Segregation of Concrete

Table of Contents

Segregation of concrete is defined as the process of separating the ingredients of a heterogeneous mixture so that their distribution becomes irregular.

Additionally, segregation refers to the separation of new concrete components, resulting in a non-uniform mix. This is a separation of coarse aggregate from the mortar that occurs as a result of either heavy material sinking to the bottom or the aggregate separating from the mix as a result of poor placement.

Factors that increase segregation

Increased particle size maximum (25mm) and fraction of bigger particles.
Coarse aggregate has a high specific gravity.
Decreased fine particle content.
The form and texture of the particles.
Ratio of water to cement.

Good handling and placement techniques are most important in prevention of segregation.

Forms of Segregation of Concrete

There are two forms of segregation:

In the first type, coarse particles separate out more readily than tiny particles do.
The second kind of segregation happens most often in wet mixtures and is characterized by the separation of (cement+water) from the mixture.

Causes of Segregation of Concrete

Concrete with a high water-cement ratio. This is often the case when concrete is mixed on-site by unskilled workers.
When concrete is excessively vibrated using mechanical needle vibrators, the heavier particles drop to the bottom and the lighter cement sand paste rises to the top. This prohibition extends to the use of a vibrator to distribute a huge pile of concrete. This is especially true when vibration is allowed to persist for an extended period of time; as is the case with many mixes.
When concrete is poured from above in the case of subsurface foundations and rafts, it segregates.
Dropping concrete from a great height, traveling via a chute, especially with direction changes, and discharging against an obstruction.
Using coarse aggregate with a specific gravity much greater than that of fine aggregate would result in increased segregation.

Prevention of Segregation of Concrete

Wherever depth of concreting is more than 1.5 meters, it should be placed through temporary inclined chutes. The angle of inclination may be kept between 1:3 and 1:2 so that concrete from top of chutes travels smoothly to bottom.
The delivery end of chute should be as close as possible to the point of deposit.
The concrete does not have to travel too far and to be transferred directly from the wheelbarrow to the position in the form, the danger of segregation is small.
Concrete should always be placed direct in the position in which it is to remain and must not be allowed to flow or be worked along the form.
The improvement of cohesive of concrete reduces the danger of segregation. For example, entrained air in concrete controls the danger of segregation.