General Considerations for Workability of Concrete

General Considerations for Workability of Concrete

Workability

Workability represents consistency & cohesiveness of concrete

General Considerations for Workability

Water content

• The higher the water content, the higher will be the fluidity of concrete, which is one of the important factors affecting workability.

a/c Ratio

• The higher the aggregate/cement ratio, the leaner is the concrete
• In lean concrete, less quantity of paste is available for lubrication, per unit surface area of aggregate and hence the mobility reduce
• In case of rich concrete with lower aggregate/cement ratio, more paste is available to make the mix cohesive and fatty to give better  workability.

Size of Aggregate

• The bigger the size of the aggregate, the less the surface area hence, less water is required for wetting the surface and paste is required for lubricating the surface to reduce internal friction
• For a given quantity of water and paste, bigger size of aggregates will give higher workability

Shape of Aggregates

• Angular, elongated or flaky aggregate makes the concrete very harsh when compared to rounded aggregates or cubical shaped aggregates
• Being round in shape, the frictional resistance is also greatly reduced

Surface Texture

• Total surface area of rough textured aggregate is more than the surface area of smooth rounded aggregate of same volume
• Rough textured aggregate will show poor workability and smooth or glassy textured aggregate will give better workability
• Reduction of inter particle frictional resistance offered by smooth aggregates also contributes to higher workability

 Grading of Aggregates

• Better the grading, the less is the void content and higher the workability
• When the total voids are less, excess paste is available to give better lubricating effect

Use of Admixtures

• Use of air-entraining agent being surface-active, reduces the internal friction between the particles
• Air bubbles act as a sort of ball bearing between the particles to slide past each other and give easy mobility to the particles
• Plasticizers and super-plasticizers greatly improve the workability many folds