Concrete Water Tank

I want to build a round water cistren 6ft dia. X 10ft long that will be buried. I want to build it in 2ft long sections starting with the bottom and pour up to half of the tank diameter or 180 degrees then stop for the day. I will use a metal slip form and each following day pour another 2ft long section until I reach the 10ft length.

When I complete the bottom half of the tank, I will then reverse the slip form pouring the top half again in 2ft long sections.

The soil is pea sized decomposed granite with 15% clay and lots of sand.

Questions:
1) will the joints be water tight with each pour occuring the following day?

2) When completed will the tank structure be as tho I made one big pour? or will each 2ft joint act indepently from the total length?

3)Is there a time limit on when pours have to be made to be considered one continous joint?
Making the tank in halfs the bottom will have set 10days before the top half is joined at the side and end seams.

4) after the tank is complete I plan on mixing portland cement with water only, then apply to each of the seams on the inside to seal them. Can I do this or is there another method?

5) I'm planning on making the tank walls 4" thick. Adaquote?

6) I'm not planing on using any rebar. Am I going to create problems 20yrs down the road?

Any suggestions?

T_Bone

Pre-fab concrete are running about $1/gal local delivered. That was my first thought as it would make the project finsh a few days quicker but I have time, lots of it. I'm not going to be the one doing the work just supervising it. :)

Labor runs about $50 in beer and $50 in steaks and ribs, $25 in misc food. I do have to B-B-Q the steak and ribs tho.

T_Bone

Well I was trying to use mass to get away from having to use steel but that ain't gonna happen. I do like the ferro-cement idea tho as it solves the problem of trying to pour mass in one day without the cold joints.

T_Bone

No not really as I'm not a plastic person. When I was a kid I could taste the plastic in a drinking cup, my parents said I was crazy.lol

The AZ heat tears plastic and wood both all to heII. The soil here is on the acidic side. So I decided to quit fighting the enviroment and become one with nature and stick with concrete and metal.

T_Bone

SS is not forever as it too over time will have the same problems as any other metal water tank, just not as soon as the other choice of metals.

T_Bone

For your questions:
1) that's a leaky cold joint
2) independent
3) even during one day you can easily get a cold joint
4) putting portland over the cold joints won't waterproof them. You need a waterstop, either vinyl or, preferably, bentonite. The bentonite (an expansive clay) comes in tubular rolls and is foolproof.

Thanks for the websites and the ferro-cement. I did find some engineering info and (don't know how reliable the source is) ferro-cement is supposed to be 2 to 3 times (6500psi to 9600psi) as strong as concrete(3200psi). Now that supprised me. Enough info to make me look deeper into the subject.

What really shock me was that two websites, one 15000gal tank and one 1000gal tank said to fill them with water to cure them and filled with water they would cure in about 28days!

Another surprise was that diesel would leak threw the ferro-cement as it decomposes the cement due to a chemical reaction.

Looks promising tho as a water tank!

T_Bone

The book says that a 1981 gal tank (6'x7.5'd) uses 1 yd concrete for the floor with walls made of 20-2x8' lathe sheets, 12-20' #4 rebar, 1 yd of sand, 6 bags of portland, and 3-50# sacks of sealant. Lots of labor but the material's cheap.

Acidic soil should have no effect on the tank either. Exposure to strong sulfuric and other acids will harm the plastic but the amount in the soil is not likely to have any effect on the stability of the tank.

Here in coal mine country, acidic soil and upper layer ground water is all too common. Tanks used around the mines here are mostly all PVC with some ABS and the rubber/plastic compound I cannot recall the trade name of off hand. (these are less common because of high cost)

It is extremely hard to get sealed joints in concrete and keep them sealed. Most septic tanks here are pre-cast concrete, all one piece with a drop on cover that gets sealed with manhole sealant tape. Cost is the main reason as the pre-cast concrete is about 30% less than PVC for the same size tank. Strength is anothet consideration, plastic tanks, unless burried deep enough or made strong enough will not take the weight of a vehicle driving over them that a pre-cast concrete one will.

Fiberglass is another option. More money but definitely has higher resistance to chemicals, acids and oils along with being high strength and maintenance free, will also take heat/cold swings and UV exposure far better too.

Metal, except 308 or better stainless would be my last choice. One more thing to consider is liability. If you make your own tank and years from now a neighbor gets PO'ed at you and calls in DEP, you will bear the brunt of the burden. If there's a leak, you will bear the entire cost of clean-up and so forth. If you purchase a tank, you have a better margine of protection from liability especially if the purchased unit comes with a DEP/EPA approval stamp.

Years back, people in this area used everything form concrete drainage pipes standing on end to 55 gallon barrels for their septic systems. Now, there are numerous law suits filed against property owners for polution. Homeonwer insurance does not cover this and the people are left holding the bill for the clean up and repairs. Not trying to be a party pooper here, just pointing out some things you need to consider.

The refference to diesel was only a passing refference as my tank will hold potable water. EPA requires a concrete holding barrier for above grounnd fuel storage tanks at a size large enough to hold the fuel tank volume incase of a tank rupture. That led me to believe concrete was impervious to fuel oil leakage and the info I've read says it's not.

What happens with a plastic tank, PVC or fiberglass is over time rocks will rub on the tank causing a hole. Would that happen in my life time, probably not as thats a very slow process. But "if" it would it will come at a time I don't want to mess with it being 80yrs old.

Concrete on the other hand is a better choice as it's made from soil so the tank is not fighting the soil acids but lives with them. By adding 1/4tsp of dish soap per cft to the crete mix breaks the surface tension so the crete becomes water proff.

The tank has to last about another 40yrs, my life time. I have the help now to make the change. In 20yrs I may not that help and cost will be higher, so now is the time to make the change. Until Tom put me onto ferro-cement tanks I was having a hard time trying to design a tank that could be poured in one day.

Tank cost:
Around here PVC tanks are running about $1/gal or $2000 for my tank.

Metal is about $900 for SS, materials only.

Concrete or ferro-cement is about $500.

T_Bone