Aggregate grading (particle size distribution) is one of the most important characteristics affecting concrete and asphalt performance. Proper grading ensures optimal packing, workability, strength, and durability. Sieve analysis determines the percentage of particles passing through standardized sieves, creating a grading curve that must fall within specified limits for the application.
Why Grading Matters
Well-graded aggregates pack efficiently, reducing voids and cement paste requirements in concrete. Gap-graded aggregates create pervious concrete or drainage layers. Poorly graded aggregates lead to segregation, high water demand, low workability, and weak concrete. In asphalt, grading controls stability, durability, and permeability. Grading directly affects material cost and performance.
Sieve Analysis Procedure
A representative sample is washed to remove fines, oven-dried, and weighed. The sample is passed through a nest of sieves with progressively smaller openings (63mm down to 0.063mm). Each sieve is shaken for a specified time. Material retained on each sieve is weighed and expressed as a percentage of the total sample. Results are plotted as a grading curve showing cumulative percentage passing versus sieve size.
- Standard sieves: 63, 31.5, 20, 16, 10, 8, 4, 2, 1, 0.5, 0.25, 0.125, 0.063mm
- Sample size: Depends on maximum particle size (2-50kg typical)
- Washing: Removes fines smaller than 0.063mm
- Mechanical sieving: Minimum 10 minutes for reproducible results
- Precision: ±0.5% for individual sieve fractions
Grading Zones and Specifications
EN 12620 defines grading envelopes for coarse and fine aggregates. Fine aggregate grading zones (fine, medium, coarse) suit different concrete applications. Coarse aggregate gradings are designated by size ranges (e.g., 4/20mm, 8/16mm). Combined gradings must fall within specified limits. Gap gradings are used for exposed aggregate finishes or pervious concrete.
Interpretation and Quality Control
Grading curves that exceed upper limits indicate excess fines, causing high water demand. Curves below lower limits indicate harsh, poorly workable mixes. Consistency between batches is critical - variations in grading require mix design adjustments. Fineness modulus (weighted average size) provides a single-number indicator, useful for sand quality control. Regular testing (daily or per 500 tonnes) ensures consistent aggregate supply.
Conclusion
Aggregate grading analysis is fundamental to concrete and asphalt quality control. Our laboratory performs sieve analysis to EN and ASTM standards with automated sieving equipment. Contact us for comprehensive aggregate testing services.
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Applicable Standards
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