Mix proportioning
Mix proportioning, often called mix design, chooses quantities of cement, supplementary materials, water, fine and coarse aggregate and admixture to produce concrete that is workable, strong enough and durable, at least cost. In India the procedure follows IS 10262, which gives a step-by-step method, with trial mixes to confirm.
The steps run in a fixed order. Fix the target mean strength by adding a margin to the characteristic strength based on expected site variability. Select the water-cement ratio from strength relationships and check it against the durability limit for the exposure; use the lower. Choose water content for the required slump and aggregate size, reducing it if a plasticiser is used. Compute cement content and check it against minimum and maximum limits. Decide the coarse aggregate volume fraction based on aggregate size and sand zone. Then calculate the masses by absolute volume, so that all ingredient volumes plus air add up to one cubic metre.
Trial mixes in the laboratory confirm slump, cohesion and cube strengths, and the proportions are adjusted. On site, quantities are corrected for aggregate moisture. A good mix design is only the start: batching accuracy, consistent materials and statistical control of cube results keep the concrete in specification.
Use the site's own cube results to set the standard deviation once enough tests exist.
Target: f′ck = fck + 1.65 sAbsolute volume: V = C/(1000 Gc) + W/1000 + A/(1000 Ga) + air = 1 m³Cement: C = W / (w/c)Aggregate mass: total aggregate volume × proportion × G × 1000
Problem. Proportion M25 with fck = 25, s = 4 MPa, w/c = 0.45, water 180 kg, air 1 percent, coarse aggregate 0.62 of aggregate volume. Gc = 3.15, Gfa = 2.65, Gca = 2.74.
- Target = 25 + 1.65 × 4 = 31.6 MPa. Cement = 180 / 0.45 = 400 kg.
- Volumes: cement 400/3 150 = 0.127; water 0.180; air 0.010. Aggregate volume = 1 − 0.317 = 0.683 m³.
- Coarse = 0.683 × 0.62 × 2.74 × 1 000 = 1 160 kg; fine = 0.683 × 0.38 × 2.65 × 1 000 = 688 kg.
- Trial proportions per m³: 400 : 688 : 1 160 with 180 kg water, then confirm by trials.
Answer. Cement 400 kg, sand 688 kg, coarse 1 160 kg, water 180 kg per m³ (trial)
Quick quiz
1What two checks decide the w/c ratio?
Strength requirement and durability limit; take the lower.
2What principle sets aggregate masses?
Absolute volume: all ingredient volumes add to 1 m³.
3Why are trial mixes needed?
To confirm workability and strength with actual materials.
- IS 456 (India): Plain and reinforced concrete: general rules for materials, durability, design and construction.
- IS 10262 (India): Guidelines for proportioning concrete mixes.
- IS 383 (India): Coarse and fine aggregate for concrete: requirements.
- IS 269 (India): Ordinary Portland cement: requirements.
Clauses and documents to read
- IS 10262:2019 (concrete mix proportioning, whole standard)
- IS 456:2000 cl. 9 (concrete mix proportioning)
- IS 383:2016 (aggregate zones)
Cited by number and clause only. We do not reproduce clause text, tables or figures (BIS Act 2016, s.10(5) and s.11). Check the current edition and amendments before use.
References and further reading
Standard texts, listed in no order of merit. We do not copy text, figures, tables or solved problems from any book; our explanations and examples are original.
- M. S. Shetty, Concrete Technology: Theory and Practice, S. Chand, latest edition.
- A. M. Neville, Properties of Concrete, Pearson, 5th edition.
- P. K. Mehta, P. J. M. Monteiro, Concrete: Microstructure, Properties, and Materials, McGraw Hill, latest edition.
Free and official sources
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