Best waterproofing method 1

[cvlenv]

good day...
we are to construct again a water storage tank; this time, a 2-basin reinforced concrete water storage tank. one chamber will hold sludge from "blowdown" operation of water clarifiers and the other chamber will hold the treated water. what could be the best waterproofing method to prevent possible seepage and contamination to the treated water?

thanks in advance for any suggestions & recommendations...

 

[bimr]

Actually, good design will prevent cross contamination.

It is not acceptable to have a waste tank separated from treated water with just a common wall between the two waters.

You will find phrases such as "Design shall prevent cross connections and there shall be no common walls between potable and non?potable water."

The answer is to design 2 separate tanks with an air gap between. You should also seal the concrete tanks. Contact Tnemec for a coating recommendation.

 

[cvlenv]

thanks bimr...

when you say "air gap" would a 2" gap between the RC walls of the two tanks be enough?

 

[JedClampett]

An air gap of only 2 inches will be hard to build and inspect. I'm hoping that whoever permits this requires that the gap can be observed to make sure there's no liquid build up within it.
If you're tight on space, I would still make the gap no less than 2'-0". That should give enough room to build forms and get them out.
Unless the sludge has a corrosive component I wouldn't coat the concrete. Your best water proofing method is 12 inch walls, waterstopped joints and good workmanship.

 

[bimr]

I did not mean an actual air gap, just physical separation. You need a physical separation of least a few feet if the tanks are to be constructed of concrete for constructability purposes as JedClampett states. You have to have space to place and remove the formwork.

 

[cvlenv]

thanks JedClampett...

yes bimr, air gap i mean also a 2nd wall a few inches away from the 1st wall.

since there is a space limit for the required volume of the sludge tank, i am thinking of a 0.40-m gap enough to give space for waterproofing works..my next concern would be : the tank are covered with suspended slab, that includes the "gap" between then. shall i install an air vent for the said gap?

 

[bimr]

One would think that if the area between the tanks is free draining, that air venting is not required.

 

[cvlenv]

i see...thanks bimr!

one crazy idea had popped up from my not-so-brainy head : how would you think if i would consider that there wont be a gap anymore? the 1st wall shall be the form siding for the 2nd wall. first i will pour concrete for the 1st RC wall then after form-stripping & waterproofing of the face adjacent, will do the formworks and concreting of the 2nd RC wall...

would that be acceptable in engineering practice?

 

[JedClampett]

I wouldn't do it. You're never going to know if there is cross contamination. If the sludge level is high and the treated level is low, there will be a pressure head pushing the sludge through the walls. I'll agree that it's very unlikely to have leakage over such an arrangement, but if there is, you're going to have to tear the whole thing down.
We work in the water and wastewater areas exclusively. Our saying is if you have a 4,000,000 gallon reservoir full of potable water and add one drop of sewage, what do you have? 4,000,000 gallons of sewage.

 

[bimr]

I would not do it either. You should have physical separation.

Another consideration should be for the piping. You have to allow space for the piping as it enters and exits tanks.

 

[cvlenv]

to bimr..there wont be piping system in the gap between the walls

anyway, thank you very very much guys for the info and recommendations...they helped a lot...

 

[cvlenv]

good day to all...

if, may i seek your idea on the actual volume of poured concrete versus the estimated theoretical volume as referred from the construction drawings...

could there be any difference between them? sometimes i get this estimated volume of readymix concrete and then during the actual pouring, there is a deviation, ie: the actual poured volume is somewhat greater than the estimated volume..

how was that? could there be a sort of factor to be used in the estimated volume to achieve the "actual" volume?

what are some factors to be considered in estimating the volume of concrete to be poured, if there are any??

 

[hokie66]

There should be very little difference. If your calculations are accurate, and further the forms are placed correctly and slab thicknesses are controlled, quantities should be within 2%. So if your site controls are adequate, the other possibility is that the concrete supplier is shortchanging you. Try ordering 1 m^3, have a prepared box waiting, and direct the readymix driver to put it in the box.

 

[Ron]

Have your testing laboratory do a "yield" test on the concrete. This is a standardized method using the unit weight, air content, and the batch weights. In the US, it is done under ASTM C138. I'm not sure what standards you use, but likely you have something similar available. If you add all the batch weights and divide by the wet density of the concrete, you'll determine the "yield".

 

[cvg]

most engineers round up to be conservative. This would make the actual poured volume come out less than the estimated volume. If you are consistenly seeing poured volumes coming out larger, either the engineer or estimater is making mistakes or your supplier is also rounding up to "sell more" concrete.

 

[JedClampett]

Are they giving you the "poured" number or the delivered amount? Since the contractors don't want to be caught short, they request extra and dump it in a waste pile on the site.

 

[cvlenv]

thank you guys...

these would help us a lot...

 

[cvlenv]

good day...
could anyone provide a sample computation in determining the weight of aggregates (washed sand and crushed G-3/4 gravel) per volume of concrete for a 3500psi capacity at 28days?
please include also the number of liters of water for every volume of concrete.

thank you