As a builder, you always need a concrete mixture that is strong and easy to apply. For this, you have to know about the workability of concrete.
Therefore, we have explained all the factors that can affect concrete workability with a standard mix-ratio. Moreover, you will also see several tests to check a mixture.
What is Workability of Concrete?
Workability of concrete means how easily you can mix, place and consolidate freshly prepared concrete. Suppose you are doing the job of construction. So in this case, concrete workability will be your convenience to make different structures without losing its strength.
If a concrete has good workability, then workers can easily pour it into molds and also spread around steel bars & corners. Major things which decide the workability of concrete include ratio of water, cement and sand etc.
Factors Affecting Workability of Concrete
Ratio of Cement & Water
You have to add a balanced amount of water and cement in a mixture to increase its workability. Actually, when you add more water in the mixture it becomes more fluid and workable. Especially, when the space is tight or the design is complex.
On the other hand, less water based mixtures may create many problems. But it is used to make water tanks, high rise buildings etc.
Aggregation of Size and Shape
Well, aggregates are stones that are mixed into concrete. If you use bigger and flat stones they can create more empty spaces. And you will find it difficult to work with. But when you add small rounded stones they will make the mixture smooth and durable.
Admixtures in Concrete
If you want to make the mixture more workable then you can use special ingredients. Some common additives are water reducer, plasticizers and superplasticizers. When you put this type of ingredients into a mixture they reduce the need of water.
Sand & Cement Ratio
A higher cement and sand ratio means you will get more paste in the concrete. Which improves the workability of your mixture. On its opposite side, a low ratio can make the mix hard and difficult to handle.
Mixing Method of Concrete
When you mix concrete properly, it means cement, sand, stones, admixtures and water are spread out evenly. If you mix insufficiently then the mixture can become dry and hard to handle.
Standard Concrete Mix Ratio
You can read this table if you want to make a balanced and strong concrete mixture that can pass all tests.
| Factors | Workability | Best Ratio |
| Water/Cement Ratio | More water makes better flow | 0.4 to 0.6 |
| Aggregate | Less cement means less lubrication | 4:1 to 6:1 |
| Aggregate size | Bigger size needs less mixture | 10 mm – 20 mm |
| Aggregate Shape | Round shapes make a good paste | Rounded |
| Admixtures | Help you to spread more cement | 0.2% to 2% |
| Time & temperature | Warmer and more time make cement set faster | 10°C to 25°C |
Types of Workability of Concrete
Unworkable Concrete
As its name shows, this type of concrete is not easy to apply. It is caused when the amount of water is low and cement is high in a mixture. But, this concrete is still used in large and thicker concrete frames. For example, in construction of dams, support pillars and bridges.
Medium Workable Concrete
Well, you can get this when you add a balanced amount of water, cement and admixtures. So, it is easy for you to handle as compared to unworkable concrete. Therefore, it is commonly used at construction sites. For instance, you can use it to make beams, floors, walls and foundations.
Highly Workable Concrete
This is the mixture with excess water, which makes it easy to use and spread. But it needs extra care so that the compound does not get segregated. You can use it in curved designs and tight spaces.
It is also suitable for you if you want to pump concrete on a high rise building. Furthermore, in case of under water construction and Self-Consolidating Concrete it works best.
Workability Test of Concrete / Measurement of Workability
How to check the workability of concrete? You can check the workability of the concrete mixtures via these common tests.
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Slump Test of Concrete
The slump test is the most common method that you can use to measure workability of concrete. Basically, you place a cone-shaped mold on the ground and fill it with fresh concrete. After that, you lift the cone straight up if the concrete settles down easily it is more workable.
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Compaction test of concrete
In this test, you take a specific amount of fresh concrete and fall it into the cylinder. You have to fall from a certain height and observe its behaviour. If more concrete fits into the cylinder then it is more softer and workable. And less concrete represents less workability.
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Flow Table Test of Concrete
You can see a cone shaped mould and a flat metal table in this test. You can use this cone in the same way as in the slump test but the difference is the flow table. In this case, you pour the concrete on the table from the cone and check its diameter. Therefore, if it spreads more on the table you will find the mixture more workable.
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Vee-Bee Test of Concrete
This test checks how fast the fresh concrete can fill and settle down into a certain shape. If your concrete is more workable and smooth then it will be filled fastly. But if it takes more time then it is less workable.
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Kelly Ball Test of Concrete
Do you want to check the workability in the fastest manner? Well, you can use the Kelly Ball test for this. Basically, this test includes a heavy metal ball (30 pounds and 6 inches wide) that is shaped like a half sphere.
You can calculate the workability by depth of the ball. So, if the ball sinks deeper into the mixture then it is more good to use. On the other hand, when you see it does not go down easily then it is harder.
Workability of Concrete Can be Improved By
- You can increase the water ratio according to the cement.
- If you add more rounded and smooth aggregates it can be more durable.
- You should increase the mixing time. For this, make sure that each component of concrete is squashed well.
- The temperature also affects workability so you can increase its temperature while mixing.
- Non-porous aggregates are more suitable to enhance the flow so you can add them.
- Addition of admixture like plasticizer or water reducer can make concrete more long lasting.
What is the Characteristic Strength of Concrete?
Characteristics strength tells you the minimum strength that you may expect from a mixture. Well, as an engineer this strength test helps you to trust a mixture’s quality.
For this, you have to test many samples. This test gives you the exact result after 28 days on 100 cubes of dried concrete. So, when 95% of cubes meet the average value of the test (20 MPa) then your mixture is strong enough.
Final Thoughts
Finally, we can say that the workability of concrete is the main thing that matters the most for you. But you must adjust it according to the needs of your project.
So, make sure you add a balanced amount of each component. And test it before usage.
FAQs
Which Chemical Admixtures are Used in Concrete?
Commonly, you can find admixtures like plasticizers, superplasticizers, retarders, accelerators and air entraining agents.
How to Mix Concrete by Hand?
You have to combine all dry materials then make a well in the center. After this, add water and mix it until you get a workable consistency.
How Higher Workability of Concrete is Required?
Usually, for higher workability, a slump value between 100 mm to 180 mm is required.
