For manufacturing fly-ash building bricks used in walls and partitions, select the standard mix proportion (by parts) of fly ash, sand (or stone dust), and lime adopted in common practice. Choose one best ratio.

Introduction / Context:Fly-ash bricks are made by proportioning fly ash with sand/stone dust and lime (often with a small gypsum additive). This tests recall of a widely used baseline proportion used in production lines and quality control.

Given Data / Assumptions:

• Three constituents: fly ash, sand (or stone dust), and lime.
• We want a typical production mix yielding adequate early strength and dimensional stability.

Concept / Approach:

Industrial practice commonly targets a high fly-ash fraction for pozzolanic reaction with lime, with sand providing skeleton and workability. A representative proportion accepted in many plants is 70:20:10 (fly ash : sand : lime) by parts, sometimes with 1–2 parts gypsum as a setting regulator.

Step-by-Step Solution:

Verification / Alternative check:

Plant trials and compressive strength testing (e.g., 7/28-day) confirm that 70:20:10 consistently meets performance, subject to curing and gypsum addition.

Why Other Options Are Wrong:

80:13:7: sand too low; workability and packing issues. 60:35:5: lime too low; slower strength gain. None of these: incorrect because 70:20:10 is a valid standard mix.

Common Pitfalls:

Ignoring gypsum role; skipping curing humidity; assuming one ratio covers all fly-ash qualities.

Final Answer:

70 : 20 : 10