Why well-graded aggregate is better

A well-graded aggregate has particles of all sizes from large to small, in proportions that fill the voids.

Why it is better

• Minimum voids: small particles fill the gaps between large ones, so the paste required is less and cement is saved.
• Better workability with lower water: reduces segregation and bleeding.
• Higher density and strength for the same cement content and lower permeability, so better durability.
• Less shrinkage and creep (less paste).
• Uniform, cohesive mixes without honeycombing; easier compaction and finishing.
• Compared with single-size (many voids, high paste demand) and gap-graded (risk of segregation) aggregates, well graded gives the most economical mix.

Basis for judging well graded

1. Sieve analysis (IS 2386 Part 1): the percentage passing each IS sieve should lie within the IS 383 limits (Table 7 for coarse aggregate, Table 9 for fine zones I-IV).
2. The grading curve is smooth and continuous with no flat steps.
3. Fineness modulus within the required range (e.g. 2.6-3.0 for medium sand; all-in 3.5-6.5).
4. Coefficients: uniformity coefficient $C_u = D_{60}/D_{10}$ (large, above 4-6 for well-graded) and curvature coefficient $C_c = D_{30}^2/(D_{10} D_{60})$ between 1 and 3.
5. Practical check: lowest void content (loose/rodded bulk density test) among combinations.