Concrete workability is counted as one of the physical parameters of it which determines the strength, durability, cost of labor and appearance of the finished product. There are various materials that affect the workability of concrete such as cement concrete, water content, sand and aggregate properties like size, shape, grading, mix design ratio and use of admixtures.
The workability of concrete depends on the convenience with which it is mixed and sent to the construction site, placed in forms and compacted. Concrete is considered to be workable when it is easily placed and compacted without segregation. Unworkable concrete requires more effort to be compressed properly.
The following are the factors that affect the workability of concrete
1. Water content
Water content is one of the most important factors of workability. The water content refers to the water-cement ratio. A small water-cement ratio indicates a high level of cement which is responsible for poor workability. Again, an increased water-cement ratio means better workability. This is why it is vital to maintain an optimum water-cement ratio to balance the workability and strength of the concrete.
2. Size of aggregate
The surface area of aggregates is completely dependent on the size of aggregates. For a unit volume of aggregates of larger size, the surface area is less in comparison with the same volume of aggregates of smaller size. The demand for cement quantity increases with the increase in the surface to apply the paste on the entire surface of aggregates. Therefore, the smaller size of aggregate with equal water content is less workable than the large size aggregate.
3. Shape of aggregate
The shape of the aggregate also influences the workability of concrete. It is evident that the round shaped aggregate is easy to mix than the aggregates with elongated, angular and flaky shapes due to poor frictional resistance. The surface of round aggregate also has less area compared to the surface of elongated or irregular shaped aggregates. This results in a less requirement of water for the same workability of concrete. This is the reason why sands are usually chosen for concrete as they are of the round shape.
4. Grading of aggregate
Well-graded aggregates have the tendency to fill up voids and achieve workability. A better grading indicates fewer voids and the availability of excess paste for an improved lubricating effect. The excess amount of paste makes the mixture cohesive and prevents segregation from increasing the workability in the result.
5. The surface texture of aggregates
A smooth surface of aggregates ensures higher workability than rough and uneven textured aggregates. This is because roughly textured aggregates have a high friction and segregation tendency. The non-saturated aggregates require more water than non-absorbent aggregates which are more workable.
6. Use of admixtures
Admixtures also have the capability to increase workability. Sometimes admixtures are used only to fulfill the purpose of increasing workability and some admixtures improve workability to increase as a side effect of its main purpose.
High temperature decreases workability and also increases slump loss. Concrete slump loss is less affected by the weather in stiff mixes as such mixes do not get influenced by a change in water content.
Now when you know about the elements that could affect concrete workability let’s have a look at the ways you can improve it;
- Increasing water-cement ratio
- Using round shaped smooth aggregate
- Increasing the mixing temperature
- Using nonporous and saturated aggregate
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