[Best Guide] Workability of Concrete - Factors Affecting Workability
Today we learn about What is the workability of concrete? and also Discuss the factors affecting workability to clear the full concept behind workability
Workability of Concrete
In fresh concrete, concrete in the plastic state, which can be moulded into desired shape the theoretical w/c ratio to meet the requirements of water for chemical combination with cement, and to occupy the gel-space is about 0.4 for maximum strength.
The w/c ratio used at the site may vary because of:
- The presence of free surface moisture in the aggregates, and
- The absorption of moisture by the dry or porous aggregates.
Because of the above limitations another characteristic workability. Which is again a reflection of the w/c ratio, becomes important.
The theoretical w/c ratio used will not give the maximum strength because of the reasons stated above.
100 percent compaction of concrete will give maximum strength and this can be obtained by increasing the w/c ratio.
The water lubricates the concrete which can be compacted at the site with the specified efforts. The lubrication required for handling concrete without segregation, for placing without loss of homogeneity. Compacting with specified effort and for easy finish are indications of workable concrete.
Deﬁned Workability as per Road Research Laboratory
As per Road Research Laboratory U.K. workability is deﬁned as the property of concrete which determines the amount of useful internal work necessary to produce full compaction.
It can also be defined as the ease with which concrete can be compacted 100 % with regard to the mode of compaction and place of deposition.
Workability is different from consistency. The latter indicates the degree of fluidity of mobility. Concrete with high consistency need not be workable for a particular job.
For example, a concrete workable for foundation may not be workable for the slab. Even for slab different workability will be required for compaction by hand than that by vibration. It is because to the requirement of workability is less.
Factor Affecting Workability
A workable concrete exhibits very little internal friction between the particles forming the concrete and overcomes the frictional resistance offered by the internal surface of formwork as well as that by the reinforcement contained in the concrete with just the amount of compacting efforts forthcoming.
The factors helping concrete to achieve these are as follows:
The fluidity of concrete increases with water content.
At site, the normal precise is to increase the water content to make the concrete workable which lowers strength.
In controlled concrete, this cannot be resorted and even in uncontrolled concrete, this should be the last choice.
However, in case, if more water is added due to any reason the cement content should be proportionally increased.
Aggregate cement ratio influences the workability to a large extent.
The higher the ratio leaner will be the concrete. In lean concrete, paste available for lubrication per unit Surface area of aggregates will be less and hence the workability is reduced.
For big size aggregate the total surface area to be wetted is less, also less paste is required for lubricating the surface to reduce internal friction.
For a given water content big size aggregate gives high workability.
Shape of Aggregates
For a given water content, round and cubical shape aggregates are more workable than rough, angular, or flaky aggregates. because the former type of aggregates requires less cement paste for lubrication as these have less surface area and lesser voids.
In the case of round aggregates, frictional resistance is also small so less lubrication is required. For this season river, sand and gravel provide greater workability than crushed sand and aggregates.
A rough surface aggregate will have more surface area than a smooth round textured aggregate.
Hence, the latter will be more workable for the reasons discussed above.
Grading of Aggregates
Properly graded aggregates are more workable. It is so because such a mix will have least voids and thus excess cement paste will be available as a lubricant. This also prevents segregation.
Air entrained concrete is more workable. It is so because air forms bubbles, on which the aggregates slide past each other increasing the workability. Another factor is that air-entraining agents are surface-active and they reduce the internal friction between the aggregates.
FAQ 1: What is the Workability of concrete?
The workability of concrete is the property which required as an internal work to provide fully compacted concrete without segregation
FAQ 2: What is the Requirement for Good Concrete?
1. Mixability The mixability of concrete plays a great role to produce homogeneous green concrete from the ingredient of the mixing batch under the action made during mixing 2. Stability Stability define in the way like segregation should not happen in concrete during mixing, transportation, placing, compaction 3. Transportability Transportation is the ability of green concrete to keep its structure homogeneous free from the effect of segregation during the time period of transportation of concrete 4. Mobility This is also called flowability Mobility is the property of concrete mix to be arranged and cast in any shape which forms around the reinforcement bars without compromising with quality or homogeneity under available resources tools of casting at the site of construction project 5. Compatibility Compactibility defined as the ability of green concrete mix to be fully compacted into the desired shape and remove voids and make concrete dense Good concrete is that which does not have a void or fewer voids like the elimination of 99% voids The best workable concrete is that which satisfies the above specification. The word ‘workability’ notes a much wider and deeper meaning than the word ‘consistency’ Consistency is a general term in civil engineering which indicate the degree of mobility/fluidity The workability of concrete can be improved greatly by adopting and improving the above requirement
FAQ 3: Deﬁne Workability of Concrete
The workability can be defined in many ways as below 1. It defines the ease with which concrete can be mixed, transported, placed and compacted. 2. IS: 6461 part-VII -1973 defines “Workability as that property of green concrete or cement mortar which determines the case & homogeneity with which it can be mixed, placed, compacted and finished 3. As per Road Research Laboratory of U.K. workability is defined as “the property of concrete which determines the amount of useful internal work necessary to produce full compaction 4. The Different requirements of partial properties of concrete like mobility, stability, mixability, transportability, castability, compactability and finishability are altogether referred to as ‘workability’. which is known as composite property
FAQ 4: What are the Factors Affecting Workability?
1. Water Content 2. Mix Proportions 3. Size of aggregates 4. Shape of Aggregate 5. Surface Texture of aggregate 6. Grading of Aggregate 7. Use of Admixture 8. Time 9. Temperature 10. Properties of Cement 11. Environmental Conditions