- Asked 4/32
- 2079 Baisakh · 2 marks
- 2075 Ashwin · 3+2 marks
- 2073 Shrawan · 2 marks
- 2067 Magh (old course) · 2+3 marks
Nominal mix and design mix
Short answer
Nominal mix uses fixed volume proportions (e.g., 1:1.5:3 for M20) without lab design, permitted up to M20 for minor works. Design mix is calculated from material tests (IS 10262) for target strength with optimized cement. In field, use nominal mix only up to M20, batch by weight or gauge box accounting for sand bulking, control w/c, and test cubes.
What is nominal mix of concrete? How does it differ from design mix, and how is it used in the field (points to be considered in using nominal mix)?
A nominal mix is a concrete mix with fixed proportions of cement, sand and aggregate by volume (e.g. 1:1.5:3 for M20, 1:2:4 for M15), which is expected from experience to give the required strength without a laboratory design. IS 456 cl. 9.3 permits it for M5, M7.5, M10, M15 and M20 grades on small or unimportant jobs.
Differences
| Point | Nominal mix | Design mix |
|---|---|---|
| Proportions | Fixed by volume (M20: 1:1.5:3) | Calculated and confirmed by trials (IS 10262) for the materials used |
| Basis | Experience / code | Laboratory tests on the actual materials |
| Quality control | Little | Strict, with testing |
| Cement content | Conservative, higher | Optimised, economical |
| Strength | Not guaranteed (may be under or over) | Target strength is attained |
| Use | Minor works; up to M20 (IS 456 cl. 9.3) | All important works, M25 and above, large jobs |
| Water | Fixed quantity per bag (IS 456 Table 9), often adjusted by site judgement | w/c controlled and fixed |
Points to consider when using a nominal mix in the field
- Use it only up to M20 grade (IS 456); keep within the proportions of Table 9 (total aggregate per 50 kg of cement, sand proportion, water per 50 kg of cement).
- Batching by weight is preferable; if batching is by volume, use a gauge box sized for one 50 kg bag (35 L) and allow for the bulking of sand.
- Use sand and aggregate that meet IS 383, with proper grading, and clean water.
- Keep the w/c as low as workability permits (not above 0.5-0.6 for M20).
- Mix thoroughly, compact properly, and cure for at least 7 days.
- Make cube tests; if the cubes fail, change to a design mix.
✓ Answer checked by Claude Opus 5.5 (high effort)
Related questions
- ACI mix design for M35 concrete (numerical) · Concrete Technology and Masonry Structure, chapter 3 · asked 2×
- ACI mix design for M25 concrete (numerical) · Concrete Technology and Masonry Structure, chapter 3 · asked 2×
- Fundamental concepts of concrete mix design · Concrete Technology and Masonry Structure, chapter 3
- ACI mix design for 25 MPa concrete (numerical) · Concrete Technology and Masonry Structure, chapter 3
- DOE mix design for M25 concrete (numerical) · Concrete Technology and Masonry Structure, chapter 3
- Principles of mix design; factors not in DOE · Concrete Technology and Masonry Structure, chapter 3
- Site engineer uses weaker mortar and concrete mix · Engineering Professional Practice, chapter 7
- Marshall method of bituminous mix design · Transportation Engineering I, chapter 6 · asked 9×
- Stagnation points in 2D velocity field · Fluid Mechanics, chapter 4
- Design discharge for surface drainage, bunded field · Irrigation and Drainage Engineering, chapter 9
All Concrete Technology and Masonry Structure chapter 3 questions →