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rokosz 11-10-2013 02:36 PM

Too Soon for a 1000 lb gas tank?
Hiya, I messed up a bit here.

I'm pouring a 4" concrete slab tomorrow (72"x54") over 4" tamped gravel.

The temperature over the next 48 hrs will vary between 32 & 55.

the slab is for a 500gal capacity 1000lb+ gas tank.

The tank supposed to be installed the next day (maximum 24 hrs since pouring).

I'm thinking thats too much load too soon for the slab.

But still trying to talk myself into that its ok: There are 4 feet on the tank -- If I assume 9 sq inches per foot(ing) thats 36 sq inches bearing a load of 1000lbs+ (about 28lbs per sq inch).

OK to put the tank on 24 hours after pour or are those pointy legs going to poke right through the slab?

thanks folks. I don't think I can trust the Gasco to give me an answer that might impact their appointment! Bryan

kok328 11-10-2013 03:56 PM

This late in the game, the best you could do is go get some 2"x8' pressure treated lumber to put under the legs of the tank in order to spread the load. Are they wanting to bolt the tank to the slab?

JoeD 11-10-2013 07:14 PM

That is very much too soon. However it also depends how heavy the tank is empty. Don't fill it for at least a week. 28 days is better. The concrete will be soft and easily marked if they drag the tank.

CallMeVilla 11-10-2013 11:02 PM

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WOW ! In a hurry much? Even a week of curing would have helped but ONE DAY?

Yes, you are asking for cracks and failure in the slab.

Here is the typical concrete curing curve which can help you to decide when to load the slab with your tank. (Frankly, I would reschedule for a two week minimum delay!)

mudmixer 11-11-2013 05:35 AM

What kind of cement in the concrete mix used? - High early, early or or regular Type 1 Portland cement?

How rich of a mix?

It is better to plan ahead on the mix used, especially if you know that setting the tank soon will be important.

4" is quite thin and 6" will always be better when it comes to any loads and the amount needed is minimal material cost and the clean-up time is the same.

That is a pretty small amount of concrete and then worry about it at the last minute. - You will always have the same scratching of surface and a few extra days of curing will cost nothing, independent of the thickness.


rokosz 11-11-2013 08:27 PM

Hi folks, thanks for the advice. the slab is in 7 hours, could still stick my thumbin if i wanted. Snow and rain for the morning. I used sakrete Hightstrength mix and a little left over 5000psi.

put off the tank install until Friday -- won't let 'em fill it for a while after that, gotta wait on the electrician anyway for the genny install. I'm gonna em sakrete, see what they think...

BridgeMan 11-11-2013 09:02 PM

You mentioned snow--not good. If your fresh concrete is allowed to freeze early in the curing process, you can count on it being ruined and turning into gravel before too long. Time to rip it all out and start over.

rokosz 11-12-2013 03:57 PM

rather than wait for sakrete to respond a simple websearch of "pouring concrete in cold weather" gave alot of information. I'm glad its November and not March -- the ground is still warm. I took a pantload of fibreglass batts and some rigid foundation insulation and surround-mounded it on the slab. Ambient temp right now 32 going to 24 tonight. Once this snap clears out (Thursday AM) I'll give the slab some water.

Diy has so many exciting opportunities

BridgeMan 11-12-2013 07:13 PM

Concrete that has frozen will give off a pungent odor--much stronger and slightly "sweeter" than the smell of unfrozen (just green) concrete. If you can still easily scratch the surface with your thumbnail in a week, plan on complete removal and replacement in the future. It will never "heal" itself.

You would have done well to place a layer of heavy plastic of the fresh concrete, under your insulating layer. It would have helped prevent freezing by retaining the heat of hydration given off by hydrating Portland cement particles, when they lock onto water molecules in the mix.

rokosz 11-12-2013 08:33 PM

Ahhh, but I did. Fist bump to you B'Man. I put a 3 or 4 mil sheet that's actually double (or triple?) folded and extends beyond the forms directly on the slab. I'd done it, consciously, to keep the batts from getting wet... When I've poured slabs in proper weather I'd always covered them with plastic to keep them from drying out before I could get to the next round of wetting down.
Only downside -- I didn't cover the slab at all until alot of the puddles (bleeding?) had cooked off (about 5 hours after finishing off) -- but well before the temps fell below 40.

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