Aggregates MCQ with answer and solution

Concept

Aggregate shape, surface texture, and interparticle friction directly influence the workability, strength, and durability of concrete.

Step-by-step solution

1. Analyze option (A): More surface area means more paste is required to coat the particles, thereby reducing workability for a given water-cement ratio. 2. Analyze option (B): Crushed aggregates are angular and have rough textures, causing more internal friction and resulting in lower workability than rounded aggregates. 3. Analyze option (C): Good interlocking of angular or crushed aggregates enhances the load-bearing capacity and shear strength of the concrete matrix. 4. Analyze option (D): Irregular or angular aggregates have a higher surface area-to-volume ratio compared to smooth, rounded aggregates of the same volume.

Explanation

Good interlocking of aggregates provides higher frictional resistance and structural stability, which significantly increases the compressive and shear strength of concrete. Rounded aggregates provide less interlocking compared to angular or crushed aggregates.

Why the other options are wrong

A: More surface area increases paste demand, thus decreasing workability. B: Crushed aggregates have more friction, lowering workability compared to rounded aggregates. D: Irregular or angular aggregates have a higher surface-area-to-volume ratio than smooth rounded aggregates.

Shortcut

Remember that rounded aggregates give better workability, while angular/crushed aggregates give better strength due to interlocking.

Common mistake

Confusing workability with strength; angular aggregates increase strength due to interlocking but decrease workability.