- 2064 Jestha (old course)
OPC versus PPC
Short answer
O PC is clinker with gypsum, P PC contains 15-35% pozzolana like fly ash, making it finer, lower early strength, lower heat, better chemical resistance, denser pore structure, but requires longer curing. O PC gains strength faster and is used for precast work.
Differentiate Ordinary Portland Cement (OPC) and Portland Pozzolana Cement (PPC) in terms of their physical and chemical properties.
OPC is made by grinding clinker with gypsum (IS 269). PPC is made by inter-grinding (or blending) OPC clinker and gypsum with 15-35% fly ash or other pozzolana (IS 1489 Part 1).
| Point | OPC | PPC |
|---|---|---|
| Composition | Clinker + 3-5% gypsum | Clinker + gypsum + 15-35% pozzolana (fly ash/calcined clay) |
| Fineness (Blaine) | Not less than 225 m/kg | Not less than 300 m/kg (finer) |
| Initial setting time | Not less than 30 min | Not less than 30 min |
| Final setting time | Not more than 600 min | Not more than 600 min |
| Early strength | Higher (3 and 7 day) | Lower early strength |
| 28-day strength (min.) | 33/43/53 MPa | 33 MPa; continues to gain strength later |
| Heat of hydration | Higher | Lower (suitable for mass concrete) |
| Free lime / Ca(OH) | More | Less, as the pozzolana consumes it |
| Workability and cohesion | Normal | Better, due to the fine spherical fly ash particles |
| Permeability | Higher | Lower; denser pore structure |
| Sulphate and chemical resistance | Poor to fair | Better |
| Curing | Normal (7 days) | Needs longer curing (10 days) |
| Colour | Grey | A slightly different shade of grey, depending on the pozzolana |
| Chemical limits | MgO max 6%; loss on ignition max 5% | MgO max 6%; loss on ignition max 5% |
| Cost | Higher | Cheaper and environmentally friendly |
PPC is preferred for plastering, mass concrete and marine works; OPC is used where fast strength gain is required (precast work, early formwork removal).
✓ Answer checked by Claude Opus 5.5 (high effort)
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