- 2067 Magh (old course) · 2+3 marks
Physical properties of OPC and concrete behaviour
Short answer
F ineness affects hydration rate and bleeding; standard consistency indicates water demand; initial set allows placement time; soundness ensures volume stability; compressive strength defines grade; heat of hydration influences thermal cracking; specific gravity is ~3.15.
Write short notes on the physical properties of ordinary Portland cement and their effects on concrete behaviour.
Physical properties of OPC (tested as per IS 4031; limits as per IS 269:2015):
| Property | Requirement / typical | Effect on concrete behaviour |
|---|---|---|
| Fineness | Specific surface not less than 225 m/kg (Blaine); residue on 90 micron sieve about 10% | Finer cement hydrates faster: higher early strength and heat, better workability and less bleeding; but more shrinkage and cracking |
| Standard consistency | 26-33% water | Gives the water content for the Vicat tests; a high value means a higher water demand |
| Setting time | Initial not less than 30 min; final not more than 600 min | Initial set gives time for mixing, transport and placing; final set limits the time before forms can be removed and curing started |
| Soundness | Le Chatelier expansion not more than 10 mm; autoclave expansion not more than 0.8% | Excess free lime or MgO causes later expansion and cracking |
| Compressive strength | 3, 7 and 28-day strengths: for 43 grade, 23, 33 and 43 MPa | Basis for the concrete grade |
| Heat of hydration | OPC typically about 80-90 cal/g at 7 days (no limit in IS 269); low-heat cement (IS 12600) is limited to 65 cal/g at 7 days and 75 cal/g at 28 days | High heat causes thermal cracking in mass concrete |
| Specific gravity | About 3.15 | Used in mix design and volume calculations |
Also, the loss on ignition (maximum 5%) and insoluble residue (maximum 4%) indicate quality.
✓ Answer checked by Claude Opus 5.5 (high effort)
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