Grading is the representation of the particles size in a sample of aggregates. Good grading of aggregates implies that a sample of aggregate contains all the standard fraction in the required proportions.
Grading of Aggregates for Construction
- The principle of grading of aggregates is that the smaller the sized particles the more they fill the voids between the large sized particles.
- Proper grading of aggregates improves the workability, uniformity, homogeneity, and finishing qualities of concrete mix.
- A good grading system will help in ensuring strength, durability etc of the concrete.
Classification of Aggregates Based on Gradation
Based on gradation, the aggregates can be classified as:
- Poorly Graded Aggregates
- Well Graded
- Gap Graded
Well Graded Aggregates in Construction
An aggregates sample is said to be well graded if it has a good representation of the particles of all the sizes. It will help the concrete mix to acquire minimum voids and will require the lesser amount of cement in order to fill up the voids. This will finally lead to the economy. Well, graded aggregates increase the particle surface area. This is most preferred aggregates in construction.
Uses of Well Graded Aggregates
- Concrete Works - R.C.C and P.C.C Works
- Pavement Construction
- Foundations Works
- Full Compacted Concrete Manufacture
Poorly Graded Aggregates
In the case of poorly graded aggregates, all the particles are of the same size. This produces a large volume of voids. This mix will demand a large amount of cement.
Gap Graded Aggregates
These are a sample of aggregates where one or more sizes of aggregates are omitted. These are generally used for architectural or aesthetic purposes.
Uses of Gap Graded Aggregates
- Sand required will be around 26% and this will be 40% in the case of well-graded aggregates
- Lower amount of cement and lower water cement ratio is demanded
- Gap graded aggregates will have a lower surface area, this is due to high percentage of coarse aggregates and low percentage of fine aggregates
Limitations of Gap Graded Aggregates
- The mix of gap graded aggregates are more prone to segregation
- The mix will bring in the anticipated workability