Short Answer:

The shape and texture of aggregates refer to their outer appearance and surface feel. Aggregates can be angular, rounded, flaky, or elongated in shape, and their texture can be smooth or rough. These physical properties play an important role in how concrete behaves during mixing, placing, and hardening.

In concrete, angular and rough-textured aggregates form stronger bonds with cement, increasing strength, but may reduce workability. Rounded and smooth-textured aggregates improve workability but may lower bonding strength. So, choosing the right shape and texture depends on the type of construction and strength needed.

Detailed Explanation:

Shape and texture of aggregates

The shape and texture of aggregates are two important physical characteristics that affect the performance of concrete. These properties influence the workability, strength, and durability of the concrete mix. Understanding the effect of shape and texture helps engineers make better decisions during the design and selection of materials.

Shape of Aggregates:

The shape of aggregate particles can be categorized as:

• Rounded: Naturally formed by water, like river gravel. They have smooth surfaces and are easy to mix.
• Angular: Sharp edges and corners, usually from crushed stones. They create strong bonds with cement.
• Flaky: Thin and flat particles with less thickness compared to other dimensions.
• Elongated: Long and narrow particles.
• Flaky and elongated: A mix of both, generally avoided due to poor strength performance.

Texture of Aggregates:

Texture means the surface feel of the particles:

• Smooth-textured aggregates: Have polished or glassy surfaces; they don’t bond strongly with cement.
• Rough-textured aggregates: Have irregular, gritty surfaces; they develop strong mechanical bonds with the cement paste.

Effect on Concrete:

1. Workability:
   Workability means how easily concrete can be mixed, placed, and compacted. Rounded and smooth aggregates improve workability because they roll over each other easily. In contrast, angular and rough aggregates reduce workability but increase bonding.
2. Strength of Concrete:
   Angular and rough aggregates form strong interlocking and good bonds with cement paste. This improves the strength and stiffness of concrete. Rounded or smooth aggregates provide lower strength due to poor bonding.
3. Cement Requirement:
   Rough and angular aggregates need more cement and water to coat their surfaces and fill voids, which can increase the cost. Smooth aggregates need less cement and water.
4. Durability:
   The bond between aggregates and cement affects how well the concrete holds up over time. A strong bond (from rough, angular aggregates) helps resist cracks and weathering better than smooth, rounded aggregates.
5. Segregation and Bleeding:
   Poorly shaped aggregates, especially flaky and elongated ones, can lead to segregation and uneven distribution of materials, which affects the concrete quality. Rounded aggregates are less likely to segregate.
6. Compaction and Finish:
   Smooth and rounded aggregates give a better surface finish but may compromise strength. Angular ones give rough finishes but improve stability.

In practical construction, engineers aim to use a mix of aggregate shapes to balance workability and strength. For example, a combination of rounded and angular aggregates may be used in concrete to get both easy mixing and good strength.

Conclusion:

The shape and texture of aggregates have a direct effect on the concrete’s workability, strength, and durability. Angular and rough-textured aggregates provide better bonding and strength, while rounded and smooth aggregates enhance workability. Selecting the right type based on construction needs helps achieve better performance and longer life of concrete structures