Clause 4.6 brings together all the preceding steps into a complete mix calculation using the absolute volume method. The volume of concrete (1 m³ = 1000 litres) is the sum of volumes of water, cement, chemical admixture, and all-in aggregate (CA + FA). The aggregate volumes are derived by subtracting paste volume from total volume, then splitting between CA and FA using the proportions from Clause 4.5. Individual aggregate quantities are obtained by multiplying volumes with their respective specific gravities and density of water.
Key Requirements
•Total volume of concrete = 1 m³ = 1000 litres
•Volume of cement = mass of cement / (specific gravity of cement × 1000)
•Volume of water = mass of water / (specific gravity of water × 1000)
•Volume of admixture = mass of admixture / (specific gravity of admixture × 1000)
•Volume of all-in aggregate = 1 - (volume of cement + volume of water + volume of admixture + volume of entrapped air)
•Entrapped air: 3% for 10 mm MSA, 2% for 20 mm MSA, 1% for 40 mm MSA
•Mass of CA = volume of CA × specific gravity of CA × 1000
•Mass of FA = volume of FA × specific gravity of FA × 1000
Reference Tables
Entrapped Air Content (Clause 4.6)
Nominal Max Aggregate Size (mm)
Entrapped Air (%)
10
3
20
2
40
1
Worked Example — M25 Concrete Mix Design (20 mm MSA, Moderate Exposure, OPC 53)
Specific gravities assumed: Cement = 3.15, FA = 2.65, CA = 2.68. Actual values from lab tests should be used in practice.
Formulas
V_agg = 1 - [C/(Sc × 1000) + W/1000 + V_air]
Volume of total aggregate (CA + FA) per cubic metre of concrete
V_agg = Volume of all-in aggregate in m³C = Mass of cement in kgSc = Specific gravity of cement (typically 3.15 for OPC)W = Mass of water in kgV_air = Volume of entrapped air as fraction (0.01, 0.02, or 0.03)
Mass of CA = V_agg × p × S_ca × 1000
Mass of coarse aggregate per cubic metre
1000 = Density of water in kg/m³V_agg = Volume of all-in aggregate in m³p = Proportion of CA from Clause 4.5 (e.g., 0.62)S_ca = Specific gravity of coarse aggregate (typically 2.68)
Mass of FA = V_agg × (1 - p) × S_fa × 1000
Mass of fine aggregate per cubic metre
1000 = Density of water in kg/m³V_agg = Volume of all-in aggregate in m³(1 - p) = Proportion of FA (complement of CA proportion)S_fa = Specific gravity of fine aggregate (typically 2.65)
Practical Notes
✓The absolute volume method is the standard approach in IS 10262:2019. It assumes all volumes add up to exactly 1 m³ — in practice, yield may vary by 1-2% due to aggregate shape, air content, and compaction.
✓Always verify specific gravities of cement, FA, and CA from actual lab tests (IS 2386 for aggregates, IS 4031 for cement). Using assumed values can cause errors of 20-40 kg/m³ in aggregate quantities.
✓For the worked example: the mix ratio 1:1.83:3.02 at W/C 0.50 is a typical M25 mix. In practice with OPC 53 and good aggregates, this achieves 33-38 MPa at 28 days.
✓Unit weight check: 372 + 681 + 1123 + 186 = 2362 kg/m³. Normal concrete unit weight is 2300-2400 kg/m³. If your total is outside this range, recheck calculations.
Common Mistakes
⚠Forgetting to account for entrapped air — omitting 2% air for 20 mm MSA adds about 50 kg of phantom aggregate to the mix.
⚠Using saturated-surface-dry (SSD) specific gravity for volume calculation but not correcting for actual moisture content in batch weights.
⚠Not cross-checking the total: cement + water + FA + CA should sum to approximately 2300-2400 kg/m³ for normal-weight concrete.
⚠Rounding off intermediate calculations too aggressively — carry at least 4 decimal places for volumes.