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
Green concrete or fresh concrete is a recently mixed mixture of various ingredients in a certain fixed amount which can be moulded into any desired shape and size as per requirement
The ingredient of concrete mix like cement, sand, aggregate and water also admixture if any mix together to obtain required properties of concrete
The performance of concrete depends on lots of varies factors or change with respect to shape, size, strength, durability, shrinkage, creep and many more
So that you should satisfy a certain requirement such as degree of workability of concrete, stability, transportability, moulding ability, compatibility and finish ability so you must full article with the presence of mind
IS Code for Workability of concrete is IS 1199
Requirement for Good Concrete
Good workable concrete must have the following requirements which are explained below
Mixability
Stability
Transportability
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
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
Define workability of concrete and explain briefly the factors affecting workability
Define Workability of Concrete
All types of construction work demand particular workability
For example, concrete is well workable for mass concrete work is not suitable for slab construction
Therefore, the word ‘workability’ take to the specification of types of work, design of reinforcement, section thickness and also a mode of compaction
Hence, the workability can be defined in many ways as below
- It defines the ease with which concrete can be mixed, transported, placed and compacted.
- 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
- 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
- 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
Factors Affecting Workability
Factors affecting the workability of concrete mix depend on varies aspect with is listed below because each and every material which mix in concrete play a role in workability of concrete
Measurement of workability of concrete depends also on the following factors
The following are the factors affecting the workability of concrete
- Water Content
- Mix Proportions
- Size of aggregates
- Shape of Aggregate
- Surface Texture of aggregate
- Grading of Aggregate
- Use of Admixture
- Time
- Temperature
- Properties of Cement
- Environmental Conditions
Water content | Water Cement Ratio
An increase in the water content results in an increase in the workability of concrete and vice-verse. Too much water content (i.e. high water-cement ratio) makes the concrete highly workable but may lead to bleeding and segregation
The workability of any grade of concrete mainly depend upon the W/C ratio means to depend on the amount of water added into the concrete mix in which water plays a great role as a lubricant in green concrete
The mobility/fluidity increase with the addition of water into concrete which is an important factor affecting the workability
On the site of construction, many non-technical supervisors/labour/contractors resort to adding more water for increasing workability but it creates a major issue of segregation on their side addition of only water which increases w/c ratio which makes concrete mix leaner hence its become the reason of decreased strength of concrete
Increasing water content without verifying results in increase workability but at some point reached where segregation and bleeding occur in the mix and also bring other problems like shrinkage and creep in concrete
So you have to maintain water/cement ratio so the strength of concrete does not Sacrifice
Mix Proportions
Ingredient of concrete-like cement, fine aggregate, coarse aggregate and water is determined during mix design cancellation for any particular construction work after testing of materials used in construction
The aggregate/cement ratio is also an important factor that affects the workability of concrete. In the higher aggregate/cement ratio cement paste is available in low amount in concrete which make leaner concrete hence the mobility of aggregate in concrete is restrainer end of result reduce of workability
On another hand, In the case of rich concrete in which the aggregate/cement ratio is high so in that case more cement paste available for lubrication of aggregate which gives the better workability
Size of Aggregate
The larger size of aggregate means is the lower the surface area hence required less amount water for wetting the aggregate surface and also a low amount of cement paste required to make lubricate the surface of aggregates
So for the same water/cement ratio, the larger size of aggregate will offer higher workability
The size of the aggregates determines the void content in concrete. Aggregates amount to about 70-75% of the total volume of concrete.
Smaller the specific surface area of aggregates, more water is available and thus workability increases
Note: Size of aggregate has restricted some criteria because the size of the aggregate effect in the placement of reinforcement design
Shape of Aggregate
The shape and size is a great influencer in the workability of concrete.
For the same volume of aggregate in concrete. Rounded aggregates give higher workability than angular and flaky aggregates. In other words, a reduction in the total specific area of aggregates gives rise to higher workability
For the same W/C ratio
- The rounded and cubicle shaped type aggregate required less amount of cement paste for lubrication and offer higher workability of concrete
- Angular and rough aggregate required a large quantity of paste for lubrication so alternatively workability educes also increase elongation and flakiness of aggregate which reduce workability
Surface Texture of Aggregates
- It is simple math that for the same quantity of aggregate, the total surface area of rough aggregate is higher than the surface area of smooth aggregate
So less amount paste required for smooth aggregate so it gives better workability compared to rough aggregate
But smooth texture aggregate give low internal particle friction resistance
For the same volume of aggregate in concrete. Rounded aggregates give higher workability than angular and flaky aggregates. In other words, a reduction in the total specific area of aggregates gives rise to higher workability
Grading of aggregate
A well-graded aggregate means a lower amount of voids in concrete so when total voids are loess then it provides the good effect of lubricating
In sort better grading = Fewer voids = high workability
Use of admixture
Read Already published articles about admixture like
what is admixture? | Use of admixture | Types, classification with advantage and disadvantage so must read that article
Time
The workability of green/fresh concrete loses their workability with the passing of time after mixing of materials because of moisture loss happen due to absorbed by aggregate or evaporation and also consumed during hydration of cement
I try to explain in a mathematical way by the example of slump test results like
If your concrete mix has a slump of 125 mm then it may lose a 50 mm slump means 40% slump loss in the first one hour
In compacting factor, concrete workability decreases about 0.10 during the first one hour from mixing materials
Fresh concrete is more workable and its workability reduces as time passes due to the loss of moisture from the concrete
Temperature
The effect of temperature on the workability of concrete is something like this way
Workability is also affected by temperatures because in higher temperature water losses also high means W/C ratio decrease also concrete turn in less lubrication in sort with a degree of temperature workability also changes
Properties of Cement
The properties of cement affect the workability of concrete to a great extent. A rapid hardening cement will reduce the workability as compared to OPC because the former hydrates more rapidly than the later
Environmental Conditions
The workability of concrete gets affected by environmental conditions.
In hot weather conditions, more water is required to maintain the workability of concrete.
The amount of mixing water to bring about a certain change in the workability increases with temperature
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
