Concrete Mix & Volumes
- Dry volume of concrete = Wet volume × 1.54.
- 1 Bag cement = 0.035 m³ (1.25 cu.ft).
- 1 m³ M20 = 8 bags cement.
- 1 m³ M25 = 11 bags cement.
- 1 m³ concrete = 2.4 tonnes approx.
- For 100 sq.ft built-up area = 3.8 m³ concrete.
- For roof slab = 0.1 m³ concrete/sq.ft.
- For PCC (1:4:8), cement = 220 kg/m³.
- For RCC (1:1.5:3), cement = 320 kg/m³.
- 1 cum PCC (1:3:6) = 220 kg cement + 670 kg sand + 1250 kg agg.
🔹 Cement Consumption
- 1 m³ M20 = 320 kg cement.
- 1 m³ M25 = 400 kg cement.
- 1 bag = 28.8 kg/cu.ft.
- 100 bags cement = 3.5 m³ M20 concrete.
- 1 bag cement in plaster (1:4, 12mm thick) = 20 sq.ft.
- 1 bag cement in brickwork mortar (1:6) = 30 sq.ft (9” wall).
- Mortar yield from 1 bag = 0.034 m³.
- Cement wastage = 2% site loss.
- Storage life of cement = 3 months safe.
- Stack height of cement bags ≤ 15 bags.
🔹 Sand & Aggregate
- Sand required = 0.45 m³ per 1 m³ RCC.
- Aggregate = 0.9 m³ per 1 m³ RCC.
- Sand in M20 concrete = 35% of total volume.
- Aggregate wastage = 2%.
- Sand wastage = 8%.
- 1 cum RCC requires ~ 700 kg sand.
- 1 cum RCC requires ~ 1250 kg aggregate.
- FM (fineness modulus) for RCC sand = 2.5–3.0.
- Water absorption of aggregates = 0.5–2%.
- Bulking of sand = 20–30% (use correction).
🔹 Water in Concrete
- Water-cement ratio (W/C) for M20 = 0.45–0.50.
- For 1 bag cement → water = 34–36 litres.
- 1 cum RCC needs 180 litres water approx.
- Excess water ↑ shrinkage cracks.
- For PCC (1:4:8), W/C = 0.55.
- Potable water suitable for concrete if pH > 6.
- Sea water not allowed for RCC (chlorides).
- Curing water consumption = 3–4 m³ per 100 m² slab.
- Initial curing = 7 days min.
- Full curing for RCC = 14 days (OPC), 21 days (PPC).
🔹 Reinforcement Steel
- Steel in slab = 1% of concrete volume.
- Steel in beam = 2% of concrete volume.
- Steel in column = 2.5%.
- Steel in footing = 0.8%.
- Avg. RCC = 80–100 kg steel per m³ concrete.
- 1 ton steel = 135 m of 16mm dia bar.
- Development length (Ld) = 47 × dia (M20, Fe415).
- Overlap length in tension = 50d.
- Overlap length in compression = 40d.
- Steel wastage allowance = 3–5%.
- Binding wire = 1.5% of steel weight.
- Cover for slab = 20 mm.
- Cover for beam = 25 mm.
- Cover for footing = 50 mm.
- Cover for column = 40 mm.
- Hook length for stirrups = 10d.
- Chair spacing in slab = 1 m c/c.
- Lap splices staggered by minimum 75 mm.
- Steel unit weight = 7850 kg/m³.
- Density of mild steel = 7.85 g/cm³.
🔹 Shuttering / Formwork
- Shuttering area = 6 × concrete volume (m²).
- For beam/column = 20 m² shuttering per m³ concrete.
- For slab = 12 m² shuttering per m³ concrete.
- 1 m² shuttering = 0.22 plywood sheets.
- Plywood reuse = 8–12 times.
- Steel shuttering plates reuse = 40–50 times.
- Shuttering oil = 1 litre/15 m² area.
- Removal time for slab = 14 days.
- Removal time for beam/column = 21 days.
- Props for slab > 4.5 m span retained = 14 days + propping.
🔹 Ready-Mix Concrete (RMC)
- RMC density = 2400 kg/m³.
- Transit mixer = 6 m³ capacity.
- Pump output = 30–50 m³/hr.
- Vibrator coverage = 5–6 m³/hr per needle.
- Slump for PCC = 75–100 mm.
- Slump for RCC = 100–125 mm.
- Slump for pumping = 125–150 mm.
- Needle vibrator spacing = 0.5 m.
- Vibrator time = 5–15 sec.
- Workability loss after 45 min = 25%.
🔹 Testing & Quality
- Cube test sample size = 150 × 150 × 150 mm.
- Cube strength at 7 days = 70% of 28-day strength.
- Cube strength at 3 days = 40%.
- Slump test cone = 300 mm height.
- Rebound hammer ± 15% accuracy.
- Core test cylinder = 150 mm dia × 300 mm high.
- Compaction factor for RCC = 0.85–0.92.
- Workability test frequency = every 25 m³ concrete.
- Cube test frequency = 1 set/30 m³ concrete.
- Acceptance criteria = fck + 1.65σ.
🔹 Wastage & Costing
- Concrete wastage allowance = 2–3%.
- Steel wastage = 3–5%.
- Cement wastage = 2%.
- Sand wastage = 8%.
- Aggregate wastage = 2%.
- Labour output concreting = 3–4 m³ per mason/day.
- Labour output shuttering = 10 m²/day.
- Curing labour output = 100 m²/day.
- Avg. RCC cost = ₹6500–7500 per m³ (India 2025).
- RCC concrete = 40–50% of total building cost.
