Factors affecting concrete

The main factors affecting the workability of concrete are given below.

Water content
Mix the proportions.
The size of collections

Use of compounds
Form of Collections
Classification of Collections

1. Water content: Water content in a given volume of concrete will have a significant influence on the workability. The higher the water content per cubic metre of concrete, the higher will be the fluidity of concrete, which is one of the important factors affecting workability. However, increasing the water content must be the last option to be taken for improving the workability. More water can be added, provided a correspondingly higher quantity of cement is also added to keep the water–cement ratio constant, so that the strength remains the same.
2. Mix proportions: Aggregate–cement ratio is an important factor affecting workability. The higher the aggregate–cement ratio, the leaner is the concrete. In the case of lean mix, less quantity of paste is available for providing lubrication and, hence, the mobility of aggregate is restrained. On the other hand, in the case of rich concrete with lower aggregate–cement ratio, more paste is available to make the mix cohesive and fatty to give better workability.
3. Size of aggregates: The bigger the size of aggregates, less quantity of water and paste will be required. Hence, for a given quantity of water and paste, bigger size of aggregates will give greater workability. The above will be true within certain limits.
4. Shape of aggregates: The shape of aggregates greatly influences the workability. Angular, elongated or flaky aggregates make the aggregate very harsh when compared to round- or cubical-shaped aggregates. Contribution to greater workability of rounded aggregates is due to the fact that for a given volume or weight it will have less surface area and less voids than angular or flaky aggregates.
5. Grading of aggregates: This is one of the factors which will have maximum influence on workability. A well-graded aggregate is the one which has least amount of voids in a given volume. Other factors being constant, when the total voids are less, excess paste should be available to give better lubricating effect.
6. Use of admixtures: Of all the factors, which affect workability, the most important factor is the use of admixtures. Admixture is defined as a material, other than cement, water and aggregates, that is used as an ingredient of concrete and is added to the batch immediately before or during mixing. Plasticizers and superplasticizers are admixtures that greatly improve the workability many folds. The use of air entraining agents reduces the internal friction between the particles and gives easy mobility to the particles. Similarly, the fine glassy pozzolana materials, in spite of increasing the surface area, offer better lubricating effects for increasing the workability.