Aggregate grading and workability — interpreting the grading curve Which statements about aggregate grading and its effect on concrete are correct?

Introduction / Context:
Aggregate grading influences packing density, paste demand, and segregation resistance. Both continuously graded and gap-graded systems are used, depending on the desired workability and finish while meeting stability requirements.

Given Data / Assumptions:

• Grading curve is plotted as percent passing vs. sieve size.
• Concrete proportioning aims to minimize voids and paste demand while maintaining cohesion.
• Gap grading is executed with care to avoid segregation.

Concept / Approach:

While continuous grading often yields low voids, well-designed gap gradings can also achieve dense packing with appropriate fines and admixtures. Omitting a size appears as a flat segment on the grading curve. However, removing too much intermediate size can reduce interlock among fractions, increasing segregation risk even if short-term workability seems to improve.

Step-by-Step Solution:

Verification / Alternative check:

Mix design references describe both continuous and gap gradings, cautioning about stability and segregation control (e.g., fines content, admixtures, optimized packing models).

Why Other Options Are Wrong:

• “None” conflicts with established grading behavior; each statement reflects recognized practice.

Common Pitfalls:

• Equating “flowability” with “stability”; gap-graded mixes can be fluid yet prone to segregation without adequate fines.

Final Answer:

All of the above.