Effect of Flakiness of Aggregate on the Strength of Concrete

Flakiness of aggregate refers to the condition where the majority of particles have a thickness less than their other two dimensions. This characteristic can have a significant effect on the strength of concrete in which it is used. Let's discuss this in detail:

1. Definition of Flakiness
Flakiness is a measure of the flatness or elongation of the aggregate particles. It is expressed as a percentage by weight of particles whose least dimension (thickness) is less than 0.6 times their mean dimension.

2. Decreases Strength
The flakiness of aggregate has a detrimental effect on the strength of concrete. When flaky aggregates are used, the bond between the aggregate particles and the cement paste is reduced. This leads to a decrease in the overall strength of the concrete.

3. Reduced Bonding
Flaky aggregates have a larger surface area compared to their volume, which results in a reduced bonding area with the cement paste. As a result, the interlocking between the aggregate particles and the paste is weakened. This reduces the ability of concrete to resist compressive forces, ultimately leading to a decrease in strength.

4. Poor Interlocking
Flaky aggregates tend to have irregular shapes and sharp edges. These irregularities prevent the aggregates from fitting together tightly, resulting in poor interlocking. As a result, the concrete becomes more susceptible to cracking and deformation under load, leading to reduced strength.

5. Increased Porosity
The presence of flaky aggregates in concrete also increases its porosity. The voids between the irregularly shaped particles are not effectively filled with cement paste, leading to increased permeability. This porosity allows moisture and harmful substances to penetrate the concrete, further weakening its structure and reducing strength.

6. Decreased Workability
Flaky aggregates have a higher surface area, which tends to absorb more water from the mix. This results in a decrease in workability of the concrete. Poor workability can lead to inadequate compaction, which in turn affects the strength and durability of the concrete.

In conclusion, the flakiness of aggregate has a significant negative impact on the strength of concrete. It reduces the bonding between aggregate particles and the cement paste, weakens interlocking, increases porosity, and decreases workability. Therefore, the correct answer is option 'C' - flakiness decreases the strength of the concrete.