Reinforcing an RCC (Reinforced Cement Concrete) underground water tank is crucial to ensure its structural integrity, prevent cracking or leakage, and resist pressure from the surrounding soil and water. Here are the key methods to reinforce an RCC underground water tank:
1. Steel Reinforcement (Rebar)
- Description: Steel bars (rebars) are embedded within the concrete to provide tensile strength, as concrete itself is strong in compression but weak in tension.
- How to Reinforce:
- Reinforcement Mesh: Use steel rebars (typically high-strength steel) in a mesh pattern (grid layout) for both the walls and base of the tank. The rebar diameter and spacing depend on the tank’s size, capacity, and the structural loads it needs to withstand.
- Double Layer of Rebars: In large tanks, use double layers of steel reinforcement (on both inner and outer surfaces) for walls and slabs to resist internal water pressure and external soil pressure.
- Correct Cover: Ensure that there is adequate concrete cover (typically 20-50 mm) around the rebars to protect them from corrosion due to moisture or water infiltration.
- Purpose: Rebars prevent cracking due to tensile stress and resist the lateral and vertical loads acting on the tank (such as soil pressure and water pressure).
2. Additional Horizontal and Vertical Reinforcement
- Horizontal Reinforcement: Horizontal bars (ring beams or circumferential reinforcements) are placed around the tank to counteract the hoop stress created by water pressure. These bars are especially important in round or cylindrical tanks.
- Vertical Reinforcement: Vertical steel bars are used to resist vertical loads and provide extra support for the walls, especially near the corners and junctions where stresses are higher.
3. Shear Reinforcement
- Description: Shear reinforcement, often in the form of stirrups or additional rebar at specific angles, is added to resist shear forces that can cause diagonal cracking.
- How to Reinforce:
- Stirrups or Links: Use steel stirrups or hoops spaced at regular intervals around the rebars in the walls and floor to counteract shear stress.
- Extra Stirrups at Junctions: Concentrate additional shear reinforcement around the corners or where the walls meet the floor, as these areas are prone to higher stress.
- Purpose: Shear reinforcement helps in handling diagonal shear forces, particularly near the edges and corners of the tank.
4. Waterproofing Admixtures
- Description: Waterproofing admixtures (chemicals added to concrete) help make the RCC tank watertight and prevent leaks due to cracks or porosity in the concrete.
- How to Reinforce:
- Hydrophobic Admixtures: Add hydrophobic admixtures like crystalline waterproofing compounds to the concrete mix. These chemicals react with water and concrete to form crystals that block the capillaries, making the tank water-resistant.
- Water-Reducing Admixtures: Use water-reducing admixtures or plasticizers to improve the workability of concrete and reduce its permeability, resulting in a denser and more watertight structure.
- Purpose: These admixtures enhance the water-resistance of the concrete and minimize cracking caused by water penetration, thus reinforcing the tank’s durability.
5. External Waterproofing Membrane
- Description: Apply an external waterproofing membrane to the exterior of the tank, particularly for underground tanks where moisture from the surrounding soil can penetrate the concrete.
- How to Reinforce:
- Bituminous Coatings: Apply bituminous or asphalt-based waterproofing coatings to the outer walls of the tank to prevent moisture from entering.
- Polymer-Based Membranes: Use polymer-based waterproofing membranes, which provide a flexible layer of protection against water ingress and resist cracking or deformation over time.
- Double Layer Membranes: In high-water table areas or where soil conditions are harsh, consider using a double-layer waterproofing system for added protection.
- Purpose: External waterproofing prevents groundwater from penetrating the tank walls and causing structural damage or corrosion of the reinforcement.
6. Post-Tensioning
- Description: Post-tensioning is a technique where steel cables or tendons are stretched after the concrete has cured to add additional compressive force to the structure, improving its resistance to cracking and leakage.
- How to Reinforce:
- Install Tendons: Insert high-strength steel tendons or cables within ducts in the concrete structure, which are then tensioned after the concrete has set.
- Tensioning: Apply tension to the cables to put the concrete into compression, thereby counteracting tensile forces that might otherwise cause cracking.
- Purpose: Post-tensioning enhances the strength and durability of large or complex water tanks, reducing the risk of leaks and structural failure over time.
7. Control Joints and Expansion Joints
- Description: Control and expansion joints are designed to accommodate movements in the concrete due to temperature changes, shrinkage, or external loads, preventing uncontrolled cracking.
- How to Reinforce:
- Control Joints: These are saw cuts or pre-formed weak points in the concrete surface that control where cracks will occur due to shrinkage.
- Expansion Joints: For larger tanks, include expansion joints that allow for the expansion and contraction of the concrete due to temperature variations, without causing stress or cracking.
- Seal Joints: Seal these joints with flexible sealants like silicone or rubber to prevent water infiltration.
- Purpose: Control and expansion joints help prevent structural cracking by allowing the concrete to expand and contract without creating stress in the main structure.
8. Thickening of Walls and Slab
- Description: Increasing the thickness of the tank’s walls and slab adds additional compressive strength to resist external and internal loads.
- How to Reinforce:
- Base Slab Thickness: Increase the thickness of the base slab to handle the weight of the water and prevent upward pressure from groundwater (especially in high water table areas).
- Wall Thickness: Thicker walls improve resistance to lateral soil pressure and water pressure from inside the tank.
- Thicken at Stress Points: Focus on thickening the concrete at stress points like the base-wall junctions, corners, and areas subjected to high loading.
- Purpose: A thicker slab and walls help in reducing the risk of structural failure, enhancing the tank’s ability to handle both water pressure and external ground forces.
9. Proper Curing of Concrete
- Description: Proper curing ensures that the concrete reaches its full strength and reduces the chances of cracking, which is especially important for water tanks.
- How to Reinforce:
- Wet Curing: Keep the concrete wet for an extended period (at least 7-14 days) by covering it with wet burlap, plastic sheets, or continuously spraying water.
- Curing Compounds: Use curing compounds that form a protective layer over the surface, preventing water loss during the curing process.
- Purpose: Proper curing reduces shrinkage cracks, enhances the concrete’s strength, and ensures that the tank remains watertight over time.
10. Anchoring the Tank
- Description: In areas with high groundwater levels, underground tanks can experience buoyancy forces that push the tank upward. Anchoring helps resist these forces.
- How to Reinforce:
- Concrete Deadman Anchors: Place concrete deadman anchors or tie-downs around the base of the tank and secure the tank with straps or cables to prevent floating.
- Weight of the Slab: Increase the weight of the slab or foundation to counteract buoyant forces.
- Ground Anchors: Use ground anchors or piers driven deep into the ground to hold the tank in place.
- Purpose: Anchoring prevents the tank from floating or shifting due to buoyant forces, particularly in areas with a high water table or during floods.
11. Sloped Base for Sludge Removal
- Description: A sloped base ensures that any sediment or sludge that accumulates at the bottom of the tank can easily be removed.
- How to Reinforce:
- Sloped Design: Design the base with a slight slope toward the drainage point or sump, facilitating easy sludge removal.
- Reinforce at Low Points: Reinforce the concrete at the lowest points where water pressure and sediment loads are highest.
- Purpose: This method ensures easy maintenance and cleaning of the tank and helps avoid long-term buildup of sediment, which could lead to tank degradation.
Summary of Reinforcement Techniques:
- Steel Reinforcement (Rebars): Provides tensile strength to resist internal and external forces.
- Shear and Vertical Reinforcement: Resists shear forces and enhances stability.
- Waterproofing: Admixtures, external membranes, and coatings ensure the tank remains watertight.
- Post-Tensioning: Increases compressive strength and prevents cracks.
- Thickened Walls and Base: Increases the structural strength of the tank.
- Anchoring: Prevents buoyancy forces from shifting or lifting the tank.
- Control and Expansion Joints: Mitigates cracking due to temperature changes and movement.
By using these reinforcement techniques, you
