Concrete Slab + Large Fish Tank = Worried, will it be okay?

[BeanAnimal]

It's supposed to be thicker under the walls on a mono pour.
Everything I have ever read or been told and the google pictures I am now looking at because you made me second guess also confirm that.

You are referring to a Monolithic Slab. The footers are integrated into the slab and not poured separately. The transition from the footer to the floor is somewhat gradual and may extend out a foot two from the wall, possible more depending on footer depth and soil conditions. . This is to prevent stress cracking do to an abrupt change in thickness.

I assume that these are becoming more popular, but I still rarely see them (at least in the northeast) and instead almost universally see floating slabs poured after the footers and walls are laid. While they can be used for below grade "basement" type construction, they typically (at least in my experience) are not. They are also not well suited to uneven terrain.

I am sure that there are statistics somewhere and/or even a geographical breakdown.

In any case, the photos above are a traditional footer and slab foundation.

 

[Thetankdoctor]

I have my 1000g on my slab for 14+ years no with no issues. I think it will be fine

 

[exnisstech]

I set my lift on a concrete slab and only have two pads about 12 inches that contact the floor and I pick cars up. I think you'll be fine.

 

[BeanAnimal]

I think the general guideline for a 4" thick slab of unknown composition and substrate is ~40 lbs per square foot live load for large distributed loads. For smaller overall loads (in context to floor area) I wouldn't go over 60-70 lbs per square foot without consulting an engineer.

 

[iReefer12]

70/80lbs sqft? That seems very low for concrete. That would mean I should not be able to stand on one foot as a 200lb man no?

 

[tinyfellows]

Why would the slab be thicker near the walls? A basement o foundation slab would typically be uniform thickness. It may or may not have integrated footers, depending on frost depth.

A lot of contractors will dig a little deeper on the edges to allow rebar to be drilled in at an angle and bent to match the rest of grade

 

[The_Paradox]

70/80lbs sqft? That seems very low for concrete. That would mean I should not be able to stand on one foot as a 200lb man no?

I think he is referencing standard compression concrete with no reinforcement and poor support. Reinforced the number is closer to 100 times that. No idea how your foundation was built but hard to imagine it has no bar or mesh in it. For the weight you are talking you are fine.

 

[iReefer12]

I found this table when trying to find out if my basement floor has rebar, I wondered whether there was a code that required it. Didn’t find anything in the building codes about rebar, but thought this could be interesting. What is (f c)?

 

[The_Paradox]

I found this table when trying to find out if my basement floor has rebar, I wondered whether there was a code that required it. Didn’t find anything in the building codes about rebar, but thought this could be interesting. What is (f c)?

If you’re in the US you have a reinforced foundation.

 

[iReefer12]

Yeah, and home was built in 2018

 

[BeanAnimal]

70/80lbs sqft? That seems very low for concrete. That would mean I should not be able to stand on one foot as a 200lb man no?

Load ratings are for large distributed loads over the whole floor, not single individual items. Your home's floor is likely built to a live load rating of 40 pounds per square foot.

So yes, as a 200 pound man you can stand on one foot on your living room or garage floor with a point load of of 200 pounds concentrated on .5 square feet.

You can put you gun safe on the same floor, and it may be 80 pounds per square foot.

Let's say your room is 10' x 10' = 100 square feet - the live load ~40 pounds per square would be rated at ~4,000 pounds.

What you can't do is take a 5' x 10' item that is 80 pounds per square foot for a total of 4,000 pounds and sit it in the middle of the floor and expect no deflection. It is not distributed, but unlike your foot, the aggregate load is far higher.

Likewise, if your room was 10' x 10' of snow, it may have fairly high aggregate load rating. You could ride a sled accross it or set a 10' x 10' wooden deck on it and it would not sink. You can even strap a set of snow shoes on and walk on on it without sinking... But your bare foot will plunge right through.

You have to take load ratings into context - they are just one parameter that tells you how strong a floor is.

 

[BeanAnimal]

If you’re in the US you have a reinforced foundation.

The floor may or may not be a foundation and as mentioned above, most residential slabs on grade, basement, garage, etc. will not have reinforcement bar in them. They may have wire mesh, which is NOT structural reinforcement and often too low in the slab to do anything. Mesh simply serves to keep cracks from separating.

 

[BeanAnimal]

What is (f c)?

It is the parameter typically designated for compressive strength.

That table shows the typical minimums. Your floor is more than likely 3500psi or better. Most batch plants will shoot for at least 3000 psi for general concrete. If they target 2500 psi, there is a chance that samples come up short.

Your tank will be fin on the floor without reinforcement. I wouldn't put a home gym next to it and ghost ride 500 pound deadlifts without knowing its thickness or how well the substrate was compacted.

 

[BeanAnimal]

A lot of contractors will dig a little deeper on the edges to allow rebar to be drilled in at an angle and bent to match the rest of grade

I am not sure the context - but even if this were the case, it is not structural floor reinforcement. It is to tie the floors to the walls.

 

[PotatoPig]

A lot of contractors will dig a little deeper on the edges to allow rebar to be drilled in at an angle and bent to match the rest of grade

Slabs on grade are often thickened to about twice the typical thickness around the perimeter for a strip about a foot wide, but are not tied into the walls. The thicker strip helps stop the perimeter of the slab from curling up as the concrete cures.

I found this table when trying to find out if my basement floor has rebar, I wondered whether there was a code that required it. Didn’t find anything in the building codes about rebar, but thought this could be interesting. What is (f c)?

There’s almost no chance your slab has anything more than a wire mesh in it to control cracking when the concrete cures. This is typical of virtually all slabs on grade outside of heavy industrial settings.

If you’re up for some reading try the US Army Corps of Engineers design guide for concrete floor slabs on grade for heavy loads (it’s publicly available - just google it). Nobody qualified to could or would responsibly tell you what your slab is able to carry though without an evaluation - a local engineer would probably come out and tell you if they reckon you’re good to go for about the price of two MP40 power heads… so a small part of the overall budget for a tank this size.

 

[BeanAnimal]

Nobody qualified to could or would responsibly tell you what your slab is able to carry though without an evaluation - a local engineer would probably come out and tell you if they reckon you’re good to go for about the price of two MP40 power heads… so a small part of the overall budget for a tank this size.

Yep - best case they would assume local code, possibly bring out a useless durometer or rebound resilometer and tell you that you are at 3500 psi or whatever and wish you luck after they take your money.

Worst case - you open a can of worms that you will never stuff back in the can when he says he can't OK the plan without coring and lab testing. Your jurisdiction requires reporting of all residential engineering and therefor your local bureaucrats get involved.

Next thing you know you will need building permits, plumbing permits and electrical permits and when you go to get those the zoning guy sees your water volume and says he is sorry, but anything over 100 gallons requires a zoo permit.

You get the zoo permit application but now you need grey water disposal permits, inspections and ADA access even though you are not a zoo, because that is what the zoo permit requires... Your AHJ turns the permit application over to the tax assessment office and they send a guy out to reassess your home value and your taxes go up, along with your insurance. But your adjuster asks why and then tells you they have to drop you because they don't allow zoos in basements.

If you think that sounds crazy.... it is, but crazy things like that actually happen more often than you would expect or think possible.

TLDR - your aquarium is not that big. If the slab is on grade/basement it will be fine.

 

[The_Paradox]

I am not sure the context - but even if this were the case, it is not structural floor reinforcement. It is to tie the floors to the walls.

They are referring to a footer.

“According to the U.S. building codes, the minimum rebar requirements for footings vary depending on the size and type of the structure being built. Generally, a minimum of two #4 bars are required for residential footing. The rebar should be placed in a grid pattern with a spacing of no more than 18 inches apart.”

 

[BeanAnimal]

They are referring to a footer.

“According to the U.S. building codes, the minimum rebar requirements for footings vary depending on the size and type of the structure being built. Generally, a minimum of two #4 bars are required for residential footing. The rebar should be placed in a grid pattern with a spacing of no more than 18 inches apart.”

I think you keep confusing the context here.

We are not talking about footers. We are talking about a basement slab poured on grade or a floating slab. See the photos early in the thread. The walls sit on a foundation, there is dirt in between. Yes the footers will have reinforcing bar in them. The basement slab was poured after the walls and unless the house plans called for a machine shop in the basement, there will not be rebar in the slab.

Yes - the footer will be wider than the walls with the wall centered over the footer. The width typically dictated by the height (number of stories) that the house will rise above it and the type of construction (wood framed, masonry, etc.) No, the slab does not typically rest on the footer, but it in some cases it may. The footer is not floor reinforcing. It is to hold the walls above it.

 

[The_Paradox]

I think you keep confusing the context here.

We are not talking about footers. We are talking about a basement slab poured on grade or a floating slab. See the photos early in the thread. The walls sit on a foundation, there is dirt in between. Yes the footers will have reinforcing bar in them. The basement slab was poured after the walls and unless the house plans called for a machine shop in the basement, there will not be rebar in the slab.

I was just clarifying why they thought the edges were thicker than the field. Remesh that is commonly used does increase compressive strength slightly but its primary purpose is to increase tension strength as you pointed out. Either way to the OPs question, even the most craptastic concrete should be well over 2000psi after 90% cure more than enough for an aquarium.

 

[YOYOYOReefer]

My 650 gallon 8x8 hot tubs been sitting for 8 years on a pad of 4 inch quick Crete bags just dumped and leveled and hosed in place. No rebar. And it’s Chicago weather. Way overtinking this Cements the best