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Plain cement concrete (PCC) is a fundamental component of building construction, serving to prevent direct contact between reinforcement concrete and soil or water. This article delves into the intricacies of laying PCC, offering insights into the materials used, the procedure, dos and don’ts, and the advantages it brings to construction projects.
In this article, we study the procedure of laying PCC, dos and don’ts and advantages of laying plain cement concrete.
Material Used in Plain Cement Concrete
The general specifications of materials used in PCC are –
1. Coarse Aggregate
The coarse aggregate employed in PCC must consist of hard, broken stone such as granite, devoid of dust, dirt, and foreign matter. It should ideally be 20 mm or smaller and pass through a 5mm square mesh. Proper grading ensures that voids do not exceed 42%.
2. Fine Aggregate
Portland Pozzolana cement (P.P.C) is the preferred choice for PCC, meeting necessary specifications regarding tensile and compressive stresses, as well as fineness.
3. Cement
Portland Pozzolana cement (P.P.C) is normally used for plain cement concrete. It should conform to the specifications and shall have the required tensile and compressive stresses and fineness.
4. Water
Water used in PCC must be clean and devoid of harmful substances like oils, acids, alkalis, salts, or organic growth. Potable water with a pH value not less than 6 is recommended, adhering to permissible limits for solids as per IS 456:2000 Clause 5.4.
Proportioning of Plain Cement Concrete
Proportioning is crucial and can vary based on specific requirements or specifications. Typically, a 1:2:4 or 1:3:6 mix is used. Measurement can be achieved through weight batching or volume batching, with the latter involving the use of a suitable measuring box equivalent to one bag of cement.
Mixing of Plain Cement Concrete
Mixing of PCC can be done either manually or by the means of machines :
Hand Mixing
Suitable for small-scale projects, hand mixing requires a clean, watertight surface. Sand and cement are mixed thoroughly before adding coarse aggregate and water, ensuring even color and consistency.
Machine Mixing
Dry coarse aggregate, fine aggregate, and cement are placed in respective hoppers. After initial mixing, water is gradually added to achieve the specific water-cement ratio, ensuring a uniform mix.
Laying of Plain Cement Concrete
PCC is laid in layers not exceeding 150mm thickness, with mechanical vibrators used for thorough compaction. Hand compaction may be necessary in certain areas to ensure complete compaction and proper alignment within formwork. Compaction must be completed within thirty minutes of water addition to prevent premature setting.
Curing of Plain Cement Concrete
Freshly laid concrete should be protected from rain and covered with moist materials to prevent rapid drying. Curing, essential for strength development, involves maintaining a moist environment for at least 14 days.
Dos and Don’ts of PCC Works
Dos
- Ensure PCC shuttering matches exact size and thickness requirements.
- Mix water with cement in measured quantities as per the water/cement ratio.
- Utilize 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.
- Never proceed with PCC without formwork.
- Refrain from pouring concrete without proper leveling and compaction.
- Avoid pouring concrete from a height exceeding 1.5m into the pit.
- Prevent excess cement mortar on top of PCC for a smooth finish.
Advantages of Laying Plain Cement Concrete
- Ensures required cover to bottom reinforcement by providing a firm base for cover blocks.
- Facilitates achieving the effective depth of RCC members, enhancing dimensional accuracy.
- Prevents direct contact between reinforcement steel bars and chemically active ground soil, reducing the risk of corrosion.
- Simplifies the placement of steel cages, enhancing productivity.
- Acts as a barrier against soil, promoting better bonding with overlayed structural grade concrete.
In conclusion, plain cement concrete serves as a vital foundation for construction projects, offering structural stability, durability, and protection against environmental factors. Adhering to proper procedures and standards is paramount to ensuring the quality and longevity of PCC installations.