What is the maximum allowed Loss on Ignition (LOI) for fly ash in concrete?

5.0% by mass as per Table 1. (Can be extended up to 7.0% if agreed upon for certain specific applications).

What is the required fineness for fly ash used as pozzolana?

It must have a minimum specific surface area of 320 m2/kg or maximum 34% retention on a 45-micron sieve (Table 2).

What is the difference between siliceous and calcareous fly ash?

Siliceous fly ash has reactive calcium oxide less than 10%, while calcareous fly ash has reactive calcium oxide between 10% and 25%.

IS 3812 Part 1

: 2021

Pulverized Fuel Ash - Specification: Part 1 For use as pozzolana in cement, cement mortar and concrete

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This standard specifies the chemical and physical requirements for pulverized fuel ash (fly ash) intended for use as a pozzolana in the manufacture of Portland pozzolana cement, and as an admixture in cement mortar and concrete.

Specifies requirements for pulverized fuel ash (fly ash) for use as a pozzolanic admixture in cement, mortar, and concrete, improving their properties.

Quick Reference Values

Fineness (Blaine's specific surface)Min 320 m2/kg

Particles retained on 45-micron sieve (wet sieving)Max 34%

Loss on ignition (LOI)Max 5.0%

Moisture contentMax 2.0%

SiO2 + Al2O3 + Fe2O3 (Siliceous Fly Ash)Min 70.0% by mass

SiO2 + Al2O3 + Fe2O3 (Calcareous Fly Ash)Min 50.0% by mass

Compressive strength at 28 daysMin 80% of control mix strength

Practical Notes

High Loss on Ignition (LOI) in fly ash can significantly increase the demand for air-entraining and water-reducing admixtures, negatively impacting concrete workability.

Always verify the fineness of fly ash; coarser fly ash (retained heavily on a 45-micron sieve) will exhibit poor pozzolanic activity and lower concrete strength.

Calcareous fly ash (often from lignite coal) has higher reactive calcium content than siliceous fly ash, affecting early strength development.