Factors affecting workability

1 - water content: 

• Fluidity of concrete increases with water content because addition of water enhance interpartical lubrication 
• At site it is normal practice to increase the water content to make the concrete warkable which lowers the strength 
• In controlled concrete this cannot be resorted and even in uncontrolled concrete this should be the last choice 
• But in case if more water is added due to any reason the cement content should be proportional increased 

  2- mix proportions : 

• Aggregate cement ratio influences the workability to a large extent . The higher the ratio leaner will be the concrete. Lean concrete paste available for lubrication of per unit surface area of aggregates will be less and hence the warkability is reduced 

  3- shape of aggregates : 

•     Big size aggregate  the total surface area to be wetted is less paste is required for lubricating the surface to reduce internal friction .for a given water content big size aggregate give high warkability 

4 - shape of aggregates : 

• At a given water content , round and cubical shape aggregate are more warkable then rough , angular or flaky aggregates , because these type of aggregates requires less cement paste for lubrication as these have less surface  area and lesser voids.
• In round aggregate frictional resistance is small , so less lubrication is required .for this reason river sand and gravel provide greater workability then crushed sand and aggregate 

5- surface texture : 

• Rough surface aggregate will have more surface  area than a smooth round textured aggregate  agger gate . Therefore smooth will be more warkable

6 -Grading of aggregates: 

• Well greded aggregates are more workable . Because such a mix will have  least voides and thus excess cement paste will be available as lubricant 

7- Admixtures:  

• Air entrained concrete is more workable , Because air forms bubbles , on which the aggregates slids past each other increasing  the workability.
• Air entraining agents are surface active and they reduce the internal friction between the aggregates