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IS 3812:2023 Part 1 is the Indian Standard (BIS) for pulverized fuel ash - specification - part 1: for use in cement, cement mortar and concrete. This standard specifies the physical and chemical requirements for pulverized fuel ash (fly ash) used as a pozzolana in cement, cement mortar, and concrete. It defines the limits for critical parameters like fineness, loss on ignition, and reactive silica to ensure proper strength development and long-term durability in concrete mixtures.
Specifies requirements for fly ash used as an admixture or ingredient in cement, mortar, and concrete for sustainable construction.
Quick Reference — Top IS 3812 Part 1:2023 Values
Key chemical and physical property limits for Super Fine (SF), Fine (F), and Coarse (C) grades of pulverized fuel ash (fly ash).
✓ Verified 2026-04-27
Reference
Value
Clause
Grades of Fly Ash— Classification is based on fineness.
Super Fine (SF), Fine (F), Coarse (C)
Cl. 4
Sum of (SiO₂ + Al₂O₃ + Fe₂O₃)— Minimum pozzolanic content for all grades.
≥ 70.0 %
Cl. 5.1 (Table 1)
Silicon Dioxide (SiO₂) Content— Minimum requirement for all grades.
≥ 35.0 %
Cl. 5.1 (Table 1)
Loss on Ignition (LOI)— Maximum unburnt carbon content for all grades.
≤ 5.0 %
Cl. 5.1 (Table 1)
Magnesium Oxide (MgO) Content— Maximum limit for all grades.
≤ 5.0 %
Cl. 5.1 (Table 1)
Sulphur Trioxide (SO₃) Content— Maximum limit for all grades.
≤ 3.0 %
Cl. 5.1 (Table 1)
Available Alkalis (Na₂O eq.)— Maximum limit to control alkali-silica reaction.
≤ 1.5 %
Cl. 5.1 (Table 1)
Chloride Content— Maximum limit to prevent reinforcement corrosion.
≤ 0.05 %
Cl. 5.1 (Table 1)
Fineness (Specific Surface) - Super Fine (SF)— Minimum value by Blaine's air permeability method.
≥ 450 m²/kg
Cl. 6.1 (Table 2)
Fineness (Specific Surface) - Fine (F)— Minimum value by Blaine's air permeability method.
≥ 320 m²/kg
Cl. 6.1 (Table 2)
Fineness (Specific Surface) - Coarse (C)— Minimum value by Blaine's air permeability method.
≥ 200 m²/kg
Cl. 6.1 (Table 2)
Particles Retained on 45µ Sieve - Super Fine (SF)— Maximum percentage by mass.
≤ 12 %
Cl. 6.1 (Table 2)
Particles Retained on 45µ Sieve - Fine (F)— Maximum percentage by mass.
≤ 34 %
Cl. 6.1 (Table 2)
Particles Retained on 45µ Sieve - Coarse (C)— Maximum percentage by mass.
≤ 50 %
Cl. 6.1 (Table 2)
Lime Reactivity (Avg. Comp. Strength)— Minimum requirement for all grades.
≥ 4.5 MPa
Cl. 6.1 (Table 2)
Compressive Strength at 28 days— Of corresponding plain cement mortar cube strength.
≥ 80 %
Cl. 6.1 (Table 2)
Soundness (Autoclave Expansion)— Maximum expansion for all grades.
≤ 0.8 %
Cl. 6.1 (Table 2)
Drying Shrinkage at 28 days— Maximum shrinkage for all grades.
≤ 0.15 %
Cl. 6.1 (Table 2)
Moisture Content— Maximum percentage by mass for all grades.
≤ 2.0 %
Cl. 6.1 (Table 2)
⚠ Verify against the latest BIS/IRC publication and project specifications. Amendment Slips may modify values.
Overview
Status
Current
Usage level
Essential
Domain
Materials Science — Green Building and Sustainability
! High Loss on Ignition (LOI) indicates unburnt carbon, which can increase water demand and absorb air-entraining or superplasticizing admixtures, reducing their effectiveness.
! Fineness of fly ash significantly impacts its pozzolanic activity; coarser fly ash reduces the rate of strength development.
! Siliceous fly ash and calcareous fly ash possess different reactive properties and must be correctly identified and tested before finalizing a concrete mix design.
Standard Specification for Coal Fly Ash and Raw or Calcined Natural Pozzolan for Use in Concrete
Specifies requirements for fly ash for use as a supplementary cementitious material in concrete.
EN 450-1:2012+A1:2022CEN (European Committee for Standardization)
HighCurrent
Fly ash for concrete - Part 1: Definition, specifications and conformity criteria
Defines and gives specifications for siliceous fly ash for use as a Type II addition in concrete.
AS 3582.1:2016Standards Australia (AU)
HighCurrent
Supplementary cementitious materials, Part 1: Fly ash
Specifies requirements for fly ash for use as a supplementary material in cement, mortar and concrete.
CSA A3001-18CSA Group (CA)
MediumCurrent
Cementitious materials for use in concrete
Covers all supplementary cementitious materials, including specific types of fly ash (F, CI, CH).
Key Differences
≠IS 3812 specifies two fineness grades (Grade I: ≤12% retained on 45µm sieve; Grade II: ≤34%), allowing for superfine ash. ASTM C618 has a single primary limit of ≤34%, which only corresponds to the coarser IS Grade II.
≠The Indian standard requires a higher 28-day Strength Activity Index of ≥80%, whereas ASTM C618 requires ≥75% at either 7 or 28 days, making the IS requirement more stringent for later-age strength contribution.
≠IS 3812 sets a stricter limit on Loss on Ignition (LOI) at a maximum of 5.0%. The standard limit in ASTM C618 is higher at 6.0%, although performance-based exceptions exist.
≠The maximum permissible Total Sulfur content (as SO₃) is lower in IS 3812 (≤3.5%) compared to ASTM C618, which allows up to 5.0% for both Class F and Class C fly ash.
Key Similarities
≈Both IS 3812 (Siliceous/Calcareous) and ASTM C618 (Class F/Class C) use a similar classification system based on the sum of key oxides (SiO₂, Al₂O₃, Fe₂O₃) and calcium oxide content.
≈For siliceous (IS) and Class F (ASTM) fly ash, both standards mandate a minimum sum of oxides (SiO₂ + Al₂O₃ + Fe₂O₃) of 70%.
≈Both standards specify an identical maximum limit of 0.8% for soundness, as determined by the autoclave expansion test, ensuring long-term volume stability in concrete.
≈The test methodology for determining fineness, a key physical property, is consistent across both standards, utilizing the wet sieving method with a 45-micron (No. 325) sieve.
Parameter Comparison
Parameter
IS Value
International
Source
Strength Activity Index (28 days)
≥ 80%
≥ 75%
ASTM C618-22a
Loss on Ignition (LOI)
≤ 5.0%
≤ 6.0%
ASTM C618-22a
Fineness (retained on 45 µm sieve)
≤ 12% (Grade I) / ≤ 34% (Grade II)
≤ 34%
ASTM C618-22a
Sum of Oxides (SiO₂+Al₂O₃+Fe₂O₃) for Siliceous/Class F
≥ 70.0%
≥ 70.0%
ASTM C618-22a
Soundness (Autoclave Expansion)
≤ 0.8%
≤ 0.8%
ASTM C618-22a
Total Sulfur (as SO₃)
≤ 3.5%
≤ 5.0% (for Class C/F)
ASTM C618-22a
Chloride Content
≤ 0.05%
≤ 0.10%
EN 450-1:2012+A1:2022
Reactive Silica (for Siliceous Ash)
≥ 20%
≥ 25%
EN 450-1:2012+A1:2022
⚠ Verify details from original standards before use
Key Values7
Quick Reference Values
Fineness (Specific Surface by Blaine's)Minimum 320 m2/kg
Loss on ignition (LOI)Maximum 5.0 percent
Moisture contentMaximum 2.0 percent
Soundness by autoclave test expansionMaximum 0.8 percent
Lime reactivityMinimum 4.5 N/mm2
Total SiO2, Al2O3 and Fe2O3 (Siliceous Fly Ash)Minimum 70.0 percent
Compressive strength at 28 daysMinimum 80 percent of control mix
What is the maximum permissible Loss on Ignition (LOI) for fly ash in concrete?+
5.0 percent as per Table 1.
What is the minimum fineness required for fly ash to be used in cement and concrete?+
320 m2/kg tested by Blaine's air permeability method as per Table 2.
How is fly ash classified in this standard?+
It is classified as Siliceous Pulverized Fuel Ash and Calcareous Pulverized Fuel Ash based on reactive calcium oxide content and total SiO2 + Al2O3 + Fe2O3.
What is the moisture content limit for fly ash?+
The moisture content should not exceed 2.0 percent by mass (Table 2).