Difficulty: Easy
Correct Answer: 70 : 20 : 10
Explanation:
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:
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
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