Surface Coatings for Concrete and Failures 4

[WoodyPE]

Has anyone come up with a surface coating on concrete that doesn't fail under forklift traffic. Moisture gradient (from vapor transmission through the slab) can casue coatings to form blisters that eventually fail. Epoxy coatings tend to crack at the microscopic level.

Has anyone tried fiberglass reinforced sheets anchored to the floor? The thermal expansion coefficient should be pretty close to concrete.

 

[beton1]

Have not heard of this application; strengthening members yes. Forklift traffic is a problem with concrete floors, however the problem is broad in nature. Subgrade and base preparation, proper techniques, detailing etc. are all part of the overall system performance. It is difficult to solve the issue strictly from a 'top-down' approach.

 

[Ron]

beton1....the problem is not structural. It is one of surface durability.

WoodyPE...in Cain's article he makes some nice, safe, theoretical recommendations; but in general, they are not practical to implement. While I agree that a water-cement ratio of 0.45 would help tremendously, you're not likely to get that with typical warehouse slab construction.

Many will blame the issue on groundwater and water vapor migrating through the soil, into the concrete, then onto the surface. That's not the way it happens.

Moisture vapor on the surface of the concrete in floor slabs is more likely to come from excessive mix water than any other source. If not given adequate time and ambient conditions to evaporate, it can be a problem for many years.

What to use? It depends on the amount of moisture vapor transmission and/or the ambient in-situ relative humidity in the concrete.

If you have not already done so, you need to do several tests. The first is the typical anhydrous calcium chloride test for moisture vapor transmission (ASTM F1869). The second test is to determine the in-situ relative humidity of the floor slab, and do this on a gradient basis to determine the humidity with depth. This is ASTM F2170. Once you have determined these two parameters, then you can decide which system to use or if you will need to apply a sealer or use other mitigation methods before you coat the floor.

We have used epoxies, methacrylates, urethanes, and acrylics with success but under different conditions. Each has its limitations. I was surprised at your statement of microcracking in the epoxy. That's very unusual. Unless you have seen that first hand, I would be skeptical. I do a lot of microscopy on concrete and floor coverings. That is extremely rare and not inherent to epoxy coatings in general. They are usually the more durable of the coatings.

Fiberglass sheets mounted to the floor would not likely work. First they would have to have a slip resistant coating on them. Second, the wheel stresses at the bottom of the unbonded fiberglass layer are going to be very high and will likely cause fatigue failure of the sheets, particularly in wheel paths and at joints.

Timing of application, ambient humidity and temperature, ventilation, and experience of the applicator certainly play significant roles in the success of any coating.

Don't forget to check the surface finish of the concrete itself. Very hard troweled surfaces can cause problems with coating adhesion (which can lead to blistering) and might need to be roughened before application. That can be done chemically or through abrasive blasting.

 

[WoodyPE]

Thank you Ron, et al.

First of all it is very easy to apply a long-lasting slip-proof surface on FRP, as it readily accepts many types of adhesives and resins for bonding purposes.

Secondly, FRP is used as a ground-mat for heavy equipment. It is also used as humvie armor, and on highway bridge decks. A 3/4 inch plate is almost impervious to bullet penetration. AS tough as it is, should forklift traffic be a problem?

Check out the technology. It has come such a long way:

http://www.martinmarietta.com/Products/composites.asp

http://www.martinmarietta.com/Products/blastpanels.asp

http://www.martinmarietta.com/Products/roadtraks.asp

http://www.martinmarietta.com/Products/transonite.asp

http://www.mdacomposites.org/mda/frp_product_gateway.htm

 

[Ron]

No question it's tough stuff, but is it affordable and practical for use on warehouse floors.

The contact stress on a thin membrane over a stiff matrix such as concrete due to a forklift is very high...higher than the loading that would be placed on the membrane by a tracked vehicle. I'm fairly sure you would see fatigue issues with the material if unbonded.

I agree that a non-slip surfacing could be added, but that's additional cost as well.

I think FRP is a great product in many applications...I'm just not sure this is an appropriate application, from a cost standpoint and a practicality standpoint.

 

[beton1]

Agree with you Ron; your second post is more in line with my thinking as well. What I was trying to say originally, is there are many factors (and different material coating applications as you note) and there is no miracle product.
We have done numerous repairs, but have often qualified this with the owner: it may be a recurring problem that will be likely need to be addressed again, especially with forklift traffic. It all depends on money owners wish to spend, be that originally for new construction or rehab work, and extent of repairs. The long term is often neglected by owners with fixed budgets.

 

[WoodyPE]

Metal tractors from earth-moving equipment has metal protrusions that forklifts don't have. It eats up asphalt pavement in just one pass. But FRP can take it.

Did you see the aircraft hangers with FRP flooring?

I have no faith in surface coatings. Sometimes I see cracks in epoxy coatings not long after they are poured. We've used novolac, urethane, various epoxies, various preps. None of it works.

We've used acid brick but that is even more expensive than FRP. It can last 30 years or more, but it's really hard to service.

As for fatigue on an FRP panel, if it happens then replace the panel. The panels would be anchored to the floor and sealed around the edges. The underside of the panels could be vented to a common pipe. This could be slightly pressurized to check for leaks.

 

[Ron]

I'm surprised that you have not had success with epoxy coatings. That has not been our experience.

As for the cracks you see in the epoxy, please describe or attach a photo. I'm interested in the cause.

 

[WoodyPE]

We have a lead acid battery plant, and our forklifts weigh 12K lbs including the load.

We have plants around the world, and they all have the same experience -- epoxy resin fails. If you get 6 years out of it you are doing good.

One plant gave the floor coating specialist everything they wanted -- ployethelene before the concrete was poured, a 30 day cure, moisture checks, the whole nine yards. The floor coater got to decide when to do it. Their floor failed in 5 years. Some might say they didn't know what they were doing, but that's all they do and they are a chain franchise.

As for the cracks in the expoxy -- it happens more with the faster curing types. A 24 hour cure seems to do better.
After a couple of years, blisters start becoming visible and they grow until they break. I don't know of anyone that really wants epoxy flooring in our industry compared to acid brick.

No coating is going to expand the same as concrete, and it is not very flexible, hence it will form cracks over time, especially with forklift traffic riding over it. I can break epoxy with my fingers.

As I said before -- I have no faith on floor coatings -- they are destined to fail because concrete needs to breathe.

 

[jheidt2543]

Here are a few thoughts I would consider:

1. Is this floor already constructed? If so, before you can put any type of new coating on it, the existing floor must be prepared by removal of any existing coating and/or cure-sealer put on at the time of construction. This can be done by shot blasting, acid-etching, or grinding the existing surface coating off. I’ve been involved in all three and there are pros and cons to each and one of the biggest problems is how to legally dispose of the residue.

2. If this floor is already constructed, is there a vapor barrier under it? Ron mentioned, aside from vapor transmission from the subgrade (if there is no vapor barrier), evaporation / transmission of excess mixing water can take months to level off – that’s the reason for pouring slabs-on-grade with as low a mixing water content as possible.

3. Regarding the reinforced fiberglass sheets, I’ve never seen this done. Perhaps one of the manufacturers can fill you in and SHOW you some successful projects. BUT, I sure wouldn’t want to be the guinea pig for something like this. No matter what you do to a floor like this, you own it.

4. The other option, if you have your heart set on trying it, is to do a trial area that covers both storage and isle-way floors, maybe a 6’ wide x 10’ long patch and monitor it for 6-12 months to see how it holds up under traffic.

5. We had our best luck with warehouse floors by wet-curing the floor for 7 days, let it sit for 30 days, then acid washing it with a riding floor scrubber, water rinsing it, then applying a water soluble fluorosilicate liquid hardener. There is no smell, you can get on the floor the next day and the floor does not dust. Another feature is that fork truck tires don’t leave black marks as easily as the high solids cure-n-sealers do.

6. There are still lots of heated arguments about whether to use a vapor barrier under new floor slabs, I still recommend them. After the floor is cured and mixing water evaporated (hopefully without curing the slab), the vapor barrier starts its’ useful life by preventing vapor transmission from the subgrade. If you ever want to put a new coating on the floor, you’ll be glad you have a vapor barrier under it.

 

[hokie66]

Have you tried steel fibers in the concrete? They improve the toughness of the surface. Our coal mine clients insist on steel fiber floors in their workshops, but that is primarily for maintenance of D11's, etc, not big forklifts. If this is a recurring problem, maybe you need to look at a different type forklift, one with pneumatic tyres.

 

[Ron]

jheidt and hokie bring up excellent points. A fluosilicate hardener is a good idea. In fact, looking at one of your link photos of the FRP manufacturing plant, it looks like that's what they used.

I assume you have an ambient chemical influence on your floor coatings. This could be a cause for early failure. I also see your need to protect the concrete from acid, so a fluosilicate might not be the answer in your case, but should still be considered if the ambient conditions can be worked out.

No coating will last forever in an industrial environment. If you are getting 5 years of good performance from a coating in an aggressive environment with heavy use as you've noted, consider that to be fairly good, remove the residual coating every 5 years and recoat.

I also disagree with your statement that coatings are destined to fail because concrete needs to breath. Concrete can do just fine with coating and the coatings can perform for their applications if matched to the conditions.

 

[WoodyPE]

Our concrete floors are pre-existing, but as I already said, we gave our floor coating expert everything he wanted in a brand new facility with concrete poured from scratch on top of polyethelene, and it failed just like everything else. He was there every step of the way, and was given all the waiting time he wanted before applying the coating. It failed anyway in only 5 years just like all the other plants - then the blame game.

I haven't seen a concrete floor anywhere in an industrial or commercial application that doesn't get cracks in it.
In my opinion it is destined to fail over time. You can disagree all you want, but I have never seen what I would call a successful floar coating anywhere regardless of environment. They eventually pit, and the floor cracks too -- just give it time. Maybe somebody here can do better, but given all the failures, what is one success worth?

Acid etching has been tried and we in plant engineering do not think it is a good idea. For starters, acid and concrete are a real bad combination. We've seen enough of it to know.

I have other plant engineers that agree. I can show you five different plants where the same thing happens. In five years a floor coating is a goner -- take your pick on the type. At least we can get 30 or more years out of acid brick though it costs at least $65 per square foot.

 

[jheidt2543]

WoodyPE:

Are you talking a WAREHOUSE FLOOR or a PRODUCTION FLOOR? I've been on a number of food plant projects where acid resistant floor brick are used with an epoxy grout. They stand up pretty well, but nothing lasts for ever. The dairy plants I've been in do replace their floors every 10 years or so as part of a regular maintenance program and that's due to the lactic acid deterioration from MILK!

Foundries and heavy industrial floors are a different problem, where thick shake on floor hardeners are required. But these places take a beating and floor replacement in heavily used (abused) areas is normal.

A warehouse floor is different. You should be able to construct one that is useable for a much longer period of time. As far as concrete floors cracking, if you are willing to pay the price, use an expansive cement and a higher reinforcing ratio. A WAREHOUSE built in the 1980's with "Chem-Comp" cement and #4 rebar @ 16" o.c. each way is till in good condition with no expansion joints, no control joints and no column boxouts. The only problems they have is where the forktruck drivers hit the storage racks and pull the racking anchor bolts out of the floor.

As far as coatings go, sometimes the new ones aren't as good as the old time tested ones. UPS specs tounge oil for their Transfer Station floors with a hard burned in troweled finish, they get a lot of wear and stand up very well.

 

[WoodyPE]

P.S. Ron,

Regarding concrete, I'm sure you can do what others have not in our plant floor coating experiences. Some of our "field experts" weren't much better than the average concrete contracter. On the otherhand, I've met some very respectable experts here at the TIPS forum.

Regardless of how good your solution is, however, the typical concrete laborer and floor coater around here are mexicans that can't speak english. There are a few good concrete contractors around and there are more that are not so good.

 

[jheidt2543]

WoodyPE;

You do make a good point about the quality of the concrete crew. In years past, the union training programs produced some very good tradesmen - cement finishers and construction laborers. Those quality tradesmen are getting to retirement age and they are not being replaced very fast.

 

[WoodyPE]

"A warehouse floor is different. You should be able to construct one that is useable for a much longer period of time. As far as concrete floors cracking, if you are willing to pay the price, use an expansive cement and a higher reinforcing ratio. A WAREHOUSE built in the 1980's with "Chem-Comp" cement and #4 rebar @ 16" o.c. each way is till in good condition with no expansion joints, no control joints and no column boxouts. The only problems they have is where the forktruck drivers hit the storage racks and pull the racking anchor bolts out of the floor."

I'm sure you've had the success, and I'm glad to hear someone wins for a change. On the otherhand, our contactors don't seem to have the control needed to get the right results. We are almost always dealing with a pre-existing concrete floor in our industrial application and everyone is pushed for time to get it up and running. after re-reading the posts, I suspect this a significant part of our problems -- nobody has the time to do it right, and the operating folks want the floor yesterday.

 

[Ron]

WoodyPE...don't get me wrong. Coatings on concrete floors do not happen easily. You are right to be skeptical, but also from some of your comments, I think you've been given some bad information along the way.

The best floor slabs on grade are those that have properly designed and controlled concrete mixes, coupled with proper control jointing, finished properly, then cured properly. As long as concrete has been around, it remains a mystery to many contractors....even those who place it daily. I see so many examples of poor concrete placement by very experienced concrete subcontractors it isn't even funny.

Your application presents an aggressive environment in at least two respects. First, there's the forklift traffic. Assuming you are using solid tire forklifts, you have to be concerned about the abrasion on the surface as well as making sure the surface is not too slippery. Further, the contact stresses are high, so the potential for surface damage is high as well. A poor finish will soon appear from that type of repetitive stress. Secondly, you have the issue of an aggressive chemical environment. You're right...acid and concrete do not generally mix well.

You actually have more options than you might think. I realize you are limited in the skilled workforce area and the competence of the contractors, but some tight control during construction by a capable engineer with concrete materials experience and coating experience will get you a long way toward the performance you want. There are numerous coatings that are or can be formulated for acid resistance, abrasion resistance, and bonding.....certainly for less than $65/sf, even if they only last for 10 years or so.

Your application is probably worse than most, so make sure that whatever route you choose, it is one that is proven in a similar condition.

Good luck.

 

[WoodyPE]

Ron,

Thanks for the tips. Our concrete has been in place for more than 30 years, so we aren't talking about new concrete here.

Check out this product called "Fiberplate" made by Fibergrate:

http://www.fibergrate.com/product_detail.asp?id=21&pselect=8#8

 

[kslee1000]

So many experts here, really don't want to expose my ignorance on this subject, and the arguments around it.
However, I couldn't stop to think and ask: What is the definition of "failure of a driving/walking surface"?

In Chicago, it's pot holes on pavement, or chunk of concrete splitted and set unevenly on sidewalks. Both create hazardous conditions for the end users. How's the crack on my basement floor, well, I don't like seeing them day-in day-out, but it stayed there for more than several decades, and the floor is still serving. The same logic applies to many other environments that having concrete flooring.

I think my point is: as an engineer, we try to deliver the best solution within the budget. From there on, the owner, and the user shall understand there is nothing wrong with a few surface cracks, if there is no causes other than the nature of the paving material, and it is still in serving shape (no tripping/slipping). But if insisted upon to remediate, run a cost-effective study, let the owner makes the decision on $$$, then go for it, with someone in mind that you can plant the blames later on for a new, unproven product.