WHAT IS GRAIN SIZE ANALYSIS.

Test for grain size analysis or sieve analysis of aggregates are done to determine its particle size distribution, fineness modulus, effective size and uniformity coefficient.

  • Particle size distribution
Particle size distribution of an aggregate as determined by sieve analysis is known as "Grading of aggregate". Sieve analysis is the operation of dividing a sample of aggregate into various fractions each consisting of particles of same size.the sieve analysis is conducted to determine the particle size distribution in a sample of aggregate which we call gradation of aggregate.

  • Fineness modulus
fineness modulus is index number obtained by adding the total percentage of the sample of an aggregate retained on each of a specified series of sieves and dividing the sum by 100.

Limits of Fineness Modulus of Sand

Maximum size of aggregate
Fineness modulus
Minimum
Maximum
Fine Aggregate23.5
Coarse aggregate 20mm66.9
Coarse aggregate 40mm6.97.5
Coarse aggregate 75mm7.58.0
If the test aggregate gives higher fineness modulus the mix will be harsh and if on the other hand gives a lower fineness modulus it gives uneconomical mix .

  • Effective Size of Aggregates

Effective size (in microns) is the maximum particle size of the smallest 10% of the aggregate or it is the sieve opening corresponding to 10% finer and is designated by the symbol D10.

  • Uniformity Coefficient of Aggregates

This is the ratio of the maximum size of the smallest 60% to the effective size. Uniformity coefficient = D60/D10.

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