IS 1489 fixes the permitted proportion of pozzolana in the blended cement and the chemical limits (SO₃, MgO, chloride, loss on ignition, etc.). Critically, the pozzolana itself must conform — fly ash to IS 3812 Part 1, calcined clay to IS 1344 — because coarse/high-LOI fly ash or under-calcined clay is a poor or harmful pozzolana, not an economy.
Key Requirements
•Pozzolana proportion within the IS 1489 specified range for the blended cement
•Chemical limits: SO₃, MgO, chloride, loss on ignition within the spec
•Pozzolana conforms — fly ash to IS 3812 Part 1 (fineness/LOI/reactivity); calcined clay to IS 1344
•Chloride contributes to the IS 456 total-chloride budget for RCC
•Verify by chemical analysis on a representative sample (IS 3535 sampling)
Practical Notes
✓PPC performance is contingent on the pozzolana: coarse/high-LOI fly ash or under-calcined clay under-reacts and can break admixture dosing — the input spec is part of the cement spec.
✓High-LOI fly ash adsorbs admixtures (water-reducers/AEA) — a hidden cause of erratic PPC concrete.
Common Mistakes
⚠Assuming any fly ash/clay qualifies (ignoring IS 3812 / IS 1344 conformity).