PCC in construction stands for Plain Cement Concrete. It is a composite material made by mixing cement, fine aggregate (sand), and coarse aggregate (gravel or crushed stone) with water. Unlike Reinforced Cement Concrete (RCC), PCC does not contain any steel reinforcement. It is a basic but essential construction material primarily used for its high compressive strength.
The Composition and Mix Ratios of PCC
The properties of PCC depend on the ratio in which its three main components are mixed. These mix ratios, also known as grades of concrete, determine the compressive strength of the hardened concrete.
The mix ratio is expressed as a proportion of Cement : Fine Aggregate : Coarse Aggregate.
| Grade of Concrete | Mix Ratio (Cement : Sand : Aggregate) | Compressive Strength (after 28 days) | Common Uses |
|---|---|---|---|
| M10 | 1 : 3 : 6 | 10 N/mm² | Leveling courses, base coats for floors, and other non-structural work. |
| M15 | 1 : 2 : 4 | 15 N/mm² | The most common grade for PCC. Used for bed concrete, foundations, and floor slabs that are not subjected to heavy loads. |
| M20 | 1 : 1.5 : 3 | 20 N/mm² | Used for applications requiring higher strength, such as pavements or heavier-duty flooring. |
For example, a 1:2:4 mix means that for every 1 part of cement, 2 parts of sand and 4 parts of coarse aggregate are used.
Key Properties of Plain Cement Concrete
PCC has distinct properties that define its use in construction.
- High Compressive Strength: Its main advantage is that it is very strong in compression, meaning it can withstand heavy loads that press down on it. This is why it is excellent for foundations.
- Low Tensile Strength: PCC is very weak in tension. It cannot resist forces that try to pull it apart or bend it. This is its biggest limitation and the reason why it is not used for structural elements like beams, columns, or suspended slabs that are subject to bending.
- Durability: It is a durable and long-lasting material that is resistant to weathering.
- Workability: When freshly mixed, PCC is in a plastic state, allowing it to be poured and molded into any desired shape using formwork.
Common Uses of PCC in Construction
Given its properties, PCC is used in applications where the primary load is compressive and there are no significant tensile stresses.
- Foundations and Footings: It is widely used to create a level and firm base (bed concrete) for the foundation of a building. A layer of PCC is laid before the RCC footing is constructed on top of it.
- Floor Slabs (on Grade): For ground-floor slabs that are directly supported by the earth, PCC is a common choice.
- Pavements and Walkways: It is used for constructing light-duty pavements, sidewalks, and pathways.
- Leveling Course: A thin layer of PCC is often laid on an uneven surface to create a perfectly level base for subsequent construction work.
- Filling and Backfilling: It is used as a filler material in various construction contexts.
PCC vs. RCC (Reinforced Cement Concrete)
The main difference is the absence of steel reinforcement.
| Feature | PCC (Plain Cement Concrete) | RCC (Reinforced Cement Concrete) |
|---|---|---|
| Composition | Cement, sand, aggregate, water. | Cement, sand, aggregate, water, and steel reinforcement bars (rebars). |
| Strength | Strong in compression, weak in tension. | Strong in both compression and tension (the steel takes care of the tensile forces). |
| Use | Used for compressive members like foundations, base courses, and ground slabs. | Used for structural members subjected to bending and tension, like beams, columns, suspended slabs, and lintels. |
PCC is a fundamental material in the construction industry. Understanding its properties and uses is essential knowledge for any student of civil engineering, just as understanding the basics of an electric drive is for an automobile engineer. The standards for concrete in India are governed by the Bureau of Indian Standards (BIS) through various IS codes.
Frequently Asked Questions (FAQs)
What is the full form of PCC in construction?
The full form of PCC is Plain Cement Concrete. It is a mixture of cement, sand (fine aggregate), and gravel (coarse aggregate) with water, which hardens into a strong, solid mass. It does not contain any steel reinforcement.
What is PCC used for?
PCC is primarily used in construction for applications where high compressive strength is needed and there are no tensile forces. Its most common uses include creating a base for foundations, ground-level flooring, and pavements.
What is the standard PCC mix ratio?
The most commonly used mix ratio for general PCC work is 1:2:4 (1 part cement, 2 parts sand, 4 parts coarse aggregate), which corresponds to the M15 grade of concrete. For leveling and non-critical work, a 1:3:6 (M10) ratio is also used.
What is the main difference between PCC and RCC?
The main difference is reinforcement. PCC is ‘plain’ and has no steel reinforcement, making it strong only in compression. RCC is ‘reinforced’ with steel bars, which gives it the ability to resist tensile (bending) forces, making it suitable for structural elements like beams and slabs.
Why is a layer of PCC laid below a foundation?
A layer of PCC is laid below the main RCC foundation to provide a clean, level, and firm surface. This prevents the RCC from coming into direct contact with the soil, which could lead to water from the concrete seeping into the soil or harmful chemicals from the soil affecting the steel reinforcement.