Aggregates as the skeleton
- Aggregates occupy much of the volume in concrete and road layers; size, shape, texture, and strength affect workability and performance.
- A suitable combined grading helps control voids and the amount of paste required, but must fit the application and specification.
Sampling and grading
- Obtain a representative sample and reduce it with a suitable splitter; poor sampling invalidates an otherwise precise grading test.
- Sieve analysis separates fractions by aperture and calculates retained or passing percentages to build a grading curve.
- Shape indices and sand-equivalent or methylene-blue tests help identify unfavourable particles and clay-rich fines.
Strength and durability
- Abrasion or fragmentation tests compare aggregate resistance to wear and impact.
- Moisture, salt, freeze-thaw, and weathering cycles explore environmental stability; density and absorption help describe porosity.
- For pavements, polishing and friction tests provide information about texture evolution and skid resistance.
Reporting
- Record source, lot, preparation, mass, sieves, and moisture condition; report the standard and fractions tested.
- Compare results with current contractual limits. No single test replaces an overall aggregate assessment.
Grading and property calculations
- Percent passing: P(d) = 100 · [1 − Mr(d)/M], where Mr(d) is cumulative mass retained up to sieve d and M is total dry test mass.
- Fineness modulus: FM = ΣRac/100, the sum of cumulative retained percentages on the sieve series specified by the method. Compare only values calculated with the same series.
- Grading coefficients: Cu = D60/D10 and Cc = D30²/(D10·D60), using D10, D30, and D60 from the grading curve. Interpretation depends on the classification system and aggregate type.
- Water absorption: A = 100 · (MSSD − Mdry)/Mdry. Distinguish this from total moisture and free surface moisture when correcting batch water.
Educational reference guide. Check the current standard, calculation assumptions, and project specification before applying a procedure or acceptance criterion.