What is the maximum allowed loss on ignition (LOI) for fly ash used in concrete?

The maximum LOI is 5.0% by mass as per Table 1.

What is the minimum fineness required for fly ash?

320 m2/kg when tested by Blaine's permeability method (Table 2).

What is the permissible limit for chloride content in fly ash?

Total chlorides should not exceed 0.05% by mass (Table 1).

How is the pozzolanic strength contribution of fly ash evaluated?

By testing compressive strength at 28 days, which must be at least 80% of the plain cement control mix (Table 2).

IS 3812

: 2019

Pulverized Fuel Ash (PFA) for Use in Cement Mortar and Concrete - Specification

CurrentFrequently UsedSpecificationMaterials Science · Coastal and Marine Engineering

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This standard specifies the physical and chemical requirements for pulverized fuel ash (commonly known as fly ash) intended for use as a pozzolana in cement, cement mortar, and concrete. It defines the testing methods and acceptable limits to ensure the durability, workability, and strength development of fly ash-blended cementitious mixtures.

Specifies requirements for pulverized fuel ash (fly ash) for use as a supplementary cementitious material in concrete to enhance durability in marine environments.

Quick Reference Values

Fineness (Blaine's permeability), Min320 m2/kg

Loss on ignition (LOI), Max5.0 percent

Total chlorides (as Cl), Max0.05 percent

Soundness by Autoclave expansion, Max0.8 percent

Lime reactivity, Min4.5 N/mm2

Compressive strength at 28 days, Min80 percent of control mix

Silicon dioxide plus aluminium oxide plus iron oxide, Min70.0 percent

Practical Notes

Always verify the Loss on Ignition (LOI) value; high unburnt carbon can severely disrupt the effectiveness of air-entraining admixtures and reduce long-term durability.

Ensure the fly ash has a fineness greater than or equal to the cement it replaces to guarantee proper pore refinement and a robust pozzolanic reaction.

Quality of fly ash can vary significantly between power plants and even across different batches; regular testing for lime reactivity and chemical consistency is essential.