Introduction of concrete

# Definition of concrete :
The concrete is the mixture of sand, aggregate and water and sometime admixture in required propotion.

# Hardening of concrete is cause by the chemical reaction between water and cement. And this reaction continues for

long time and so concrete growing stength for long period.

# concrete may be RCC, PCC, Prestressed etc.

# concrete have more compressive strength and very low tensile strength.

# low tensile strength caused cracking easily in the wall.

# high compressive stegth caused weathing and corrosive effect minimal.

# In the condition of tension, the steel bar and fiber used to strength the concrete called reinforced concrete cement (RCC) otherwise Plane cement concrete (PCC).

# Prestressed cement concrete, in this concrete stress are applied prior to use; strong enough to bear tensile as well as compressive force.

# Properties :
1. It should be durable.
2. It should have high compressive strength.
3. It should be impermeable.
4. It should have low dimension change.
5.free from seggretion( separation of course aggregate)
6. Free from bleeding ( separtion of cement paste in main use)

# grade of concrete may be expressed in Mpa(N/mm^2).

# In designation of concrete M is mix.

# M10, M15, M20 - Ordinary concrete

# M25, M30, M35, M40, M45, M50, M55 - Standard cement.

# M60, M65, M70, M75, M80 is high stength concrete.

# Advantage of concrete :
1. Concrete is economical.
2. High compressive strength.
3. Durable.

#Disadvantage :
1. High tensile strength.
2. Fresh concrete shrinks on drying and hardened concrete expands on wetting.
3. It expand and contracts.
4. Creep
5. Lack of ductility.

# Admixture may be defined as a material other than cement, water and aggregates which is used as concrete indegrediant before and during mixing
     There are two types of admixture.
              ● chemical admixture : accelerator and accelerating admixture, plasticizers, water proofing admixture, colouring admixture.

             ● Mineral admixture : Rice husk ash, surkhi, silica