Workability of concrete
The ability of raw or fresh concrete mixture to be worked is referred to as workability of concrete. To put it another way, workability refers to how easy it is to place something, and “workable concrete” refers to concrete that is both easy to place and easy to compact without causing any segregation in the mix.
Concrete has an important quality known as workability, which is closely connected to both strength and compaction. Not all varieties of concrete are designed to have the same level of workability. When compared to a bulk concrete body, a thin portion that is inaccessible or a substantially reinforced piece requires a greater degree of workability. As a result, we are unable to establish a universally applicable workability criteria for casting works.
Both workability and compaction are extremely closely related to one another.
How does concrete workability affect the finished product?
The Workability of Concrete determines whether the finished product can be laid without any segregation or if the entire mass of concrete is required to be compacted. Once it is compacted, it usually takes time for the mass of wet concrete to dry.
10 Factors affecting Workability of Concrete
- Cement content in concrete & its properties
- Water content of concrete
- Mix proportions of concrete
- Aggregate Grading (Size Distribution)
- Physical properties of aggregates (Shape, Surface Texture, Porosity etc.)
- Use of admixtures in concrete
- Use of supplementary cementitious materials
- Ambient Temperature
- Humidity of the environment
Factors to determine Workability of Concrete:
- The mass density of the mixture
- Presence of water in the mixture
- The thickness of the grout
- Presence of water in the grout
Some other essential properties that affect the Workability of Concrete:
- Baking temperature of the mix
- Surface, mixing, and pumping of the concrete
- Pressure of the mix
- Compression of the mix (Mode of compaction)
- Pour (radial pouring and elliptical pouring)
- Quality of the grout
Types of workability of Concrete
There are two types of concrete used for the construction of any structure- Medium Workable concrete and Highly Workable Concrete. Unworkable Concrete is avoided.
Unworkable concrete, often known as hard concrete, has very little water. Hand mixing such concrete is difficult. This kind of concrete has highly segmented aggregates. Additionally, keeping the consistency of the concrete mix is difficult.
Medium workable concrete
The majority of construction work is done using this type of concrete. This form of concrete is quite simple to mix, transport, pour, and compact, and it does so without segregation or loss of homogeneity.
Medium workable concrete has a water-cement ratio of 0.4 to 0.55. This type of concrete has minimal reinforcing
High workable concrete
This kind of concrete is exceptionally simple to mix, transport, lay, and compress due to its high water content. When adequate concrete compaction is not possible, it is used for concreting. The disadvantage of using this kind of concrete is that it is prone to segregation and homogeneity loss.
Factors Influencing Concrete Workability
Workability and other attributes of any concrete mix design are affected by a variety of variables, including the proportions and characteristics of ingredients as well as the properties of admixtures. The following are some of the elements that contribute to workability:
If there is a larger percentage of cement or cementitious ingredients, the concrete will typically have a higher strength, and if there is the appropriate quantity of water, there will be more paste on the surface of the aggregates, making the consolidation process simpler and improving the finish.
If there is not enough water for adequate hydration, the mix will not be helpful, which will make it difficult to put and complete. This will result in poor strength development. It is possible that adding an excessive amount of water may boost workability since this will make it simpler to position and consolidate. However, because of the potential for a negative influence on segregation, finishing processes, and ultimate strength, it is imperative that this issue be treated with extreme caution.
Size of Aggregate
If the aggregate size is smaller, it indicates there is greater surface area, which necessitates more water and cement paste, or vice versa. If the size of the aggregate is big, then it will have pores that will enable water to readily flow through it, which will result in an improvement in the workability of the concrete. More cement paste is required to cover the whole of the aggregate surface area whenever the surface area of the aggregates rises. Therefore, mixtures that include smaller particles are more difficult to deal with in comparison to mixes that contain aggregates of a higher size.
Shape of Aggregate
Because there is less resistance to friction when round aggregates are used, elongated, angular, and flaky particles are more difficult to mix than round aggregates. Aggregates that are spherical instead of elongated or irregular in form have a smaller surface area than other types of aggregates. It will be necessary to use less water to get the same workability in the concrete. Because of its round composition, river sands are often used in the concrete.
If the shape of the aggregate is of irregular shape, which is due to which the load is distributed unevenly. This will affect the working of concrete.
Grading of Aggregate
If the grading of the aggregate is not perfect, then the aggregate will get heavy, and the actual grit will be less than the desired amount. As the aggregate, becomes heavy, it tends to curl. Hence, high gradation reduces the volume of the aggregates. If aggregates are well graded, the void content will be lower and the workability will be better, thus the aggregate should be well-graded as much as feasible.
The surface of the material having a glossy or rough texture will affect the smoothness of the concrete. The surfaces of the aggregate usually have irregular shapes, coarse, medium and fine surfaces.
If the aggregates’ surfaces are smooth or have a glassy texture, it will reduce the frictional resistance and also the surface area and have greater workability.
Amount of Cement
The ratio of fine aggregates to coarse aggregates in relation to cement amount is determined by the mix proportion of concrete. More cement paste will cover the aggregate surface and fill voids if the cement amount is increased by increasing the paste’s fluidity.
Also, more amount of water is required to increase of mix proportion of concrete, hence increasing the workability of concrete.
Either on purpose or unintentionally, several kinds of admixtures have the effect of changing the workability of freshly mixed concrete.
Surfactants, such as superplasticizers, lessen the attraction between cement and aggregate particles. This makes it possible for mixes to be quite flowable, despite the fact that they do not suffer from the strength-depleting and segregation-causing effects that are caused by an excessive amount of water.
Depending on the type of admixture used, it can increase or decrease the workability of concrete significantly. Plasticizers and superplasticizers (also called water-reducing concrete admixtures) improve the workability of concrete even when the water/cement ratio is low.
The workability of concrete is also substantially improved by using an air-entraining admixture. It works by producing a large number of air bubbles that serve as rollers between aggregate particles, decreasing friction between them.
Additives / Supplementary Cementitious Materials
Metals are largely permeable to Cement and Aggregate in nature, which can be converted into acidic or basic which result in the high workability of concrete, or such other components such as silica and lime can be added to achieve specific water absorption capacity, thereby helping to reduce the rate of hardening of the concrete.
Supplementary cementitious agents include fly ash, fibres, silica fume, and slag cement. The addition of fly ash to concrete lowers the quantity of water that must be used to attain the same level of workability or slump value. This improves the concrete’s workability.
The workability of concrete refers to the ease with which it can be mixed, placed, compacted, and finished. Workability is a function of the water-cement ratio, aggregate type and size, and the age and curing conditions of the concrete. Improving workability can be achieved by adding water, using a plasticizer or superplasticizer, or by adding air entrainment. However, too much water can lead to lower strength, increased shrinkage, and increased segregation of the aggregate.