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Mechanical properties; ranking aggregate grading

Short answer

Mechanical properties: crushing, impact, abrasion value and hardness. Grading is ranked by sieve analysis: dry sample, sieve, plot per cent passing curve; compare with IS 383 limits; well-graded if within limits and smooth. Fineness modulus further ranks fineness.

Define mechanical properties of aggregate. How do you rank the aggregate grading in the lab?

Mechanical properties of aggregate are those that describe how an aggregate behaves under load, shock and wear. They include:

  • Crushing value (strength under gradual compression),
  • Impact value (toughness under sudden load),
  • Abrasion value (resistance to wear, Los Angeles test),
  • Hardness and toughness (resistance to scratching, to breaking). These are tested by IS 2386 Part 4 and they affect the strength and durability of concrete, particularly in pavements and wearing surfaces.

Ranking the grading of aggregate in the laboratory

Grading is checked by sieve analysis (IS 2386 Part 1):

  1. Oven-dry a representative sample (e.g. 5 kg of coarse, 500 g of sand).
  2. Sieve through the stack of IS sieves arranged in decreasing size (80, 40, 20, 10, 4.75 mm, 2.36 mm, 1.18 mm, 600, 300, 150 micron) on a mechanical shaker for about 10 min.
  3. Weigh the material retained on each sieve; calculate % retained, cumulative % retained and % passing.
  4. Plot % passing against sieve size (log scale) to get the grading curve.
  5. Rank/classify: compare with the limits in IS 383 (Tables 7 and 9): well graded if within limits; classify sand into Zone I-IV; compute the fineness modulus (coarser = higher FM) to rank samples from fine to coarse. The sample whose curve lies inside the limits and is smooth is ranked best; gap-graded or single-size samples rank lower.

✓ Answer checked by Claude Opus 5.5 (high effort)

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