How to Make RCC Bottom Slab of UGWT

In last post we discussed "Earth Excavation techniques and precautions of Under Ground Water Tank". Today we will make the RCC bottom slab of that UGWT.
under ground water tank
Before starting bottom slab work we need to prepare the base. Properly compact and level the base soil. Make 3 inches brick soling above base soil. See "how to make brick soling". After finish brick soling make 2 inches thick PCC. See "how to make PCC".

We need the following materials to make the bottom slab of RCC under ground water tank -
* Steel bar (as per drawing)
* Binding wire
* Concrete ingredients (cement, sand and stone chips)
* Water proofing sheet
* Foam lube (concrete admixture) etc.

Form work:
Making Form work for UGWT is simple. Just fix side shutter all around water tank. The height of side shutter will be 1 foot and 4 inches. Since our bottom slab height is 10 inches and chamber height is 6 inches so the formwork height is 1 foot and 4 inches. See the above image.

In construction project you should have a complete set of drawing sheets. In those drawings you must have a "structural drawing sheet" for water tank's reinforcement details. The sheet will look like the above image with details reinforcement. Place the bottom slab reinforcement as per drawing. And also place the water tank's wall reinforcement as shown in the drawing. At last, place chamber reinforcement as shown in the above image. One thing I would like to clear here that is the chamber. What is the chamber? Why is it provided? Chamber is a sloped concrete portion provided in the corner of wall and bottom slab junction of water tank. It is provided to prevent water penetration through joint. See the image above.

Concrete Casting:
For this small quantity of concrete volume we normally depend upon mixture machine. See "how to mix concrete with mixture machine". You may also like to read "how to control quality when mixing concrete with mixture machine". Add 200 milliliter foam lube with one bag cement mixture or as per manufacturer instruction.

We suggest, do chamber casting simultaneously with bottom slab. If you do so there will be no joint in the bottom slab and wall junction. And the Joint will be in wall above chamber's top portion. And we will provide water proofing sheet in the upper portion of the chamber where joint will be. So it is better to keep the concrete joint in the water tank's wall. Another thing, placing water proofing sheet in the joint of wall and bottom slab is difficult because of chamber rod.

Following these small techniques you can make the water tank completely leakage proof. Leakage in under ground water tank is difficult to repair. So be careful.

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