Slab On Grade Toughness and Additional Reinforcing

[marinaman]

I have a project where an owner is wanting a slab-on-grade designed for an industrial application. This client will be operating heavy machinery on the slab-on-grade, such as tracked excavators....and will occasionally have dumptrucks and forklifts running atop this slab-on-grade. Also, part of this slab-on-grade will support 55 gallon drums stacked (2) high.

With all that said, I have requested a subgrade modulus recommendation from the geotechnical engineer of which I will use when I design the structural reinforcing for the slab. The question I have is, how do you guys toughen the surface of a slab such as this, to help it last for a decent period of time, given the surface will be subject to a pretty abrasive user?

I've been thinking about using fibermesh (such as Novomesh 950) as a secondary reinforcing in this slab, to help toughen the surface and reduce the amount of drying and shrinkage cracking....but I'm not sure if I should go this route, go the route of steel fiber reinforcing, or perhaps use some other method of toughening all together.

Or does the slab even need toughening on the surface?

What are your thoughts?

 

[hawkaz]

Most problems in these slabs are at the joints. I would recommend diamond dowels and dowel baskets

 

[TehMightyEngineer]

Tracked vehicles are the second most abusive thing I've ever seen put on an industrial slab. I've seen a 15 year old elevated floor slab wore through 12 inches of concrete under heavy tracked skid loaders and the impact of medium sized logs (ground wood pulp mill). The only thing I've personally see withstand it was metal floor grating embedded in the concrete. However, that's an old school approach and there are better ways from what I've read. Fibers alone wont be enough for your application in my opinion. They do increase the abrasion resistance but not enough for heavy tracks on a regular basis.

Check out some of these topics for some ideas:
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Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[SlideRuleEra]

I read through all of the excellent links provided by TME, and concur with the recommendations:

1. Concrete with 4000 psi + compressive strength.
2. Highest quality subgrade preparation.
3. Reinforced (with rebar) concrete.
4. Steel fibers in addition to adequate rebar.

Also, agree with hawkaz to use doweled joints.

Close space the joints, as if the concrete had no reinforcing.

To this, list suggest making the slab 12" thick (minimum) to allow meaningful use of top and bottom rebar mats (IMHO, anything less than 12" thick the top and bottoms mats are too close together for beneficial use). The issue is not necessary strength - it's keeping the slab rigid.

Also, insist on true wet curing, not moist curing, not curing compound - and do so continuously for 7 to 10 days.

For heavy duty slabs on grade (including some tracked vehicle use) at electric generating stations, we had a minimum design: 12" thick, #4 rebar @ 12", each way, top and bottom.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[hokie66]

I too agree with most of the recommendations which SRE has listed. I also agree that plastic fibres are useless in abrasion resistance, but steel fibres are very beneficial. I agree with hawkaz that joints are most often the problem, and I would eliminate as many joints as possible. If you have steel fibres AND reinforcement, just let cracks happen where they want. Joints in an industrial floor are just straight cracks which cause problems, while naturally forming irregular cracks with reinforcement crossing the cracks/joints don't cause the same degree of problems.

 

[TehMightyEngineer]

I think one thing you should make clear to your client is that a concrete slab for heavy industrial uses will not be indestructible unless you embed large amounts of steel plate or floor grating in the concrete. Any concrete topping, fiber mix concrete, or other way you use to harden the concrete will ultimately require maintenance.

One thing I've seen done in the past was embed steel floor grating in areas that fork trucks and tracked vehicles have to make sharp turns. Straight runs usually have much less wear due to vehicles.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Brad805]

Many of our clients want embedded steel plates for cats or excavators. We use 36" or 48" x 1/2" or 3/4" plate. Sometimes we make them replaceable, but that adds to the cost. There is a significant cost to this, but it saves them putting down rubber tires all the time. If you are in a cold climate, the problem is they weld ice lugs onto the tracks. An ice lug is basically a 1/2"x3"x2" +- plates welded to the tracks at random locations. Ice lugs ruin slabs.

 

[bigmig]

For slabs that will just get beat and beat, it is common to have a sacrificial concrete thickness that is considered "armour" and will need replacing when the time comes.
Expensive, but in some cases, worth it.

 

[TehMightyEngineer]

I've seen the same thing bigmig talked about on a slab or two. They used a thick concrete topping that was a noticeably different color than the regular concrete and it was easy to see when you had worn through the topping. This is probably the cheapest industrial slab system to install as you can design the actual slab for a normal mix; but is most expensive in the long run.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Ron]

Agree with hokie66, SRE and TME on recommendations (except I have one of my rare disagreements with hokie66's recommendation to just let the cracks happen...tracks get caught in those "random" cracks and tear up the surface). When I design an industrial slab for tracked vehicles, I use "armored" joints. Those are back-to-back angles at the joints, anchored into the concrete with shear studs. Dowels are included.

 

[thaidavid40]

All of the tank turning pads we design for the Army's training ranges have steel fiber in them for toughness, and to make the surface more wear resistant. Many of these outdoor slabs face tank tracks, and freeze-thaw cycles successfully, for many years of service.
Dave

Thaidavid

 

[TehMightyEngineer]

Interesting thaidavid; do you do anything else special other than steel fiber? Specialized mix? Toppings? My understanding is tank treads are almost or just as bad as a very heavy excavator.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com

 

[Gumpmaster]

I've used specialized floor toppings such as these:

Emerytop

MasterTop

Super Euco Top

You can place them quite thick and they're very abrasion resistant. I've used 2" toppings with no negative reports. I guess you could go thicker. The product tech reps should be able to provide useful life based on different scenarios and thicknesses.

 

[TehMightyEngineer]

I imagine you might be able to get a small sample of the floor toppings and some redimix and do some very simple abrasion tests at low cost.

Professional and Structural Engineer (ME, NH)
American Concrete Industries

http://www.americanconcrete.com