Aggregates for very high-strength concrete — preferred rock type To obtain very high-strength concrete, which aggregate type from the list below is generally preferred because of its high strength and low porosity?

Introduction / Context:
In high-strength concrete (HSC), aggregate quality becomes critical. Strong, dense, and low-absorption aggregates reduce weak links and help realize high paste strengths in the composite material.

Given Data / Assumptions:

• Targeting very high compressive strength concrete.
• Conventional OPC or blended cements with proper admixtures.
• Good curing and low water–binder ratios.

Concept / Approach:
Dense, fine-grained igneous rocks like granite, basalt (trap rock), or diabase exhibit high compressive strength and low porosity, making them suitable for HSC. Heavyweight ores such as magnetite or barite are chosen for radiation shielding, not necessarily for strength optimization. Volcanic scoria is porous and used for lightweight concretes, which generally have lower compressive strengths than HSC.

Step-by-Step Solution:

Verification / Alternative check:
Case studies of HSC commonly use granite/basalt aggregates with low absorption to achieve strengths exceeding conventional limits.

Why Other Options Are Wrong:

• Magnetite, barite: chosen for unit weight, not necessarily best strength.
• Volcanic scoria: lightweight and porous, not for very high strength.
• Sandstone: comparatively weaker and more absorptive.

Common Pitfalls:
Assuming heavyweight aggregates automatically yield higher strength; ignoring aggregate–paste interfacial transition zone quality.

Final Answer:
Granite (fine-grained trap/igneous rock)