An excess of flaky particles in concrete aggregates :
Correct Answer: D. All option are correct
📚 Detailed Explanation: Effects of Excess Flaky Particles in Concrete
Flaky aggregate particles (thin, plate-like) are undesirable in concrete because their unusual geometry creates multiple problems that compound each other. Their high surface-area-to-volume ratio means they demand more cement paste to coat them, and their plate-like shape disrupts packing and flow in the fresh mix.
Why D (All option are correct) is correct: (1) Workability decreases because flat particles interlock and create friction in the fresh mix, resisting flow more than equidimensional particles would. (2) More water and sand needed to restore workability — but this raises the w/c ratio, reducing strength. (3) Durability is affected because flaky particles create preferential planes of weakness (cracks propagate along flat particle faces), and the higher water content increases porosity and permeability.
Effects of Excess Flaky Aggregate
| Effect | Mechanism | Consequence |
|---|---|---|
| Reduced workability | High friction between flat particles | Difficult placement and compaction |
| Higher water demand | Large surface area to wet + restore flow | Raised w/c ratio, lower strength |
| Reduced durability | Planes of weakness + higher porosity | Cracking, reduced lifespan |
Key Concepts for Students
- Flakiness index ≤35% per IS 383 for use in concrete; excess flakiness is a rejection criterion for aggregate.
- Flaky particles can also cause segregation of the mix during transport or placing, as they tend to migrate to the edges of forms.
- Quarries control flakiness by adjusting crusher jaw settings and screening out excessively thin product.