Concrete: A Complete Overview
1. Definition of Concrete
Concrete is a composite construction material consisting of:-Binding material (usually cement)- Inert aggregates (coarse and fine)
-Water
- Admixtures (optional)
Concrete = Cement + Sand + Aggregates + Water (+ Admixtures)
It gains strength by hydration and hardens over time.
2. Classification Based on Binding Material
- Lime Concrete (Hydraulic Lime)
- Asphalt Concrete (Bitumen)
- Cement Concrete (Ordinary Portland Cement)
3. Grades of Concrete (IS 456:2000)
Nominal Mix Concrete:
M5 (1:5:10) - 5 MPa
M7.5 (1:4:8) - 7.5 MPa
M10 (1:3:6) - 10 MPa
M15 (1:2:4) - 15 MPa
M20 (1:1.5:3) - 20 MPa
M25 (1:1:2) - 25 MPa
Design Mix Concrete:
M30 - High-rise, RCC roads
M35 - Bridges
M40 - Flyovers
M45 - Silos
M50+ - Prestressed bridges, nuclear plants
4. Advantages of Concrete
- High compressive strength
- Durable and long life
- Castable into any shape
- Fire and water resistance
- Cost-effective and locally available
- Low maintenance
- Thermal mass property
- Can use recycled materials
5. Disadvantages of Concrete
- Low tensile strength
- Brittle
- Heavy weight
- Slow strength gain
- Environmental impact (CO2)
- Skilled handling required
- Risk of cracking
- High formwork cost
- Difficult to modify
- Loses strength in fire
6. Reinforced Cement Concrete (RCC)
Concrete + Steel = Reinforced Cement Concrete (RCC)
Uses:
- Longitudinal bars
- Stirrups
- Cover protection
Applications:
- Beams, Columns
- Slabs, Footings
- Bridges, Tunnels, Dams
7. Properties of Concrete
Fresh Concrete:
- Workability
- Consistency
- Segregation
- Bleeding
- Setting Time
- Plastic Shrinkage
- Air Entrainment
- Temperature Effects
Hardened Concrete:
- Compressive Strength
- Tensile Strength
- Durability
- Density
- Permeability
- Shrinkage & Creep
- Modulus of Elasticity
- Fire Resistance
8. Key Concrete Operations
- Batching
- Mixing
- Transporting
- Placing
- Compacting
- Finishing
- Curing
- Deshuttering
9. Degree of Compaction (DoC)
DoC = Density of Compacted / Fully Compacted
Range: 0.90 to 1.0
Tools:
- Needle Vibrator
- Surface Vibrator
- Tamping Rod
Benefits:
- Better strength
- Durability
- Bonding with rebar
- Good finish
10. Concrete Testing Summary
- Compressive Strength: Cube Test (IS 516)
- Workability: Slump Test
- Tensile Strength: Split Cylinder Test
- Density: Weighing Hardened Sample
- Durability: Rapid Chloride Penetration Test
