Plain Cement Concrete (PCC) in Building Construction
Plain Cement Concrete (PCC) is essential in construction, acting as a protective layer between the soil or water and reinforcement concrete. This guide explores the materials used, the procedures for laying PCC, the dos and don’ts, and its advantages in construction projects.
Materials Used in PCC
- Coarse Aggregate
- Description: Hard, broken stone such as granite, free from dust, dirt, and foreign matter.
- Specifications: Should be 20 mm or smaller and pass through a 5 mm square mesh, with voids not exceeding 42%.
- Fine Aggregate
- Description: Sand that is clean and well-graded, free from impurities.
- Specifications: Should meet the necessary standards for fineness and cleanliness.
- Cement
- Type: Portland Pozzolana Cement (P.P.C)
- Specifications: Must conform to standards for tensile and compressive stresses and fineness.
- Water
- Description: Clean water, free from harmful substances like oils, acids, alkalis, salts, or organic growth.
- Specifications: Potable water with a pH value not less than 6, adhering to IS 456:2000 Clause 5.4 for permissible limits of solids.
Proportioning of PCC
- Common Mix Ratios: 1:2:4 or 1:3:6, depending on project specifications.
- Measurement Methods: Weight batching or volume batching (using a measuring box equivalent to one bag of cement).
Mixing of PCC
- Hand Mixing
- Suitable For: Small-scale projects.
- Procedure: Mix sand and cement thoroughly on a clean, watertight surface, add coarse aggregate and water, ensuring an even color and consistency.
- Machine Mixing
- Suitable For: Large-scale projects.
- Procedure: Place dry coarse aggregate, fine aggregate, and cement in respective hoppers, mix initially, and then add water gradually to achieve the desired water-cement ratio and uniform mix.
Laying of PCC
- Layer Thickness: Should not exceed 150 mm.
- Compaction: Use mechanical vibrators for thorough compaction. Hand compaction may be necessary in certain areas.
- Timing: Compaction must be completed within 30 minutes of adding water to prevent premature setting.
Curing of PCC
- Protection: Freshly laid concrete should be protected from rain and covered with moist materials to prevent rapid drying.
- Duration: Maintain a moist environment for at least 14 days to develop strength.
Dos and Don’ts of PCC Works
Dos:
- Ensure the PCC shuttering matches the exact size and thickness requirements.
- Mix water with cement in measured quantities as per the water/cement ratio.
- Use chutes or additional labor for pouring concrete in deeper areas.
- Remove loose materials from pit sides to prevent collapse during concreting.
- Implement dewatering if the water table is high during concreting.
Don’ts:
- Avoid mixing materials on bare land.
- Do not proceed with PCC without formwork.
- Refrain from pouring concrete without proper leveling and compaction.
- Avoid pouring concrete from a height exceeding 1.5 meters into the pit.
- Prevent excess cement mortar on top of PCC for a smooth finish.
Advantages of Laying PCC
- Protective Base: Provides a firm base for cover blocks, ensuring required cover to bottom reinforcement.
- Dimensional Accuracy: Facilitates achieving the effective depth of RCC members.
- Corrosion Protection: Prevents direct contact between reinforcement steel bars and chemically active ground soil, reducing the risk of corrosion.
- Ease of Placement: Simplifies the placement of steel cages, enhancing productivity.
- Barrier Function: Acts as a barrier against soil, promoting better bonding with overlaid structural grade concrete.
Conclusion
Plain Cement Concrete (PCC) is a vital component in construction, ensuring structural stability, durability, and protection against environmental factors. Adhering to proper procedures and standards is crucial for the quality and longevity of PCC installations.
