--- title: "Factors in mix design; Indian method" subject: "Concrete Technology and Masonry Structure" chapter: 3 key: "semester_5/concrete_technology_and_masonry_structure:mix-design-factors-indian-method" source: https://www.bctengineer.com/q/semester_5/concrete_technology_and_masonry_structure/mix-design-factors-indian-method site: BCT Engineering --- # Factors in mix design; Indian method Concrete Technology and Masonry Structure · Chapter 3: Mix design of concrete and property of green concrete - Asked in: 2065 Shrawan (old course), 5+5 marks - Video: [Indian Standard Method of Concrete Mix Design - Advanced Concrete Technology](https://www.youtube.com/watch?v=iDzPbj8uTjw) — Ekeeda - 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/mix-design-factors-indian-method - Whole chapter: https://www.bctengineer.com/md/semester_5/concrete_technology_and_masonry_structure/chapter-3 ## Question What are the different factors influencing concrete mix design? How is concrete mix designed using the Indian Mix Design Method? ## Short answer Factors: strength grade and target mean, workability, exposure/durability limits, max aggregate size and grading, cement type, w/c ratio, admixtures, material properties. Indian method (IS 10262): target strength f'ck = fck + 1.65 s; select w/c from strength curve and durability; water from table based on slump and aggregate; cement = water/w/c; aggregate volumes from tables; trial mixes adjust. ## Answer #### Factors influencing concrete mix design 1. **Characteristic strength** required (grade) and the target mean strength; level of quality control (standard deviation). 2. **Workability** required (slump, compaction factor) for the type of placing and compaction. 3. **Durability / exposure condition**: maximum w/c ratio and minimum cement content (IS 456 Table 5). 4. **Maximum size, shape and grading of aggregate**, and the zone of the fine aggregate. 5. **Type and grade of cement**, and its specific gravity. 6. **Water-cement ratio** and water content. 7. **Admixtures** and mineral additives. 8. **Properties of materials**: specific gravity, absorption, moisture and bulking. 9. **Placing conditions**: reinforcement density, section size, temperature, and method of transport. 10. **Economy** and the materials available. #### Indian method (IS 10262:2009, revised 2019) The mix is designed in these steps: 1. Collect the data: grade, aggregate size, workability, exposure, cement, specific gravities and so on. 2. **Target strength** $f'_{ck} = f_{ck} + 1.65 s$ (Table 1: s = 4 for M20/M25, 5 for M30 and above, for good site control); the 2019 revision also requires at least $f_{ck} + X$, whichever is higher. 3. **w/c ratio** from the strength-w/c relationship (Fig 1 of the 2019 revision: 28-day strength vs w/c for 33/43/53 grade cement), checked against IS 456 Table 5; adopt the lower. 4. **Water content** from Table 2 (186 kg/m$^3$ for 20 mm angular aggregate at 50 mm slump; $\pm 3\%$ for each 25 mm change in slump; reduce by about 10 kg for sub-angular, 20 kg for gravel with some crushed particles and 25 kg for rounded gravel; reduce by 20% or more with a superplasticiser). 5. **Cement content** = water / (w/c); check the minimum (IS 456 Table 5) and the maximum limit of 450 kg/m$^3$. 6. **Volume of coarse aggregate** from Table 3 (size, fine aggregate zone, for w/c 0.5; change by 0.01 for each 0.05 change in w/c). 7. **Absolute volume calculation**: the volume of concrete minus the volumes of water, cement, admixture and air gives the aggregate volume, which is split into FA and CA by the CA fraction. 8. **Trial mixes** to check workability and strength, then adjust. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which factor can override the strength requirement in choosing w/c? A. Placing method B. Sand colour C. Mixer type D. Durability / exposure limits of IS 456 Table 5 Answer: D. Max w/c and min cement for the exposure may govern over strength. (Key point: Exposure) 2. Target strength by IS 10262 is A. fck + 1.65 s (or fck + X, whichever is higher) B. fck + 0.825 s C. fck - 4 D. 1.5 fck Answer: A. Take the higher of fck + 1.65 s and fck + X. (Key point: Target strength IS) 3. In IS 10262 Table 2, the base water content is 186 kg/m3 for 20 mm at 50 mm slump; how does it change with slump? A. +/-10% for each 25 mm B. +/-3% for each 25 mm change in slump C. No change D. +/-3% for each 100 mm Answer: B. Water is adjusted by about 3% for every 25 mm change in slump. (Key point: Water content) 4. The cement content calculated is checked against A. a maximum of 300 kg/m3 only B. a minimum of 450 kg/m3 C. a minimum from IS 456 Table 5 and a maximum of 450 kg/m3 D. no limits Answer: C. It must meet the durability minimum and not exceed 450 kg/m3. 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