The ease with which concrete is placed, compacted, transported, and finished without segregate is known as workability of Concrete. Concrete has good workability gives good strength and durability. It is the property of fresh concrete.
The factors that affect the workabilities of concrete, such as Water content, Mix proportions (Aggregate /cement ration), Size of aggregates, the shape of aggregates, the surface texture of aggregates, grading of aggregates and use of admixtures.
Factors Affecting Workability of Concrete
The workability of concrete is directly proportional to water content. As water content increases, workability also increases. Increase in water content in concrete causes bleeding. Hence, the strength decreases, and setting time increases. Cement slurry will come out near the batching area. If the amount of water is less in concrete then strength also increases but workability decreases. Quantity of water helps to achieve the hydration process.
Mix Proportions or Aggregate / cement Ratio
Before knowing this topic Aggregate/cement ration, let me remind you of the difference between lean concrete mix and Rich concrete mix.
Lean mix: It is Plain cement concrete (PCC) with a mix ratio of 1:3:6. It contains less than 10% cement and used as mass concrete, foundation, or pavement. In the case of the lean mix, the amount of aggregate is more as compared than cement i.e. higher the Aggregate cement ratio which means aggregate absorb more water from the mix, reducing the water-cement ratio.
Rich mix: Rich concrete means quantity of cement which is more than 15%. Grade of concrete of Rich Mix such M20 (1: 1.5: 3), M25 (1: 1: 2). Where 1: Cement, 1.5: Sand, 3: Aggregate. In case of Rich Mix, amount of aggregates is lower and cement content is more. More paste is available to make the mix cohesive and fatty to give better workability.
Size of aggregate
Aggregates having larger in size has less surface area that requires less amount of water for lubricating the surface to reduce the friction. Hence concrete has larger in size has more workability. The larger size of the Aggregate required a good amount of compaction due to the presence of porosity.
Shape of aggregates
The shape of the aggregates is one of the important influencing factors of workability. Rounded and cubical aggregates have less surface area require less quantity of paste for lubrication and provide good workability. Angular and Flakey aggregates have more surface area requires more quantity of paste for lubrication and reduces workability.
Surface texture of aggregates
Rounded aggregate has less surface area and smooth surface as compared to angular aggregates.
Hence smooth texture aggregate have better workability as compared to rough texture aggregates.
The Admixture such as Plasticizer and super-plasticizers increases the workability. Using the entertaining agent being surface-active reduces the internal friction between the particles which improves workability.