Construction aggregates are classified based on grades as well-graded, poorly graded, and gap graded. Grading is the representation of the particle size in a sample of aggregates. Good grading of aggregates implies that a sample of aggregate contains all the standard fractions in the required proportions.
The principle of grading 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 the 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
1. Well-Graded Aggregates in Construction
An aggregate sample is said to be well-graded if it has a good representation of particles of all sizes. It will help the concrete mix to acquire minimum voids and will require a lesser amount of cement to fill up the voids. This will finally lead to the economy. Well, graded aggregates increase the particle surface area. This is the most preferred aggregate 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
2. Poorly Graded Aggregates
In the case of poorly graded aggregates, all the aggregates are of the same size. This produces a large volume of voids. This mix will demand a large amount of cement.
3. 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
- The lower amount of cement and the lower water-cement ratio is demanded
- Gap-graded aggregates will have a lower surface area, this is due to the high percentage of a coarse aggregate percentage of fine aggregates
Limitations of Gap-Graded Aggregates
- The mix of gap-graded aggregates is more prone to segregation
- The mix will bring in the anticipated workability