SlabCalc LogoSlabCalc Concrete Technical Division

Aggregate Gradation

The distribution of particle sizes in aggregate, affecting workability and strength

Aggregate gradation is the distribution of particle sizes in aggregate, affecting workability, strength, economy, and durability. Well-graded aggregate with a range of sizes from coarse to fine packs efficiently, requiring less cement paste. Gap-graded aggregate with missing intermediate sizes creates problems: poor workability, segregation, honeycombing.

Why It Matters

Aggregate occupies 60-75% of concrete volume. Its particle size distribution profoundly affects concrete properties. Well-graded aggregate creates strong, workable, economical concrete. Poorly graded aggregate causes problems even with good cement and proper proportions.

Aggregate suppliers provide gradation information. Specifications define acceptable gradations for different applications. For residential concrete, verify supplier meets ASTM C33 specifications—this ensures acceptable gradation.

Technical Details

Gradation measurement:

  • Sieve analysis (ASTM C136)
  • Series of sieves with decreasing openings
  • Percentage passing each sieve plotted
  • Compared to specification limits

Well-graded characteristics:

  • Continuous range of sizes
  • Adequate fines (passing #200 sieve)
  • Proper proportion of each size
  • Efficient packing
  • Lower void content

Gap-graded problems:

  • Missing intermediate sizes
  • Poor packing
  • High void content
  • More paste needed
  • Segregation prone
  • Harsh, unworkable mix

Gradation specifications:

  • ASTM C33 for concrete aggregates
  • Size number (e.g., #57, #67 stone)
  • Maximum size and nominal maximum size
  • Acceptable ranges for each sieve

Effects on concrete:

  • Workability: Well-graded flows better, finishes easier
  • Strength: Efficient packing increases strength
  • Economy: Less cement needed for well-graded
  • Durability: Dense packing reduces permeability
  • Pumpability: Proper gradation essential for pumping

Learn More

← Browse all glossary terms