Bulking and Fineness of Aggregates

Bulking is the increase in the volume of fine aggregate due to the presence of moisture. It is expressed as a percentage increase in volume. The bulking of fine aggregate is a significant factor that affects the volume of concrete produced. The fineness of aggregates is also an important factor that affects the properties of concrete. The following is a detailed explanation of the relationship between bulking and fineness of aggregates:

Bulking and Fineness of Aggregates

Bulking and fineness are two different properties of aggregates. However, there is a correlation between them. Fineness refers to the grain size distribution of aggregates. The fineness of aggregates is determined by the size of the sieve opening through which the aggregates pass. The fineness of aggregates is expressed in terms of the percentage of weight retained on each sieve. The fineness of aggregates is classified into four categories, namely:

Coarse aggregates: retained on 4.75 mm sieve
Fine aggregates: pass through 4.75 mm sieve and retained on 75 microns sieve
Very fine aggregates: pass through 75 microns sieve and retained on 45 microns sieve
Ultra-fine aggregates: pass through 45 microns sieve

Bulking is the increase in the volume of fine aggregate due to the presence of moisture. It occurs due to the formation of a film of water around each particle of fine aggregate, which reduces the effective specific gravity of the aggregate. The amount of bulking depends on the moisture content, shape, and surface texture of the aggregate. The bulking of fine aggregate is expressed as a percentage increase in volume.

Relationship between Bulking and Fineness

The fineness of aggregates affects the amount of bulking. The following are the effects of fineness on bulking:

Decreases with Fineness: The amount of bulking decreases with the fineness of aggregates. This is because fine aggregates have a higher surface area than coarse aggregates, which results in a greater amount of water film formation. However, the water film thickness is less in fine aggregates, which reduces the amount of bulking.

Increases with Fineness: The amount of bulking increases with the fineness of aggregates. This is because fine aggregates have a higher surface area than coarse aggregates, which results in a greater amount of water film formation. The water film thickness is also more in fine aggregates, which increases the amount of bulking.

Conclusion

In conclusion, the relationship between bulking and fineness of aggregates is complex. The amount of bulking depends on the moisture content, shape, and surface texture of the aggregate. The fineness of aggregates affects the amount of bulking, and it can either decrease or increase the amount of bulking depending on the size of the aggregates. Therefore, it is important to consider both bulking and fineness of aggregates when designing concrete mixes.