Principle of R.F. and Construction Materials
In the ITI Draughtsman Civil trade, understanding the principle of Representative Fraction (R.F.) along with knowledge of construction materials is essential. R.F. is widely used in drawing to represent objects in proportion, while materials such as stones, bricks, lime, pozzolanic substances, and cement are fundamental in construction work.
Principle of R.F. (Representative Fraction)
Representative Fraction (R.F.) is defined as the ratio of the length on a drawing to the actual length of the object, both expressed in the same units.
R.F. = Length on Drawing / Actual Length
- Used for scaling drawings accurately
- Maintains proportion between drawing and real object
- Commonly used in plans, maps, and layouts
Materials: Stones
Characteristics:
- High strength and durability
- Resistance to weathering
- Low water absorption
Types:
- Igneous (Granite, Basalt)
- Sedimentary (Sandstone, Limestone)
- Metamorphic (Marble, Slate)
Uses:
- Foundations and walls
- Road construction
- Decorative works
Bricks
Manufacturing Process:
- Preparation of clay
- Moulding
- Drying
- Burning in kilns
Characteristics of Good Bricks:
- Uniform shape and size
- Hard and durable
- Low water absorption
- Clear ringing sound when struck
Types:
- First-class bricks
- Second-class bricks
- Third-class bricks
- Hollow bricks
Uses:
- Wall construction
- Partition walls
- Pavements
Hollow Bricks: These bricks have cavities which reduce weight and improve insulation. They are commonly used in modern construction.
Lime
Characteristics:
- Good binding property
- Plastic and workable
- Slow setting
Types:
- Fat lime
- Hydraulic lime
- Poor lime
Manufacturing:
- Obtained by burning limestone in kilns
- Followed by slaking with water
Uses:
- Mortar preparation
- Whitewashing
- Plastering work
Pozzolanic Materials
Pozzolanic materials are siliceous or aluminous substances which, in the presence of water, react with lime to form cementitious compounds.
Characteristics:
- Improves strength and durability
- Reduces heat of hydration
- Enhances resistance to chemicals
Types:
- Natural pozzolana (volcanic ash)
- Artificial pozzolana (fly ash, burnt clay)
Uses:
- Used in cement manufacturing
- Improves concrete properties
Cement
Manufacturing Process:
- Crushing and grinding of raw materials
- Mixing and heating in rotary kiln
- Clinker formation
- Grinding with gypsum
Characteristics:
- High compressive strength
- Good binding property
- Durability
Types:
- Ordinary Portland Cement (OPC)
- Portland Pozzolana Cement (PPC)
- Rapid Hardening Cement
- Low Heat Cement
Uses:
- Concrete construction
- Plastering and masonry work
- Structural works
Tests of Good Cement:
- Fineness test
- Setting time test
- Soundness test
- Strength test
Conclusion
The principle of R.F. and knowledge of construction materials such as stones, bricks, lime, pozzolanic materials, and cement are essential for the ITI Draughtsman Civil trade. These concepts help students prepare accurate drawings and understand practical construction techniques.
By mastering these topics, students can develop strong technical skills and contribute effectively to the construction industry.