WORKABILITY OF CONCRTE

 Workability Of Concrete

Workability of concrete is the property of freshly mixed concrete which determines the ease and homogeneity with which it can be mixed, placed, consolidated and finished as defined by ACI Standard 116R-90 (ACI 1990b).

Workability is a property that directly impacts strength, quality, appearance and even the cost of labor for placement and finishing operations.Concrete is said to be workable when it is easily placed and compacted homogeneously i.e without bleeding or segregation.

Types Of  Workability Of Concrete

1. Unworkable Concrete
2. Medium Concrete
3. Highly Workable Concrete

1. Unworkable Concrete

An unworkable concrete also called as harsh concrete, is a concrete with a very little amount of water in it.The hand mixing of such concrete is very difficult.This type of concrete has a high segregation of aggregates and it is very difficult to maintain the homogeneity of concrete mix and compaction of concrete requires much effort.Water cement ratio of such concrete is below 0.4.

2. Medium Concrete

Medium workable concrete is preferred in most construction works.This type of concrete is relatively easy to mix, transport, place and compact without much segregation and loss of homogeneity.Water cement ratio for medium workable concrete is 0.4 to 0.55.

3. Highly Workable Concrete

A highly workable concrete is very easy to mix, transport, place and compact because of high water content.It is used for concreting where effective compaction of concrete is not possible.The problem in using this type of concrete is that there are high chances of segregation and loss of homogeneity.Such concrete is used in case of heavy reinforcement is used where vibration of concrete is not possible.Water cement ratio in such type of concrete is more than 0.55.

Factors Affecting Workability Of Concrete

• Water cement ratio.
• Type of construction work.
• Method of mixing of concrete.
• Method of placement of concrete.
• Method of compaction of concrete.
• Method of transmission of concrete.
• Temperature of the concrete mix.
• Thickness of concrete sections.
• Environmental condition.

Method Of Improving The Workability Of Concrete

• Increase water cement ratio.
• Increase the size of aggregate.
• Increase the mixing time of concrete.
• Increase the mixing temperature of concrete.
• Use non porous and saturated aggregates.
• Adding appropriate admixtures in concrete.
• Use well rounded and smooth aggregate instead of irregular shape.

Methods Of Determining Workability Of Concrete

• Slump test.
• Flow test.
• Kelly ball test.
• Compacting factor test.
• Vee Bee consistometer test.