Nominal mixes — determine the corresponding legacy grade If the nominal volumetric proportion of concrete ingredients (cement : sand : coarse aggregate) is 1 : 3 : 6, the corresponding legacy grade designation is:
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AM 100
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BM 150
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CM 200
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DM 250
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EM 300
Answer
Correct Answer: M 100
Explanation
Introduction / Context:Traditional Indian practice associated nominal mixes with legacy “M” grades (kg/cm² based), e.g., 1:3:6, 1:2:4, 1:1.5:3. Understanding these helps interpret older drawings and specifications still in circulation.
Given Data / Assumptions:
- Nominal proportion 1 : 3 : 6 by volume.
- Standard workability and curing conditions assumed.
- Legacy grade mapping (approximate characteristic strength).
Concept / Approach:
Historically, 1:3:6 corresponds to about 10 MPa characteristic strength, labeled M 100 (≈ 100 kg/cm²). Likewise, 1:2:4 maps to M 150, and 1:1.5:3 maps to M 200, acknowledging variability due to materials and site control.
Step-by-Step Solution:
Identify mix → 1:3:6 → lowest cement content of the common nominal series.Link to grade → ≈ 10 MPa → M 100.Verification / Alternative check:
Older handbooks and IS-era tables list this mapping for guidance; modern design prefers designed mixes (MPa-based) rather than nominal mixes.
Why Other Options Are Wrong:
- M 150, M 200, M 250, M 300 correspond to richer mixes than 1:3:6.
Common Pitfalls:
- Confusing modern MPa grades (M20, M25) with legacy M 200, M 250 labels.
Final Answer:
M 100.