The workability of concrete is extremely important, as is the compressive strength of the concrete. If the concrete is not viable, the construction work will be very difficult. It is very difficult to process concrete with low workability. Furthermore, this can lead to quality issues during construction.
Additionally, workable concrete allows for easier concrete .
Due to the low workability of concrete, the following problems may occur
- Poor compression
- Honeycomb formation
- Difficulty in concrete flow in areas with higher reinforcement density
- Difficulties in handling concrete on the construction site
For works to be carried out without major difficulties, workable concrete is essential. Therefore, it is very important to study the factors that affect the workability of concrete.
Factors affecting the workability of concrete
- Water-cement ratio
- Mixing proportions
- Aggregate size
- Shape of the aggregates
- Classification of aggregates
- Surface texture of aggregates
- Influence of clay content
- Effect of recycled fine aggregates
- Use of additives
- Use of additional cementitious materials
- Time
- temperature
Water-cement ratio
The water-cement ratio is an indicator of the water content added to a concrete mix. The water-cement ratio specified in the recipe is kept constant for a specific concrete mix. This means that a constant water content is added to the concrete mix.
The more water there is in the concrete, the easier the concrete will be to process. However, we cannot add as much water as we want. Water should only be added as directed in the mixture.
Mixing proportions
The ratio of aggregates to cement influences the workability of concrete. As the ratio of aggregates to cement increases, there is less cement paste. Therefore, processability is reduced.
Reducing the aggregate-cement ratio leads to an improvement in the workability of concrete. Furthermore, this ratio is controlled by the composition of the mixture to achieve the required concrete consistency.
Aggregate size
Aggregate size has a significant influence on the workability of concrete.
The larger aggregate has a larger surface area. However, if we consider the same volume of aggregates, the sample with smaller aggregates has a greater total surface area than the sample with larger aggregates.
With smaller aggregates, more water is needed to make the concrete workable. With larger aggregates, less water is also needed to make the concrete workable.
Shape of the aggregates
The shape of the aggregate has a significant influence on the workability of concrete. The following types of aggregates can be observed. Additionally, the Aggregate Testing article discusses available tests for aggregates.
- Angular unit
- flaky aggregate
- Elongated aggregate
- Rounded aggregate
- Underground aggregate
- Cubic aggregate
In general, round aggregates are easier to mix compared to other types of aggregates. Irregular types of aggregates are more difficult to process for the reasons mentioned above.
Classification of aggregates
Well-graded aggregates guarantee better workability of the concrete.
When aggregates are well graded, voids in the concrete are minimal. This improves the workability of the concrete.
Additionally, reducing voids in the concrete prevents the concrete from separating.
Surface texture of aggregates
Aggregates with a smoother surface produce a more workable concrete mix than those with a rough surface.
A rough surface creates more friction, which reduces workability.
Furthermore, when the surface structure is smoother, water absorption is less and workability is comparatively improved.
Influence of clay content
In ancient construction, clay was added to concrete to replace cement. This reduced construction costs.
When building brick walls, plastering can be done with the addition of clay.
The illustration, taken from a technical document, shows the variation in concrete consistency and setting times.
As can be seen in the figure above, the clay content of concrete has a significant impact on its consistency.
Effect of recycled fine aggregates
Recycled fine aggregates are produced in the testing laboratory by breaking down concrete cubes.
This material is not commonly used in construction.
Based on one of the studies carried out on the topic, they determined the following relationship.
Additions
There are different types of concrete additives and their intended use is also diverse.
There are additives that improve the workability of concrete without adding water to the concrete.
This is a great advantage because good workability with lower water content allows the concrete's strength to be increased.
For example, if we use the control mix for certain water-cement ratios, we obtain some workability. If we add a water-reducing additive without changing the water-cement ratio, we will obtain greater workability than the control mixture.
This allows us to reduce the water content to adapt to processability. If we use the same cement content, the water/cement ratio will decrease. Furthermore, the strength of the concrete increases.
Furthermore, by adding water reducer we can reduce the water content as described above. This way, we can reduce the cement content to maintain the same water/cement ratio. This does not change the strength of the concrete.
In short, when we reach the exact inflection point, we can control the workability of the concrete with additives.
Use of complementary cementitious materials
We use fly ash , GGBs silica powder etc. are used as cementitious materials in the production of concrete.
The article Cement and Cement Additives Discuss the materials added to concrete.
They are added to concrete as a substitute or additive.
For example, when we make concrete for thick layers of concrete, fly ash is added to the concrete to reduce the heat generated during the hydration process.
These materials have a greater surface area compared to cement and improve the reactivity of concrete.
By adding similar additives to cement, the workability of concrete can be improved.
Time
The influence of time on the workability of concrete is well known.
No matter what we do, we cannot control the decline in concrete's workability.
With conventional mixing, concrete slump decreases quickly.
However, adding additives like Flowing Agent can maintain the fall for a certain period of time. It may be enough to continue construction.
After a certain period of time, the value begins to drop rapidly despite the addition of an additive.
temperature
Increasing the temperature in concrete increases the rate of evaporation of water in the concrete mix. This leads to reduced processability.
Method to Limit Concrete Temperature is an article that explains the procedure to reduce the temperature rise in concrete. Additionally, this article is not directly related to this topic.
Ambient temperature also directly influences the workability of concrete. As the temperature increases, evaporation increases.
Methods for measuring concrete workability
Measuring methods can be classified according to the type of concrete present.
- Normal concrete
- Self-compacting concrete
The above classification was made to define the abatement tests.
Normal concrete
For normal concrete, we check slump, which can be seen as a workability indicator to ensure the condition of the concrete before concreting.
The Concrete Testing article provides detailed information about concrete testing. You can find more information about drop testing here.
Self-compacting concrete
Numerous tests are available to check the consistency of concrete. The following table lists test details.
| Fill test | Passing the skills test | Segregation resistance test |
| Soil Drop Test | J ring test | V funnel in T 5 protocol |
| T 50cm drop | L-box test | GTM Screen Stability Test |
| V funnel test | U-Box Test | |
| Orimet | Box fill test |
