Segregation in Concrete

SEGREGATION OF CONCRETE

What is Segregation:

Segregation in concrete is a case of particle segregation in concrete applications. Common forms are

• Separation of Coarse aggregate from the concrete mixture,

• Separation of Cement pastes from the concrete during its plastic stage.

• Separation of water from the concrete mix (Bleeding in concrete)

Segregation in concrete is commonly thought of as separation of some size groups of aggregates from cement mortar in isolated locations with corresponding deficiencies of these materials in other locations.

Segregation also occurs due to over-vibration or compaction of concrete, in which cement paste comes to the top and aggregates settles at the bottom.

Internal Factors for Segregation:

Segregation could result from internal factors such as concrete that is not proportioned properly and not mixed adequately, or too workable a mix.

External Factors for Segregation:

Segregation from external factors include too much vibration, improper transportation, placement, or adverse weather conditions.

Segregation is also caused by dropping concrete from more than 1 m.

Measures to reduce Segregation:

• Concrete should not be dropped from more heights

• Concrete should be placed through temporary inclined chutes for heights more than 1 m.

• The angle of inclination may be kept between 1:3 and 1:2 for smooth travel of concrete.

• The delivery end of chute should be as close as possible to the point of deposit.

• Adding air entraining agents, admixtures and pozzolanic materials increase the viscosity, thereby reduce segregation.

• Segregation can be controlled by maintaining proper proportioning the mix.

• Water content should not be more than the desired amount.

• Formwork should not have any leakages.

Tests for Segregation:

• Random ultrasonic testing should be conducted for any presence of segregation.

• Segregation can be rectified by pressure grounding with special chemical compounds.

• After rectifying the defects by pressure grouting core test has to be performed to ensure that the strength of concrete has reached to the desired level.