What is Concrete

 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