Chemical Requirements (LSF, C₃A, MgO, SO₃, Chloride)
IS 8112 fixes the OPC 43 chemical limits: lime saturation factor and the alumina/silica moduli, C₃A (heat and sulphate-attack driver), MgO (soundness/periclase), SO₃, insoluble residue, loss on ignition and chloride. The chemistry explains and bounds heat of hydration, soundness and durability, and is verified by IS 4032 chemical analysis on a representative sample.
Key Requirements
•LSF and alumina/silica moduli within the specified range
•C₃A, MgO, SO₃, insoluble residue, loss on ignition and chloride within IS 8112 limits
•Chemistry verified by IS 4032 analysis on a representative sample (IS 3535)
•High C₃A/fineness → more heat; high MgO → soundness risk — chemistry should explain the physical behaviour
•Chloride limit relevant to the IS 456 total-chloride budget for RCC
Practical Notes
✓Chemistry and physical results should agree (high C₃A/fineness → more heat; high MgO → soundness risk); a contradiction usually means a test/calibration fault.
✓OPC 43's modest C₃A/heat (vs 53) is part of why it is the calmer general-purpose cement.
Common Mistakes
⚠Accepting chemistry on the mill tag without IS 4032 testing of a representative sample.
⚠Ignoring chemistry's link to heat/soundness behaviour.
⚠Overlooking the chloride contribution to the IS 456 budget.