About this code
Specification for fly ash used as a pozzolana — fineness, lime reactivity, soundness, and chemical composition limits.
Key sections
- 01Classification (Siliceous, Calcareous)
- 02Chemical limits
- 03Physical requirements
- 04Testing
Critical clauses
Clause 5.0Fineness
Min 320 m2/kg by Blaine.
In practiceFly ash from ESPs is finer.
Clause 6.0Lime Reactivity
>= 4.5 N/mm2 at 8 days.
In practiceIndicates pozzolanic activity.
Practical implications
For specifiers
Specify fly ash class.
For suppliers
Quarterly source testing.
For executors
Cure 14 days.
FAQs
Can fly ash exceed 35% of cementitious?
Yes for HVFA mixes — IS 456 clause 5.2 allows beyond limits with proven performance.
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