Segregation is the separation of concrete ingredients from one another. Concrete is one of the most used construction materials. It consists of coarse aggregate, fine aggregate, cement and water. There are many reasons for the cause of segregation. This article is about segregation and bleeding and their types, causes and remedies
What is Segregation in Concrete?
Workability is an important property of concrete that reflects how easily we can place a particular concrete mix . Good concrete should be uniformly mixed and easily placeable without segregation or bleeding.
What is segregation?
Segregation of concrete is the separation of ingredients in concrete. Since concrete is a non-homogeneous material, improper mixing is the main reason for the segregation. It occurs during transporting, handling and placing of concrete. Also, it affects the concrete properties. The strength of concrete decreases and leads to cracking. Therefore it should be properly mixed before use in construction.
Causes of Segregation in Concrete
A good quality concrete mix is prepared by considering factors like the size of aggregate, water-cement ratio, compaction, etc. They are many reasons for the causes of segregation. They are
- Improper mixing of concrete ingredients
- Excess use of water
- Poorly grading of aggregates
- difference in the aggregate sizes
- Due to improper handling of concrete
- Difference in the specific gravity of aggregates
- Improper vibration of concrete
- Placing of concrete from greater heights
- Improper transporting of concrete
- Long time Mixing of concrete
Prevention of segregation is very important as it adversely affects the properties of concrete.
Types of Segregation
Segregation occurs in three types such as
- Separation of water and cement from other ingredients
- Segregation of coarse aggregate
- Separation of water content
Segregation is hard to measure since there is no particular test for determining it. However, the Flow table test measures the segregation. Also, the slump test of concrete can give an idea about segregation. Coarse aggregate in concrete tends to settle down from other ingredients. Usually, It occurs when the concrete mix is dry. While segregation by separation of water content occurs due to an insufficient amount of fine aggregates or due to the use of an excess amount of water content.
Bleeding
Segregation occurs when the principal ingredients in a concrete mix – in other words, gravel aggregate, cement, and water – separate prior to and during the curing process. Moreover, Segregation causes excessive amounts of water to rise to the surface. This process is know as bleeding. Bleeding is also similar to segregation in which the water in the concrete rises to the surface of the concrete. As a result, the concrete becomes porous and weak.
Bleeding affects its strength and its durability of concrete . Likewise, It breaks the bond between the concrete and steel reinforcement. However, a proper proportion of concrete ingredients and controlled vibration can reduce bleeding. Moreover, air entraining admixtures can also be used for reduce bleeding.
Causes of bleeding in concrete
The main causes of bleeding in concrete mix is as follows
- Segregation is the main cause of bleeding in concrete
- High water cement ratio causes bleeding.
- Type of cement used and quantity of fine aggregate
- Over vibration
How to reduce bleeding in concrete?
By adapting the following methods bleeding can be reduced
- Minimum water cement ratio should be maintained.
- A proper design mix
- Use mineral admixtures like fly ash
- Use air entrapping admixtures
- Maintain fine aggregate ratio