Aggregates MCQ with answer and solution

Concept

Coarse aggregate for high-strength concrete

Formula

NONE

Step-by-step solution

1. For high-strength concrete (M60 and above), the failure plane frequently traverses coarse aggregate particles rather than circumventing them. 2. Crushed stone from dense, hard igneous rocks (such as granite or basalt) provides high crushing strength and impact resistance. 3. The angular shape and rough surface texture maximize mechanical interlocking and interfacial transition zone bond strength. 4. Therefore, crushed angular stone from hard igneous rock is preferred. Answer: B

Explanation

In high-strength concrete mixtures of grade M60 and above, aggregate crushing strength and the bond across the interfacial transition zone become critical limiting factors. Crushed angular stone quarried from dense igneous rocks provides angular mechanical interlocking and a rough surface texture that forms an exceptional bond with the mortar matrix. Smooth or weak aggregates fail prematurely under high triaxial stresses.

Why the other options are wrong

A) Smooth gravel has low surface roughness, resulting in a weak interfacial bond that limits compressive strength. C) Lightweight expanded clay produces lightweight concrete with lower compressive strength. D) Recycled concrete aggregate contains porous adhered mortar that lowers elastic modulus and strength.

Shortcut

High-strength concrete (M60+) = Angular crushed igneous rock for superior bond and aggregate strength.

Common mistake

Selecting smooth river gravel for reduced water demand, ignoring that smooth aggregate faces debond easily under high compressive loads.