The correct answer is option 'C': Flaky aggregates.

Flaky aggregates are one of the factors that can significantly affect the durability of concrete. These aggregates have a flat and elongated shape, with a high surface area compared to their volume. This shape is detrimental to the strength and durability of concrete due to the following reasons:

1. Poor interlocking: Flaky aggregates do not interlock well with each other or with the cement paste, leading to reduced bond strength. This weak interlocking results in decreased load-bearing capacity and increased vulnerability to cracking and structural failures.

2. Increased water demand: Flaky aggregates have a higher water demand compared to other types of aggregates. This increased water demand leads to a higher water-cement ratio, which negatively affects the strength and durability of concrete. The excess water also contributes to increased shrinkage and permeability, making the concrete more susceptible to damage from environmental factors such as freeze-thaw cycles and chemical attack.

3. Reduced workability: Flaky aggregates tend to have a rough surface texture, which reduces the workability of the concrete mix. Workability refers to the ease with which the concrete can be placed, compacted, and finished. Poor workability can result in inadequate compaction, leading to voids and weak zones within the concrete.

4. Increased segregation: The flat and elongated shape of flaky aggregates makes them prone to segregation during the mixing, transportation, and placing processes. Segregation occurs when the different components of the concrete mix separate, with the heavier aggregates settling at the bottom and the lighter cement paste rising to the top. This non-uniform distribution of materials further compromises the strength and durability of the concrete.

5. Greater susceptibility to wear and abrasion: Flaky aggregates have a higher susceptibility to wear and abrasion compared to rounded or irregular aggregates. This is because their flat and elongated shape makes them more prone to breaking and chipping under applied loads, leading to loss of concrete volume and reduced durability.

In summary, the use of flaky aggregates in concrete can have detrimental effects on its durability. These aggregates inhibit proper interlocking, increase water demand, reduce workability, promote segregation, and increase susceptibility to wear and abrasion. It is important to carefully select aggregates with favorable shape characteristics to ensure the desired strength and durability of concrete structures.