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Gradation; function of admixture

Short answer

Gradation is the particle size distribution from sieve analysis; good gradation minimises voids, improving workability and economy. Admixtures modify fresh or hardened concrete properties: increase workability, control setting, entrain air, enhance durability, reduce water or bleeding, and save cement.

What do you mean by gradation? What is the function of admixture?

Gradation (grading) is the distribution of aggregate particle sizes in a sample, found by sieve analysis (IS 2386 Part 1) and expressed as the percentage passing (or retained) on a series of standard sieves. Good gradation, within IS 383 limits, means a smooth continuous grading curve with minimum voids, giving workable, economical and strong concrete.

Function of admixture: An admixture (IS 9103) is a material added in small quantities to concrete during or before mixing, to modify its properties. Its functions include:

  • Increase workability or reduce water content (plasticisers, superplasticisers).
  • Accelerate setting and early strength (accelerators) or delay setting (retarders) for hot weather and long transport.
  • Entrain air to improve frost resistance (air-entraining agents).
  • Improve durability, reduce permeability and heat (pozzolans, fly ash, silica fume).
  • Reduce bleeding, segregation and shrinkage, and save cement.

✓ Answer checked by Claude Opus 5.5 (high effort)

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