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Can you describe the terms of workability, consistency, cohesiveness of freshly concrete?

workability is a property of concrete defining the ease of placing and compacting concrete. workability consists of two aspects consistency and cohesiveness of concrete. workability depends on several factors:

  1. W/C: increasing of water-cement ratio will increase concrete workability but it will reduce the strength of the concrete mix. increasing water-cement ration will increase concrete permeability and this will reduce concrete strength and durability. on the other hand, using concrete with little water insufficient to interact with cement particle to cause hydration this will result in strength reduction. W/C usually ranges from 0.35-0.40.
  2. size of aggregate: Bigger size of aggregate means lesser surface area. as a result, the amount of water required for wetting the aggregate surface is lesser than the smaller size.and this will result in higher workability for the same water content.
  3. the shape of aggregate: aggregate with elongated flaky shapes will reduce the workability of concrete compared to round or cubical aggregate.
  4. Grading of aggregate: well-graded aggregate will enhance concrete mix workability. when the voids are reduced, extra paste will be available to give better lubricating effects.
  5. using of admixture: adding of admixture such as superplasticizers helps in increasing concrete mix workability and reduce W/C. 

consistency of concrete, consistency is the degree of concrete wet-ness on another word how much concrete is wet or how easily fresh concrete flow, increasing consistency means increasing the water content but this doesn't mean increasing the workability, the increasing of consistency of fresh concrete may cause segregation and this will lead to separation of aggregate and cement paste which complicate the process of placing and compacting concrete. 

figure 1

the cohesiveness of concrete can describe the ability of concrete mix to hold all ingredients together, concrete mix can be categorized into harsh, sticky and plastic, it is not recommended to use harsh concrete mix because ingredients tend to separate and segregate, excess or very low water are the main cause for producing harsh concrete mix, also using of angular and elongated aggregate can result in harsh concrete mix. 
using of a large amount of fine materials such as cement, fine aggregate or rock dust will result in a sticky concrete mix, sticky concrete mix required high water content to produce a workable mix, this will result in reduced strength and durability of concrete, the water content can be reduced by using admixture.
the plastic mix is in between harsh and sticky mixes, and concrete in this state will be placed and compacted without segregation. workability is a function of consistency and cohesiveness, to produce a workable concrete, the mix should have good consistency(being able to flow) and good cohesiveness(ability to hold all ingredients together)


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