--- title: "Nominal mix and design mix" subject: "Concrete Technology and Masonry Structure" chapter: 3 key: "semester_5/concrete_technology_and_masonry_structure:nominal-vs-design-mix" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/nominal-vs-design-mix site: BCT Engineering --- # Nominal mix and design mix Concrete Technology and Masonry Structure · Chapter 3: Mix design of concrete and property of green concrete - Asked in: 2079 Baisakh, 2 marks; 2075 Ashwin, 3+2 marks; 2073 Shrawan, 2 marks; 2067 Magh (old course), 2+3 marks (asked 4 times) - Video: [Nominal mix and design mix - Difference between Nominal mix and Design mix for Concrete](https://www.youtube.com/watch?v=t3R3vjH3P54) — Engr Sami - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/nominal-vs-design-mix - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-3 ## Question 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)? ## 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. ## Answer 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 1. 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). 2. 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**. 3. Use sand and aggregate that meet IS 383, with proper grading, and clean water. 4. Keep the w/c as low as workability permits (not above 0.5-0.6 for M20). 5. Mix thoroughly, compact properly, and cure for at least 7 days. 6. Make cube tests; if the cubes fail, change to a design mix. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. A nominal mix has... A. Proportions by lab trials B. Fixed volume proportions from experience, e.g. 1:1.5:3 for M20 C. Guaranteed strength D. Strict control Answer: B. It needs no lab design but strength is not guaranteed. (Key point: Nominal mix) 2. IS 456 permits nominal mix up to... A. M20 B. M30 C. M40 D. M50 Answer: A. M5 to M20 on small or unimportant jobs. (Key point: Grade limit) 3. When batching nominal mix by volume you must... A. Ignore sand moisture B. Allow for bulking of sand using a gauge box C. Use any water D. Skip curing Answer: B. Moist sand bulks and gives less sand by weight. 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