22.2.4. Shape of aggregates

Aggregates which happen to fall in a particular size range may have rounded, cubical, angular, flaky or elongated particles.

Aggregates can come in different shapes depending on how they were formed. The main types mentioned are rounded, cubical, angular, flaky, and elongated particles. Each shape affects how the aggregate interacts in pavement applications. For example, rounded aggregates are often smoother and can interlock less effectively compared to angular aggregates, which have more edges to create a stronger bond.

Imagine trying to build a tower out of different types of blocks. If you use perfectly rounded balls, it would be hard to stack them firmly without them rolling away. However, if you use angular blocks, they fit together more tightly, making a more stable structure. Similarly, angular aggregates provide better interlocking in pavement.

It is evident that the flaky and elongated particles will have less strength and durability when compared with cubical, angular or rounded particles of the same aggregate.

Flaky and elongated aggregates often lead to weaker pavement because their shape does not allow for effective interlocking and bonding with the binding materials like cement or asphalt. When these shapes are used in construction, they contribute less to the overall stability and durability of the pavement compared to their cubical, angular, or rounded counterparts, which fit more securely together.

Think about a puzzle. If some pieces are long and thin (like elongated particles), they don’t fit well with the others and may create gaps. Flatter pieces (like flaky particles) can slide around easily, making the puzzle less stable. In the same way, using the right shapes in aggregates fills in gaps and creates a stronger pavement.

Hence too flaky and too much elongated aggregates should be avoided as far as possible.

In pavement construction, it is crucial to select aggregates that are not overly flaky or elongated. The recommendation is to steer clear of these shapes to ensure the strength and durability of the pavement. This selection process is vital, as the integrity of the pavement directly affects its lifespan and the safety of vehicles using it.

Consider a car parked on a soft surface like sand. If the sand is loose (representing flaky aggregates), the car would sink, and the foundation would be unstable. In contrast, a firm and stable surface—like gravel with proper shapes—allows the car to sit securely without any sinking, much like using the right aggregate shapes creates a solid pavement.

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