Aggregate Shape – which is unsuitable for high-strength concrete and tensioned pavements? Identify the type of aggregate that is generally not suitable for producing high-strength concrete and for pavements subjected to tensile stresses.

Introduction / Context:
Aggregate shape influences packing, interlock, and the quality of the interfacial transition zone in concrete. For high-strength concrete and slabs/pavements experiencing tensile stresses, selection of aggregate shape is important for both strength and toughness.

Given Data / Assumptions:

• Aggregates are clean and properly graded.
• High-strength concrete aims for low w/c and dense microstructure.
• Pavements under tension need reliable crack resistance and fatigue performance.

Concept / Approach:

Flaky particles have small thickness compared with their other dimensions, leading to poor load transfer, higher surface area (thus higher paste demand), and a tendency to break under compaction or load. They align during placing, creating planes of weakness. Angular aggregates, while increasing paste demand relative to rounded particles, provide better interlock and strength. Rounded aggregates improve workability but may reduce interlock; still, they are preferable to flaky particles for strength and fatigue resistance.

Step-by-Step Solution:

Verification / Alternative check:

Specifications limit flakiness index for high-performance concrete; rigid pavement guidelines discourage flaky/elongated particles to avoid cracking and raveling.

Why Other Options Are Wrong:

Rounded/irregular/angular particles can be used with proper design; none has the inherent structural weakness of flaky particles.

Common Pitfalls:

Confusing flaky with elongated; both are limited but flaky is especially detrimental for high-strength requirements.

Final Answer:

Flaky aggregate