CONCRETE

CONCRETE

Concrete is made by mixing: Cement, water, fine aggregates, coarse aggregates and admixtures (if required).

Properties of concrete

Properties of Fresh Concrete are

a) Workability

b) Consistency

c) Segregation

d) Bleeding

e) Setting Time

a) Workability

The concrete mix should be workable, so that it can be placed and consolidated properly by the workmen.

 b) Consistency

Consistency is the fluidity or degree of wetness of concrete. It is a major factor in indicating the workability of freshly mixed concrete.

c) Segregation

Segregation refers to a separation of the components of fresh concrete, resulting in a non-uniform mix. The primary causes of segregation are differences in specific gravity and size of constituents of concrete. Moreover, improper mixing, improper placing and improper consolidation also lead to segregation.

 d) Bleeding

Bleeding is the tendency of water to rise to the surface of freshly placed concrete. It is caused by the inability of solid constituents of the mix to hold all of the mixing water as they settle down. It is special case of segregation

e) Setting Time

The transition process of changing of concrete from plastic state to hardened state. Setting of concrete is based or related to the setting of cement paste. Thus cement properties greatly affect the setting time. 

f) Temperature

The higher the temperature of the concrete at placement the greater the initial rate of strength development, but the lower long-term strength. This is why important to reduce the temperature of 

fresh concrete when concreting in hot climate.

Properties of Hardened Concrete

a) Strength

b) Permeability & durability

c) Durability

d) creep deformations

a) Strength 

The strength of concrete is basically referred to compressive strength.

Strength of Concrete depends on

–Strength of cement paste

 –Strength of aggregate

– Interface between cement paste and aggregates

 b) Permeability & durability

The permeability of concrete is controlled by capillary pores. The permeability depends mostly on w/c, age, degree of hydration. In general the higher the strength of cement paste, the higher is the durability & the lower is the permeability.

c) Durability

Concrete should be strong and durable.

Durability increases with density of concrete.

 d)  Creep Deformations   

Creep in concrete can reduce the pre-stress and possibly lead to cracking