Containment slab and sacrificial slab 1

[marinaman]

I've got a client who wants a slab to serve two purposes:

First, he wants the slab to be durable enough to accept having track excavators operate on the surface.

Secondly, he wants the slab to also not allow liquids to pass through the slab and enter the soil below. Tanker trucks will be pulling up on these slabs and if they spill some liquid, the liquid needs to not be able to pass through the slab.

I'm thinking a two slab system of some sort. A structural base slab, overlain in a sealing surface of some type, overlain in a sacrificial concrete slab. Has anyone done this? Are there any design guides for this?

 

[hokie66]

How large is the slab in plan?

 

[thaidavid40]

For the top slab, look to the UFC design guides from the USACE for tank turning pads. These pads are used at the intersections of tank trails in the various training ranges. They have to stand up to repeated wear from the tank treads as they turn from trail to trail. Using steel fiber in the concrete mix helps considerably.
Dave

Thaidavid

 

[marinaman]

The plan size of the slab is 100' x 75'. Within this area are three pits used to mix solids and liquids. The tankers pull along side the pits and empty their load into the pits.

The solids and liquids are mixed via track excavators.

I need a durable surface, and, I need the slab to act as containment, where if liquid is spilled, it will not get into the soil below.

Since track excavators will be used, I can't coat the slab surface with a sealing epoxy or some other liquid barrier because the tracks will rub it off. This is why I'm considering a double slab with a barrier system between slabs.

Has anyone seen this before? Seen any design guides, text books, or articles about slabs in this type of environment?

 

[SlideRuleEra]

...need the slab to act as containment, where if liquid is spilled, it will not get into the soil below.

Is this a "best efforts" situation, or is there established criteria for how much "leakage" is allowed?
Specifying "zero" leakage is usually not considered a realistic industrial requirement.

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[cvg]

an HDPE or PVC membrane liner or even a GCL liner might be a cheaper and more effective option. concrete cracks and may not provide adequate containment

 

[BUGGAR]

Any chance you could put hard rubber grousers on the tracks?

 

[Teguci]

You should look up "concrete topped plaza system."

I have designed several of these for lightly loaded parking decks. I'd suggest the following warnings for your system:
- This is not a lightly loaded system
- I would expect the top concrete wear course to be significantly damaged. A closely spaced top reinforcing mat should be anticipated.

Start with calling/contacting the waterproofing vendors. They should each have details for their systems. Make sure they provide a slip layer so that the top and bottom slabs do not place a high shearing stress through the waterproofing membrane when loaded.

 

[hokie66]

Agree with SRE on the "zero leakage". I would ditch the two slab approach, and concentrate my efforts on one slab with steel fibres for toughness, a lot of reinforcement for crack control. No joints.

 

[rb1957]

not to derail the serious discussion, but does anyone else find the term "sacrificial slab" mildly amusing/scary ?

another day in paradise, or is paradise one day closer ?

 

[hokie66]

It is neither amusing or scary to me. Nevertheless, I try to avoid the concept.

 

[marinaman]

I've attached a few sketches of the floor.

Sketch 1 is simply the general floor layout.

Sketch 2 is where I'd probably try and place control joints, if this slab did not have to be more of a barrier system for the tanker liquids. But since it does have to not allow liquids to penetrate, I can't use 2, as there's too many joints in bad places.

Sketch 3 is what the floor would look like if I left the joints out of the area where tankers unload. Probably can't do this as the floor will need to be "hosed down" every now and then over a bigger area than just where tankers unload.

Sketch 4 is what I'm leaning toward. I'm abandoning the (2) slab idea and going with one slab. I'm thinking of having a sufficient thickness, and heavily reinforced, to keep the cracks closed. I'm thinking of using regular mild reinforcing, but providing a very dense, top and bottom mat of reinforcing, with the pit corners reinforced, with a very low w/c ratio concrete mix.

A post-tensioned slab is not a good option, as I'm sure modifications to the slab will be requested over time....whether its changes to the pits, addition of machinery foundations, etc etc. This client is prone to these items.

I've abandoned type K concrete, due to the issues with warp depending upon the assumed expansion and contraction and its interaction with the amount of reinforcing provided. Too much reinforcing restrains and warps, not enough, and there are other problems. To me, there's just too many undefinable variables to make this a good option for this application....not to mention I would need both a contractor and supplier who knows the ins and outs of type K....which I do not have.

This is why I'm leaning toward a slab with at least 0.5% steel in each direction, top and bottom, and eliminating joints in the area that I want an impermeable surface.

 

[SlideRuleEra]

Keeping pollutants (coal, ash, FGD sludge, oil, etc.) from getting into the ground is an important objective at electric generating stations. I've had plenty of opportunities to deal with this.

The first step is keep the pollutants from accumulating on the slab:

1. Slope the entire slab, none of it is level.
2. Set the perimeter at a constant elevation; the highest elevation of the slab.
3. Make all slopes at least 2%.
4. Direct the slopes to a liquid collection sump in the interior (or edge) of the slab. If one of the 3 planned pits is not suitable for this service, add a fourth pit dedicated to liquid collection.
5. Pumps and piping from this sump (probably designed by others) should direct the collected liquid (wash-down water, rainfall, product spillage, etc.) to a lined holding pond. The contents of this pond should be recycled, treated, or sequestered in an environmentally responsible manner. Solids that accumulate in both the sump and the lined pond will have to be manually removed periodically.

It does no good to have an (essentially) impermeable flat slab that allows pollutants to accumulate and eventually contaminate the soil surrounding the slab's perimeter.

A curb at the slab's perimeter may seem to be a good addition... but the heavy equipment will quickly demolish it.

After setting the slopes and establishing a pollutant collection / disposal system, everything else (joints, liners, etc.) is an incremental improvement.

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[hokie66]

I see no need for any joints if you provide 0.5% steel. Joints are just straight cracks, and a nuisance to maintain. Top and bottom? I don't think that is necessary. Maybe 0.6% Ag total.

I still think that steel fibres, in addition to what you have proposed, would make the surface a lot more resistant to damage from the tracked equipment. The bars won't do anything to toughen the cover concrete.

 

[DETstru]

Not sure what types of liquids this really applies to but I've often used crystalline integral waterproofing as an admixture in the concrete. I've used it in many elevator pits and also on an large penguin aquarium project.

BASF and Xypex are the brands I've used but I believe there are others.