Concrete Aggregates – Key qualities per IS 383 (formerly IS: 383–1963) According to Indian Standard requirements for concrete aggregates, a good aggregate should be chemically inert in cement paste, sufficiently strong to resist loads, and hard as well as durable against weathering and abrasion. Which option best captures these requirements?

Introduction / Context:
Aggregates constitute the bulk of concrete volume, so their properties directly influence fresh and hardened performance. Indian Standards (commonly referred to as IS 383 in its older and newer editions) specify requirements for aggregates used in concrete. A “good” aggregate must satisfy several criteria simultaneously, not just one, to ensure strength, durability, and compatibility with cement paste.

Given Data / Assumptions:

• We are considering aggregates intended for structural concrete.
• Requirements relate to mechanical and chemical suitability.
• Environmental exposure may include moisture cycles and abrasion.

Concept / Approach:
Three pillars define a suitable aggregate: chemical inertness (to prevent harmful reactions such as alkali–silica reaction with reactive silica or deleterious impurities), sufficient mechanical strength (crushing, impact, abrasion resistance), and hardness/durability (to resist polishing, weathering, freeze–thaw in appropriate climates, and long-term breakdown). A deficiency in any one aspect can compromise the entire concrete system.

Step-by-Step Solution:
Identify chemical requirement: aggregate should not react deleteriously with cement pore solution → chemically inert.Identify mechanical requirement: aggregate must resist loads and handling → sufficiently strong.Identify durability requirement: aggregate should resist wear and weather → hard and durable.Therefore, the comprehensive choice that satisfies all three is “All of the above”.

Verification / Alternative check:
Aggregate tests such as alkali reactivity, specific gravity/absorption, Los Angeles abrasion, aggregate crushing value, and soundness collectively verify these properties. Meeting limit values across these tests aligns with the “good aggregate” definition.

Why Other Options Are Wrong:

• (a), (b), or (c) alone miss other critical dimensions; one property alone cannot define a good aggregate.
• “None of these” contradicts standard requirements for concrete aggregates.

Common Pitfalls:
Assuming a strong but chemically reactive aggregate is acceptable; in reality, reactivity can cause long-term expansion and cracking. Similarly, a chemically inert but weak or soft aggregate can lead to surface wear and loss of strength.

Final Answer:
All of the above