Permissible dust content in aggregates: identify the correct upper limits of dust for different grading/workability conditions used in concrete production

Introduction / Context:
Fine dust in aggregates alters water demand and cohesion. Codes permit different dust limits based on grading and target workability so that mixes remain cohesive without excessive water.

Given Data / Assumptions:

• Three scenarios—coarse/low workability, fine/low workability, fine/high workability.
• Limits are expressed as percentage of total aggregates.

Concept / Approach:
Coarser grading tolerates less dust (around 5%). Finer grading in low workability permits ~10%. High workability mixes with fine grading can handle up to ~20% fines as cohesion is needed to resist segregation.

Step-by-Step Solution:
Check each limit for each case as per standard practice.All three statements align with permissible ranges.Hence, choose all the above.

Verification / Alternative check:
Guidance found in IS 383 and concrete QC manuals supports these upper bounds under specified conditions.

Why Other Options Are Wrong:

• Any single choice alone omits the other valid cases specified by codes.

Common Pitfalls:

• Failing to adjust water content or admixtures when fines content is high.

Final Answer:
all the above