintenance Manual (Department of National Defense, Canada’s equivalent to the US DOD) makes no mention of hydrocarbon attack of concrete.

The Canadian concrete code (CSA A23.1 para 15.8 ) calls for “Concrete exposed to heavy concentrations of light mineral oils, industrial chemicals, or trade wastes shall be given a protective coating..” There is a note that refers to PCA bulletin Effects of Substances on Concrete and Guide to Protective Treatments. 1S00I.07T, 1989. It might have some guidance that could help you.

I would always use sulphate resistant concrete when in contact with ground. I’d suggest that as a minimum you use 32 MPAa maximum water cement ratio 0.45 and entrained air of 6 to 9 % for max 10 mm aggregate, 5 to 8% for 14-20 mm aggregate and 4 to 7 % for 28-40 mm aggregate. (These values are right out of CSA A23.1)

If there is oil contamination on the existing concrete this should be removed by either steam or chemical cleaning or removal of the contaminated concrete depending on extent of contamination or the overlay will not bond to the existing layer.

Also pay particular attention to the curing of the concrete. This will increase resistance to all types of chemical attacks as well as freeze thaw.









Rick Kitson MBA P.Eng

Construction Project Management
From conception to completion

http://www.kitsonengineering.com

 

[gtrainor]

Thanks for the reply. Freeze is not a problem. It's in the deserts of Arizona. It's all concrete, and the damage was only in the area where the oil (or something) from the helicopter drips onto the concrete. It's not spalling but rather only the thin layer covering the aggregate is gone. It looks like washed concrete just after set where the aggregates get exposed. I'm not sure of the w/c ratio, air entrainment, or mix design. They just want to see if my design can resist the damage that's happening to the existing concrete.

 

[BigH]

Was the existing concrete surface adequately finished on completion. If you watch slabs being poured, sometimes, the finishers do not remove the laitenance (sorry, I always get the spelling wrong) - that water and cement which rises to the surface during setting. This leaves a thin film of weak grout on surface after water evaporates. Unless properly removed at time of placement and then proper finishing/troweling/floor finisher applied, you might get this spalling.

I think that RDK gave a great comprehensive note. Keep up good work!

Best regards.

 

[gtrainor]

Apparently it was a good finish. The thing is that the existing concrete was done years ago, so I have no idea what or how the concrete was done. The only signs of failure is where the oil is dripping from the copters. I am looking for a sealant or something that will resist the petroleum drips. If I can't find anything, I may suggest super high strength concrete just in the area where they leak.

 

[jheidt2543]

There are urethane and epoxy coatings that are resistant to petroleum products. Talk to representatives that handle Sonoborn or Sika products. They can be used on new and existing concrete surfaces. Surface preparation is very important and will likely require either acid etching or shot blasting the concrete surface.

 

[Ron]

gtrainor...RDK gave good info on concrete. It is generally not affected by petroleum products.

You mention the desert of Arizona. This could be a clue when mixed with the petroleum. If your aggregates are porous, or if your concrete matrix was a bit porous near the surface, then petroleum products penetrating into the matrix can then be heated by the sun on the concrete and the resulting vapor pressure increase, particularly at the aggregate interface level where the tensile bond is less than the matrix tensile strength, can cause "flaking" or minor spalling. Keep in mind that this process can also be "fatigue" oriented in that multiple times of building vapor pressure will ultimately fail the concrete on a "sub-macro" level (not really microscopic, but not larger spalls either). Couple this with the abrasion/localized impact of the landings and you could easily rationalize your result.

How to fix? Dense, high quality concrete, 4000 psi or higher. Use dense aggregates with low absorption capability. You could consider using a hardtopping or coating, but I think good dense concrete with a hard trowelled surface and wet curing for at least 14 days will give good service in this application. If you need to reduce the "slipperness" of a hard trowelled finish then roughen it after curing with abrasive wheels or brushes, but get the hard trowelling done first.

 

[gtrainor]

Thanks for the replys. Ron, I like the idea about how the concrete might be failing. As you might imagine, the surface temps can get up to 150+ F in the summer. I think I'll try the long cure-high strength and check out a coating that jheidt2543 has given. Thanks all! and Merry Christmas.